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Materials, Volume 9, Issue 6 (June 2016)

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Cover Story An enzymatically mineralized collagen gel in which human dermal fibroblasts were encapsulated [...] Read more.
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Open AccessArticle Development of Biomimetic NiTi Alloy: Influence of Thermo-Chemical Treatment on the Physical, Mechanical and Biological Behavior
Materials 2016, 9(6), 402; doi:10.3390/ma9060402
Received: 6 April 2016 / Revised: 11 May 2016 / Accepted: 17 May 2016 / Published: 24 May 2016
Cited by 1 | PDF Full-text (2055 KB) | HTML Full-text | XML Full-text
Abstract
A bioactive layer, free of nickel, has been performed for its greater acceptability and reliability in clinical applications for NiTi shape memory alloys. In the first step, a safe barrier against Ni release has been produced on the surface by means of a
[...] Read more.
A bioactive layer, free of nickel, has been performed for its greater acceptability and reliability in clinical applications for NiTi shape memory alloys. In the first step, a safe barrier against Ni release has been produced on the surface by means of a thicker rutile/anastase protective layer free of nickel. In the second step, a sodium alkaline titanate hydrogel, which has the ability to induce apatite formation, has been performed from oxidized surface. An improvement of host tissue–implant integration has been achieved in terms of Ni ions release and the bioactivity of the treated NiTi alloys has been corroborated with both in vitro and in vivo studies. The transformation temperatures (As, Af, Ms, and Mf), as well as the critical stresses (σβ⇔M), have been slightly changed due to this surface modification. Consequently, this fact must be taken into account in order to design new surface modification on NiTi implants. Full article
(This article belongs to the Section Biomaterials)
Open AccessArticle Fabrication of Gold-Coated Ultra-Thin Anodic Porous Alumina Substrates for Augmented SERS
Materials 2016, 9(6), 403; doi:10.3390/ma9060403
Received: 21 April 2016 / Revised: 17 May 2016 / Accepted: 19 May 2016 / Published: 24 May 2016
Cited by 2 | PDF Full-text (2545 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Anodic porous alumina (APA) is a nanostructured material used as a template in several nanotechnological applications. We propose the use of APA in ultra-thin form (<100 nm) for augmented surface-enhanced Raman scattering (SERS). Here, the effect of in-depth thinning of the APA nanostructures
[...] Read more.
Anodic porous alumina (APA) is a nanostructured material used as a template in several nanotechnological applications. We propose the use of APA in ultra-thin form (<100 nm) for augmented surface-enhanced Raman scattering (SERS). Here, the effect of in-depth thinning of the APA nanostructures for possible maximization of SERS was addressed. Anodization was carried out on ultra-thin films of aluminum on glass and/or silicon, followed by pore-opening. Gold (Au) was overcoated and micro‑Raman/SERS measurements were carried out on test target analytes. Finite integration technique simulations of the APA-Au substrate were used both for the experimental design and simulations. It was observed that, under optimized conditions of APA and Au thickness, the SERS enhancement is higher than on standard APA-Au substrates based on thin (~100 nm) APA by up to a factor of ~20 for test molecules of mercaptobenzoic acid. The agreement between model and experimental results confirms the current understanding of SERS as being mainly due to the physical origin of plasmon resonances. The reported results represent one step towards micro-technological, integrated, disposable, high-sensitivity SERS chemical sensors and biosensors based on similar substrates. Full article
Open AccessFeature PaperArticle Synthesis, Characterization, and Electropolymerization of Extended Fused-Ring Thieno[3,4-b]pyrazine-Based Terthienyls
Materials 2016, 9(6), 404; doi:10.3390/ma9060404
Received: 28 April 2016 / Revised: 13 May 2016 / Accepted: 18 May 2016 / Published: 26 May 2016
Cited by 2 | PDF Full-text (2407 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The synthesis, characterization, and electropolymerization of a series of extended fused-ring thieno[3,4-b]pyrazine-based terthienyls are reported. The target terthienyls contain a central extended thieno[3,4-b]pyrazine analogue containing 2-thienyl units at the reactive α-positions of the central thiophene. The extended fused-ring thieno[3,4-
[...] Read more.
The synthesis, characterization, and electropolymerization of a series of extended fused-ring thieno[3,4-b]pyrazine-based terthienyls are reported. The target terthienyls contain a central extended thieno[3,4-b]pyrazine analogue containing 2-thienyl units at the reactive α-positions of the central thiophene. The extended fused-ring thieno[3,4-b]pyrazine analogues studied include acenaphtho[1,2-b]thieno[3,4-e]pyrazine, dibenzo[f,h]thieno[3,4-b]quinoxaline, and thieno[3′,4′:5,6]-pyrazino[2,3-f][1,10]phenanthroline. Comparison of the electrochemical and photophysical properties to simple thieno[3,4-b]pyrazine-based terthienyls and their polymeric analogues are reported in order to provide structure-function relationships within this series of compounds and materials. Full article
(This article belongs to the Special Issue Electroactive Polymers)
Open AccessFeature PaperArticle Bioactive and Antibacterial Glass Powders Doped with Copper by Ion-Exchange in Aqueous Solutions
Materials 2016, 9(6), 405; doi:10.3390/ma9060405
Received: 31 March 2016 / Revised: 10 May 2016 / Accepted: 18 May 2016 / Published: 24 May 2016
Cited by 2 | PDF Full-text (11196 KB) | HTML Full-text | XML Full-text
Abstract
In this work, two bioactive glass powders (SBA2 and SBA3) were doped with Cu by means of the ion-exchange technique in aqueous solution. SBA2 glass was subjected to the ion-exchange process by using different Cu salts (copper(II) nitrate, chloride, acetate, and sulphate) and
[...] Read more.
In this work, two bioactive glass powders (SBA2 and SBA3) were doped with Cu by means of the ion-exchange technique in aqueous solution. SBA2 glass was subjected to the ion-exchange process by using different Cu salts (copper(II) nitrate, chloride, acetate, and sulphate) and concentrations. Structural (X-ray diffraction-XRD), morphological (Scanning Electron Microscopy-SEM), and compositional (Energy Dispersion Spectrometry-EDS) analyses evidenced the formation of crystalline phases for glasses ion-exchanged in copper(II) nitrate and chloride solutions; while the ion-exchange in copper(II) acetate solutions lead to the incorporation of higher Cu amount than the ion-exchange in copper(II) sulphate solutions. For this reason, the antibacterial test (inhibition halo towards S. aureus) was performed on SBA2 powders ion-exchanged in copper(II) acetate solutions and evidenced a limited antibacterial effect. A second glass composition (SBA3) was developed to allow a greater incorporation of Cu in the glass surface; SBA3 powders were ion-exchanged in copper(II) acetate solutions (0.01 M and 0.05 M). Cu-doped SBA3 powders showed an amorphous structure; morphological analysis evidenced a rougher surface for Cu-doped powders in comparison to the undoped glass. EDS and X-ray photoelectron spectroscopy (XPS) confirmed the Cu introduction as Cu(II) ions. Bioactivity test in simulated body fluid (SBF) showed that Cu introduction did not alter the bioactive behaviour of the glass. Finally, inhibition halo test towards S. aureus evidenced a good antimicrobial effect for glass powders ion-exchanged in copper(II) acetate solutions 0.05 M. Full article
(This article belongs to the Special Issue Bioactive Glasses)
Open AccessArticle A Comparative Study on Permanent Mold Cast and Powder Thixoforming 6061 Aluminum Alloy and Sicp/6061Al Composite: Microstructures and Mechanical Properties
Materials 2016, 9(6), 407; doi:10.3390/ma9060407
Received: 24 April 2016 / Revised: 15 May 2016 / Accepted: 18 May 2016 / Published: 24 May 2016
Cited by 1 | PDF Full-text (11896 KB) | HTML Full-text | XML Full-text
Abstract
Microstructural and mechanical characterization of 10 vol% SiC particles (SiCp) reinforced 6061 Al-based composite fabricated by powder thixoforming (PTF) was investigated in comparison with the PTF and permanent mold cast (PMC) 6061 monolithic alloys. The results reveal that the microstructure of
[...] Read more.
Microstructural and mechanical characterization of 10 vol% SiC particles (SiCp) reinforced 6061 Al-based composite fabricated by powder thixoforming (PTF) was investigated in comparison with the PTF and permanent mold cast (PMC) 6061 monolithic alloys. The results reveal that the microstructure of the PMC alloy consists of coarse and equiaxed α dendrites and interdendritic net-like eutectic phases. However, the microstructure of the PTF composite, similar to that of the PTF alloy, consists of near-spheroidal primary particles and intergranular secondarily solidified structures except SiCp, which are distributed in the secondarily solidified structures. The eutectics amount in the PTF materials is distinctly lower than that in the PMC alloy, and the microstructures of the former materials are quite compact while that of the latter alloy is porous. Therefore, the PTF alloy shows better tensile properties than the PMC alloy. Owing to the existence of the SiC reinforcing particles, the PTF composite attains an ultimate tensile strength and yield strength of 230 MPa and 128 MPa, representing an enhancement of 27.8% and 29.3% than those (180 MPa and 99 MPa) of the PTF alloy. A modified model based on three strengthening mechanisms was proposed to calculate the yield strength of the PTF composite. The obtained theoretical results were quite consistent with the experimental data. Full article
Open AccessArticle A Series of Zr-Based Bulk Metallic Glasses with Room Temperature Plasticity
Materials 2016, 9(6), 408; doi:10.3390/ma9060408
Received: 18 April 2016 / Revised: 10 May 2016 / Accepted: 17 May 2016 / Published: 25 May 2016
Cited by 2 | PDF Full-text (9129 KB) | HTML Full-text | XML Full-text
Abstract
A group of plastic Zr-Al-Ni-Cu bulk metallic glasses (BMGs) with low Zr content was developed and their thermal and mechanical properties were investigated. The results show that these Zr-based BMGs have a single crystallization event for all heating rates in the studied temperature
[...] Read more.
A group of plastic Zr-Al-Ni-Cu bulk metallic glasses (BMGs) with low Zr content was developed and their thermal and mechanical properties were investigated. The results show that these Zr-based BMGs have a single crystallization event for all heating rates in the studied temperature region. The glass transition temperature Tg decreases with increasing Zr content for all heating rates. There are two melting procedures for the BMGs whose Zr content is less than 52 at %, while three melting procedures for the other Zr-based BMGs. The second melting procedure is split into two melting procedures for Zr52.5Al12.2Ni12.6Cu22.7 and Zr53Al11.6Ni11.7Cu23.7 BMGs, while the first melting procedure is split into two melting procedures for the other BMGs. The activation energy decreases with increasing sensitivity index β for the studied Zr-based BMGs. The plastic strain εp is in the region of 0.2%–19.1% for these Zr-based BMGs. Both yield strength σy and fracture strength σf are smallest for Zr55Al8.9Ni7.3Cu28.8 BMG whose εp is largest among all studied Zr-based BMGs and reaches up to 19.1%. In addition, the mechanism for the large difference of the plasticity among the studied Zr-based BMGs is also discussed. Full article
(This article belongs to the Section Structure Analysis and Characterization)
Open AccessFeature PaperArticle A Discussion on the Interpretation of the Darcy Equation in Case of Open-Cell Metal Foam Based on Numerical Simulations
Materials 2016, 9(6), 409; doi:10.3390/ma9060409
Received: 8 April 2016 / Revised: 13 May 2016 / Accepted: 20 May 2016 / Published: 25 May 2016
Cited by 3 | PDF Full-text (2508 KB) | HTML Full-text | XML Full-text
Abstract
It is long known that for high-velocity fluid flow in porous media, the relation between the pressure drop and the superficial velocity is not linear. Indeed, the classical Darcy law for shear stress dominated flow needs to be extended with a quadratic term,
[...] Read more.
It is long known that for high-velocity fluid flow in porous media, the relation between the pressure drop and the superficial velocity is not linear. Indeed, the classical Darcy law for shear stress dominated flow needs to be extended with a quadratic term, resulting in the empirical Darcy–Forchheimer model. Another approach is to simulate the foam numerically through the volume averaging technique. This leads to a natural separation of the total drag force into the contribution of the shear forces and the contribution of the pressure forces. Both representations of the total drag lead to the same result. The physical correspondence between both approaches is investigated in this work. The contribution of the viscous and pressure forces on the total drag is investigated using direct numerical simulations. Special attention is paid to the dependency on the velocity of these forces. The separation of the drag into its constituent terms on experimental grounds and for the volume average approach is unified. It is shown that the common approach to identify the linear term with the viscous forces and the quadratic term with the pressure forces is not correct. Full article
(This article belongs to the Special Issue Metal Foams: Synthesis, Characterization and Applications)
Open AccessFeature PaperArticle Design of Inorganic Polymer Mortar from Ferricalsialic and Calsialic Slags for Indoor Humidity Control
Materials 2016, 9(6), 410; doi:10.3390/ma9060410
Received: 7 March 2016 / Revised: 11 May 2016 / Accepted: 19 May 2016 / Published: 24 May 2016
Cited by 2 | PDF Full-text (17836 KB) | HTML Full-text | XML Full-text
Abstract
Amorphous silica and alumina of metakaolin are used to adjust the bulk composition of black (BSS) and white (WSS) steel slag to prepare alkali-activated (AAS) mortars consolidated at room temperature. The mix-design also includes also the addition of semi-crystalline matrix of river sand
[...] Read more.
Amorphous silica and alumina of metakaolin are used to adjust the bulk composition of black (BSS) and white (WSS) steel slag to prepare alkali-activated (AAS) mortars consolidated at room temperature. The mix-design also includes also the addition of semi-crystalline matrix of river sand to the metakaolin/steel powders. The results showed that high strength of the steel slag/metakaolin mortars can be achieved with the geopolymerization process which was particularly affected by the metallic iron present into the steel slag. The corrosion of the Fe particles was found to be responsible for porosity in the range between 0.1 and 10 µm. This class of porosity dominated (~31 vol %) the pore network of B compared to W samples (~16 vol %). However, W series remained with the higher cumulative pore volume (0.18 mL/g) compared to B series, with 0.12 mL/g. The maximum flexural strength was 6.89 and 8.51 MPa for the W and B series, respectively. The fracture surface ESEM observations of AAS showed large grains covered with the matrix assuming the good adhesion bonds between the gel-like geopolymer structure mixed with alkali activated steel slag and the residual unreacted portion. The correlation between the metallic iron/Fe oxides content, the pore network development, the strength and microstructure suggested the steel slag's significant action into the strengthening mechanism of consolidated products. These products also showed an interesting adsorption/desorption behavior that suggested their use as coating material to maintain the stability of the indoor relative humidity. Full article
(This article belongs to the Special Issue Advances in Geopolymers and Alkali-Activated Materials)
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Open AccessArticle In Vitro Assessment of the Antibacterial Potential of Silver Nano-Coatings on Cotton Gauzes for Prevention of Wound Infections
Materials 2016, 9(6), 411; doi:10.3390/ma9060411
Received: 22 February 2016 / Revised: 12 May 2016 / Accepted: 16 May 2016 / Published: 25 May 2016
PDF Full-text (4949 KB) | HTML Full-text | XML Full-text
Abstract
Multidrug-resistant organisms are increasingly implicated in acute and chronic wound infections, thus compromising the chance of therapeutic options. The resistance to conventional antibiotics demonstrated by some bacterial strains has encouraged new approaches for the prevention of infections in wounds and burns, among them
[...] Read more.
Multidrug-resistant organisms are increasingly implicated in acute and chronic wound infections, thus compromising the chance of therapeutic options. The resistance to conventional antibiotics demonstrated by some bacterial strains has encouraged new approaches for the prevention of infections in wounds and burns, among them the use of silver compounds and nanocrystalline silver. Recently, silver wound dressings have become widely accepted in wound healing centers and are commercially available. In this work, novel antibacterial wound dressings have been developed through a silver deposition technology based on the photochemical synthesis of silver nanoparticles. The devices obtained are completely natural and the silver coatings are characterized by an excellent adhesion without the use of any binder. The silver-treated cotton gauzes were characterized through scanning electron microscopy (SEM) and thermo-gravimetric analysis (TGA) in order to verify the distribution and the dimension of the silver particles on the cotton fibers. The effectiveness of the silver-treated gauzes in reducing the bacterial growth and biofilm proliferation has been demonstrated through agar diffusion tests, bacterial enumeration test, biofilm quantification tests, fluorescence and SEM microscopy. Moreover, potential cytotoxicity of the silver coating was evaluated through 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide colorimetric assay (MTT) and the extract method on fibroblasts and keratinocytes. Inductively coupled plasma mass spectrometry (ICP-MS) was performed in order to determine the silver release in different media and to relate the results to the biological characterization. All the results obtained were compared with plain gauzes as a negative control, as well as gauzes treated with a higher silver percentage as a positive control. Full article
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Open AccessArticle Influence of Composition on the Environmental Impact of a Cast Aluminum Alloy
Materials 2016, 9(6), 412; doi:10.3390/ma9060412
Received: 5 April 2016 / Revised: 3 May 2016 / Accepted: 17 May 2016 / Published: 25 May 2016
Cited by 1 | PDF Full-text (551 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The influence of alloy composition on the environmental impact of the production of six aluminum casting alloys (Al Si12Cu1(Fe), Al Si5Mg, Al Si9Cu3Zn3Fe, Al Si10Mg(Fe), Al Si9Cu3(Fe)(Zn) and Al Si9) has been analyzed. In order to perform a more precise environmental impact calculation,
[...] Read more.
The influence of alloy composition on the environmental impact of the production of six aluminum casting alloys (Al Si12Cu1(Fe), Al Si5Mg, Al Si9Cu3Zn3Fe, Al Si10Mg(Fe), Al Si9Cu3(Fe)(Zn) and Al Si9) has been analyzed. In order to perform a more precise environmental impact calculation, Life Cycle Assessment (LCA) with ReCiPe Endpoint methodology has been used, with the EcoInvent v3 AlMg3 aluminum alloy dataset as a reference. This dataset has been updated with the material composition ranges of the mentioned alloys. The balanced, maximum and minimum environmental impact values have been obtained. In general, the overall impact of the studied aluminum alloys varies from 5.98 × 10−1 pts to 1.09 pts per kg, depending on the alloy composition. In the analysis of maximum and minimum environmental impact, the alloy that has the highest uncertainty is AlSi9Cu3(Fe)(Zn), with a range of ±9%. The elements that contribute the most to increase its impact are Copper and Tin. The environmental impact of a specific case, an LED luminaire housing made out of an Al Si12Cu1(Fe) cast alloy, has been studied, showing the importance of considering the composition. Significant differences with the standard datasets that are currently available in EcoInvent v3 have been found. Full article
Open AccessArticle Novel Dental Cement to Combat Biofilms and Reduce Acids for Orthodontic Applications to Avoid Enamel Demineralization
Materials 2016, 9(6), 413; doi:10.3390/ma9060413
Received: 23 March 2016 / Revised: 15 May 2016 / Accepted: 18 May 2016 / Published: 25 May 2016
PDF Full-text (2027 KB) | HTML Full-text | XML Full-text
Abstract
Orthodontic treatments often lead to biofilm buildup and white spot lesions due to enamel demineralization. The objectives of this study were to develop a novel bioactive orthodontic cement to prevent white spot lesions, and to determine the effects of cement compositions on biofilm
[...] Read more.
Orthodontic treatments often lead to biofilm buildup and white spot lesions due to enamel demineralization. The objectives of this study were to develop a novel bioactive orthodontic cement to prevent white spot lesions, and to determine the effects of cement compositions on biofilm growth and acid production. 2-methacryloyloxyethyl phosphorylcholine (MPC), nanoparticles of silver (NAg), and dimethylaminohexadecyl methacrylate (DMAHDM) were incorporated into a resin-modified glass ionomer cement (RMGI). Enamel shear bond strength (SBS) was determined. Protein adsorption was determined using a micro bicinchoninic acid method. A dental plaque microcosm biofilm model with human saliva as inoculum was used to investigate metabolic activity, colony-forming units (CFU) and lactic acid production. Incorporating 3% of MPC, 1.5% of DMAHDM, and 0.1% of NAg into RMGI, and immersing in distilled water at 37 °C for 30 days, did not decrease the SBS, compared to control (p > 0.1). RMGI with 3% MPC + 1.5% DMAHDM + 0.1% NAg had protein amount that was 1/10 that of control. RMGI with triple agents (MPC + DMAHDM + NAg) had much stronger antibacterial property than using a single agent or double agents (p < 0.05). Biofilm CFU on RMGI with triple agents was reduced by more than 3 orders of magnitude, compared to commercial control. Biofilm metabolic activity and acid production were also greatly reduced. In conclusion, adding MPC + DMAHDM + NAg in RMGI substantially inhibited biofilm viability and acid production, without compromising the orthodontic bracket bond strength to enamel. The novel bioactive cement is promising for orthodontic applications to hinder biofilms and plaque buildup and enamel demineralization. Full article
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Open AccessArticle Inhibition of Cariogenic Plaque Formation on Root Surface with Polydopamine-Induced-Polyethylene Glycol Coating
Materials 2016, 9(6), 414; doi:10.3390/ma9060414
Received: 15 February 2016 / Revised: 17 May 2016 / Accepted: 23 May 2016 / Published: 25 May 2016
Cited by 1 | PDF Full-text (3764 KB) | HTML Full-text | XML Full-text
Abstract
Root caries prevention has been a challenge for clinicians due to its special anatomical location, which favors the accumulation of dental plaque. Researchers are looking for anti-biofouling material to inhibit bacterial growth on exposed root surfaces. This study aimed to develop polydopamine-induced-polyethylene glycol
[...] Read more.
Root caries prevention has been a challenge for clinicians due to its special anatomical location, which favors the accumulation of dental plaque. Researchers are looking for anti-biofouling material to inhibit bacterial growth on exposed root surfaces. This study aimed to develop polydopamine-induced-polyethylene glycol (PEG) and to study its anti-biofouling effect against a multi-species cariogenic biofilm on the root dentine surface. Hydroxyapatite disks and human dentine blocks were divided into four groups for experiments. They received polydopamine-induced-PEG, PEG, polydopamine, or water application. Contact angle, quartz crystal microbalance, and Fourier transform infrared spectroscopy were used to study the wetting property, surface affinity, and an infrared spectrum; the results indicated that PEG was induced by polydopamine onto a hydroxyapatite disk. Salivary mucin absorption on hydroxyapatite disks with polydopamine-induced-PEG was confirmed using spectrophotometry. The growth of a multi-species cariogenic biofilm on dentine blocks with polydopamine-induced-PEG was assessed and monitored by colony-forming units, confocal laser scanning microscopy, and scanning electron microscopy. The results showed that dentine with polydopamine-induced-PEG had fewer bacteria than other groups. In conclusion, a novel polydopamine-induced-PEG coating was developed. Its anti-biofouling effect inhibited salivary mucin absorption and cariogenic biofilm formation on dentine surface and thus may be used for the prevention of root dentine caries. Full article
(This article belongs to the Section Biomaterials)
Open AccessArticle Quantitative and Qualitative Analysis of Surface Modified Cellulose Utilizing TGA-MS
Materials 2016, 9(6), 415; doi:10.3390/ma9060415
Received: 31 March 2016 / Revised: 13 May 2016 / Accepted: 20 May 2016 / Published: 25 May 2016
Cited by 2 | PDF Full-text (3909 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
With the aim to enhance interfacial adhesion of a hydrophobic polymer matrix and cellulosic fibers and fillers, chemical surface modifications with silane coupling agents are performed. Thermogravimetric analysis (TGA) could be used to determine the degree of surface functionalization. However, similar thermal properties
[...] Read more.
With the aim to enhance interfacial adhesion of a hydrophobic polymer matrix and cellulosic fibers and fillers, chemical surface modifications with silane coupling agents are performed. Thermogravimetric analysis (TGA) could be used to determine the degree of surface functionalization. However, similar thermal properties of treated and untreated cellulose hamper a precise determination of silane loading. This contribution deals with quantitative determination of silane loading combining both TGA and elemental analysis. Firstly, silane modified celluloses were studied by FT-IR, Raman, solid state NMR spectroscopy, and polarized light microscopy in order to determine functional groups and to study the impact of chemical treatment on cellulose morphology. Secondly, thermal stability and pyrolysis processes were studied by TG-MS analysis. In order to determine the exact silane loading, the mass percentages of the appropriate elements were quantified by elemental analysis and correlated with the charred residues determined by TGA yielding a linear dependency. With that correlation, it was possible to determine silane loadings for additional samples utilizing simple TGA measurements. The main advantage of that approach is that only one calibration is necessary for routine analyses of further samples and TGA-MS coupling gives additional information on thermal stability and pyrolysis routes, simultaneously. Full article
(This article belongs to the Special Issue Bio- and Natural-Fiber Composites)
Open AccessArticle Reuse of Boron Waste as an Additive in Road Base Material
Materials 2016, 9(6), 416; doi:10.3390/ma9060416
Received: 18 March 2016 / Revised: 14 May 2016 / Accepted: 19 May 2016 / Published: 26 May 2016
Cited by 2 | PDF Full-text (2323 KB) | HTML Full-text | XML Full-text
Abstract
The amount of boron waste increases year by year. There is an urgent demand to manage it in order to reduce the environmental impact. In this paper, boron waste was reused as an additive in road base material. Lime and cement were employed
[...] Read more.
The amount of boron waste increases year by year. There is an urgent demand to manage it in order to reduce the environmental impact. In this paper, boron waste was reused as an additive in road base material. Lime and cement were employed to stabilize the waste mixture. Mechanical performances of stabilized mixture were evaluated by experimental methods. A compaction test, an unconfined compressive test, an indirect tensile test, a modulus test, a drying shrinkage test, and a frost resistance test were carried out. Results indicated that mechanical strengths of lime-stabilized boron waste mixture (LSB) satisfy the requirements of road base when lime content is greater than 8%. LSB can only be applied in non-frozen regions as a result of its poor frost resistance. The lime–cement-stabilized mixture can be used in frozen regions when lime and cement contents are 8% and 5%, respectively. Aggregate reduces the drying shrinkage coefficient effectively. Thus, aggregate is suggested for mixture stabilization properly. This work provides a proposal for the management of boron waste. Full article
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Open AccessFeature PaperArticle Roles of Extracellular Polysaccharides and Biofilm Formation in Heavy Metal Resistance of Rhizobia
Materials 2016, 9(6), 418; doi:10.3390/ma9060418
Received: 28 March 2016 / Revised: 9 May 2016 / Accepted: 17 May 2016 / Published: 26 May 2016
Cited by 3 | PDF Full-text (1254 KB) | HTML Full-text | XML Full-text
Abstract
Bacterial surface components and extracellular compounds, particularly flagella, lipopolysaccharides (LPSs), and exopolysaccharides (EPSs), in combination with environmental signals and quorum-sensing signals, play crucial roles in bacterial autoaggregation, biofilm development, survival, and host colonization. The nitrogen-fixing species Sinorhizobium meliloti (S. meliloti) produces
[...] Read more.
Bacterial surface components and extracellular compounds, particularly flagella, lipopolysaccharides (LPSs), and exopolysaccharides (EPSs), in combination with environmental signals and quorum-sensing signals, play crucial roles in bacterial autoaggregation, biofilm development, survival, and host colonization. The nitrogen-fixing species Sinorhizobium meliloti (S. meliloti) produces two symbiosis-promoting EPSs: succinoglycan (or EPS I) and galactoglucan (or EPS II). Studies of the S. meliloti/alfalfa symbiosis model system have revealed numerous biological functions of EPSs, including host specificity, participation in early stages of host plant infection, signaling molecule during plant development, and (most importantly) protection from environmental stresses. We evaluated functions of EPSs in bacterial resistance to heavy metals and metalloids, which are known to affect various biological processes. Heavy metal resistance, biofilm production, and co-culture were tested in the context of previous studies by our group. A range of mercury (Hg II) and arsenic (As III) concentrations were applied to S. meliloti wild type strain and to mutant strains defective in EPS I and EPS II. The EPS production mutants were generally most sensitive to the metals. Our findings suggest that EPSs are necessary for the protection of bacteria from either Hg (II) or As (III) stress. Previous studies have described a pump in S. meliloti that causes efflux of arsenic from cells to surrounding culture medium, thereby protecting them from this type of chemical stress. The presence of heavy metals or metalloids in culture medium had no apparent effect on formation of biofilm, in contrast to previous reports that biofilm formation helps protect various microorganism species from adverse environmental conditions. In co-culture experiments, EPS-producing heavy metal resistant strains exerted a protective effect on AEPS-non-producing, heavy metal-sensitive strains; a phenomenon termed “rescuing” of the non-resistant strain. Full article
(This article belongs to the Special Issue Biofilm and Materials Science)
Open AccessArticle Mechanical Properties and Durability of Ultra High Strength Concrete Incorporating Multi-Walled Carbon Nanotubes
Materials 2016, 9(6), 419; doi:10.3390/ma9060419
Received: 5 May 2016 / Revised: 5 May 2016 / Accepted: 18 May 2016 / Published: 27 May 2016
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Abstract
In this work, the effect of the addition of multi-walled carbon nanotubes (MWCNTs) on the mechanical properties and durability of ultra high strength concrete (UHSC) is reported. First, the MWCNTs were dispersed by a nano sand-mill in the presence of a surfactant in
[...] Read more.
In this work, the effect of the addition of multi-walled carbon nanotubes (MWCNTs) on the mechanical properties and durability of ultra high strength concrete (UHSC) is reported. First, the MWCNTs were dispersed by a nano sand-mill in the presence of a surfactant in water. The UHSC specimens were prepared with various amounts of MWCNTs, ranging from 0% to 0.15% by weight of cement (bwoc). Results indicated that use of an optimal percentage of MWCNTs (0.05% bwoc) caused a 4.63% increase in compressive strength and a 24.0% decrease in chloride diffusion coefficient of UHSC at 28 days curing. Moreover, the addition of MWCNTs also improved the flexural strength and deformation ability. Furthermore, a field-emission scanning electron microscopy (FE-SEM) was used to observe the dispersion of MWCNTs in the cement matrix and morphology of the hardened cement paste containing MWCNTs. FE-SEM observation revealed that MWCNTs were well dispersed in the matrix and no agglomerate was found and the reinforcing effect of MWCNTs on UHSC was thought to be pulling out and microcrack bridging of MWCNTs, which transferred the load in tension. Full article
(This article belongs to the Section Advanced Composites)
Open AccessArticle Room Temperature Consolidation of a Porous Poly(lactic-co-glycolic acid) Matrix by the Addition of Maltose to the Water-in-Oil Emulsion
Materials 2016, 9(6), 420; doi:10.3390/ma9060420
Received: 22 February 2016 / Revised: 20 May 2016 / Accepted: 23 May 2016 / Published: 27 May 2016
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Abstract
In composite materials made of polymer matrices and micro-nano dispersed compartments, the morphology of the dispersed phase can strongly affect several features of the final material, including stability, loading efficiency, and kinetic release of the embedded molecules. Such a polymer matrix composite can
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In composite materials made of polymer matrices and micro-nano dispersed compartments, the morphology of the dispersed phase can strongly affect several features of the final material, including stability, loading efficiency, and kinetic release of the embedded molecules. Such a polymer matrix composite can be obtained through the consolidation of the continuous polymer phase of a water-in-oil (W/O) emulsion. Here, we show that the morphology of the dispersed phase in a poly(lactic-co-glycolic acid, PLGA) matrix can be optimized by combining an effective mild temperature drying process with the addition of maltose as a densifying compound for the water phase of the emulsion. The influence of this addition on final stability and consequent optimal pore distribution was theoretically and experimentally confirmed. Samples were analyzed in terms of morphology on dried flat substrates and in terms of rheology and interfacial tension at the liquid state. While an increase of interfacial tension was found following the addition of maltose, the lower difference in density between the two emulsion phases coming from the addition of maltose allowed us to estimate a reduced creaming tendency confirmed by the experimental observations. Rheological measurements also confirmed an improved elastic behavior for the maltose-containing emulsion. Full article
(This article belongs to the Special Issue Biodegradable and Bio-Based Polymers)
Open AccessArticle Modeling Cyclic Fatigue Hysteresis Loops of 2D Woven Ceramic Matrix Composites at Elevated Temperatures in Steam
Materials 2016, 9(6), 421; doi:10.3390/ma9060421
Received: 20 March 2016 / Revised: 3 May 2016 / Accepted: 18 May 2016 / Published: 27 May 2016
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Abstract
In this paper, the cyclic fatigue hysteresis loops of 2D woven SiC/SiC ceramic matrix composites (CMCs) at elevated temperatures in steam have been investigated. The interface slip between fibers and the matrix existing in matrix cracking modes 3 and 5, in which matrix
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In this paper, the cyclic fatigue hysteresis loops of 2D woven SiC/SiC ceramic matrix composites (CMCs) at elevated temperatures in steam have been investigated. The interface slip between fibers and the matrix existing in matrix cracking modes 3 and 5, in which matrix cracking and interface debonding occurred in longitudinal yarns, is considered as the major reason for hysteresis loops of 2D woven CMCs. The hysteresis loops of 2D SiC/SiC composites corresponding to different peak stresses, test conditions, and loading frequencies have been predicted using the present analysis. The damage parameter, i.e., the proportion of matrix cracking mode 3 in the entire matrix cracking modes of the composite, and the hysteresis dissipated energy increase with increasing fatigue peak stress. With increasing cycle number, the interface shear stress in the longitudinal yarns decreases, leading to transition of interface slip types of matrix cracking modes 3 and 5. Full article
(This article belongs to the Section Advanced Composites)
Open AccessArticle Effect of Tartaric Acid on Hydration of a Sodium-Metasilicate-Activated Blend of Calcium Aluminate Cement and Fly Ash F
Materials 2016, 9(6), 422; doi:10.3390/ma9060422
Received: 26 April 2016 / Revised: 20 May 2016 / Accepted: 23 May 2016 / Published: 27 May 2016
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Abstract
An alkali-activated blend of aluminum cement and class F fly ash is an attractive solution for geothermal wells where cement is exposed to significant thermal shocks and aggressive environments. Set-control additives enable the safe cement placement in a well but may compromise its
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An alkali-activated blend of aluminum cement and class F fly ash is an attractive solution for geothermal wells where cement is exposed to significant thermal shocks and aggressive environments. Set-control additives enable the safe cement placement in a well but may compromise its mechanical properties. This work evaluates the effect of a tartaric-acid set retarder on phase composition, microstructure, and strength development of a sodium-metasilicate-activated calcium aluminate/fly ash class F blend after curing at 85 °C, 200 °C or 300 °C. The hardened materials were characterized with X-ray diffraction, thermogravimetric analysis, X-ray computed tomography, and combined scanning electron microscopy/energy-dispersive X-ray spectroscopy and tested for mechanical strength. With increasing temperature, a higher number of phase transitions in non-retarded specimens was found as a result of fast cement hydration. The differences in the phase compositions were also attributed to tartaric acid interactions with metal ions released by the blend in retarded samples. The retarded samples showed higher total porosity but reduced percentage of large pores (above 500 µm) and greater compressive strength after 300 °C curing. Mechanical properties of the set cements were not compromised by the retarder. Full article
(This article belongs to the Special Issue Advances in Geopolymers and Alkali-Activated Materials)
Open AccessFeature PaperArticle Modeling of the Kinetics of Supercritical Fluid Extraction of Lipids from Microalgae with Emphasis on Extract Desorption
Materials 2016, 9(6), 423; doi:10.3390/ma9060423
Received: 25 March 2016 / Revised: 3 May 2016 / Accepted: 17 May 2016 / Published: 27 May 2016
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Abstract
Microalgae contain valuable biologically active lipophilic substances such as omega-3 fatty acids and carotenoids. In contrast to the recovery of vegetable oils from seeds, where the extraction with supercritical CO2 is used as a mild and selective method, economically viable application of
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Microalgae contain valuable biologically active lipophilic substances such as omega-3 fatty acids and carotenoids. In contrast to the recovery of vegetable oils from seeds, where the extraction with supercritical CO2 is used as a mild and selective method, economically viable application of this method on similarly soluble oils from microalgae requires, in most cases, much higher pressure. This paper presents and verifies hypothesis that this difference is caused by high adsorption capacity of microalgae. Under the pressures usually applied in supercritical fluid extraction from plants, microalgae bind a large fraction of the extracted oil, while under extremely high CO2 pressures their adsorption capacity diminishes and the extraction rate depends on oil solubility in supercritical CO2. A mathematical model for the extraction from microalgae was derived and applied to literature data on the extraction kinetics in order to determine model parameters. Full article
(This article belongs to the Special Issue Optimisation and Scale-Up of Supercritical Fluid Extraction Processes)
Open AccessArticle The Lightweight Design of a Seismic Low-Yield-Strength Steel Shear Panel Damper
Materials 2016, 9(6), 424; doi:10.3390/ma9060424
Received: 21 March 2016 / Revised: 19 May 2016 / Accepted: 25 May 2016 / Published: 27 May 2016
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Abstract
The lightweight design and miniaturization of metallic dampers have broad application prospects in seismic engineering. In this study, the superplastic property and the maximum energy dissipation capacity per unit mass of low-yield-strength steel (LYS) are investigated via comparison with those of several common
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The lightweight design and miniaturization of metallic dampers have broad application prospects in seismic engineering. In this study, the superplastic property and the maximum energy dissipation capacity per unit mass of low-yield-strength steel (LYS) are investigated via comparison with those of several common metallic damping materials by tests. Additionally, the boundary constraints of an LYS shear panel damper are studied further. Our experimental results suggest that LYS is an excellent damping material for achieving the lightweight design goal. A novel design of a lightweight damper, having excellent deformation ability and robust mechanical properties, is presented. The findings of this study are expected to be useful in understanding the lightweight design of dampers. Full article
(This article belongs to the Section Structure Analysis and Characterization)
Open AccessCommunication Preparation of Layer-by-Layer Films Composed of Polysaccharides and Poly(Amidoamine) Dendrimer Bearing Phenylboronic Acid and Their pH- and Sugar-Dependent Stability
Materials 2016, 9(6), 425; doi:10.3390/ma9060425
Received: 21 April 2016 / Revised: 6 May 2016 / Accepted: 25 May 2016 / Published: 28 May 2016
Cited by 2 | PDF Full-text (1669 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Layer-by-layer films composed of polysaccharides and poly(amidoamine) dendrimer bearing phenylboronic acid (PBA-PAMAM) were prepared to study the deposition behavior of the films and their stability in buffer solutions and in sugar solutions. Alginic acid (AGA) and carboxymethylcellulose (CMC) were employed as counter-polymers in
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Layer-by-layer films composed of polysaccharides and poly(amidoamine) dendrimer bearing phenylboronic acid (PBA-PAMAM) were prepared to study the deposition behavior of the films and their stability in buffer solutions and in sugar solutions. Alginic acid (AGA) and carboxymethylcellulose (CMC) were employed as counter-polymers in constructing LbL films. AGA/PBA-PAMAM films were successfully prepared at pH 6.0–9.0, whereas the preparation of CMC/PBA-PAMAM film was unsuccessful at pH 8.0 and 9.0. The results show that the LbL films formed mainly through electrostatic affinity between PBA-PAMAM and polysaccharides, while, for AGA/PBA-PAMAM films, the participation of boronate ester bonds in the films was suggested. AGA/PBA-PAMAM films were stable in the solutions of pH 6.0–9.0. In contrast, CMC/PBA-PAMAM films decomposed at pH 7.5–9.0. The AGA/PBA-PAMAM films decomposed in response to 5–30 mM fructose at pH 7.5, while the films were stable in glucose solutions. Thus, AGA is useful as a counter-polymer for constructing PBA-PAMAM films that are stable at physiological pH and decompose in response to fructose. Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle Engineering and Scaling the Spontaneous Magnetization Reversal of Faraday Induced Magnetic Relaxation in Nano-Sized Amorphous Ni Coated on Crystalline Au
Materials 2016, 9(6), 426; doi:10.3390/ma9060426
Received: 10 March 2016 / Revised: 25 April 2016 / Accepted: 25 May 2016 / Published: 28 May 2016
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Abstract
We report on the generation of large inverse remanent magnetizations in nano-sized core/shell structure of Au/Ni by turning off the applied magnetic field. The remanent magnetization is very sensitive to the field reduction rate as well as to the thermal and field processes
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We report on the generation of large inverse remanent magnetizations in nano-sized core/shell structure of Au/Ni by turning off the applied magnetic field. The remanent magnetization is very sensitive to the field reduction rate as well as to the thermal and field processes before the switching off of the magnetic field. Spontaneous reversal in direction and increase in magnitude of the remanent magnetization in subsequent relaxations over time were found. All of the various types of temporal relaxation curves of the remanent magnetizations are successfully scaled by a stretched exponential decay profile, characterized by two pairs of relaxation times and dynamic exponents. The relaxation time is used to describe the reduction rate, while the dynamic exponent describes the dynamical slowing down of the relaxation through time evolution. The key to these effects is to have the induced eddy current running beneath the amorphous Ni shells through Faraday induction. Full article
(This article belongs to the Section Structure Analysis and Characterization)
Open AccessArticle Two Novel C3N4 Phases: Structural, Mechanical and Electronic Properties
Materials 2016, 9(6), 427; doi:10.3390/ma9060427
Received: 26 April 2016 / Revised: 20 May 2016 / Accepted: 24 May 2016 / Published: 30 May 2016
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Abstract
We systematically studied the physical properties of a novel superhard (t-C3N4) and a novel hard (m-C3N4) C3N4 allotrope. Detailed theoretical studies of the structural properties, elastic properties, density
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We systematically studied the physical properties of a novel superhard (t-C3N4) and a novel hard (m-C3N4) C3N4 allotrope. Detailed theoretical studies of the structural properties, elastic properties, density of states, and mechanical properties of these two C3N4 phases were carried out using first-principles calculations. The calculated elastic constants and the hardness revealed that t-C3N4 is ultra-incompressible and superhard, with a high bulk modulus of 375 GPa and a high hardness of 80 GPa. m-C3N4 and t-C3N4 both exhibit large anisotropy with respect to Poisson’s ratio, shear modulus, and Young’s modulus. Moreover, m-C3N4 is a quasi-direct-bandgap semiconductor, with a band gap of 4.522 eV, and t-C3N4 is also a quasi-direct-band-gap semiconductor, with a band gap of 4.210 eV, with the HSE06 functional. Full article
(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)
Open AccessFeature PaperArticle Using Central Composite Experimental Design to Optimize the Degradation of Tylosin from Aqueous Solution by Photo-Fenton Reaction
Materials 2016, 9(6), 428; doi:10.3390/ma9060428
Received: 18 March 2016 / Revised: 11 April 2016 / Accepted: 24 May 2016 / Published: 30 May 2016
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Abstract
The feasibility of the application of the Photo-Fenton process in the treatment of aqueous solution contaminated by Tylosin antibiotic was evaluated. The Response Surface Methodology (RSM) based on Central Composite Design (CCD) was used to evaluate and optimize the effect of hydrogen peroxide,
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The feasibility of the application of the Photo-Fenton process in the treatment of aqueous solution contaminated by Tylosin antibiotic was evaluated. The Response Surface Methodology (RSM) based on Central Composite Design (CCD) was used to evaluate and optimize the effect of hydrogen peroxide, ferrous ion concentration and initial pH as independent variables on the total organic carbon (TOC) removal as the response function. The interaction effects and optimal parameters were obtained by using MODDE software. The significance of the independent variables and their interactions was tested by means of analysis of variance (ANOVA) with a 95% confidence level. Results show that the concentration of the ferrous ion and pH were the main parameters affecting TOC removal, while peroxide concentration had a slight effect on the reaction. The optimum operating conditions to achieve maximum TOC removal were determined. The model prediction for maximum TOC removal was compared to the experimental result at optimal operating conditions. A good agreement between the model prediction and experimental results confirms the soundness of the developed model. Full article
(This article belongs to the Special Issue Advancement of Photocatalytic Materials 2016)
Open AccessArticle Characterization of an Amorphous Titanium Oxide Film Deposited onto a Nano-Textured Fluorination Surface
Materials 2016, 9(6), 429; doi:10.3390/ma9060429
Received: 6 May 2016 / Revised: 19 May 2016 / Accepted: 26 May 2016 / Published: 31 May 2016
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Abstract
The photocatalytic activity of an amorphous titanium oxide (a-TiOx) film was modified using a two-step deposition. The fluorinated base layer with a nano-textured surface prepared by a selective fluorination etching process acted as growth seeds in the subsequent a-TiOx deposition.
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The photocatalytic activity of an amorphous titanium oxide (a-TiOx) film was modified using a two-step deposition. The fluorinated base layer with a nano-textured surface prepared by a selective fluorination etching process acted as growth seeds in the subsequent a-TiOx deposition. A nanorod-like microstructure was achievable from the resulting a-TiOx film due to the self-assembled deposition. Compared to the a-TiOx film directly deposited onto the untreated base layer, the rate constant of this fluorinate-free a-TiOx film surface for decomposing methylene blue (MB) solution that was employed to assess the film’s photocatalytic activity was markedly increased from 0.0076 min−1 to 0.0267 min−1 as a mechanism for the marked increase in the specific surface area. Full article
(This article belongs to the Special Issue Selected Papers from ICASI 2016)
Open AccessArticle Reactions in Electrodeposited Cu/Sn and Cu/Ni/Sn Nanoscale Multilayers for Interconnects
Materials 2016, 9(6), 430; doi:10.3390/ma9060430
Received: 17 March 2016 / Revised: 3 May 2016 / Accepted: 19 May 2016 / Published: 31 May 2016
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Abstract
Miniaturization of electronic devices has led to the development of 3D IC packages which require ultra-small-scale interconnections. Such small interconnects can be completely converted into Cu-Sn based intermetallic compounds (IMCs) after reflow. In an effort to improve IMC based interconnects, an attempt is
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Miniaturization of electronic devices has led to the development of 3D IC packages which require ultra-small-scale interconnections. Such small interconnects can be completely converted into Cu-Sn based intermetallic compounds (IMCs) after reflow. In an effort to improve IMC based interconnects, an attempt is made to add Ni to Cu-Sn-based IMCs. Multilayer interconnects consisting of stacks of Cu/Sn/Cu/Sn/Cu or Cu/Ni/Sn/Ni/Sn/Cu/Ni/Sn/Ni/Cu with Ni = 35 nm, 70 nm, and 150 nm were electrodeposited sequentially using copper pyrophosphate, tin methanesulfonic, and nickel Watts baths, respectively. These multilayer interconnects were investigated under room temperature aging conditions and for solid-liquid reactions, where the samples were subjected to 250 °C reflow for 60 s and also 300 °C for 3600 s. The progress of the reaction in the multilayers was monitored by using X-ray Diffraction, Scanning Electron Microscope, and Energy dispersive X-ray Spectroscopy. FIB-milled samples were also prepared for investigation under room temperature aging conditions. Results show that by inserting a 70 nanometres thick Ni layer between copper and tin, premature reaction between Cu and Sn at room temperature can be avoided. During short reflow, the addition of Ni suppresses formation of Cu3Sn IMC. With increasing Ni thickness, Cu consumption is decreased and Ni starts acting as a barrier layer. On the other hand, during long reflow, two types of IMC were found in the Cu/Ni/Sn samples which are the (Cu,Ni)6Sn5 and (Cu,Ni)3Sn, respectively. Details of the reaction sequence and mechanisms are discussed. Full article
Open AccessFeature PaperArticle Microstructured Polymer Blend Surfaces Produced by Spraying Functional Copolymers and Their Blends
Materials 2016, 9(6), 431; doi:10.3390/ma9060431
Received: 20 April 2016 / Revised: 18 May 2016 / Accepted: 24 May 2016 / Published: 31 May 2016
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Abstract
We described the fabrication of functional and microstructured surfaces from polymer blends by spray deposition. This simple technique offers the possibility to simultaneously finely tune the microstructure as well as the surface chemical composition. Whereas at lower polymer concentration, randomly distributed surface micropatterns
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We described the fabrication of functional and microstructured surfaces from polymer blends by spray deposition. This simple technique offers the possibility to simultaneously finely tune the microstructure as well as the surface chemical composition. Whereas at lower polymer concentration, randomly distributed surface micropatterns were observed, an increase of the concentration leads to significant changes on these structures. On the one hand, using pure homopolystyrene fiber-like structures were observed when the polymer concentration exceeded 30 mg/mL. Interestingly, the incorporation of 2,3,4,5,6-pentafluorostyrene changed the morphology, and, instead of fibers, micrometer size particles were identified at the surface. These fluorinated microparticles provide superhydrophobic properties leading to surfaces with contact angles above 165°. Equally, in addition to the microstructures provided by the spray deposition, the use of thermoresponsive polymers to fabricate interfaces with responsive properties is also described. Contact angle measurements revealed variations on the surface wettability upon heating when blends of polystyrene and polystyrene-b-poly(dimethylaminoethyl methacrylate) are employed. Finally, the use of spraying techniques to fabricate gradient surfaces is proposed. Maintaining a constant orientation, the surface topography and thus the contact angle varies gradually from the center to the edge of the film depending on the spray angle. Full article
(This article belongs to the Special Issue Polymer Blends and Compatibilization) Printed Edition available
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Open AccessArticle Optimizing the Pore Structure of Bio-Based ACFs through a Simple KOH–Steam Reactivation
Materials 2016, 9(6), 432; doi:10.3390/ma9060432
Received: 21 March 2016 / Revised: 15 May 2016 / Accepted: 24 May 2016 / Published: 31 May 2016
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Abstract
Highly microporous bio-based activated carbon fibers (ACFs) were prepared through a simple reactivation method. Sawdust, as the starting material, was liquefied and melt-spun to produce the precursor fibers. Then, the precursor fibers were activated by KOH and reactivated by steam. By varying the
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Highly microporous bio-based activated carbon fibers (ACFs) were prepared through a simple reactivation method. Sawdust, as the starting material, was liquefied and melt-spun to produce the precursor fibers. Then, the precursor fibers were activated by KOH and reactivated by steam. By varying the conditions of the two activation processes, the formation mechanism of the pore structure was studied, and the result showed that steam reactivation has a positive effect on the development of microporosity. The sample with the optimal condition exhibited the highest specific surface area of 2578 m2·g−1 as well as the largest pore volume of 1.425 cm3·g−1, where micropores contributed 70.3%. Due to its excellent texture properties, the ACF exhibited a high adsorption capacity of 1934 mg/g for iodine. Full article
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Open AccessArticle Effect of Rolling Route on Microstructure and Tensile Properties of Twin-Roll Casting AZ31 Mg Alloy Sheets
Materials 2016, 9(6), 433; doi:10.3390/ma9060433
Received: 6 April 2016 / Revised: 18 May 2016 / Accepted: 24 May 2016 / Published: 1 June 2016
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Abstract
Twin-roll casting AZ31 Mg alloy sheets have been fabricated by normal unidirectional-rolling, head-to-tail rolling, and clock-rolling, respectively. It has been demonstrated that head-to-tail rolling is the most effective to refine the microstructure and weaken the basal texture among the three rolling routes. Excellent
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Twin-roll casting AZ31 Mg alloy sheets have been fabricated by normal unidirectional-rolling, head-to-tail rolling, and clock-rolling, respectively. It has been demonstrated that head-to-tail rolling is the most effective to refine the microstructure and weaken the basal texture among the three rolling routes. Excellent integrated tensile properties can be obtained by the head-to-tail rolling. The yield strength, ultimate tensile strength, and plastic elongation are 196 MPa, 301 MPa, and 28.9%, respectively. The strength can benefit from the fine grains (average value of 4.0 μm) of the AZ31 alloy processed by the head-to-tail rolling route, while the excellent plastic elongation is achieved owing to the weakened basal texture besides the fine grains. Results obtained here can be used as a basis for further study of some simple rolling methods, which is critical to the development of Mg alloys with high strength and plasticity. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
Open AccessArticle Effects of Temperature on the Compressive Strength Parallel to the Grain of Bamboo Scrimbe
Materials 2016, 9(6), 436; doi:10.3390/ma9060436
Received: 6 April 2016 / Revised: 23 May 2016 / Accepted: 27 May 2016 / Published: 2 June 2016
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Abstract
The objective of this study was to investigate the compressive strength parallel to the grain of bamboo scrimber during and after exposure to various temperatures, in a range from 20 to 225 °C. These data were used to provide a basis for the
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The objective of this study was to investigate the compressive strength parallel to the grain of bamboo scrimber during and after exposure to various temperatures, in a range from 20 to 225 °C. These data were used to provide a basis for the evaluation of the fire performance of bamboo structures. A total of 152 specimens, assembled as group “during-fire” and “post-fire”, were tested during and after exposure to high temperatures. The experimental results indicated that there were significant differences in compressive properties between the “during-fire” and “post-fire” groups. At one temperature level, the compressive strength and modulus of elasticity of the “post-fire” group were significantly higher than those properties of the “during fire” group, but the ductility coefficient was reversed. FTIR analysis results showed that 175 °C was a key turning point, at which thermal decomposition occurred in the cellulose of the bamboo and phenolic resin. Full article
(This article belongs to the Special Issue Bio- and Natural-Fiber Composites)
Open AccessArticle The Simple Lamb Wave Analysis to Characterize Concrete Wide Beams by the Practical MASW Test
Materials 2016, 9(6), 437; doi:10.3390/ma9060437
Received: 9 April 2016 / Revised: 9 May 2016 / Accepted: 27 May 2016 / Published: 2 June 2016
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Abstract
In recent years, the Lamb wave analysis by the multi-channel analysis of surface waves (MASW) for concrete structures has been an effective nondestructive evaluation, such as the condition assessment and dimension identification by the elastic wave velocities and their reflections from boundaries. This
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In recent years, the Lamb wave analysis by the multi-channel analysis of surface waves (MASW) for concrete structures has been an effective nondestructive evaluation, such as the condition assessment and dimension identification by the elastic wave velocities and their reflections from boundaries. This study proposes an effective Lamb wave analysis by the practical application of MASW to concrete wide beams in an easy and simple manner in order to identify the dimension and elastic wave velocity (R-wave) for the condition assessment (e.g., the estimation of elastic properties). This is done by identifying the zero-order antisymmetric (A0) and first-order symmetric (S1) modes among multimodal Lamb waves. The MASW data were collected on eight concrete wide beams and compared to the actual depth and to the pressure (P-) wave velocities collected for the same specimen. Information is extracted from multimodal Lamb wave dispersion curves to obtain the elastic stiffness parameters and the thickness of the concrete structures. Due to the simple and cost-effective procedure associated with the MASW processing technique, the characteristics of several fundamental modes in the experimental Lamb wave dispersion curves could be measured. Available reference data are in good agreement with the parameters that were determined by our analysis scheme. Full article
(This article belongs to the Special Issue Acoustic Waves in Advanced Materials)
Open AccessArticle Bio-Inspired Supramolecular Chemistry Provides Highly Concentrated Dispersions of Carbon Nanotubes in Polythiophene
Materials 2016, 9(6), 438; doi:10.3390/ma9060438
Received: 7 April 2016 / Revised: 17 May 2016 / Accepted: 27 May 2016 / Published: 2 June 2016
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Abstract
In this paper we report the first observation, through X-ray diffraction, of noncovalent uracil–uracil (U–U) dimeric π-stacking interactions in carbon nanotube (CNT)–based supramolecular assemblies. The directionally oriented morphology determined using atomic force microscopy revealed highly organized behavior through π-stacking
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In this paper we report the first observation, through X-ray diffraction, of noncovalent uracil–uracil (U–U) dimeric π-stacking interactions in carbon nanotube (CNT)–based supramolecular assemblies. The directionally oriented morphology determined using atomic force microscopy revealed highly organized behavior through π-stacking of U moieties in a U-functionalized CNT derivative (CNT–U). We developed a dispersion system to investigate the bio-inspired interactions between an adenine (A)-terminated poly(3-adeninehexyl thiophene) (PAT) and CNT–U. These hybrid CNT–U/PAT materials interacted through π-stacking and multiple hydrogen bonding between the U moieties of CNT–U and the A moieties of PAT. Most importantly, the U···A multiple hydrogen bonding interactions between CNT–U and PAT enhanced the dispersion of CNT–U in a high-polarity solvent (DMSO). The morphology of these hybrids, determined using transmission electron microscopy, featured grape-like PAT bundles wrapped around the CNT–U surface; this tight connection was responsible for the enhanced dispersion of CNT–U in DMSO. Full article
(This article belongs to the Special Issue Advances in Bendable and Soft Material Film)
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Open AccessArticle A New Non-Destructive TDR System Combined with a Piezoelectric Stack for Measuring Properties of Geomaterials
Materials 2016, 9(6), 439; doi:10.3390/ma9060439
Received: 29 February 2016 / Revised: 12 May 2016 / Accepted: 27 May 2016 / Published: 2 June 2016
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Abstract
Dry density and water content are two important factors affecting the degree of soil compaction. Conventional methods such as the sand cone test and the plate load test are used to measure such properties for evaluating the degree of compaction and the stiffness
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Dry density and water content are two important factors affecting the degree of soil compaction. Conventional methods such as the sand cone test and the plate load test are used to measure such properties for evaluating the degree of compaction and the stiffness of soil in the field. However, these tests are generally very time-consuming and are inherent with some errors depending on the operator (in particular for the sand cone test). Elastic modulus is an indicator to describe the stress-strain behavior of soil and in some cases is used as a design input parameter. Although a rod type TDR (Time Domain Reflectometry) system has been recently proposed to overcome some shortcomings of the conventional methods (particularly the sand cone test), it requires driving the probes into the ground, thus implying that it is still a time-consuming and destructive testing method. This study aims to develop a new non-destructive TDR system that can rapidly measure the dry density, water content, and elastic modulus of soil on the surface of compacted soil, without disturbing the ground. In this study, the Piezoelectric Stack, which is an instrument for measuring the elastic modulus of soil, has been added to the TDR system with a flat type probe, leading to a non-destructive TDR system that is capable of measuring the dry density, water content, and elastic modulus of soil. The new TDR system developed is light enough for an engineer to carry. Results of the standard compaction and TDR tests on sand showed that the dry densities and the moisture contents measured with the new TDR system were in good agreement with those measured with the standard compaction test, respectively. Consequently, it appears that the new TDR system developed will be very useful to advance the current practice of compaction quality control. Full article
Open AccessArticle An Investigation into the Use of Manufactured Sand as a 100% Replacement for Fine Aggregate in Concrete
Materials 2016, 9(6), 440; doi:10.3390/ma9060440
Received: 13 April 2016 / Revised: 18 May 2016 / Accepted: 26 May 2016 / Published: 2 June 2016
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Abstract
Manufactured sand differs from natural sea and river dredged sand in its physical and mineralogical properties. These can be both beneficial and detrimental to the fresh and hardened properties of concrete. This paper presents the results of a laboratory study in which manufactured
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Manufactured sand differs from natural sea and river dredged sand in its physical and mineralogical properties. These can be both beneficial and detrimental to the fresh and hardened properties of concrete. This paper presents the results of a laboratory study in which manufactured sand produced in an industry sized crushing plant was characterised with respect to its physical and mineralogical properties. The influence of these characteristics on concrete workability and strength, when manufactured sand completely replaced natural sand in concrete, was investigated and modelled using artificial neural networks (ANN). The results show that the manufactured sand concrete made in this study generally requires a higher water/cement (w/c) ratio for workability equal to that of natural sand concrete due to the higher angularity of the manufactured sand particles. Water reducing admixtures can be used to compensate for this if the manufactured sand does not contain clay particles. At the same w/c ratio, the compressive and flexural strength of manufactured sand concrete exceeds that of natural sand concrete. ANN proved a valuable and reliable method of predicting concrete strength and workability based on the properties of the fine aggregate (FA) and the concrete mix composition. Full article
(This article belongs to the Section Advanced Composites)
Open AccessArticle Development of Styrene-Grafted Polyurethane by Radiation-Based Techniques
Materials 2016, 9(6), 441; doi:10.3390/ma9060441
Received: 23 February 2016 / Revised: 27 May 2016 / Accepted: 31 May 2016 / Published: 2 June 2016
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Abstract
Polyurethane (PU) is the fifth most common polymer in the general consumer market, following Polypropylene (PP), Polyethylene (PE), Polyvinyl chloride (PVC), and Polystyrene (PS), and the most common polymer for thermosetting resins. In particular, polyurethane has excellent hardness and heat resistance, is a
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Polyurethane (PU) is the fifth most common polymer in the general consumer market, following Polypropylene (PP), Polyethylene (PE), Polyvinyl chloride (PVC), and Polystyrene (PS), and the most common polymer for thermosetting resins. In particular, polyurethane has excellent hardness and heat resistance, is a widely used material for electronic products and automotive parts, and can be used to create products of various physical properties, including rigid and flexible foams, films, and fibers. However, the use of polar polymer polyurethane as an impact modifier of non-polar polymers is limited due to poor combustion resistance and impact resistance. In this study, we used gamma irradiation at 25 and 50 kGy to introduce the styrene of hydrophobic monomer on the polyurethane as an impact modifier of the non-polar polymer. To verify grafted styrene, we confirmed the phenyl group of styrene at 690 cm−1 by Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) and at 6.4–6.8 ppm by 1H-Nuclear Magnetic Resonance (1H-NMR). Scanning Electron Microscope (SEM), X-ray Photoelectron Spectroscopy (XPS), Thermogravimetric Analysis (TGA) and contact angle analysis were also used to confirm styrene introduction. This study has confirmed the possibility of applying high-functional composite through radiation-based techniques. Full article
(This article belongs to the Special Issue Polymer Blends and Compatibilization) Printed Edition available
Open AccessArticle Development of in-Situ Al-Si/CuAl2 Metal Matrix Composites: Microstructure, Hardness, and Wear Behavior
Materials 2016, 9(6), 442; doi:10.3390/ma9060442
Received: 24 April 2016 / Revised: 26 May 2016 / Accepted: 31 May 2016 / Published: 2 June 2016
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Abstract
In the present work, in-situ metal matrix composites were fabricated through squeeze casting. The copper particles were dispersed with different weight percentages (3%, 6%, 10%, and 15%) into Al-12% Si piston alloy. Also, heat treatments were performed at 380 °C and 450 °C
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In the present work, in-situ metal matrix composites were fabricated through squeeze casting. The copper particles were dispersed with different weight percentages (3%, 6%, 10%, and 15%) into Al-12% Si piston alloy. Also, heat treatments were performed at 380 °C and 450 °C for holding times of 6 and 18 h. The microstructures, X-ray diffractometer (XRD) pattern, hardness, and wear characteristics were evaluated. The results showed that these copper particles have reacted with the aluminum under all of the aforementioned processing conditions resulting in the formation of fine copper aluminide intermetallics. Most of the intermetallics were CuAl2, while AlCu appeared in a small ratio. Additionally, these intermetallics were homogenously distributed within the alloy matrix with up to 6% Cu addition. The amounts of those intermetallics increased after performing heat treatment. Most of these intermetallics were CuAl2 at 380 °C, while the Cu-rich intermetallics appeared at 450 °C. Increasing the holding time to 18 h, however, led to grain coarsening and resulted in the formation of some cracks. The hardness of the resulting composite materials was improved. The hardness value reached to about 170 HV after heat treating at 380 °C for 8 h. The wear resistance of the resulting composite materials was remarkably improved, especially at lower additions of Cu and at the lower heat treatment temperature. Full article
Open AccessArticle The Lateral Compressive Buckling Performance of Aluminum Honeycomb Panels for Long-Span Hollow Core Roofs
Materials 2016, 9(6), 444; doi:10.3390/ma9060444
Received: 9 May 2016 / Revised: 9 May 2016 / Accepted: 27 May 2016 / Published: 3 June 2016
Cited by 6 | PDF Full-text (2952 KB) | HTML Full-text | XML Full-text
Abstract
To solve the problem of critical buckling in the structural analysis and design of the new long-span hollow core roof architecture proposed in this paper (referred to as a “honeycomb panel structural system” (HSSS)), lateral compression tests and finite element analyses were employed
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To solve the problem of critical buckling in the structural analysis and design of the new long-span hollow core roof architecture proposed in this paper (referred to as a “honeycomb panel structural system” (HSSS)), lateral compression tests and finite element analyses were employed in this study to examine the lateral compressive buckling performance of this new type of honeycomb panel with different length-to-thickness ratios. The results led to two main conclusions: (1) Under the experimental conditions that were used, honeycomb panels with the same planar dimensions but different thicknesses had the same compressive stiffness immediately before buckling, while the lateral compressive buckling load-bearing capacity initially increased rapidly with an increasing honeycomb core thickness and then approached the same limiting value; (2) The compressive stiffnesses of test pieces with the same thickness but different lengths were different, while the maximum lateral compressive buckling loads were very similar. Overall instability failure is prone to occur in long and flexible honeycomb panels. In addition, the errors between the lateral compressive buckling loads from the experiment and the finite element simulations are within 6%, which demonstrates the effectiveness of the nonlinear finite element analysis and provides a theoretical basis for future analysis and design for this new type of spatial structure. Full article
(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)
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Open AccessFeature PaperArticle In Situ Elevated Temperature Testing of Fly Ash Based Geopolymer Composites
Materials 2016, 9(6), 445; doi:10.3390/ma9060445
Received: 11 April 2016 / Revised: 26 May 2016 / Accepted: 30 May 2016 / Published: 3 June 2016
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Abstract
In situ elevated temperature investigations using fly ash based geopolymers filled with alumina aggregate were undertaken. Compressive strength and short term creep tests were carried out to determine the onset temperature of viscous flow. Fire testing using the standard cellulose curve was performed.
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In situ elevated temperature investigations using fly ash based geopolymers filled with alumina aggregate were undertaken. Compressive strength and short term creep tests were carried out to determine the onset temperature of viscous flow. Fire testing using the standard cellulose curve was performed. Applying a load to the specimen as the temperature increased reduced the temperature at which viscous flow occurred (compared to test methods with no applied stress). Compressive strength increased at the elevated temperature and is attributed to viscous flow and sintering forming a more compact microstructure. The addition of alumina aggregate and reduction of water content reduced the thermal conductivity. This led to the earlier onset and shorter dehydration plateau duration times. However, crack formation was reduced and is attributed to smaller thermal gradients across the fire test specimen. Full article
(This article belongs to the Special Issue Advances in Geopolymers and Alkali-Activated Materials)
Open AccessArticle The Effect of the Melt Viscosity and Impregnation of a Film on the Mechanical Properties of Thermoplastic Composites
Materials 2016, 9(6), 448; doi:10.3390/ma9060448
Received: 6 April 2016 / Revised: 28 May 2016 / Accepted: 1 June 2016 / Published: 3 June 2016
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Abstract
Generally, to produce film-type thermoplastic composites with good mechanical properties, high-performance reinforcement films are used. In this case, films used as a matrix are difficult to impregnate into tow due to their high melt viscosity and high molecular weight. To solve the problem,
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Generally, to produce film-type thermoplastic composites with good mechanical properties, high-performance reinforcement films are used. In this case, films used as a matrix are difficult to impregnate into tow due to their high melt viscosity and high molecular weight. To solve the problem, in this paper, three polypropylene (PP) films with different melt viscosities were used separately to produce film-type thermoplastic composites. A film with a low melt viscosity was stacked so that tow was impregnated first and a film with a higher melt viscosity was then stacked to produce the composite. Four different composites were produced by regulating the pressure rising time. The thickness, density, fiber volume fraction (Vf), and void content (Vc) were analyzed to identify the physical properties and compare them in terms of film stacking types. The thermal properties were identified by using differential scanning calorimetry (DSC) and dynamical mechanical thermal analysis (DMTA). The tensile property, flexural property, interlaminar shear strength (ILSS), and scanning electron microscopy (SEM) were performed to identify the mechanical properties. For the films with low molecular weight, impregnation could be completed fast but showed low strength. Additionally, the films with high molecular weight completed impregnation slowly but showed high strength. Therefore, appropriate films should be used considering the forming process time and their mechanical properties to produce film-type composites. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
Open AccessArticle Flexible Epoxy Resin Formed Upon Blending with a Triblock Copolymer through Reaction-Induced Microphase Separation
Materials 2016, 9(6), 449; doi:10.3390/ma9060449
Received: 24 April 2016 / Revised: 25 May 2016 / Accepted: 1 June 2016 / Published: 3 June 2016
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Abstract
In this study, we used diglycidyl ether bisphenol A (DGEBA) as a matrix, the ABA block copolymer poly(ethylene oxide–b–propylene oxide–b–ethylene oxide) (Pluronic F127) as an additive, and diphenyl diaminosulfone (DDS) as a curing agent to prepare flexible epoxy resins
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In this study, we used diglycidyl ether bisphenol A (DGEBA) as a matrix, the ABA block copolymer poly(ethylene oxide–b–propylene oxide–b–ethylene oxide) (Pluronic F127) as an additive, and diphenyl diaminosulfone (DDS) as a curing agent to prepare flexible epoxy resins through reaction-induced microphase separation (RIMPS). Fourier transform infrared spectroscopy confirmed the existence of hydrogen bonding between the poly(ethylene oxide) segment of F127 and the OH groups of the DGEBA resin. Small-angle X-ray scattering, atomic force microscopy, and transmission electron microscopy all revealed evidence for the microphase separation of F127 within the epoxy resin. Glass transition temperature (Tg) phenomena and mechanical properties (modulus) were determined through differential scanning calorimetry and dynamic mechanical analysis, respectively, of samples at various blend compositions. The modulus data provided evidence for the formation of wormlike micelle structures, through a RIMPS mechanism, in the flexible epoxy resin upon blending with the F127 triblock copolymer. Full article
(This article belongs to the Special Issue Polymer Blends and Compatibilization) Printed Edition available
Open AccessArticle An Approach to Solid-State Electrical Double Layer Capacitors Fabricated with Graphene Oxide-Doped, Ionic Liquid-Based Solid Copolymer Electrolytes
Materials 2016, 9(6), 450; doi:10.3390/ma9060450
Received: 25 March 2016 / Revised: 21 May 2016 / Accepted: 30 May 2016 / Published: 6 June 2016
Cited by 4 | PDF Full-text (4192 KB) | HTML Full-text | XML Full-text
Abstract
Solid polymer electrolyte (SPE) composed of semi-crystalline poly (vinylidene fluoride-hexafluoropropylene) [P(VdF-HFP)] copolymer, 1-ethyl-3-methylimidazolium bis (trifluoromethyl sulphonyl) imide [EMI-BTI] and graphene oxide (GO) was prepared and its performance evaluated. The effects of GO nano-filler were investigated in terms of enhancement in ionic conductivity along
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Solid polymer electrolyte (SPE) composed of semi-crystalline poly (vinylidene fluoride-hexafluoropropylene) [P(VdF-HFP)] copolymer, 1-ethyl-3-methylimidazolium bis (trifluoromethyl sulphonyl) imide [EMI-BTI] and graphene oxide (GO) was prepared and its performance evaluated. The effects of GO nano-filler were investigated in terms of enhancement in ionic conductivity along with the electrochemical properties of its electrical double layer capacitors (EDLC). The GO-doped SPE shows improvement in ionic conductivity compared to the P(VdF-HFP)-[EMI-BTI] SPE system due to the existence of the abundant oxygen-containing functional group in GO that assists in the improvement of the ion mobility in the polymer matrix. The complexation of the materials in the SPE is confirmed in X-ray diffraction (XRD) and thermogravimetric analysis (TGA) studies. The electrochemical performance of EDLC fabricated with GO-doped SPE is examined using cyclic voltammetry and charge–discharge techniques. The maximum specific capacitance obtained is 29.6 F∙g−1, which is observed at a scan rate of 3 mV/s in 6 wt % GO-doped, SPE-based EDLC. It also has excellent cyclic retention as it is able keep the performance of the EDLC at 94% even after 3000 cycles. These results suggest GO doped SPE plays a significant role in energy storage application. Full article
(This article belongs to the Section Energy Materials)
Open AccessFeature PaperArticle Propagation of Ultrasonic Guided Waves in Composite Multi-Wire Ropes
Materials 2016, 9(6), 451; doi:10.3390/ma9060451
Received: 17 April 2016 / Revised: 24 May 2016 / Accepted: 1 June 2016 / Published: 6 June 2016
Cited by 3 | PDF Full-text (17715 KB) | HTML Full-text | XML Full-text
Abstract
Multi-wire ropes are widely used as load-carrying constructional elements in bridges, cranes, elevators, etc. Structural integrity of such ropes can be inspected by using non-destructive ultrasonic techniques. The objective of this work was to investigate propagation of ultrasonic guided waves (UGW) along
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Multi-wire ropes are widely used as load-carrying constructional elements in bridges, cranes, elevators, etc. Structural integrity of such ropes can be inspected by using non-destructive ultrasonic techniques. The objective of this work was to investigate propagation of ultrasonic guided waves (UGW) along composite multi-wire ropes in the cases of various types of acoustic contacts between neighboring wires and the plastic core. The modes of UGW propagating along the multi-wire ropes were identified using modelling, the dispersion curves were calculated using analytical and semi-analytical finite element (SAFE) techniques. In order to investigate the effects of UGW propagation, the two types of the acoustic contact between neighboring wires were simulated using the 3D finite element method (FE) as well. The key question of investigation was estimation of the actual boundary conditions between neighboring wires (solid or slip) and the real depth of penetration of UGW into the overall cross-section of the rope. Therefore, in order to verify the results of FE modelling, the guided wave penetration into strands of multi-wire rope was investigated experimentally. The performed modelling and experimental investigation enabled us to select optimal parameters of UGW to be used for non-destructive testing. Full article
(This article belongs to the Special Issue Acoustic Waves in Advanced Materials)
Open AccessArticle Synthesis and Characterization of New Chlorhexidine-Containing Nanoparticles for Root Canal Disinfection
Materials 2016, 9(6), 452; doi:10.3390/ma9060452
Received: 20 April 2016 / Revised: 19 May 2016 / Accepted: 30 May 2016 / Published: 7 June 2016
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Abstract
Root canal system disinfection is limited due to anatomical complexities. Better delivery systems of antimicrobial agents are needed to ensure efficient bacteria eradication. The purpose of this study was to design chlorhexidine-containing nanoparticles that could steadily release the drug. The drug chlorhexidine was
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Root canal system disinfection is limited due to anatomical complexities. Better delivery systems of antimicrobial agents are needed to ensure efficient bacteria eradication. The purpose of this study was to design chlorhexidine-containing nanoparticles that could steadily release the drug. The drug chlorhexidine was encapsulated in poly(ethylene glycol)–block–poly(l-lactide) (PEG–b–PLA) to synthesize bilayer nanoparticles. The encapsulation efficiency was determined through thermogravimetric analysis (TGA), and particle characterization was performed through microscopy studies of particle morphology and size. Their antimicrobial effect was assessed over the endodontic pathogen Enterococcus faecalis. The nanoparticles ranged in size from 300–500 nm, which is considered small enough for penetration inside small dentin tubules. The nanoparticles were dispersed in a hydrogel matrix carrier system composed of 1% hydroxyethyl cellulose, and this hydrogel system was observed to have enhanced bacterial inhibition over longer periods of time. Chlorhexidine-containing nanoparticles demonstrate potential as a drug carrier for root canal procedures. Their size and rate of release may allow for sustained inhibition of bacteria in the root canal system. Full article
Open AccessCommunication Experimental Ultrasound Transmission through Fluid-Solid and Air-Solid Phononic Plates
Materials 2016, 9(6), 453; doi:10.3390/ma9060453
Received: 22 April 2016 / Revised: 31 May 2016 / Accepted: 3 June 2016 / Published: 7 June 2016
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Abstract
Underwater ultrasonic transmissions for fluid-solid and air-solid phononic brass plates are reported in this work. Although the structure is roughly the same, experimental results show very different behaviour between fluid-solid and air-solid phononic plates, due to most of the properties of the fluid-solid
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Underwater ultrasonic transmissions for fluid-solid and air-solid phononic brass plates are reported in this work. Although the structure is roughly the same, experimental results show very different behaviour between fluid-solid and air-solid phononic plates, due to most of the properties of the fluid-solid perforated plates rely on Fabry-Perot resonances, Wood anomalies and Lamb modes. In air-solid phononic plates Fabry-Perot resonance is highly attenuated due to impedances difference between air and water, and therefore some transmission modes are now distinguishable due to surface modes coupling. Full article
(This article belongs to the Special Issue Acoustic Waves in Advanced Materials)
Open AccessArticle Chemical Characterization and in Vitro Antibacterial Activity of Myrcianthes hallii (O. Berg) McVaugh (Myrtaceae), a Traditional Plant Growing in Ecuador
Materials 2016, 9(6), 454; doi:10.3390/ma9060454
Received: 1 February 2016 / Revised: 31 May 2016 / Accepted: 1 June 2016 / Published: 7 June 2016
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Abstract
Myrcianthes hallii (O. Berg) McVaugh (Myrtaceae) is a plant native to Ecuador, traditionally used for its antiseptic properties. The composition of the hydro-methanolic extract of this plant was determined by submitting it to ultra-high performance liquid chromatography (UHPLC) hyphenated to heated-electrospray ionization mass
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Myrcianthes hallii (O. Berg) McVaugh (Myrtaceae) is a plant native to Ecuador, traditionally used for its antiseptic properties. The composition of the hydro-methanolic extract of this plant was determined by submitting it to ultra-high performance liquid chromatography (UHPLC) hyphenated to heated-electrospray ionization mass spectrometry and UV detection. The presence of antimicrobial components prompted us to test the extract against methicillin-resistant and methicillin-susceptible Staphylococcus aureus, multidrug-resistant and susceptible Escherichia coli, Pseudomonas aeruginosa, Enterococcus spp. and Streptococcus pyogenes strains. The chromatographic analysis led to the identification of 38 compounds, including polyphenols and organic acids, and represents the first chemical characterization of this plant. The extract showed modest antibacterial activity against all tested bacteria, with the exception of E. coli which was found to be less sensitive. Whilst methicillin-resistant strains usually display resistance to several drugs, no relevant differences were observed between methicillin-susceptible and resistant strains. Considering its long-standing use in folk medicine, which suggests the relative safety of the plant, and the presence of many known antibacterial polyphenolic compounds responsible for its antibacterial activity, the results show that M. hallii extract could be used as a potential new antiseptic agent. Moreover, new anti-infective biomaterials and nanomaterials could be designed through the incorporation of M. hallii polyphenols. This prospective biomedical application is also discussed. Full article
(This article belongs to the Special Issue Anti-Infective Materials in Medicine and Technology)
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Open AccessArticle Heat Transfer Performance of Functionalized Graphene Nanoplatelet Aqueous Nanofluids
Materials 2016, 9(6), 455; doi:10.3390/ma9060455
Received: 29 April 2016 / Revised: 25 May 2016 / Accepted: 31 May 2016 / Published: 8 June 2016
Cited by 4 | PDF Full-text (2357 KB) | HTML Full-text | XML Full-text
Abstract
The low thermal conductivity of fluids used in many industrial applications is one of the primary limitations in the development of more efficient heat transfer systems. A promising solution to this problem is the suspension of nanoparticles with high thermal conductivities in a
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The low thermal conductivity of fluids used in many industrial applications is one of the primary limitations in the development of more efficient heat transfer systems. A promising solution to this problem is the suspension of nanoparticles with high thermal conductivities in a base fluid. These suspensions, known as nanofluids, have great potential for enhancing heat transfer. The heat transfer enhancement of sulfonic acid-functionalized graphene nanoplatelet water-based nanofluids is addressed in this work. A new experimental setup was designed for this purpose. Convection coefficients, pressure drops, and thermophysical properties of various nanofluids at different concentrations were measured for several operational conditions and the results are compared with those of pure water. Enhancements in thermal conductivity and in convection heat transfer coefficient reach 12% (1 wt %) and 32% (0.5 wt %), respectively. New correlations capable of predicting the Nusselt number and the friction factor of this kind of nanofluid as a function of other dimensionless quantities are developed. In addition, thermal performance factors are obtained from the experimental convection coefficient and pressure drop data in order to assess the convenience of replacing the base fluid with designed nanofluids. Full article
(This article belongs to the Special Issue Advances in Renewable Energy Conversion Materials)
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Open AccessFeature PaperArticle Mechanical Characterization and Constitutive Modeling of Human Trachea: Age and Gender Dependency
Materials 2016, 9(6), 456; doi:10.3390/ma9060456
Received: 14 April 2016 / Revised: 16 May 2016 / Accepted: 2 June 2016 / Published: 8 June 2016
Cited by 3 | PDF Full-text (2125 KB) | HTML Full-text | XML Full-text
Abstract
Tracheal disorders can usually reduce the free lumen diameter or wall stiffness, and hence limit airflow. Trachea tissue engineering seems a promising treatment for such disorders. The required mechanical compatibility of the prepared scaffold with native trachea necessitates investigation of the mechanical behavior
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Tracheal disorders can usually reduce the free lumen diameter or wall stiffness, and hence limit airflow. Trachea tissue engineering seems a promising treatment for such disorders. The required mechanical compatibility of the prepared scaffold with native trachea necessitates investigation of the mechanical behavior of the human trachea. This study aimed at mechanical characterization of human tracheas and comparing the results based on age and gender. After isolating 30 human tracheas, samples of tracheal cartilage, smooth muscle, and connective tissue were subjected to uniaxial tension to obtain force-displacement curves and calculate stress-stretch data. Among several models, the Yeoh and Mooney-Rivlin hyperelastic functions were best able to describe hyperelastic behavior of all three tracheal components. The mean value of the elastic modulus of human tracheal cartilage was calculated to be 16.92 ± 8.76 MPa. An overall tracheal stiffening with age was observed, with the most considerable difference in the case of cartilage. Consistently, we noticed some histological alterations in cartilage and connective tissue with aging, which may play a role in age-related tracheal stiffening. No considerable effect of gender on the mechanical behavior of tracheal components was observed. The results of this study can be applied in the design and fabrication of trachea tissue engineering scaffolds. Full article
(This article belongs to the Special Issue Biomaterials and Tissue Biomechanics)
Open AccessArticle Synergetic Effect of Ultrasound, the Heterogeneous Fenton Reaction and Photocatalysis by TiO2 Loaded on Nickel Foam on the Degradation of Pollutants
Materials 2016, 9(6), 457; doi:10.3390/ma9060457
Received: 30 March 2016 / Revised: 4 May 2016 / Accepted: 17 May 2016 / Published: 8 June 2016
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Abstract
The synergistic effect of ultrasound, the heterogeneous Fenton reaction and photocatalysis was studied using a nickel foam (NF)-supporting TiO2 system and rhodamine B (RhB) as a target. The NF-supporting TiO2 system was prepared by depositing TiO2 on the skeleton of
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The synergistic effect of ultrasound, the heterogeneous Fenton reaction and photocatalysis was studied using a nickel foam (NF)-supporting TiO2 system and rhodamine B (RhB) as a target. The NF-supporting TiO2 system was prepared by depositing TiO2 on the skeleton of NF repeatedly and then calcining it. To optimize the conditions and parameters, the catalytic activity was tested in four systems (ultrasound alone (US), nickel foam (NF), US/NF and NF/US/H2O2). The optimal conditions were fixed at 0.1 g/mL NF, initial 5.00 mg/L RhB, 300 W ultrasonic power, pH = 3 and 5.00 mg/L H2O2. The effects of the dissolution of nickel from NF and quenching of the Fenton reaction were studied on degradation efficiency. When the heterogeneous Fenton reaction is combined with TiO2-photocatalysis, the pollutant removal efficiency is enhanced significantly. Through this synergistic effect, 22% and 80% acetochlor was degraded within 10 min and 80 min, respectively. Full article
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Open AccessArticle Polystyrene-Poly(methyl methacrylate) Silver Nanocomposites: Significant Modification of the Thermal and Electrical Properties by Microwave Irradiation
Materials 2016, 9(6), 458; doi:10.3390/ma9060458
Received: 4 March 2016 / Revised: 2 June 2016 / Accepted: 3 June 2016 / Published: 13 June 2016
Cited by 2 | PDF Full-text (7312 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This work compares the preparation of nanocomposites of polystyrene (PS), poly(methyl methacrylate) (PMMA), and PSMMA co-polymer containing silver nanoparticles (AgNPs) using in situ bulk polymerization with and without microwave irradiation (MWI). The AgNPs prepared were embedded within the polymer matrix. A modification in
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This work compares the preparation of nanocomposites of polystyrene (PS), poly(methyl methacrylate) (PMMA), and PSMMA co-polymer containing silver nanoparticles (AgNPs) using in situ bulk polymerization with and without microwave irradiation (MWI). The AgNPs prepared were embedded within the polymer matrix. A modification in the thermal stability of the PS/Ag, PMMA/Ag, and PSMMA/Ag nanocomposites using MWI and in situ was observed compared with that of neat PSMMA, PS, and PMMA. In particular, PS/Ag, and PSMMA/Ag nanocomposites used in situ showed better thermal stability than MWI, while PMMA/Ag nanocomposites showed improved thermal stability. The electrical conductivity of the PS/Ag, PMMA/Ag, and PSMMA/Ag composites prepared by MWI revealed a percolation behavior when 20% AgNPs were used as a filler, and the conductivity of the nanocomposites increased to 103 S/cm, 33 S/cm, and 40 mS/cm, respectively. This enhancement might be due to the good dispersion of the AgNPs within the polymer matrix, which increased the interfacial interaction between the polymer and AgNPs. The polymer/Ag nanocomposites developed with tunable thermal and electrical properties could be used as conductive materials for electronic device applications. Full article
(This article belongs to the Special Issue Microwave Materials Processing)
Open AccessArticle Immobilization of Magnetic Nanoparticles onto Amine-Modified Nano-Silica Gel for Copper Ions Remediation
Materials 2016, 9(6), 460; doi:10.3390/ma9060460
Received: 26 April 2016 / Revised: 21 May 2016 / Accepted: 2 June 2016 / Published: 9 June 2016
Cited by 3 | PDF Full-text (5674 KB) | HTML Full-text | XML Full-text
Abstract
A novel nano-hybrid was synthesized through immobilization of amine-functionalized silica gel nanoparticles with nanomagnetite via a co-precipitation technique. The parameters, such as reagent concentrations, reaction temperature and time, were optimized to accomplish the nano-silica gel chelating matrix. The most proper amine-modified silica gel
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A novel nano-hybrid was synthesized through immobilization of amine-functionalized silica gel nanoparticles with nanomagnetite via a co-precipitation technique. The parameters, such as reagent concentrations, reaction temperature and time, were optimized to accomplish the nano-silica gel chelating matrix. The most proper amine-modified silica gel nanoparticles were immobilized with magnetic nanoparticles. The synthesized magnetic amine nano-silica gel (MANSG) was established and characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and vibrating sample magnetometry (VSM). The feasibility of MANSG for copper ions’ remediation from wastewater was examined. MANSG achieves a 98% copper decontamination from polluted water within 90 min. Equilibrium sorption of copper ions onto MANSG nanoparticles obeyed the Langmuir equation compared to the Freundlich, Temkin, Elovich and Dubinin-Radushkevich (D-R) equilibrium isotherm models. The pseudo-second-order rate kinetics is appropriate to describe the copper sorption process onto the fabricated MANSG. Full article
(This article belongs to the Special Issue Porous Materials for Water Technology)
Open AccessArticle Innovative Fly Ash Geopolymer-Epoxy Composites: Preparation, Microstructure and Mechanical Properties
Materials 2016, 9(6), 461; doi:10.3390/ma9060461
Received: 14 March 2016 / Revised: 5 May 2016 / Accepted: 2 June 2016 / Published: 9 June 2016
Cited by 7 | PDF Full-text (6226 KB) | HTML Full-text | XML Full-text
Abstract
The preparation and characterization of composite materials based on geopolymers obtained from fly ash and epoxy resins are reported for the first time. These materials have been prepared through a synthetic method based on the concurrent reticulation of the organic and inorganic components
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The preparation and characterization of composite materials based on geopolymers obtained from fly ash and epoxy resins are reported for the first time. These materials have been prepared through a synthetic method based on the concurrent reticulation of the organic and inorganic components that allows the formation of hydrogen bonding between the phases, ensuring a very high compatibility between them. These new composites show significantly improved mechanical properties if compared to neat geopolymers with the same composition and comparable performances in respect to analogous geopolymer-based composites obtained starting from more expensive raw material such as metakaolin. The positive combination of an easy synthetic approach with the use of industrial by-products has allowed producing novel low cost aluminosilicate binders that, thanks to their thixotropicity and good adhesion against materials commonly used in building constructions, could be used within the field of sustainable building. Full article
(This article belongs to the Special Issue Advances in Geopolymers and Alkali-Activated Materials)
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Open AccessArticle Some Issues of Shrinkage-Reducing Admixtures Application in Alkali-Activated Slag Systems
Materials 2016, 9(6), 462; doi:10.3390/ma9060462
Received: 9 May 2016 / Revised: 31 May 2016 / Accepted: 6 June 2016 / Published: 10 June 2016
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Abstract
Significant drying shrinkage is one of the main limitations for the wider utilization of alkali-activated slag (AAS). Few previous works revealed that it is possible to reduce AAS drying shrinkage by the use of shrinkage-reducing admixtures (SRAs). However, these studies were mainly focused
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Significant drying shrinkage is one of the main limitations for the wider utilization of alkali-activated slag (AAS). Few previous works revealed that it is possible to reduce AAS drying shrinkage by the use of shrinkage-reducing admixtures (SRAs). However, these studies were mainly focused on SRA based on polypropylene glycol, while as it is shown in this paper, the behavior of SRA based on 2-methyl-2,4-pentanediol can be significantly different. While 0.25% and 0.50% had only a minor effect on the AAS properties, 1.0% of this SRA reduced the drying shrinkage of waterglass-activated slag mortar by more than 80%, but it greatly reduced early strengths simultaneously. This feature was further studied by isothermal calorimetry, mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Calorimetric experiments showed that 1% of SRA modified the second peak of the pre-induction period and delayed the maximum of the main hydration peak by several days, which corresponds well with observed strength development as well as with the MIP and SEM results. These observations proved the certain incompatibility of SRA with the studied AAS system, because the drying shrinkage reduction was induced by the strong retardation of hydration, resulting in a coarsening of the pore structure rather than the proper function of the SRA. Full article
(This article belongs to the Special Issue Advances in Geopolymers and Alkali-Activated Materials)
Open AccessArticle Role of Chloride in the Corrosion and Fracture Behavior of Micro-Alloyed Steel in E80 Simulated Fuel Grade Ethanol Environment
Materials 2016, 9(6), 463; doi:10.3390/ma9060463
Received: 16 March 2016 / Revised: 9 May 2016 / Accepted: 30 May 2016 / Published: 16 June 2016
Cited by 5 | PDF Full-text (4992 KB) | HTML Full-text | XML Full-text
Abstract
In this study, micro-alloyed steel (MAS) material normally used in the production of auto parts has been immersed in an E80 simulated fuel grade ethanol (SFGE) environment and its degradation mechanism in the presence of sodium chloride (NaCl) was evaluated. Corrosion behavior was
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In this study, micro-alloyed steel (MAS) material normally used in the production of auto parts has been immersed in an E80 simulated fuel grade ethanol (SFGE) environment and its degradation mechanism in the presence of sodium chloride (NaCl) was evaluated. Corrosion behavior was determined through mass loss tests and electrochemical measurements with respect to a reference test in the absence of NaCl. Fracture behavior was determined via J-integral tests with three-point bend specimens at an ambient temperature of 27 °C. The mass loss of MAS increased in E80 with NaCl up to a concentration of 32 mg/L; beyond that threshold, the effect of increasing chloride was insignificant. MAS did not demonstrate distinct passivation behavior, as well as pitting potential with anodic polarization, in the range of the ethanol-chloride ratio. Chloride caused pitting in MAS. The fracture resistance of MAS reduced in E80 with increasing chloride. Crack tip blunting decreased with increasing chloride, thus accounting for the reduction in fracture toughness. Full article
Open AccessArticle Advances and Applications of Ion Torrent Personal Genome Machine in Cutaneous Squamous Cell Carcinoma Reveal Novel Gene Mutations
Materials 2016, 9(6), 464; doi:10.3390/ma9060464
Received: 27 March 2016 / Revised: 11 May 2016 / Accepted: 8 June 2016 / Published: 14 June 2016
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Abstract
The Ion Torrent Personal Genome Machine (Ion PGM) is a semiconductor-based sequencing technology that is high quality, scalable, and economic. Its applications include genomic sequencing, drug resistance testing, microbial characterization, and targeted sequencing in cancer studies. However, little is known about the application
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The Ion Torrent Personal Genome Machine (Ion PGM) is a semiconductor-based sequencing technology that is high quality, scalable, and economic. Its applications include genomic sequencing, drug resistance testing, microbial characterization, and targeted sequencing in cancer studies. However, little is known about the application of Ion PGM in cutaneous squamous cell carcinoma (cSCC). We therefore investigated the utility and validity of Ion PGM in cSCC and also gained a better understanding of the underlying molecular biology of cSCC. We detected novel gene mutations (KDR, FGFR2, and EGFR) in two cSCC patients. Moreover, we validated these mutations by pyrosequencing and Sanger sequencing. Our results indicated that the mutation screen using Ion PGM is consistent with traditional sequencing methods. Notably, these identified mutations were present at significantly higher rates in high-risk cSCC. Our results demonstrate a method to detect targetable genes in high-risk cSCC, and suggest that Ion PGM may enable therapeutic decision-making and future potential targets for personalized therapies in cSCC. Full article
Open AccessArticle Use of Natural-Fiber Bio-Composites in Construction versus Traditional Solutions: Operational and Embodied Energy Assessment
Materials 2016, 9(6), 465; doi:10.3390/ma9060465
Received: 20 April 2016 / Revised: 7 June 2016 / Accepted: 8 June 2016 / Published: 13 June 2016
Cited by 1 | PDF Full-text (1654 KB) | HTML Full-text | XML Full-text
Abstract
During the last decades natural polymers have become more and more frequent to replace traditional inorganic stabilizers in building materials. The purpose of this research is to establish a comparison between the most conventional building material solutions for load-bearing walls and a type
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During the last decades natural polymers have become more and more frequent to replace traditional inorganic stabilizers in building materials. The purpose of this research is to establish a comparison between the most conventional building material solutions for load-bearing walls and a type of biomaterial. This comparison will focus on load-bearing walls as used in a widespread type of twentieth century dwelling construction in Europe and still used in developing countries nowadays. To carry out this analysis, the structural and thermal insulation characteristics of different construction solutions are balanced. The tool used for this evaluation is the life cycle assessment throughout the whole lifespan of these buildings. This research aims to examine the environmental performance of each material assessed: fired clay brick masonry walls (BW), concrete block masonry walls (CW), and stabilized soil block masonry walls (SW) stabilized with natural fibers and alginates. These conventional and new materials are evaluated from the point of view of both operational and embodied energy. Full article
(This article belongs to the Special Issue Bio- and Natural-Fiber Composites)
Open AccessFeature PaperArticle Environmentally-Friendly Dense and Porous Geopolymers Using Fly Ash and Rice Husk Ash as Raw Materials
Materials 2016, 9(6), 466; doi:10.3390/ma9060466
Received: 15 May 2016 / Revised: 1 June 2016 / Accepted: 8 June 2016 / Published: 14 June 2016
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Abstract
This paper assesses the feasibility of two industrial wastes, fly ash (FA) and rice husk ash (RHA), as raw materials for the production of geopolymeric pastes. Three typologies of samples were thus produced: (i) halloysite activated with potassium hydroxide and nanosilica, used as
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This paper assesses the feasibility of two industrial wastes, fly ash (FA) and rice husk ash (RHA), as raw materials for the production of geopolymeric pastes. Three typologies of samples were thus produced: (i) halloysite activated with potassium hydroxide and nanosilica, used as the reference sample (HL-S); (ii) halloysite activated with rice husk ash dissolved into KOH solution (HL-R); (iii) FA activated with the alkaline solution realized with the rice husk ash (FA-R). Dense and porous samples were produced and characterized in terms of mechanical properties and environmental impact. The flexural and compressive strength of HL-R reached about 9 and 43 MPa, respectively. On the contrary, the compressive strength of FA-R is significantly lower than the HL-R one, in spite of a comparable flexural strength being reached. However, when porous samples are concerned, FA-R shows comparable or even higher strength than HL-R. Thus, the current results show that RHA is a valuable alternative to silica nanopowder to prepare the activator solution, to be used either with calcined clay and fly ash feedstock materials. Finally, a preliminary evaluation of the global warming potential (GWP) was performed for the three investigated formulations. With the mix containing FA and RHA-based silica solution, a reduction of about 90% of GWP was achieved with respect to the values obtained for the reference formulation. Full article
(This article belongs to the Special Issue Advances in Geopolymers and Alkali-Activated Materials)
Open AccessArticle The Repetitive Detection of Toluene with Bioluminescence Bioreporter Pseudomonas putida TVA8 Encapsulated in Silica Hydrogel on an Optical Fiber
Materials 2016, 9(6), 467; doi:10.3390/ma9060467
Received: 11 May 2016 / Revised: 2 June 2016 / Accepted: 7 June 2016 / Published: 15 June 2016
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Abstract
Living cells of the lux-based bioluminescent bioreporter Pseudomonas putida TVA8 were encapsulated in a silica hydrogel attached to the distal wider end of a tapered quartz fiber. Bioluminescence of immobilized cells was induced with toluene at high (26.5 mg/L) and low (5.3
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Living cells of the lux-based bioluminescent bioreporter Pseudomonas putida TVA8 were encapsulated in a silica hydrogel attached to the distal wider end of a tapered quartz fiber. Bioluminescence of immobilized cells was induced with toluene at high (26.5 mg/L) and low (5.3 mg/L) concentrations. Initial bioluminescence maxima were achieved after >12 h. One week after immobilization, a biofilm-like layer of cells had formed on the surface of the silica gel. This resulted in shorter response times and more intensive bioluminescence maxima that appeared as rapidly as 2 h after toluene induction. Considerable second bioluminescence maxima were observed after inductions with 26.5 mg toluene/L. The second and third week after immobilization the biosensor repetitively and semiquantitatively detected toluene in buffered medium. Due to silica gel dissolution and biofilm detachment, the bioluminescent signal was decreasing 20–32 days after immobilization and completely extinguished after 32 days. The reproducible formation of a surface cell layer on the wider end of the tapered optical fiber can be translated to various whole cell bioluminescent biosensor devices and may serve as a platform for in-situ sensors. Full article
(This article belongs to the Special Issue Smart Biomaterials and Biointerfaces)
Open AccessArticle Microbially Induced Calcite Precipitation Employing Environmental Isolates
Materials 2016, 9(6), 468; doi:10.3390/ma9060468
Received: 3 February 2016 / Revised: 19 May 2016 / Accepted: 8 June 2016 / Published: 15 June 2016
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Abstract
In this study, five microbes were employed to precipitate calcite in cohesionless soils. Four microbes were selected from calcite-precipitating microbes isolated from calcareous sand and limestone cave soils, with Sporosarcina pasteurii ATCC 11859 (standard strain) used as a control. Urease activities of the
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In this study, five microbes were employed to precipitate calcite in cohesionless soils. Four microbes were selected from calcite-precipitating microbes isolated from calcareous sand and limestone cave soils, with Sporosarcina pasteurii ATCC 11859 (standard strain) used as a control. Urease activities of the four microbes were higher than that of S. pasteurii. The microbes and urea–CaCl2 medium were injected at least four times into cohesionless soils of two different relative densities (60% and 80%), and the amount of calcite precipitation was measured. It was found that the relative density of cohesionless soils significantly affects the amount of calcite precipitation and that there is a weak correlation between urease activity and calcite precipitation. Full article
(This article belongs to the Section Biomaterials)
Open AccessArticle Fabrication of Wood-Rubber Composites Using Rubber Compound as a Bonding Agent Instead of Adhesives
Materials 2016, 9(6), 469; doi:10.3390/ma9060469
Received: 18 March 2016 / Revised: 17 April 2016 / Accepted: 31 May 2016 / Published: 14 June 2016
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Abstract
Differing from the hot-pressing method in the manufacturing of traditional wood-rubber composites (WRCs), this study was aimed at fabricating WRCs using rubber processing to improve water resistance and mechanical properties. Three steps were used to make WRCs, namely, fiber-rubber mixing, tabletting, and the
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Differing from the hot-pressing method in the manufacturing of traditional wood-rubber composites (WRCs), this study was aimed at fabricating WRCs using rubber processing to improve water resistance and mechanical properties. Three steps were used to make WRCs, namely, fiber-rubber mixing, tabletting, and the vulcanization molding process. Ninety-six WRC panels were made with wood fiber contents of 0%–50% at rotor rotational speeds of 15–45 rpm and filled coefficients of 0.55–0.75. Four regression equations, i.e., the tensile strength (Ts), elongation at break (Eb), hardness (Ha) and rebound resilience (Rr) as functions of fiber contents, rotational speed and filled coefficient, were derived and a nonlinear programming model were developed to obtain the optimum composite properties. Although the Ts, Eb and Rr of the panels were reduced, Ha was considerably increased by 17%–58% because of the wood fiber addition. Scanning electron microscope images indicated that fibers were well embedded in rubber matrix. The 24 h water absorption was only 1%–3%, which was much lower than commercial wood-based composites. Full article
(This article belongs to the Special Issue Advances in Research on Elastomers)
Open AccessArticle Structural Integrity of an Electron Beam Melted Titanium Alloy
Materials 2016, 9(6), 470; doi:10.3390/ma9060470
Received: 18 May 2016 / Revised: 2 June 2016 / Accepted: 4 June 2016 / Published: 14 June 2016
Cited by 4 | PDF Full-text (9583 KB) | HTML Full-text | XML Full-text
Abstract
Advanced manufacturing encompasses the wide range of processes that consist of “3D printing” of metallic materials. One such method is Electron Beam Melting (EBM), a modern build technology that offers significant potential for lean manufacture and a capability to produce fully dense near-net
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Advanced manufacturing encompasses the wide range of processes that consist of “3D printing” of metallic materials. One such method is Electron Beam Melting (EBM), a modern build technology that offers significant potential for lean manufacture and a capability to produce fully dense near-net shaped components. However, the manufacture of intricate geometries will result in variable thermal cycles and thus a transient microstructure throughout, leading to a highly textured structure. As such, successful implementation of these technologies requires a comprehensive assessment of the relationships of the key process variables, geometries, resultant microstructures and mechanical properties. The nature of this process suggests that it is often difficult to produce representative test specimens necessary to achieve a full mechanical property characterisation. Therefore, the use of small scale test techniques may be exploited, specifically the small punch (SP) test. The SP test offers a capability for sampling miniaturised test specimens from various discrete locations in a thin-walled component, allowing a full characterisation across a complex geometry. This paper provides support in working towards development and validation strategies in order for advanced manufactured components to be safely implemented into future gas turbine applications. This has been achieved by applying the SP test to a series of Ti-6Al-4V variants that have been manufactured through a variety of processing routes including EBM and investigating the structural integrity of each material and how this controls the mechanical response. Full article
(This article belongs to the Special Issue Metals for Additive Manufacturing)
Open AccessArticle The Effect of Ultrasonic Peening Treatment on Fatigue Performance of Welded Joints
Materials 2016, 9(6), 471; doi:10.3390/ma9060471
Received: 11 May 2016 / Revised: 1 June 2016 / Accepted: 2 June 2016 / Published: 14 June 2016
Cited by 5 | PDF Full-text (2378 KB) | HTML Full-text | XML Full-text
Abstract
Ultrasonic peening treatment (UPT) as a method of severe plastic deformation was used to treat cruciform welded joints of Q345 steel. The application of UPT achieves material surface nanocrystallization of the peening zone, reduces stress concentration, and produces residual compressive stresses at the
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Ultrasonic peening treatment (UPT) as a method of severe plastic deformation was used to treat cruciform welded joints of Q345 steel. The application of UPT achieves material surface nanocrystallization of the peening zone, reduces stress concentration, and produces residual compressive stresses at the welded toe. Micro-structure, hardness, stress relief, S-N curve, and the fatigue fracture mechanism of cruciform welded joint of Q345 steel, both before and after UPT, were analyzed in detail. The main results show that: stress concentration and residual tensile stress are the main reasons to reduce fatigue strength of cruciform welded joints. The fatigue life of cruciform welded joints is improved for surface hardening, compressive stress, and grain refinement by UPT. Residual compressive stress caused by UPT is released with the increase of fatigue life. A very significant fatigue strength improvement happens when UPT is replenished repeatedly after a certain number of cycles. Full article
(This article belongs to the Special Issue Fracture and Fatigue Mechanics of Materials)
Open AccessArticle Dedifferentiated Human Articular Chondrocytes Redifferentiate to a Cartilage-Like Tissue Phenotype in a Poly(ε-Caprolactone)/Self-Assembling Peptide Composite Scaffold
Materials 2016, 9(6), 472; doi:10.3390/ma9060472
Received: 27 April 2016 / Revised: 29 May 2016 / Accepted: 3 June 2016 / Published: 17 June 2016
Cited by 2 | PDF Full-text (4651 KB) | HTML Full-text | XML Full-text
Abstract
Adult articular cartilage has a limited capacity for growth and regeneration and, with injury, new cellular or biomaterial-based therapeutic platforms are required to promote repair. Tissue engineering aims to produce cartilage-like tissues that recreate the complex mechanical and biological properties found in vivo
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Adult articular cartilage has a limited capacity for growth and regeneration and, with injury, new cellular or biomaterial-based therapeutic platforms are required to promote repair. Tissue engineering aims to produce cartilage-like tissues that recreate the complex mechanical and biological properties found in vivo. In this study, a unique composite scaffold was developed by infiltrating a three-dimensional (3D) woven microfiber poly (ε-caprolactone) (PCL) scaffold with the RAD16-I self-assembling nanofibers to obtain multi-scale functional and biomimetic tissue-engineered constructs. The scaffold was seeded with expanded dedifferentiated human articular chondrocytes and cultured for four weeks in control and chondrogenic growth conditions. The composite constructs were compared to control constructs obtained by culturing cells with 3D woven PCL scaffolds or RAD16-I independently. High viability and homogeneous cell distribution were observed in all three scaffolds used during the term of the culture. Moreover, gene and protein expression profiles revealed that chondrogenic markers were favored in the presence of RAD16-I peptide (PCL/RAD composite or alone) under chondrogenic induction conditions. Further, constructs displayed positive staining for toluidine blue, indicating the presence of synthesized proteoglycans. Finally, mechanical testing showed that constructs containing the PCL scaffold maintained the initial shape and viscoelastic behavior throughout the culture period, while constructs with RAD16-I scaffold alone contracted during culture time into a stiffer and compacted structure. Altogether, these results suggest that this new composite scaffold provides important mechanical requirements for a cartilage replacement, while providing a biomimetic microenvironment to re-establish the chondrogenic phenotype of human expanded articular chondrocytes. Full article
(This article belongs to the Special Issue Smart Hydrogels for (Bio)printing Applications)
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Open AccessArticle Recyclability of PET/WPI/PE Multilayer Films by Removal of Whey Protein Isolate-Based Coatings with Enzymatic Detergents
Materials 2016, 9(6), 473; doi:10.3390/ma9060473
Received: 23 March 2016 / Revised: 30 May 2016 / Accepted: 6 June 2016 / Published: 14 June 2016
Cited by 2 | PDF Full-text (2389 KB) | HTML Full-text | XML Full-text
Abstract
Multilayer plastic films provide a range of properties, which cannot be obtained from monolayer films but, at present, their recyclability is an open issue and should be improved. Research to date has shown the possibility of using whey protein as a layer material
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Multilayer plastic films provide a range of properties, which cannot be obtained from monolayer films but, at present, their recyclability is an open issue and should be improved. Research to date has shown the possibility of using whey protein as a layer material with the property of acting as an excellent barrier against oxygen and moisture, replacing petrochemical non-recyclable materials. The innovative approach of the present research was to achieve the recyclability of the substrate films by separating them, with a simple process compatible with industrial procedures, in order to promote recycling processes leading to obtain high value products that will beneficially impact the packaging and food industries. Hence, polyethyleneterephthalate (PET)/polyethylene (PE) multi-layer film was prepared based on PET coated with a whey protein layer, and then the previous structure was laminated with PE. Whey proteins, constituting the coating, can be degraded by enzymes so that the coating films can be washed off from the plastic substrate layer. Enzyme types, dosage, time, and temperature optima, which are compatible with procedures adopted in industrial waste recycling, were determined for a highly-efficient process. The washing of samples based on PET/whey and PET/whey/PE were efficient when performed with enzymatic detergent containing protease enzymes, as an alternative to conventional detergents used in recycling facilities. Different types of enzymatic detergents tested presented positive results in removing the protein layer from the PET substrate and from the PET/whey/PE multilayer films at room temperature. These results attested to the possibility of organizing the pre-treatment of the whey-based multilayer film by washing with different available commercial enzymatic detergents in order to separate PET and PE, thus allowing a better recycling of the two different polymers. Mechanical properties of the plastic substrate, such as stress at yield, stress and elongation at break, evaluated by tensile testing on films before and after cleaning, were are not significantly affected by washing with enzymatic detergents. Full article
(This article belongs to the Special Issue Biodegradable and Bio-Based Polymers)
Open AccessArticle Morphological and Structural Study of a Novel Porous Nurse’s A Ceramic with Osteoconductive Properties for Tissue Engineering
Materials 2016, 9(6), 474; doi:10.3390/ma9060474
Received: 25 May 2016 / Revised: 6 June 2016 / Accepted: 7 June 2016 / Published: 15 June 2016
Cited by 9 | PDF Full-text (17887 KB) | HTML Full-text | XML Full-text
Abstract
The characterization process of a new porous Nurse’s A ceramic and the physico chemical nature of the remodeled interface between the implant and the surrounding bone were studied after in vivo implantation. Scaffolds were prepared by a solid-state reaction and implanted in New
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The characterization process of a new porous Nurse’s A ceramic and the physico chemical nature of the remodeled interface between the implant and the surrounding bone were studied after in vivo implantation. Scaffolds were prepared by a solid-state reaction and implanted in New Zealand rabbits. Animals were sacrificed on days 15, 30, and 60. The porous biomaterial displayed biocompatible, bioresorbable, and osteoconductive capacity. The degradation processes of implants also encouraged osseous tissue ingrowths into the material’s pores, and drastically changed the macro- and microstructure of the implants. After 60 healing days, the resorption rates were 52.62% ± 1.12% for the ceramic and 47.38% ± 1.24% for the residual biomaterial. The elemental analysis showed a gradual diffusion of the Ca and Si ions from the materials into the newly forming bone during the biomaterial’s resorption process. The energy dispersive spectroscopy (EDS) analysis of the residual ceramic revealed some particle categories with different mean Ca/P ratios according to size, and indicated various resorption process stages. Since osteoconductive capacity was indicated for this material and bone ingrowth was possible, it could be applied to progressively substitute an implant. Full article
(This article belongs to the Special Issue Materials for Hard and Soft Tissue Engineering: Novel Approaches)
Open AccessArticle Influence of Chlorination and Choice of Materials on Fouling in Cooling Water System under Brackish Seawater Conditions
Materials 2016, 9(6), 475; doi:10.3390/ma9060475
Received: 31 March 2016 / Revised: 25 May 2016 / Accepted: 31 May 2016 / Published: 15 June 2016
Cited by 5 | PDF Full-text (11461 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Cooling systems remove heat from components and industrial equipment. Water cooling, employing natural waters, is typically used for cooling large industrial facilities, such as power plants, factories or refineries. Due to moderate temperatures, cooling water cycles are susceptible to biofouling, inorganic fouling and
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Cooling systems remove heat from components and industrial equipment. Water cooling, employing natural waters, is typically used for cooling large industrial facilities, such as power plants, factories or refineries. Due to moderate temperatures, cooling water cycles are susceptible to biofouling, inorganic fouling and scaling, which may reduce heat transfer and enhance corrosion. Hypochlorite treatment or antifouling coatings are used to prevent biological fouling in these systems. In this research, we examine biofouling and materials’ degradation in a brackish seawater environment using a range of test materials, both uncoated and coated. The fouling and corrosion resistance of titanium alloy (Ti-6Al-4V), super austenitic stainless steel (254SMO) and epoxy-coated carbon steel (Intershield Inerta160) were studied in the absence and presence of hypochlorite. Our results demonstrate that biological fouling is intensive in cooling systems using brackish seawater in sub-arctic areas. The microfouling comprised a vast diversity of bacteria, archaea, fungi, algae and protozoa. Chlorination was effective against biological fouling: up to a 10–1000-fold decrease in bacterial and archaeal numbers was detected. Chlorination also changed the diversity of the biofilm-forming community. Nevertheless, our results also suggest that chlorination enhances cracking of the epoxy coating. Full article
(This article belongs to the Special Issue Biofilm and Materials Science)
Open AccessArticle Magnesium Modifies the Structural Features of Enzymatically Mineralized Collagen Gels Affecting the Retraction Capabilities of Human Dermal Fibroblasts Embedded within This 3D System
Materials 2016, 9(6), 477; doi:10.3390/ma9060477
Received: 14 May 2016 / Revised: 7 June 2016 / Accepted: 8 June 2016 / Published: 15 June 2016
PDF Full-text (8774 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Mineralized collagen gels have been developed as in vitro models to better understand the mechanisms regulating the calcification process and the behavior of a variety of cell types. The vast majority of data are related to stem cells and to osteoblast-like cells, whereas
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Mineralized collagen gels have been developed as in vitro models to better understand the mechanisms regulating the calcification process and the behavior of a variety of cell types. The vast majority of data are related to stem cells and to osteoblast-like cells, whereas little information is available for dermal fibroblasts, although these cells have been associated with ectopic calcification and consequently to a number of pathological conditions. Therefore, we developed and characterized an enzymatically mineralized collagen gel in which fibroblasts were encapsulated within the 3D structure. MgCl2 was also added during gel polymerization, given its role as (i) modulator of ectopic calcification; (ii) component of biomaterials used for bone replacement; and (iii) constituent of pathological mineral deposits. Results demonstrate that, in a short time, an enzymatically mineralized collagen gel can be prepared in which mineral deposits and viable cells are homogeneously distributed. MgCl2 is present in mineral deposits and significantly affects collagen fibril assembly and organization. Consequently, cell shape and the ability of fibroblasts to retract collagen gels were modified. The development of three-dimensional (3D) mineralized collagen matrices with both different structural features and mineral composition together with the use of fibroblasts, as a prototype of soft connective tissue mesenchymal cells, may pave new ways for the study of ectopic calcification. Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle Reversible pH Stimulus-Response Material Based on Amphiphilic Block Polymer Self-Assembly and Its Electrochemical Application
Materials 2016, 9(6), 478; doi:10.3390/ma9060478
Received: 19 February 2016 / Revised: 5 June 2016 / Accepted: 7 June 2016 / Published: 15 June 2016
Cited by 2 | PDF Full-text (1686 KB) | HTML Full-text | XML Full-text
Abstract
Stimulus-responsive microporous solid thin films were successfully fabricated by simple molecular self-assembly via an amphiphilic block polymer, polystryene–b–polyacrylic acid (PS–b–PAA). The solid thin films exhibit different surface morphologies in response to external stimuli, such as environments with different pH
[...] Read more.
Stimulus-responsive microporous solid thin films were successfully fabricated by simple molecular self-assembly via an amphiphilic block polymer, polystryene–b–polyacrylic acid (PS–b–PAA). The solid thin films exhibit different surface morphologies in response to external stimuli, such as environments with different pH values in aqueous solutions. The experiments have successfully applied atomic force microscope (AFM) technology to observe in-situ surface morphological changes. There is a reversible evolution of the microstructures in buffer solutions over a pH range of 2.4–9.2. These observations have been explained by positing that there is no conventional PAA swelling but that the PAA chains in the micropores stretch and contract with changes in the pH of the solution environment. The hydrophobicity of the solid thin film surface was transformed into super-hydrophilicity, as captured by optical contact angle measurements. The stimulus-responsive dynamics of pore sizes was described by a two-stage mechanism. A promising electrochemical application of this film is suggested via combination with an electrochemical impedance technique. This study is aimed at strategies for the functionalization of stimulus-responsive microporous solid thin films with reversible tunable surface morphologies, and exploring new smart materials with switch-on/switch-off behavior. Full article
(This article belongs to the Section Porous Materials)
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Open AccessArticle Anion Effects on the Ion Exchange Process and the Deformation Property of Ionic Polymer Metal Composite Actuators
Materials 2016, 9(6), 479; doi:10.3390/ma9060479
Received: 28 April 2016 / Revised: 3 June 2016 / Accepted: 8 June 2016 / Published: 15 June 2016
PDF Full-text (1662 KB) | HTML Full-text | XML Full-text
Abstract
An ionic polymer-metal composite (IPMC) actuator composed of a thin perfluorinated ionomer membrane with electrodes plated on both surfaces undergoes a large bending motion when a low electric field is applied across its thickness. Such actuators are soft, lightweight, and able to operate
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An ionic polymer-metal composite (IPMC) actuator composed of a thin perfluorinated ionomer membrane with electrodes plated on both surfaces undergoes a large bending motion when a low electric field is applied across its thickness. Such actuators are soft, lightweight, and able to operate in solutions and thus show promise with regard to a wide range of applications, including MEMS sensors, artificial muscles, biomimetic systems, and medical devices. However, the variations induced by changing the type of anion on the device deformation properties are not well understood; therefore, the present study investigated the effects of different anions on the ion exchange process and the deformation behavior of IPMC actuators with palladium electrodes. Ion exchange was carried out in solutions incorporating various anions and the actuator tip displacement in deionized water was subsequently measured while applying a step voltage. In the step voltage response measurements, larger anions such as nitrate or sulfate led to a more pronounced tip displacement compared to that obtained with smaller anions such as hydroxide or chloride. In AC impedance measurements, larger anions generated greater ion conductivity and a larger double-layer capacitance at the cathode. Based on these mechanical and electrochemical measurements, it is concluded that the presence of larger anions in the ion exchange solution induces a greater degree of double-layer capacitance at the cathode and results in enhanced tip deformation of the IPMC actuators. Full article
(This article belongs to the Special Issue Electroactive Polymers)
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Open AccessArticle Synthesis of Mixed Cu/Ce Oxide Nanoparticles by the Oil-in-Water Microemulsion Reaction Method
Materials 2016, 9(6), 480; doi:10.3390/ma9060480
Received: 25 April 2016 / Revised: 6 June 2016 / Accepted: 10 June 2016 / Published: 16 June 2016
Cited by 5 | PDF Full-text (20347 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Cerium oxide and mixed Cu/Ce oxide nanoparticles were prepared by the oil-in-water (O/W) microemulsion reaction method in mild conditions. The Cu/Ce molar ratio was varied between 0/100 and 50/50. According to X-ray diffraction (XRD), below 30/70 Cu/Ce molar ratio, the materials presented a
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Cerium oxide and mixed Cu/Ce oxide nanoparticles were prepared by the oil-in-water (O/W) microemulsion reaction method in mild conditions. The Cu/Ce molar ratio was varied between 0/100 and 50/50. According to X-ray diffraction (XRD), below 30/70 Cu/Ce molar ratio, the materials presented a single phase consistent with cubic fluorite CeO2. However, above Cu/Ce molar ratio 30/70, an excess monoclinic CuO phase in coexistence with the predominant Cu/Ce mixed oxide was detected by XRD and High-Resolution Transmission Electron Microscopy (HRTEM). Raman spectroscopy showed that oxygen vacancies increased significantly as the Cu content was increased. Band gap (Eg) was investigated as a function of the Cu/Ce molar ratio, resulting in values from 2.91 eV for CeO2 to 2.32 eV for the mixed oxide with 30/70 Cu/Ce molar ratio. These results indicate that below 30/70 Cu/Ce molar ratio, Cu2+ is at least partially incorporated into the ceria lattice and very well dispersed in general. In addition, the photodegradation of Indigo Carmine dye under visible light irradiation was explored for selected samples; it was shown that these materials can remove such contaminants, either by adsorption and/or photodegradation. The results obtained will encourage investigation into the optical and photocatalytic properties of these mixed oxides, for widening their potential applications. Full article
Open AccessArticle The Effect of Lithium Doping on the Sintering and Grain Growth of SPS-Processed, Non-Stoichiometric Magnesium Aluminate Spinel
Materials 2016, 9(6), 481; doi:10.3390/ma9060481
Received: 11 May 2016 / Revised: 2 June 2016 / Accepted: 7 June 2016 / Published: 16 June 2016
Cited by 1 | PDF Full-text (11145 KB) | HTML Full-text | XML Full-text
Abstract
The effects of lithium doping on the sintering and grain growth of non-stoichiometric nano-sized magnesium aluminate spinel were studied using a spark plasma sintering (SPS) apparatus. Li-doped nano-MgO·nAl2O3 spinel (n = 1.06 and 1.21) powders containing 0,
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The effects of lithium doping on the sintering and grain growth of non-stoichiometric nano-sized magnesium aluminate spinel were studied using a spark plasma sintering (SPS) apparatus. Li-doped nano-MgO·nAl2O3 spinel (n = 1.06 and 1.21) powders containing 0, 0.20, 0.50 or 1.00 at. % Li were synthesized by the solution combustion method and dense specimens were processed using a SPS apparatus at 1200 °C and under an applied pressure of 150 MPa. The SPS-processed samples showed mutual dependency on the lithium concentration and the alumina-to-magnesia ratio. For example, the density and hardness values of near-stoichiometry samples (n = 1.06) showed an incline up to 0.51 at. % Li, while in the alumina rich samples (n = 1.21), these values remained constant up to 0.53 at. % Li. Studying grain growth revealed that in the Li-MgO·nAl2O3 system, grain growth is limited by Zener pining. The activation energies of undoped, 0.2 and 0.53 at. % Li-MgO·1.21Al2O3 samples were 288 ± 40, 670 ± 45 and 543 ± 40 kJ·mol−1, respectively. Full article
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Open AccessArticle Spark Plasma Co-Sintering of Mechanically Milled Tool Steel and High Speed Steel Powders
Materials 2016, 9(6), 482; doi:10.3390/ma9060482
Received: 15 May 2016 / Revised: 7 June 2016 / Accepted: 9 June 2016 / Published: 16 June 2016
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Abstract
Hot work tool steel (AISI H13) and high speed steel (AISI M3:2) powders were successfully co-sintered to produce hybrid tool steels that have properties and microstructures that can be modulated for specific applications. To promote co-sintering, which is made difficult by the various
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Hot work tool steel (AISI H13) and high speed steel (AISI M3:2) powders were successfully co-sintered to produce hybrid tool steels that have properties and microstructures that can be modulated for specific applications. To promote co-sintering, which is made difficult by the various densification kinetics of the two steels, the particle sizes and structures were refined by mechanical milling (MM). Near full density samples (>99.5%) showing very fine and homogeneous microstructure were obtained using spark plasma sintering (SPS). The density of the blends (20, 40, 60, 80 wt % H13) was in agreement with the linear rule of mixtures. Their hardness showed a positive deviation, which could be ascribed to the strengthening effect of the secondary particles altering the stress distribution during indentation. A toughening of the M3:2-rich blends could be explained in view of the crack deviation and crack arrest exerted by the H13 particles. Full article
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Open AccessArticle An Artificial Neural Network-Based Algorithm for Evaluation of Fatigue Crack Propagation Considering Nonlinear Damage Accumulation
Materials 2016, 9(6), 483; doi:10.3390/ma9060483
Received: 5 March 2016 / Revised: 8 June 2016 / Accepted: 10 June 2016 / Published: 17 June 2016
Cited by 3 | PDF Full-text (5567 KB) | HTML Full-text | XML Full-text
Abstract
In the aerospace and aviation sectors, the damage tolerance concept has been applied widely so that the modeling analysis of fatigue crack growth has become more and more significant. Since the process of crack propagation is highly nonlinear and determined by many factors,
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In the aerospace and aviation sectors, the damage tolerance concept has been applied widely so that the modeling analysis of fatigue crack growth has become more and more significant. Since the process of crack propagation is highly nonlinear and determined by many factors, such as applied stress, plastic zone in the crack tip, length of the crack, etc., it is difficult to build up a general and flexible explicit function to accurately quantify this complicated relationship. Fortunately, the artificial neural network (ANN) is considered a powerful tool for establishing the nonlinear multivariate projection which shows potential in handling the fatigue crack problem. In this paper, a novel fatigue crack calculation algorithm based on a radial basis function (RBF)-ANN is proposed to study this relationship from the experimental data. In addition, a parameter called the equivalent stress intensity factor is also employed as training data to account for loading interaction effects. The testing data is then placed under constant amplitude loading with different stress ratios or overloads used for model validation. Moreover, the Forman and Wheeler equations are also adopted to compare with our proposed algorithm. The current investigation shows that the ANN-based approach can deliver a better agreement with the experimental data than the other two models, which supports that the RBF-ANN has nontrivial advantages in handling the fatigue crack growth problem. Furthermore, it implies that the proposed algorithm is possibly a sophisticated and promising method to compute fatigue crack growth in terms of loading interaction effects. Full article
(This article belongs to the Section Structure Analysis and Characterization)
Open AccessArticle A Reinvestigation of a Superhard Tetragonal sp3 Carbon Allotrope
Materials 2016, 9(6), 484; doi:10.3390/ma9060484
Received: 5 May 2016 / Revised: 8 June 2016 / Accepted: 13 June 2016 / Published: 17 June 2016
Cited by 3 | PDF Full-text (2488 KB) | HTML Full-text | XML Full-text
Abstract
I4¯–carbon was first proposed by Zhang et al., this paper will report regarding this phase of carbon. The present paper reports the structural and elastic properties of the three-dimensional carbon allotrope I4¯–carbon using first-principles density functional
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I 4 ¯ –carbon was first proposed by Zhang et al., this paper will report regarding this phase of carbon. The present paper reports the structural and elastic properties of the three-dimensional carbon allotrope I 4 ¯ –carbon using first-principles density functional theory. The related enthalpy, elastic constants, and phonon spectra confirm that the newly-predicted I 4 ¯ –carbon is thermodynamically, mechanically, and dynamically stable. The calculated mechanical properties indicate that I 4 ¯ –carbon has a larger bulk modulus (393 GPa), shear modulus (421 GPa), Young’s modulus (931 GPa), and hardness (55.5 GPa), all of which are all slightly larger than those of c-BN. The present results indicate that I 4 ¯ –carbon is a superhard material and an indirect-band-gap semiconductor. Moreover, I 4 ¯ –carbon shows a smaller elastic anisotropy in its linear bulk modulus, shear anisotropic factors, universal anisotropic index, and Young’s modulus. Full article
(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)
Open AccessArticle Oil-in-Water Self-Assembled Synthesis of Ag@AgCl Nano-Particles on Flower-like Bi2O2CO3 with Enhanced Visible-Light-Driven Photocatalytic Activity
Materials 2016, 9(6), 486; doi:10.3390/ma9060486
Received: 9 May 2016 / Revised: 7 June 2016 / Accepted: 12 June 2016 / Published: 17 June 2016
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Abstract
In this work, a series of novel flower-like Ag@AgCl/Bi2O2CO3 were prepared by simple and feasible oil-in-water self-assembly processes. The phase structures of as-prepared samples were examined by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM),
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In this work, a series of novel flower-like Ag@AgCl/Bi2O2CO3 were prepared by simple and feasible oil-in-water self-assembly processes. The phase structures of as-prepared samples were examined by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS), X-ray fluorescence spectrometer (XRF), etc. The characterization results indicated that the presence of Ag@AgCl did not affect the crystal structure, but exerted a great influence on the photocatalytic activity of Bi2O2CO3 and enhanced the absorption band of pure Bi2O2CO3. The photocatalytic activities of the Ag@AgCl/Bi2O2CO3 samples were determined by photocatalytic degradation of methylene blue (MB) under visible light irradiation. The Ag@AgCl (10 wt %)/Bi2O2CO3 composite showed the highest photocatalytic activity, degrading 97.9% MB after irradiation for 20 min, which is over 1.64 and 3.66 times faster than that of pure Ag@AgCl (calculated based on the equivalent Ag@AgCl content in Ag@AgCl (10 wt %)/Bi2O2CO3) and pure Bi2O2CO3, respectively. Bisphenol A (BPA) was also degraded to further prove the degradation ability of Ag@AgCl/Bi2O2CO3. Photocurrent studies indicated that the recombination of photo-generated electron–hole pairs was decreased effectively due to the formation of heterojunctions between flower-like Bi2O2CO3 and Ag@AgCl nanoparticles. Trapping experiments indicated that O2, h+ and Cl° acted as the main reactive species for MB degradation in the present photocatalytic system. Furthermore, the cycling experiments revealed the good stability of Ag@AgCl/Bi2O2CO3 composites. Based on the above, a photocatalytic mechanism for the degradation of organic compounds over Ag@AgCl/Bi2O2CO3 was proposed. Full article
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Open AccessArticle Preparation of Nanofibrous Structure of Mesoporous Bioactive Glass Microbeads for Biomedical Applications
Materials 2016, 9(6), 487; doi:10.3390/ma9060487
Received: 3 May 2016 / Revised: 4 June 2016 / Accepted: 13 June 2016 / Published: 17 June 2016
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Abstract
A highly ordered, mesoporous (pore size 2~50 nm) bioactive glass (MBG) structure has a greater surface area and pore volume and excellent bone-forming bioactivity compared with traditional bioactive glasses (BGs). Hence, MBGs have been used in drug delivery and bone tissue engineering. MBGs
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A highly ordered, mesoporous (pore size 2~50 nm) bioactive glass (MBG) structure has a greater surface area and pore volume and excellent bone-forming bioactivity compared with traditional bioactive glasses (BGs). Hence, MBGs have been used in drug delivery and bone tissue engineering. MBGs can be developed as either a dense or porous block. Compared with a block, microbeads provide greater flexibility for filling different-shaped cavities and are suitable for culturing cells in vitro. In contrast, the fibrous structure of a scaffold has been shown to increase cell attachment and differentiation due to its ability to mimic the three-dimensional structure of natural extracellular matrices. Hence, the aim of this study is to fabricate MBG microbeads with a fibrous structure. First, a sol-gel/electrospinning technique was utilized to fabricate the MBG nanofiber (MBGNF) structure. Subsequently, the MBGNF microbeads (MFBs) were produced by an electrospraying technology. The results show that the diameter of the MFBs decreases when the applied voltage increases. The drug loading and release profiles and mechanisms of the MFBs were also evaluated. MFBs had a better drug entrapment efficiency, could reduce the burst release of tetracycline, and sustain the release over 10 days. Hence, the MFBs may be suitable drug carriers. In addition, the cellular attachment of MG63 osteoblast-like cells is significantly higher for MFBs than for glass microbeads after culturing for 4 h. The nanofibrous structure of MFBs could provide an appropriate environment for cellular spreading. Therefore, MFBs have great potential for use as a bone graft material in bone tissue engineering applications. Full article
(This article belongs to the Special Issue Bioceramics 2016)
Open AccessArticle Processing, Mechanical and Optical Properties of Additive-Free ZrC Ceramics Prepared by Spark Plasma Sintering
Materials 2016, 9(6), 489; doi:10.3390/ma9060489
Received: 21 April 2016 / Revised: 23 May 2016 / Accepted: 9 June 2016 / Published: 18 June 2016
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Abstract
In the present study, nearly fully dense monolithic ZrC samples are produced and broadly characterized from microstructural, mechanical and optical points of view. Specifically, 98% dense products are obtained by Spark Plasma Sintering (SPS) after 20 min dwell time at 1850 °C starting
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In the present study, nearly fully dense monolithic ZrC samples are produced and broadly characterized from microstructural, mechanical and optical points of view. Specifically, 98% dense products are obtained by Spark Plasma Sintering (SPS) after 20 min dwell time at 1850 °C starting from powders preliminarily prepared by Self-propagating High-temperature Synthesis (SHS) followed by 20 min ball milling. A prolonged mechanical treatment up to 2 h of SHS powders does not lead to appreciable benefits. Vickers hardness of the resulting samples (17.5 ± 0.4 GPa) is reasonably good for monolithic ceramics, but the mechanical strength (about 250 MPa up to 1000 °C) could be further improved by suitable optimization of the starting powder characteristics. The very smoothly polished ZrC specimen subjected to optical measurements displays high absorption in the visible-near infrared region and low thermal emittance at longer wavelengths. Moreover, the sample exhibits goodspectral selectivity (2.1–2.4) in the 1000–1400 K temperature range. These preliminary results suggest that ZrC ceramics produced through the two-step SHS/SPS processing route can be considered as attractive reference materials for the development of innovative solar energy absorbers. Full article
Open AccessFeature PaperArticle Reuse of Textile Dyeing Effluents Treated with Coupled Nanofiltration and Electrochemical Processes
Materials 2016, 9(6), 490; doi:10.3390/ma9060490
Received: 25 May 2016 / Revised: 13 June 2016 / Accepted: 14 June 2016 / Published: 20 June 2016
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Abstract
The reactive dye Cibacron Yellow S-3R was selected to evaluate the feasibility of combining nanofiltration membranes with electrochemical processes to treat textile wastewater. Synthetic dyeing effluents were treated by means of two nanofiltration membranes, Hydracore10 and Hydracore50. Up to 98% of dye removal
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The reactive dye Cibacron Yellow S-3R was selected to evaluate the feasibility of combining nanofiltration membranes with electrochemical processes to treat textile wastewater. Synthetic dyeing effluents were treated by means of two nanofiltration membranes, Hydracore10 and Hydracore50. Up to 98% of dye removal was achieved. The influence of salt concentration and pH on membrane treatment was studied. The best dye removal yield was achieved at pH 3 in the presence of 60 g/L of NaCl. After the membrane filtration, the concentrate containing high dye concentration was treated by means of an electrochemical process at three different current densities: 33, 83, and 166 mA/cm2. Results showed a lineal relationship between treatment time and applied current density. Both permeates and electrochemically-decoloured effluents were reused in new dyeing processes (100% of permeate and 70% of decoloured concentrates). Dyed fabrics were evaluated with respect to original dyeing. Colour differences were found to be into the acceptance range. Full article
Open AccessArticle Spectrophotometric Evaluation of Polyetheretherketone (PEEK) as a Core Material and a Comparison with Gold Standard Core Materials
Materials 2016, 9(6), 491; doi:10.3390/ma9060491
Received: 9 May 2016 / Revised: 16 June 2016 / Accepted: 16 June 2016 / Published: 20 June 2016
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Abstract
This study investigated the colorimetric properties of different veneering materials on core materials. Standardized specimens (10 mm × 10 mm × 1.5 mm) reflecting four core (polyetheretherketone (PEEK), zirconia (ZrO2), cobalt–chromium–molybdenum alloy (CoCrMo), and titanium oxide (TiO2); thickness: 1.5
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This study investigated the colorimetric properties of different veneering materials on core materials. Standardized specimens (10 mm × 10 mm × 1.5 mm) reflecting four core (polyetheretherketone (PEEK), zirconia (ZrO2), cobalt–chromium–molybdenum alloy (CoCrMo), and titanium oxide (TiO2); thickness: 1.5 mm) and veneering materials (VITA Mark II, IPS e.max CAD, LAVA Ultimate and VITA Enamic, all in shade A3; thickness: 0.5, 1.0, 1.5 and 2 mm, respectively) were fabricated. Specimens were superimposed to assemblies, and the color was determined with a spectrophotometer (CieLab-System) or a chair-side color measurement device (VITA EasyShade), respectively. Data were analyzed using three-, two-, and one-way ANOVA, a Chi2-test, and a Wilson approach (p < 0.05). The measurements with EasyShade showed A2 for VITA Mark II, A3.5 for VITA Enamic, B2 for LAVA Ultimate, and B3 for IPS e.max CAD. LabE-values showed significant differences between the tested veneering materials (p < 0.001). CieLab-System and VITA EasyShade parameters of the different assemblies showed a significant impact of core (p < 0.001), veneering material (p < 0.001), and thickness of the veneering material (p < 0.001). PEEK as core material showed comparable outcomes as compared to ZrO2 and CoCrMo, with respect to CieLab-System parameters for each veneering material. The relative frequency of the measured VITA EasyShade parameters regarding PEEK cores also showed comparable results as compared to the gold standard CoCrMo, regardless of the veneering material used. Full article
Open AccessArticle Effect of Interface Modified by Graphene on the Mechanical and Frictional Properties of Carbon/Graphene/Carbon Composites
Materials 2016, 9(6), 492; doi:10.3390/ma9060492
Received: 27 March 2016 / Revised: 8 June 2016 / Accepted: 13 June 2016 / Published: 20 June 2016
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Abstract
In this work, we developed an interface modified by graphene to simultaneously improve the mechanical and frictional properties of carbon/graphene/carbon (C/G/C) composite. Results indicated that the C/G/C composite exhibits remarkably improved interfacial bonding mode, static and dynamic mechanical performance, thermal conductivity, and frictional
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In this work, we developed an interface modified by graphene to simultaneously improve the mechanical and frictional properties of carbon/graphene/carbon (C/G/C) composite. Results indicated that the C/G/C composite exhibits remarkably improved interfacial bonding mode, static and dynamic mechanical performance, thermal conductivity, and frictional properties in comparison with those of the C/C composite. The weight contents of carbon fibers, graphene and pyrolytic carbon are 31.6, 0.3 and 68.1 wt %, respectively. The matrix of the C/G/C composite was mainly composed of rough laminar (RL) pyrocarbon. The average hardness by nanoindentation of the C/G/C and C/C composite matrices were 0.473 and 0.751 GPa, respectively. The flexural strength (three point bending), interlaminar shear strength (ILSS), interfacial debonding strength (IDS), internal friction and storage modulus of the C/C composite were 106, 10.3, 7.6, 0.038 and 12.7 GPa, respectively. Those properties of the C/G/C composite increased by 76.4%, 44.6%, 168.4% and 22.8%, respectively, and their internal friction decreased by 42.1% in comparison with those of the C/C composite. Owing to the lower hardness of the matrix, improved fiber/matrix interface bonding strength, and self-lubricating properties of graphene, a complete friction film was easily formed on the friction surface of the modified composite. Compared with the C/C composite, the C/G/C composite exhibited stable friction coefficients and lower wear losses at simulating air-plane normal landing (NL) and rejected take-off (RTO). The method appears to be a competitive approach to improve the mechanical and frictional properties of C/C composites simultaneously. Full article
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Open AccessFeature PaperArticle Creep of Polycrystalline Magnesium Aluminate Spinel Studied by an SPS Apparatus
Materials 2016, 9(6), 493; doi:10.3390/ma9060493
Received: 8 May 2016 / Revised: 2 June 2016 / Accepted: 16 June 2016 / Published: 20 June 2016
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Abstract
A spark plasma sintering (SPS) apparatus was used for the first time as an analytical testing tool for studying creep in ceramics at elevated temperatures. Compression creep experiments on a fine-grained (250 nm) polycrystalline magnesium aluminate spinel were successfully performed in the 1100–1200
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A spark plasma sintering (SPS) apparatus was used for the first time as an analytical testing tool for studying creep in ceramics at elevated temperatures. Compression creep experiments on a fine-grained (250 nm) polycrystalline magnesium aluminate spinel were successfully performed in the 1100–1200 °C temperature range, under an applied stress of 120–200 MPa. It was found that the stress exponent and activation energy depended on temperature and applied stress, respectively. The deformed samples were characterized by high resolution scanning electron microscope (HRSEM) and high resolution transmission electron microscope (HRTEM). The results indicate that the creep mechanism was related to grain boundary sliding, accommodated by dislocation slip and climb. The experimental results, extrapolated to higher temperatures and lower stresses, were in good agreement with data reported in the literature. Full article
Open AccessFeature PaperArticle Economic Analysis of an Integrated Annatto Seeds-Sugarcane Biorefinery Using Supercritical CO2 Extraction as a First Step
Materials 2016, 9(6), 494; doi:10.3390/ma9060494
Received: 22 April 2016 / Revised: 7 June 2016 / Accepted: 15 June 2016 / Published: 21 June 2016
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Abstract
Recently, supercritical fluid extraction (SFE) has been indicated to be utilized as part of a biorefinery, rather than as a stand-alone technology, since besides extracting added value compounds selectively it has been shown to have a positive effect on the downstream processing of
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Recently, supercritical fluid extraction (SFE) has been indicated to be utilized as part of a biorefinery, rather than as a stand-alone technology, since besides extracting added value compounds selectively it has been shown to have a positive effect on the downstream processing of biomass. To this extent, this work evaluates economically the encouraging experimental results regarding the use of SFE during annatto seeds valorization. Additionally, other features were discussed such as the benefits of enhancing the bioactive compounds concentration through physical processes and of integrating the proposed annatto seeds biorefinery to a hypothetical sugarcane biorefinery, which produces its essential inputs, e.g., CO2, ethanol, heat and electricity. For this, first, different configurations were modeled and simulated using the commercial simulator Aspen Plus® to determine the mass and energy balances. Next, each configuration was economically assessed using MATLAB. SFE proved to be decisive to the economic feasibility of the proposed annatto seeds-sugarcane biorefinery concept. SFE pretreatment associated with sequential fine particles separation process enabled higher bixin-rich extract production using low-pressure solvent extraction method employing ethanol, meanwhile tocotrienols-rich extract is obtained as a first product. Nevertheless, the economic evaluation showed that increasing tocotrienols-rich extract production has a more pronounced positive impact on the economic viability of the concept. Full article
(This article belongs to the Special Issue Optimisation and Scale-Up of Supercritical Fluid Extraction Processes)
Open AccessArticle The Manufacturing of High Porosity Iron with an Ultra-Fine Microstructure via Free Pressureless Spark Plasma Sintering
Materials 2016, 9(6), 495; doi:10.3390/ma9060495
Received: 14 May 2016 / Revised: 16 June 2016 / Accepted: 17 June 2016 / Published: 21 June 2016
Cited by 4 | PDF Full-text (2059 KB) | HTML Full-text | XML Full-text
Abstract
High porosity (>40 vol %) iron specimens with micro- and nanoscale isotropic pores were fabricated by carrying out free pressureless spark plasma sintering (FPSPS) of submicron hollow Fe–N powders at 750 °C. Ultra-fine porous microstructures are obtained by imposing high heating rates during
[...] Read more.
High porosity (>40 vol %) iron specimens with micro- and nanoscale isotropic pores were fabricated by carrying out free pressureless spark plasma sintering (FPSPS) of submicron hollow Fe–N powders at 750 °C. Ultra-fine porous microstructures are obtained by imposing high heating rates during the preparation process. This specially designed approach not only avoids the extra procedures of adding and removing space holders during the formation of porous structures, but also triggers the continued phase transitions of the Fe–N system at relatively lower processing temperatures. The compressive strength and energy absorption characteristics of the FPSPS processed specimens are examined here to be correspondingly improved as a result of the refined microstructure. Full article
Open AccessArticle Plastic Behavior of Metallic Damping Materials under Cyclical Shear Loading
Materials 2016, 9(6), 496; doi:10.3390/ma9060496
Received: 20 April 2016 / Revised: 14 June 2016 / Accepted: 17 June 2016 / Published: 21 June 2016
Cited by 1 | PDF Full-text (6437 KB) | HTML Full-text | XML Full-text
Abstract
Metallic shear panel dampers (SPDs) have been widely adopted in seismic engineering. In this study, axial and torsional specimens of four types of metallic damping materials, including three conventional metallic steels as well as low yield strength steel 160 (LYS160), were tested in
[...] Read more.
Metallic shear panel dampers (SPDs) have been widely adopted in seismic engineering. In this study, axial and torsional specimens of four types of metallic damping materials, including three conventional metallic steels as well as low yield strength steel 160 (LYS160), were tested in order to investigate the material response under repeated large plastic strain and low cycle fatigue between 10 and 30 cycles. The present study demonstrated that both the deformation capacity and fatigue performance of LYS160 were underestimated by the conversion from the traditional uniaxial tensile test. The main difference in the failure mechanism between LYS160 and the three conventional materials was determined from the scanning electron microscopy data. The dominant failure mode in LYS160 is stable interlaminate slip and not bucking. Our results provide physical insights into the origin of the large deformation capacity, which is an important foundation for the lightweight design of SPDs. Full article
(This article belongs to the Section Structure Analysis and Characterization)

Review

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Open AccessReview Graphene–Gold Nanoparticles Hybrid—Synthesis, Functionalization, and Application in a Electrochemical and Surface-Enhanced Raman Scattering Biosensor
Materials 2016, 9(6), 406; doi:10.3390/ma9060406
Received: 12 April 2016 / Revised: 13 May 2016 / Accepted: 17 May 2016 / Published: 24 May 2016
Cited by 15 | PDF Full-text (4478 KB) | HTML Full-text | XML Full-text
Abstract
Graphene is a single-atom-thick two-dimensional carbon nanosheet with outstanding chemical, electrical, material, optical, and physical properties due to its large surface area, high electron mobility, thermal conductivity, and stability. These extraordinary features of graphene make it a key component for different applications in
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Graphene is a single-atom-thick two-dimensional carbon nanosheet with outstanding chemical, electrical, material, optical, and physical properties due to its large surface area, high electron mobility, thermal conductivity, and stability. These extraordinary features of graphene make it a key component for different applications in the biosensing and imaging arena. However, the use of graphene alone is correlated with certain limitations, such as irreversible self-agglomerations, less colloidal stability, poor reliability/repeatability, and non-specificity. The addition of gold nanostructures (AuNS) with graphene produces the graphene–AuNS hybrid nanocomposite which minimizes the limitations as well as providing additional synergistic properties, that is, higher effective surface area, catalytic activity, electrical conductivity, water solubility, and biocompatibility. This review focuses on the fundamental features of graphene, the multidimensional synthesis, and multipurpose applications of graphene–Au nanocomposites. The paper highlights the graphene–gold nanoparticle (AuNP) as the platform substrate for the fabrication of electrochemical and surface-enhanced Raman scattering (SERS)-based biosensors in diverse applications as well as SERS-directed bio-imaging, which is considered as an emerging sector for monitoring stem cell differentiation, and detection and treatment of cancer. Full article
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Open AccessReview Effects of Rare Earth Metals on Steel Microstructures
Materials 2016, 9(6), 417; doi:10.3390/ma9060417
Received: 6 April 2016 / Revised: 17 May 2016 / Accepted: 19 May 2016 / Published: 27 May 2016
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Abstract
Rare earth metals are used in semiconductors, solar cells and catalysts. This review focuses on the background of oxide metallurgy technologies, the chemical and physical properties of rare earth (RE) metals, the background of oxide metallurgy, the functions of RE metals in steelmaking,
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Rare earth metals are used in semiconductors, solar cells and catalysts. This review focuses on the background of oxide metallurgy technologies, the chemical and physical properties of rare earth (RE) metals, the background of oxide metallurgy, the functions of RE metals in steelmaking, and the influences of RE metals on steel microstructures. Future prospects for RE metal applications in steelmaking are also presented. Full article
(This article belongs to the Section Structure Analysis and Characterization)
Open AccessReview Calcium Phosphate as a Key Material for Socially Responsible Tissue Engineering
Materials 2016, 9(6), 434; doi:10.3390/ma9060434
Received: 15 March 2016 / Revised: 3 May 2016 / Accepted: 27 May 2016 / Published: 1 June 2016
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Abstract
Socially responsible technologies are designed while taking into consideration the socioeconomic, geopolitical and environmental limitations of regions in which they will be implemented. In the medical context, this involves making therapeutic platforms more accessible and affordable to patients in poor regions of the
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Socially responsible technologies are designed while taking into consideration the socioeconomic, geopolitical and environmental limitations of regions in which they will be implemented. In the medical context, this involves making therapeutic platforms more accessible and affordable to patients in poor regions of the world wherein a given disease is endemic. This often necessitates going against the reigning trend of making therapeutic nanoparticles ever more structurally complex and expensive. However, studies aimed at simplifying materials and formulations while maintaining the functionality and therapeutic response of their more complex counterparts seldom provoke a significant interest in the scientific community. In this review we demonstrate that such compositional simplifications are meaningful when it comes to the design of a solution for osteomyelitis, a disease that is in its natural, non-postoperative form particularly prevalent in the underdeveloped parts of the world wherein poverty, poor sanitary conditions, and chronically compromised defense lines of the immune system are the norm. We show that calcium phosphate nanoparticles, which are inexpensive to make, could be chemically designed to possess the same functionality as a hypothetic mixture additionally composed of: (a) a bone growth factor; (b) an antibiotic for prophylactic or anti-infective purposes; (c) a bisphosphonate as an antiresorptive compound; (d) a viral vector to enable the intracellular delivery of therapeutics; (e) a luminescent dye; (f) a radiographic component; (g) an imaging contrast agent; (h) a magnetic domain; and (i) polymers as viscous components enabling the injectability of the material and acting as carriers for the sustained release of a drug. In particular, calcium phosphates could: (a) produce tunable drug release profiles; (b) take the form of viscous and injectable, self-setting pastes; (c) be naturally osteo-inductive and inhibitory for osteoclastogenesis; (d) intracellularly deliver bioactive compounds; (e) accommodate an array of functional ions; (f) be processed into macroporous constructs for tissue engineering; and (g) be naturally antimicrobial. All in all, we see in calcium phosphates the presence of a protean nature whose therapeutic potentials have been barely tapped into. Full article
(This article belongs to the Special Issue Selected papers from ISN2A2016)
Open AccessReview Green Composites Made of Bamboo Fabric and Poly (Lactic) Acid for Packaging Applications—A Review
Materials 2016, 9(6), 435; doi:10.3390/ma9060435
Received: 18 January 2016 / Revised: 28 April 2016 / Accepted: 29 April 2016 / Published: 1 June 2016
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Abstract
Petroleum based thermoplastics are widely used in a range of applications, particularly in packaging. However, their usage has resulted in soaring pollutant emissions. Thus, researchers have been driven to seek environmentally friendly alternative packaging materials which are recyclable as well as biodegradable. Due
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Petroleum based thermoplastics are widely used in a range of applications, particularly in packaging. However, their usage has resulted in soaring pollutant emissions. Thus, researchers have been driven to seek environmentally friendly alternative packaging materials which are recyclable as well as biodegradable. Due to the excellent mechanical properties of natural fibres, they have been extensively used to reinforce biopolymers to produce biodegradable composites. A detailed understanding of the properties of such composite materials is vital for assessing their applicability to various products. The present review discusses several functional properties related to packaging applications in order to explore the potential of bamboo fibre fabric-poly (lactic) acid composites for packaging applications. Physical properties, heat deflection temperature, impact resistance, recyclability and biodegradability are important functional properties of packaging materials. In this review, we will also comprehensively discuss the chronological events and applications of natural fibre biopolymer composites. Full article
(This article belongs to the Section Advanced Composites)
Open AccessReview Hydrogels as a Replacement Material for Damaged Articular Hyaline Cartilage
Materials 2016, 9(6), 443; doi:10.3390/ma9060443
Received: 5 May 2016 / Revised: 24 May 2016 / Accepted: 30 May 2016 / Published: 3 June 2016
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Abstract
Hyaline cartilage is a strong durable material that lubricates joint movement. Due to its avascular structure, cartilage has a poor self-healing ability, thus, a challenge in joint recovery. When severely damaged, cartilage may need to be replaced. However, currently we are unable to
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Hyaline cartilage is a strong durable material that lubricates joint movement. Due to its avascular structure, cartilage has a poor self-healing ability, thus, a challenge in joint recovery. When severely damaged, cartilage may need to be replaced. However, currently we are unable to replicate the hyaline cartilage, and as such, alternative materials with considerably different properties are used. This results in undesirable side effects, including inadequate lubrication, wear debris, wear of the opposing articular cartilage, and weakening of the surrounding tissue. With the number of surgeries for cartilage repair increasing, a need for materials that can better mimic cartilage, and support the surrounding material in its typical function, is becoming evident. Here, we present a brief overview of the structure and properties of the hyaline cartilage and the current methods for cartilage repair. We then highlight some of the alternative materials under development as potential methods of repair; this is followed by an overview of the development of tough hydrogels. In particular, double network (DN) hydrogels are a promising replacement material, with continually improving physical properties. These hydrogels are coming closer to replicating the strength and toughness of the hyaline cartilage, while offering excellent lubrication. We conclude by highlighting several different methods of integrating replacement materials with the native joint to ensure stability and optimal behaviour. Full article
(This article belongs to the Section Biomaterials)
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Open AccessReview Methacrylate Polymer Monoliths for Separation Applications
Materials 2016, 9(6), 446; doi:10.3390/ma9060446
Received: 8 April 2016 / Revised: 10 May 2016 / Accepted: 20 May 2016 / Published: 3 June 2016
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Abstract
This review summarizes the development of methacrylate-based polymer monoliths for separation science applications. An introduction to monoliths is presented, followed by the preparation methods and characteristics specific to methacrylate monoliths. Both traditional chemical based syntheses and emerging additive manufacturing methods are presented along
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This review summarizes the development of methacrylate-based polymer monoliths for separation science applications. An introduction to monoliths is presented, followed by the preparation methods and characteristics specific to methacrylate monoliths. Both traditional chemical based syntheses and emerging additive manufacturing methods are presented along with an analysis of the different types of functional groups, which have been utilized with methacrylate monoliths. The role of methacrylate based porous materials in separation science in industrially important chemical and biological separations are discussed, with particular attention given to the most recent developments and challenges associated with these materials. While these monoliths have been shown to be useful for a wide variety of applications, there is still scope for exerting better control over the porous architectures and chemistries obtained from the different fabrication routes. Conclusions regarding this previous work are drawn and an outlook towards future challenges and potential developments in this vibrant research area are presented. Discussed in particular are the potential of additive manufacturing for the preparation of monolithic structures with pre-defined multi-scale porous morphologies and for the optimization of surface reactive chemistries. Full article
(This article belongs to the Special Issue Porous Monolithic Materials for Applications in Separation Science)
Open AccessReview Bioinspired Materials for Water Purification
Materials 2016, 9(6), 447; doi:10.3390/ma9060447
Received: 30 April 2016 / Revised: 30 May 2016 / Accepted: 31 May 2016 / Published: 3 June 2016
Cited by 1 | PDF Full-text (1449 KB) | HTML Full-text | XML Full-text
Abstract
Water scarcity issues associated with inadequate access to clean water and sanitation is a ubiquitous problem occurring globally. Addressing future challenges will require a combination of new technological development in water purification and environmental remediation technology with suitable conservation policies. In this scenario,
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Water scarcity issues associated with inadequate access to clean water and sanitation is a ubiquitous problem occurring globally. Addressing future challenges will require a combination of new technological development in water purification and environmental remediation technology with suitable conservation policies. In this scenario, new bioinspired materials will play a pivotal role in the development of more efficient and environmentally friendly solutions. The role of amphiphilic self-assembly on the fabrication of new biomimetic membranes for membrane separation like reverse osmosis is emphasized. Mesoporous support materials for semiconductor growth in the photocatalytic degradation of pollutants and new carriers for immobilization of bacteria in bioreactors are used in the removal and processing of different kind of water pollutants like heavy metals. Obstacles to improve and optimize the fabrication as well as a better understanding of their performance in small-scale and pilot purification systems need to be addressed. However, it is expected that these new biomimetic materials will find their way into the current water purification technologies to improve their purification/removal performance in a cost-effective and environmentally friendly way. Full article
(This article belongs to the Special Issue Bioinspired and Biomimetic Materials)
Open AccessReview Bio-Inspired Functional Surfaces Based on Laser-Induced Periodic Surface Structures
Materials 2016, 9(6), 476; doi:10.3390/ma9060476
Received: 28 April 2016 / Revised: 6 June 2016 / Accepted: 7 June 2016 / Published: 15 June 2016
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Abstract
Nature developed numerous solutions to solve various technical problems related to material surfaces by combining the physico-chemical properties of a material with periodically aligned micro/nanostructures in a sophisticated manner. The utilization of ultra-short pulsed lasers allows mimicking numerous of these features by generating
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Nature developed numerous solutions to solve various technical problems related to material surfaces by combining the physico-chemical properties of a material with periodically aligned micro/nanostructures in a sophisticated manner. The utilization of ultra-short pulsed lasers allows mimicking numerous of these features by generating laser-induced periodic surface structures (LIPSS). In this review paper, we describe the physical background of LIPSS generation as well as the physical principles of surface related phenomena like wettability, reflectivity, and friction. Then we introduce several biological examples including e.g., lotus leafs, springtails, dessert beetles, moth eyes, butterfly wings, weevils, sharks, pangolins, and snakes to illustrate how nature solves technical problems, and we give a comprehensive overview of recent achievements related to the utilization of LIPSS to generate superhydrophobic, anti-reflective, colored, and drag resistant surfaces. Finally, we conclude with some future developments and perspectives related to forthcoming applications of LIPSS-based surfaces. Full article
(This article belongs to the Special Issue Bioinspired and Biomimetic Materials)
Open AccessFeature PaperReview A Review on Electroactive Polymers for Waste Heat Recovery
Materials 2016, 9(6), 485; doi:10.3390/ma9060485
Received: 30 April 2016 / Revised: 1 June 2016 / Accepted: 14 June 2016 / Published: 17 June 2016
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Abstract
This paper reviews materials for thermoelectric waste heat recovery, and discusses selected industrial and distributed waste heat sources as well as recovery methods that are currently applied. Thermoelectric properties, especially electrical conductivity, thermopower, thermal conductivity and the thermoelectric figures of merit, are considered
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This paper reviews materials for thermoelectric waste heat recovery, and discusses selected industrial and distributed waste heat sources as well as recovery methods that are currently applied. Thermoelectric properties, especially electrical conductivity, thermopower, thermal conductivity and the thermoelectric figures of merit, are considered when evaluating thermoelectric materials for waste heat recovery. Alloys and oxides are briefly discussed as materials suitable for medium- and high-grade sources. Electroactive polymers are presented as a new group of materials for low-grade sources. Polyaniline is a particularly fitting polymer for these purposes. We also discuss types of modifiers and modification methods, and their influence on the thermoelectric performance of this class of polymers. Full article
(This article belongs to the Special Issue Electroactive Polymers)
Open AccessReview Antireflective Coatings: Conventional Stacking Layers and Ultrathin Plasmonic Metasurfaces, A Mini-Review
Materials 2016, 9(6), 497; doi:10.3390/ma9060497
Received: 2 May 2016 / Revised: 31 May 2016 / Accepted: 15 June 2016 / Published: 21 June 2016
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Abstract
Reduction of unwanted light reflection from a surface of a substance is very essential for improvement of the performance of optical and photonic devices. Antireflective coatings (ARCs) made of single or stacking layers of dielectrics, nano/microstructures or a mixture of both are the
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Reduction of unwanted light reflection from a surface of a substance is very essential for improvement of the performance of optical and photonic devices. Antireflective coatings (ARCs) made of single or stacking layers of dielectrics, nano/microstructures or a mixture of both are the conventional design geometry for suppression of reflection. Recent progress in theoretical nanophotonics and nanofabrication has enabled more flexibility in design and fabrication of miniaturized coatings which has in turn advanced the field of ARCs considerably. In particular, the emergence of plasmonic and metasurfaces allows for the realization of broadband and angular-insensitive ARC coatings at an order of magnitude thinner than the operational wavelengths. In this review, a short overview of the development of ARCs, with particular attention paid to the state-of-the-art plasmonic- and metasurface-based antireflective surfaces, is presented. Full article
(This article belongs to the Special Issue Green Nanotechnology)
Open AccessReview Antimicrobial Approaches for Textiles: From Research to Market
Materials 2016, 9(6), 498; doi:10.3390/ma9060498
Received: 15 April 2016 / Revised: 8 June 2016 / Accepted: 15 June 2016 / Published: 21 June 2016
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Abstract
The large surface area and ability to retain moisture of textile structures enable microorganisms’ growth, which causes a range of undesirable effects, not only on the textile itself, but also on the user. Due to the public health awareness of the pathogenic effects
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The large surface area and ability to retain moisture of textile structures enable microorganisms’ growth, which causes a range of undesirable effects, not only on the textile itself, but also on the user. Due to the public health awareness of the pathogenic effects on personal hygiene and associated health risks, over the last few years, intensive research has been promoted in order to minimize microbes’ growth on textiles. Therefore, to impart an antimicrobial ability to textiles, different approaches have been studied, being mainly divided into the inclusion of antimicrobial agents in the textile polymeric fibers or their grafting onto the polymer surface. Regarding the antimicrobial agents, different types have been used, such as quaternary ammonium compounds, triclosan, metal salts, polybiguanides or even natural polymers. Any antimicrobial treatment performed on a textile, besides being efficient against microorganisms, must be non-toxic to the consumer and to the environment. This review mainly intends to provide an overview of antimicrobial agents and treatments that can be performed to produce antimicrobial textiles, using chemical or physical approaches, which are under development or already commercially available in the form of isolated agents or textile fibers or fabrics. Full article
(This article belongs to the Special Issue Self-Cleaning and Antimicrobial Surfaces)

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Open AccessErratum Erratum: Stefanescu, E.A.; Daranga, C.; Stefanescu, C. Insight into the Broad Field of Polymer Nanocomposites: From Carbon Nanotubes to Clay Nanoplatelets, via Metal Nanoparticles. Materials 2009, 2, 2095–2153
Materials 2016, 9(6), 459; doi:10.3390/ma9060459
Received: 8 June 2016 / Revised: 8 June 2016 / Accepted: 8 June 2016 / Published: 13 June 2016
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Abstract
It has been brought to our attention that Laponite® is a trademark of BYK Additives, however the trademark symbol is missing in [1].[...] Full article
Open AccessRetraction Retraction: Sun L. et al. Porosity Defect Remodeling and Tensile Analysis of Cast Steel. Materials 2016, 9, 119, doi:10.3390/ma9020119
Materials 2016, 9(6), 488; doi:10.3390/ma9060488
Received: 17 June 2016 / Revised: 17 June 2016 / Accepted: 17 June 2016 / Published: 18 June 2016
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Abstract
We have been made aware that the figures and experimental data of this article [1] are duplicated from another publication by Hardin et al. [...] Full article
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