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Materials, Volume 6, Issue 8 (August 2013), Pages 3035-3675

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Open AccessArticle UV Spectrometric Indirect Analysis of Brominated MWCNTs with UV Active Thiols and an Alkene—Reaction Kinetics, Quantification and Differentiation of Adsorbed Bromine and Oxygen
Materials 2013, 6(8), 3035-3063; doi:10.3390/ma6083035
Received: 30 April 2013 / Revised: 12 July 2013 / Accepted: 16 July 2013 / Published: 24 July 2013
PDF Full-text (803 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Indirect UV-absorption spectrometry was shown to be a valuable tool for chemical characterization of functionalized carbon nanotubes (CNTs). It complements data from X-ray photoelectron spectroscopy (XPS) or FTIR analysis since it helps to clarify the type and concentration of functional groups. The [...] Read more.
Indirect UV-absorption spectrometry was shown to be a valuable tool for chemical characterization of functionalized carbon nanotubes (CNTs). It complements data from X-ray photoelectron spectroscopy (XPS) or FTIR analysis since it helps to clarify the type and concentration of functional groups. The principles of indirect application of UV-spectrometry and its mathematical interpretation are discussed. Their facile application, together with their adequate sensitivity and high flexibility, make UV-absorption-based approaches a valuable alternative to fluorescence spectrometry. Here, the approach was applied to the chemical analysis of oxidizing substances on CNTs. For this, pristine CNTs of low but finite oxygen content as well as brominated CNTs were analyzed by reaction in suspension with UV-active thiol reagents and a styrene derivative. It was shown that carefully selected reagents allow differentiation and quantification of bromine and generally oxidizing entities like oxygen. For brominated CNTs, it was shown that physisorbed bromine may dominate the overall bromine content. Full article
(This article belongs to the Special Issue Carbon Nanotubes)
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Open AccessArticle Enrichment of Large-Diameter Single-Walled Carbon Nanotubes (SWNTs) with Metallo-Octaethylporphyrins
Materials 2013, 6(8), 3064-3078; doi:10.3390/ma6083064
Received: 25 March 2013 / Revised: 2 July 2013 / Accepted: 16 July 2013 / Published: 24 July 2013
Cited by 5 | PDF Full-text (905 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We report here a detailed experimental investigation on noncovalent functionalization of single-walled carbon nanotubes (SWNTs) with four different metallo-octaethylporphyrins (MOEPs). It has been found that the identity of the center metal of MOEP strongly influences the solubilization of SWNTs. MnOEPs and ZnOEPs [...] Read more.
We report here a detailed experimental investigation on noncovalent functionalization of single-walled carbon nanotubes (SWNTs) with four different metallo-octaethylporphyrins (MOEPs). It has been found that the identity of the center metal of MOEP strongly influences the solubilization of SWNTs. MnOEPs and ZnOEPs successfully extracted SWNTs in methanol, as confirmed by absorption spectroscopy, while CoOEPs and CuOEPs were not able to extract SWNTs at all. Atomic force microscopy (AFM) studies revealed that large SWNTs bundles could be exfoliated into either individual SWNTs or very small bundles by complexation with ZnOEP molecules. As for enrichment of SWNTs, ZnOEPs and MnOEPs show similar diameter discrimination ability toward 76-CoMoCAT, providing the extracted SWNTs with relatively large diameters. Full article
(This article belongs to the Special Issue Carbon Nanotubes)
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Open AccessArticle Red, Green, and Blue Photoluminescence of Ba2SiO4:M (M = Eu3+, Eu2+, Sr2+) Nanophosphors
Materials 2013, 6(8), 3079-3093; doi:10.3390/ma6083079
Received: 9 May 2013 / Revised: 7 July 2013 / Accepted: 16 July 2013 / Published: 24 July 2013
Cited by 11 | PDF Full-text (753 KB) | HTML Full-text | XML Full-text
Abstract
Divalent europium doped barium orthosilicate is a very important phosphor for the production of light emitting diodes (LEDs), generally associated to the green emission color of micron-sized crystals synthesized by means of solid-state reactions. This work presents the combustion synthesis as an [...] Read more.
Divalent europium doped barium orthosilicate is a very important phosphor for the production of light emitting diodes (LEDs), generally associated to the green emission color of micron-sized crystals synthesized by means of solid-state reactions. This work presents the combustion synthesis as an energy and time-saving preparation method for very small nano-sized Ba2SiO4 particles, flexibly doped to acquire different emission energies. The size of the resulting spherical nanoparticles (NPs) of the green emitting Ba2SiO4:Eu2+ was estimated to about 35 nm applying the Scherrer equation and further characterized with aid of atomic force microscopy (AFM) as well as scanning electron microscopy (SEM). This phosphor is able to build homogeneous luminescent suspensions and was successfully down-sized without changing the optical properties in comparison to the bulk phosphors. Besides the X-ray diffraction (XRD) analysis and the different types of microscopy, the samples were characterized by luminescence spectroscopy. Undoped Ba2SiO4 NPs are not luminescent, but show characteristic red emission of the 5D07FJ (J = 0–4) electronic transitions when doped with Eu3+ ions. Moreover, these orthosilicate nanoparticles generate blue light at low temperatures due to impurity-trapped excitons, introduced by the partial substitution of the Ba2+ with Sr2+ ions in the Ba2SiO4 lattice causing a substantial distortion. A model for the temperature behavior of the defect luminescence as well as for their nature is provided, based on temperature-dependent luminescence spectra and lifetime measurements. Full article
(This article belongs to the Special Issue Luminescent Materials 2013)
Open AccessArticle Integration of Carbon Nanotubes in Microsystems: Local Growth and Electrical Properties of Contacts
Materials 2013, 6(8), 3094-3107; doi:10.3390/ma6083094
Received: 30 April 2013 / Revised: 10 July 2013 / Accepted: 18 July 2013 / Published: 24 July 2013
Cited by 3 | PDF Full-text (932 KB) | HTML Full-text | XML Full-text
Abstract
Carbon nanotubes (CNTs) have been directly grown onto a silicon microsystem by a local synthesis method. This method has potential for wafer-level complimentary metal-oxide-semiconductor (CMOS) transistor-compatible integration of CNTs into more complex Si microsystems; enabling, e.g., gas sensors at low cost. In [...] Read more.
Carbon nanotubes (CNTs) have been directly grown onto a silicon microsystem by a local synthesis method. This method has potential for wafer-level complimentary metal-oxide-semiconductor (CMOS) transistor-compatible integration of CNTs into more complex Si microsystems; enabling, e.g., gas sensors at low cost. In this work, we demonstrate that the characteristics of CNTs grown on specific locations can be changed by tuning the synthesis conditions. We also investigate the role of the contact between CNTs and the Si microsystem; observing a large influence on the electrical characteristics of our devices. Different contact modes can render either an ohmic or Schottky-like rectifying characteristics. Full article
(This article belongs to the Special Issue Carbon Nanotubes)
Open AccessArticle Use of Slag/Sugar Cane Bagasse Ash (SCBA) Blends in the Production of Alkali-Activated Materials
Materials 2013, 6(8), 3108-3127; doi:10.3390/ma6083108
Received: 28 March 2013 / Revised: 22 May 2013 / Accepted: 24 May 2013 / Published: 25 July 2013
Cited by 6 | PDF Full-text (1263 KB) | HTML Full-text | XML Full-text
Abstract
Blast furnace slag (BFS)/sugar cane bagasse ash (SCBA) blends were assessed for the production of alkali-activated pastes and mortars. SCBA was collected from a lagoon in which wastes from a sugar cane industry were poured. After previous dry and grinding processes, SCBA [...] Read more.
Blast furnace slag (BFS)/sugar cane bagasse ash (SCBA) blends were assessed for the production of alkali-activated pastes and mortars. SCBA was collected from a lagoon in which wastes from a sugar cane industry were poured. After previous dry and grinding processes, SCBA was chemically characterized: it had a large percentage of organic matter (ca. 25%). Solutions of sodium hydroxide and sodium silicate were used as activating reagents. Different BFS/SCBA mixtures were studied, replacing part of the BFS by SCBA from 0 to 40% by weight. The mechanical strength of mortar was measured, obtaining values about 60 MPa of compressive strength for BFS/SCBA systems after 270 days of curing at 20 °C. Also, microstructural properties were assessed by means of SEM, TGA, XRD, pH, electrical conductivity, FTIR spectroscopy and MIP. Results showed a good stability of matrices developed by means of alkali-activation. It was demonstrated that sugar cane bagasse ash is an interesting source for preparing alkali-activated binders. Full article
(This article belongs to the Special Issue Geopolymers and Geopolymeric Materials)
Open AccessArticle Effect of Boron-Doped Diamond Interlayer on Cutting Performance of Diamond Coated Micro Drills for Graphite Machining
Materials 2013, 6(8), 3128-3138; doi:10.3390/ma6083128
Received: 21 March 2013 / Revised: 29 May 2013 / Accepted: 19 July 2013 / Published: 25 July 2013
Cited by 3 | PDF Full-text (728 KB) | HTML Full-text | XML Full-text
Abstract
Thin boron doped diamond (BDD) film is deposited from trimethyl borate/acetone/hydrogen mixture on Co-cemented tungsten carbide (WC-Co) micro drills by using the hot filament chemical vapor deposition (HFCVD) technique. The boron peak on Raman spectrum confirms the boron incorporation in diamond film. [...] Read more.
Thin boron doped diamond (BDD) film is deposited from trimethyl borate/acetone/hydrogen mixture on Co-cemented tungsten carbide (WC-Co) micro drills by using the hot filament chemical vapor deposition (HFCVD) technique. The boron peak on Raman spectrum confirms the boron incorporation in diamond film. This film is used as an interlayer for subsequent CVD of micro-crystalline diamond (MCD) film. The Rockwell indentation test shows that boron doping could effectively improve the adhesive strength on substrate of as deposited thin diamond films. Dry drilling of graphite is chosen to check the multilayer (BDD + MCD) film performance. For the sake of comparison, machining tests are also carried out under identical conditions using BDD and MCD coated micro drills with no interlayer. The wear mechanism of the tools has been identified and correlated with the criterion used to evaluate the tool life. The results show that the multilayer (BDD + MCD) coated micro drill exhibits the longest tool life. Therefore, thin BDD interlayer is proved to be a new viable alternative and a suitable option for adherent diamond coatings on micro cutting tools. Full article
(This article belongs to the Special Issue Advances in Surface Coatings 2013)
Open AccessArticle Use of Cement Kiln Dust, Blast Furnace Slag and Marble Sludge in the Manufacture of Sustainable Artificial Aggregates by Means of Cold Bonding Pelletization
Materials 2013, 6(8), 3139-3159; doi:10.3390/ma6083139
Received: 20 May 2013 / Revised: 16 July 2013 / Accepted: 22 July 2013 / Published: 25 July 2013
Cited by 14 | PDF Full-text (829 KB) | HTML Full-text | XML Full-text
Abstract
In this work, three different samples of solid industrial wastes cement kiln dust (CKD), granulated blast furnace slag and marble sludge were employed in a cold bonding pelletization process for the sustainable production of artificial aggregates. The activating action of CKD components [...] Read more.
In this work, three different samples of solid industrial wastes cement kiln dust (CKD), granulated blast furnace slag and marble sludge were employed in a cold bonding pelletization process for the sustainable production of artificial aggregates. The activating action of CKD components on the hydraulic behavior of the slag was explored by evaluating the neo-formed phases present in several hydrated pastes. Particularly, the influence of free CaO and sulfates amount in the two CKD samples on slag reactivity was evaluated. Cold bonded artificial aggregates were characterized by determining physical and mechanical properties of two selected size fractions of the granules for each studied mixture. Eighteen types of granules were employed in C28/35 concrete manufacture where coarser natural aggregate were substituted with the artificial ones. Finally, lightweight concretes were obtained, proving the suitability of the cold bonding pelletization process in artificial aggregate sustainable production. Full article
Open AccessArticle Local Synthesis of Carbon Nanotubes in Silicon Microsystems: The Effect of Temperature Distribution on Growth Structure
Materials 2013, 6(8), 3160-3170; doi:10.3390/ma6083160
Received: 21 May 2013 / Revised: 19 July 2013 / Accepted: 22 July 2013 / Published: 26 July 2013
Cited by 2 | PDF Full-text (5813 KB) | HTML Full-text | XML Full-text
Abstract
Local synthesis and direct integration of carbon nanotubes (CNTs) into microsystems is a promising method for producing CNT-based devices in a single step, low-cost, and wafer-level, CMOS/MEMS-compatible process. In this report, the structure of the locally grown CNTs are studied by transmission [...] Read more.
Local synthesis and direct integration of carbon nanotubes (CNTs) into microsystems is a promising method for producing CNT-based devices in a single step, low-cost, and wafer-level, CMOS/MEMS-compatible process. In this report, the structure of the locally grown CNTs are studied by transmission imaging in scanning electron microscopy—S(T)EM. The characterization is performed directly on the microsystem, without any post-synthesis processing required. The results show an effect of temperature on the structure of CNTs: high temperature favors thin and regular structures, whereas low temperature favors “bamboo-like” structures. Full article
(This article belongs to the Special Issue Carbon Nanotubes)
Open AccessArticle Inorganic Nanoparticle-Modified Poly(Phenylene Sulphide)/ Carbon Fiber Laminates: Thermomechanical Behaviour
Materials 2013, 6(8), 3171-3193; doi:10.3390/ma6083171
Received: 2 May 2013 / Revised: 15 July 2013 / Accepted: 23 July 2013 / Published: 26 July 2013
Cited by 10 | PDF Full-text (1026 KB) | HTML Full-text | XML Full-text
Abstract
Carbon fiber (CF)-reinforced high-temperature thermoplastics such as poly(phenylene sulphide) (PPS) are widely used in structural composites for aerospace and automotive applications. The porosity of CF-reinforced polymers is a very important topic for practical applications since there is a direct correlation between void [...] Read more.
Carbon fiber (CF)-reinforced high-temperature thermoplastics such as poly(phenylene sulphide) (PPS) are widely used in structural composites for aerospace and automotive applications. The porosity of CF-reinforced polymers is a very important topic for practical applications since there is a direct correlation between void content and mechanical properties. In this study, inorganic fullerene-like tungsten disulphide (IF-WS2) lubricant nanoparticles were used to manufacture PPS/IF-WS2/CF laminates via melt-blending and hot-press processing, and the effect of IF-WS2 loading on the quality, thermal and mechanical behaviour of the hybrid composites was investigated. The addition of IF-WS2 improved fiber impregnation, resulting in lower degree of porosity and increased delamination resistance, compression and flexural properties; their reinforcement effect was greater at temperatures above the glass transition (Tg). IF-WS2 contents higher than 0.5 wt % increased Tg and the heat deflection temperature while reduced the coefficient of thermal expansion. The multiscale laminates exhibited higher ignition point and notably reduced peak heat release rate compared to PPS/CF. The coexistence of micro- and nano-scale fillers resulted in synergistic effects that enhanced the stiffness, strength, thermal conductivity and flame retardancy of the matrix. The results presented herein demonstrate that the IF-WS2 are very promising nanofillers to improve the thermomechanical properties of conventional thermoplastic/CF composites. Full article
(This article belongs to the Section Porous Materials)
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Open AccessArticle Fluorescent Magnetic Bioprobes by Surface Modification of Magnetite Nanoparticles
Materials 2013, 6(8), 3213-3225; doi:10.3390/ma6083213
Received: 3 June 2013 / Revised: 28 June 2013 / Accepted: 23 July 2013 / Published: 31 July 2013
Cited by 7 | PDF Full-text (648 KB) | HTML Full-text | XML Full-text
Abstract
Bimodal nanoprobes comprising both magnetic and optical functionalities have been prepared via a sequential two-step process. Firstly, magnetite nanoparticles (MNPs) with well-defined cubic shape and an average dimension of 80 nm were produced by hydrolysis of iron sulfate and were then surface [...] Read more.
Bimodal nanoprobes comprising both magnetic and optical functionalities have been prepared via a sequential two-step process. Firstly, magnetite nanoparticles (MNPs) with well-defined cubic shape and an average dimension of 80 nm were produced by hydrolysis of iron sulfate and were then surface modified with silica shells by using the sol-gel method. The Fe3O4@SiO2 particles were then functionalized with the fluorophore, fluorescein isothiocyanate (FITC), mediated by assembled shells of the cationic polyelectrolyte, polyethyleneimine (PEI). The Fe3O4 functionalized particles were then preliminary evaluated as fluorescent and magnetic probes by performing studies in which neuroblast cells have been contacted with these nanomaterials. Full article
(This article belongs to the Special Issue Luminescent Materials 2013)
Open AccessArticle A New Metasurface Superstrate Structure for Antenna Performance Enhancement
Materials 2013, 6(8), 3226-3240; doi:10.3390/ma6083226
Received: 24 June 2013 / Revised: 12 July 2013 / Accepted: 24 July 2013 / Published: 31 July 2013
Cited by 10 | PDF Full-text (1535 KB) | HTML Full-text | XML Full-text
Abstract
A new metasurface superstrate structure (MSS)-loaded dual band microstrip line-fed small patch antenna is presented in this paper. The proposed antenna was designed on a ceramic-filled bioplastic sandwich substrate with a high dielectric constant. The proposed 7 × 6 element, square-shaped, single-sided [...] Read more.
A new metasurface superstrate structure (MSS)-loaded dual band microstrip line-fed small patch antenna is presented in this paper. The proposed antenna was designed on a ceramic-filled bioplastic sandwich substrate with a high dielectric constant. The proposed 7 × 6 element, square-shaped, single-sided MSS significantly improved the bandwidth and gain of the proposed antenna. The proposed MSS incorporated a slotted patch antenna that effectively increased the measured operating bandwidth from 13.3% to 18.8% and from 14.8% to 23.2% in the lower and upper bands, respectively. Moreover, the average gain of the proposed MSS-based antenna was enhanced from 2.12 dBi to 3.02 dBi in the lower band and from 4.10 dBi to 5.28 dBi in the upper band compared to the patch antenna alone. In addition to the bandwidth and gain improvements, more directive radiation characteristics were also observed from the MSS antenna compared to the patch itself. The effects of the MSS elements and the ground plane length on the reflection coefficient of the antenna were analyzed and optimized. The overall performance makes the proposed antenna appropriate for RFID and WLAN applications. Full article
Open AccessArticle Dynamic Initiation and Propagation of Multiple Cracks in Brittle Materials
Materials 2013, 6(8), 3241-3253; doi:10.3390/ma6083241
Received: 31 May 2013 / Revised: 10 July 2013 / Accepted: 24 July 2013 / Published: 31 July 2013
Cited by 1 | PDF Full-text (461 KB) | HTML Full-text | XML Full-text
Abstract
Brittle materials such as rock and ceramic usually exhibit apparent increases of strength and toughness when subjected to dynamic loading. The reasons for this phenomenon are not yet well understood, although a number of hypotheses have been proposed. Based on dynamic fracture [...] Read more.
Brittle materials such as rock and ceramic usually exhibit apparent increases of strength and toughness when subjected to dynamic loading. The reasons for this phenomenon are not yet well understood, although a number of hypotheses have been proposed. Based on dynamic fracture mechanics, the present work offers an alternate insight into the dynamic behaviors of brittle materials. Firstly, a single crack subjected to stress wave excitations is investigated to obtain the dynamic crack-tip stress field and the dynamic stress intensity factor. Second, based on the analysis of dynamic stress intensity factor, the fracture initiation sizes and crack size distribution under different loading rates are obtained, and the power law with the exponent of −2/3 is derived to describe the fracture initiation size. Third, with the help of the energy balance concept, the dynamic increase of material strength is directly derived based on the proposed multiple crack evolving criterion. Finally, the model prediction is compared with the dynamic impact experiments, and the model results agree well with the experimentally measured dynamic increasing factor (DIF). Full article
(This article belongs to the Section Structure Analysis and Characterization)
Open AccessArticle Properties of Cast Films Made from Different Ratios of Whey Protein Isolate, Hydrolysed Whey Protein Isolate and Glycerol
Materials 2013, 6(8), 3254-3269; doi:10.3390/ma6083254
Received: 3 June 2013 / Revised: 4 July 2013 / Accepted: 24 July 2013 / Published: 2 August 2013
Cited by 21 | PDF Full-text (1032 KB) | HTML Full-text | XML Full-text
Abstract
Whey protein isolate (WPI)-based cast films are very brittle, due to several chain interactions caused by a large amount of different functional groups. In order to overcome film brittleness, plasticizers, like glycerol, are commonly used. As a result of adding plasticizers, the [...] Read more.
Whey protein isolate (WPI)-based cast films are very brittle, due to several chain interactions caused by a large amount of different functional groups. In order to overcome film brittleness, plasticizers, like glycerol, are commonly used. As a result of adding plasticizers, the free volume between the polymer chains increases, leading to higher permeability values. The objective of this study was to investigate the effect of partially substituting glycerol by hydrolysed whey protein isolate (h-WPI) in WPI-based cast films on their mechanical, optical and barrier properties. As recently published by the author, it is proven that increasing the h-WPI content in WPI-based films at constant glycerol concentrations significantly increases film flexibility, while maintaining the barrier properties. The present study considered these facts in order to increase the barrier performance, while maintaining film flexibility. Therefore glycerol was partially replaced by h-WPI in WPI-based cast films. The results clearly indicate that partially replacing glycerol by h-WPI reduces the oxygen permeability and the water vapor transmission rate, while the mechanical properties did not change significantly. Thus, film flexibility was maintained, even though the plasticizer concentration was decreased. Full article
(This article belongs to the Section Biomaterials)
Open AccessArticle Bactericidal Activity of Aqueous Acrylic Paint Dispersion for Wooden Substrates Based on TiO2 Nanoparticles Activated by Fluorescent Light
Materials 2013, 6(8), 3270-3283; doi:10.3390/ma6083270
Received: 6 May 2013 / Revised: 14 June 2013 / Accepted: 19 July 2013 / Published: 2 August 2013
Cited by 5 | PDF Full-text (561 KB) | HTML Full-text | XML Full-text
Abstract
The photocatalytic effect of TiO2 has great potential for the disinfection of surfaces. Most studies reported in the literature use UV activation of TiO2, while visible light has been used only in a few applications. In these studies, high [...] Read more.
The photocatalytic effect of TiO2 has great potential for the disinfection of surfaces. Most studies reported in the literature use UV activation of TiO2, while visible light has been used only in a few applications. In these studies, high concentrations of TiO2, which can compromise surface properties, have been used. In this work, we have developed an acrylic-water paint dispersion containing low TiO2 content (2 vol %) for the inactivation of microorganisms involved in hospital-acquired infections. The nanoparticles and the coating have been characterized using spectroscopic techniques and transmission electron microscopy, showing their homogenous dispersion in the acrylic urethane coating. A common fluorescent light source was used to activate the photocatalytic activity of TiO2. The paint dispersion showed antimicrobial activity against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. The coating containing the TiO2 nanoparticles maintained good UV stability, strong adhesion to the substrate and high hardness. Therefore, the approach used is feasible for paint formulation aimed at disinfection of healthcare surfaces. Full article
(This article belongs to the Special Issue Biointerfaces and Materials)
Open AccessArticle In Vitro Activity of Gentamicin-Loaded Bioabsorbable Beads against Different Microorganisms
Materials 2013, 6(8), 3284-3293; doi:10.3390/ma6083284
Received: 31 May 2013 / Revised: 15 July 2013 / Accepted: 26 July 2013 / Published: 5 August 2013
Cited by 2 | PDF Full-text (259 KB) | HTML Full-text | XML Full-text
Abstract
Osteomyelitis is responsible for high treatment costs, long hospital stays, and results in substantial morbidity. Treatment with surgical debridement and antibiotic-impregnated Polymethylmetacrylate (PMMA) beads is the standard of care, providing high local but low serum antibiotic concentrations, thereby avoiding systemic toxicity. However, [...] Read more.
Osteomyelitis is responsible for high treatment costs, long hospital stays, and results in substantial morbidity. Treatment with surgical debridement and antibiotic-impregnated Polymethylmetacrylate (PMMA) beads is the standard of care, providing high local but low serum antibiotic concentrations, thereby avoiding systemic toxicity. However, for several reasons, the beads require surgical removal. Alternative antibiotic delivery systems should improve the treatment of bone infection, actively encourage bone healing and require no additional surgery for removal. We investigated the activity of gentamicin-loaded bioabsorbable beads against different microorganisms (Staphylococcus epidermidis, S. aureus, Escherichia coli, Enterococcus faecalis, Candida albicans) commonly causing surgical site bone infection, by microcalorimetry. Calcium sulphate beads containing gentamicin were incubated in microcalorimetry ampoules containing different concentrations of the corresponding microorganism. Growth medium with each germ and unloaded beads was used as positive control, growth medium with loaded beads alone as negative control. Bacterial growth-related heat production at 37 °C was measured for 24 h. Cultures without gentamicin-loaded beads produced heat-flow peaks corresponding to the exponential growth of the corresponding microorganisms in nutrient-rich medium. In contrast, cultures with gentamicin-loaded beads completely suppressed heat production during 24 h, demonstrating their antibiotic activity. Gentamicin-loaded beads effectively inhibited growth of susceptible microorganisms, under the described in vitro conditions. Full article
(This article belongs to the Special Issue Biointerfaces and Materials)
Open AccessArticle Comparison of Extruded and Sonicated Vesicles for Planar Bilayer Self-Assembly
Materials 2013, 6(8), 3294-3308; doi:10.3390/ma6083294
Received: 17 June 2013 / Revised: 22 July 2013 / Accepted: 24 July 2013 / Published: 5 August 2013
Cited by 12 | PDF Full-text (474 KB) | HTML Full-text | XML Full-text
Abstract
Lipid vesicles are an important class of biomaterials that have a wide range of applications, including drug delivery, cosmetic formulations and model membrane platforms on solid supports. Depending on the application, properties of a vesicle population such as size distribution, charge and [...] Read more.
Lipid vesicles are an important class of biomaterials that have a wide range of applications, including drug delivery, cosmetic formulations and model membrane platforms on solid supports. Depending on the application, properties of a vesicle population such as size distribution, charge and permeability need to be optimized. Preparation methods such as mechanical extrusion and sonication play a key role in controlling these properties, and yet the effects of vesicle preparation method on vesicular properties and integrity (e.g., shape, size, distribution and tension) remain incompletely understood. In this study, we prepared vesicles composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid by either extrusion or sonication, and investigated the effects on vesicle size distribution over time as well as the concomitant effects on the self-assembly of solid-supported planar lipid bilayers. Dynamic light scattering (DLS), quartz crystal microbalance with dissipation (QCM-D) monitoring, fluorescence recovery after photobleaching (FRAP) and atomic force microscopy (AFM) experiments were performed to characterize vesicles in solution as well as their interactions with silicon oxide substrates. Collectively, the data support that sonicated vesicles offer more robust control over the self-assembly of homogenous planar lipid bilayers, whereas extruded vesicles are vulnerable to aging and must be used soon after preparation. Full article
(This article belongs to the Special Issue Biointerfaces and Materials)
Open AccessArticle Microstructural Characterization of Calcite-Based Powder Materials Prepared by Planetary Ball Milling
Materials 2013, 6(8), 3361-3372; doi:10.3390/ma6083361
Received: 19 April 2013 / Revised: 20 June 2013 / Accepted: 24 July 2013 / Published: 7 August 2013
Cited by 3 | PDF Full-text (325 KB) | HTML Full-text | XML Full-text
Abstract
In this work, a planetary ball milling was used to modify the surface properties of calcite-based material from waste oyster shell under the rotational speed of 200–600 rpm, grinding time of 5–180 min and sample mass of 1–10 g. The milling significantly [...] Read more.
In this work, a planetary ball milling was used to modify the surface properties of calcite-based material from waste oyster shell under the rotational speed of 200–600 rpm, grinding time of 5–180 min and sample mass of 1–10 g. The milling significantly changed the microstructural properties of the calcite-based minerals (i.e., surface area, pore volume, true density, and porosity). The surface characterization of the resulting powder should be macroporous and/or nonporous based on the nitrogen adsorption/desorption isotherms. Under the optimal conditions at the rotational speed of 400 rpm, grinding time of 30 min and sample mass of 5 g, the resulting calcite-based powder had larger specific surface area (i.e., 10.64 m2·g1) than the starting material (i.e., 4.05 m2·g−1). This finding was also consistent with the measurement of laser-diffraction (i.e., 9.7 vs. 15.0 μm of mean diameter). In addition, the results from the scanning electron microscope (SEM) observation indicated that surface roughness can be enhanced as particle size decreases as a result of particle-particle attrition. Thus, grinding the aquacultural bioresource by a high-energy ball milling can create the fine materials, which may be applied in the fields of inorganic minerals like aggregate and construction material. Full article
(This article belongs to the Special Issue Biointerfaces and Materials)
Open AccessArticle Effect of Annealing Temperature on the Water Contact Angle of PVD Hard Coatings
Materials 2013, 6(8), 3373-3386; doi:10.3390/ma6083373
Received: 27 June 2013 / Revised: 26 July 2013 / Accepted: 2 August 2013 / Published: 7 August 2013
PDF Full-text (877 KB) | HTML Full-text | XML Full-text
Abstract
Various PVD (physical vapor deposition) hard coatings including nitrides and metal-doped diamond-like carbons (Me-DLC) were applied in plastic injection and die-casting molds to improve wear resistance and reduce sticking. In this study, nitrides hcp-AlN (hexagonal close-packed AlN), Cr2N, (CrAl)2 [...] Read more.
Various PVD (physical vapor deposition) hard coatings including nitrides and metal-doped diamond-like carbons (Me-DLC) were applied in plastic injection and die-casting molds to improve wear resistance and reduce sticking. In this study, nitrides hcp-AlN (hexagonal close-packed AlN), Cr2N, (CrAl)2N) and Me-DLC (Si-DLC and Cr-DLC) coatings were prepared using a closed field unbalanced magnetron reactive sputtering system. The coatings were annealed in air for 2 h at various temperatures, after which the anti-sticking properties were assessed using water contact angle (WCA) measurements. The as-deposited hcp-AlN, Cr2N and (CrAl)2N coatings exhibit hydrophobic behavior and exhibit respective WCAs of 119°, 106° and 101°. The as-deposited Si-DLC and Cr-DLC coatings exhibit hydrophilic behavior and exhibit respective WCAs of 74° and 88°. The annealed Cr2N and (CrAl)2N coatings exhibit hydrophobic behavior with higher WCAs, while the annealed hcp-AlN, Si-DLC and Cr-DLC coatings are hydrophilic. The increased WCA of the annealed Cr2N and (CrAl)2N coatings is related to their crystal structure and increased roughness. The decreased WCA of the annealed hcp-AlN, Si-DLC and Cr-DLC coatings is related to their crystal structures and has little correlation with roughness. Full article
(This article belongs to the Special Issue Advances in Surface Coatings 2013)
Open AccessArticle Thermal Fatigue Behavior of Air-Plasma Sprayed Thermal Barrier Coating with Bond Coat Species in Cyclic Thermal Exposure
Materials 2013, 6(8), 3387-3403; doi:10.3390/ma6083387
Received: 26 June 2013 / Revised: 30 July 2013 / Accepted: 1 August 2013 / Published: 8 August 2013
Cited by 6 | PDF Full-text (2049 KB) | HTML Full-text | XML Full-text
Abstract
The effects of the bond coat species on the delamination or fracture behavior in thermal barrier coatings (TBCs) was investigated using the yclic thermal fatigue and thermal-shock tests. The interface microstructures of each TBC showed a good condition without cracking or delamination [...] Read more.
The effects of the bond coat species on the delamination or fracture behavior in thermal barrier coatings (TBCs) was investigated using the yclic thermal fatigue and thermal-shock tests. The interface microstructures of each TBC showed a good condition without cracking or delamination after flame thermal fatigue (FTF) for 1429 cycles. The TBC with the bond coat prepared by the air-plasma spray (APS) method showed a good condition at the interface between the top and bond coats after cyclic furnace thermal fatigue (CFTF) for 1429 cycles, whereas the TBCs with the bond coats prepared by the high-velocity oxygen fuel (HVOF) and low-pressure plasma spray (LPPS) methods showed a partial cracking (and/or delamination) and a delamination after 780 cycles, respectively. The TBCs with the bond coats prepared by the APS, HVOF and LPPS methods were fully delaminated (>50%) after 159, 36, and 46 cycles, respectively, during the thermal-shock tests. The TGO thickness in the TBCs was strongly dependent on the both exposure time and temperature difference tested. The hardness values were found to be increased only after the CFTF, and the TBC with the bond coat prepared by the APS showed the highest adhesive strength before and after the FTF. Full article
(This article belongs to the Special Issue Advances in Surface Coatings 2013)
Open AccessArticle Recycling of Pre-Washed Municipal Solid Waste Incinerator Fly Ash in the Manufacturing of Low Temperature Setting Geopolymer Materials
Materials 2013, 6(8), 3420-3437; doi:10.3390/ma6083420
Received: 5 June 2013 / Revised: 5 August 2013 / Accepted: 6 August 2013 / Published: 12 August 2013
Cited by 26 | PDF Full-text (805 KB) | HTML Full-text | XML Full-text
Abstract
In this work, three samples of municipal solid waste incinerators fly ash (MSWI-FA) have been stabilized in systems containing coal fly ash to create geopolymers through a polycondensation reaction. Monolithic products have been obtained with both MSWI fly ash as received and [...] Read more.
In this work, three samples of municipal solid waste incinerators fly ash (MSWI-FA) have been stabilized in systems containing coal fly ash to create geopolymers through a polycondensation reaction. Monolithic products have been obtained with both MSWI fly ash as received and after the partial removal of chloride and sulfate by water washing. The polycondensation products have been characterized qualitatively by means of Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy and quantitatively, through the determination of the volume of reacted water and silicate. Furthermore, the heavy metals and chloride releases together with the physico-mechanical properties have been evaluated on the hardened products. In conclusion, considering the technological and environmental performances of the obtained geopolymers, they could be suitable for many non-structural applications, such as backfilling of abandoned quarries, decorative materials or brick fireplaces, hearths, patios, etc. Full article
Open AccessArticle Self-Healing Characteristics of Damaged Rock Salt under Different Healing Conditions
Materials 2013, 6(8), 3438-3450; doi:10.3390/ma6083438
Received: 29 May 2013 / Revised: 6 August 2013 / Accepted: 7 August 2013 / Published: 12 August 2013
Cited by 3 | PDF Full-text (575 KB) | HTML Full-text | XML Full-text
Abstract
Salt deposits are commonly regarded as ideal hosts for geologic energy reservoirs. Underground cavern construction-induced damage in salt is reduced by self-healing. Thus, studying the influencing factors on such healing processes is important. This research uses ultrasonic technology to monitor the longitudinal [...] Read more.
Salt deposits are commonly regarded as ideal hosts for geologic energy reservoirs. Underground cavern construction-induced damage in salt is reduced by self-healing. Thus, studying the influencing factors on such healing processes is important. This research uses ultrasonic technology to monitor the longitudinal wave velocity variations of stress-damaged rock salts during self-recovery experiments under different recovery conditions. The influences of stress-induced initial damage, temperature, humidity, and oil on the self-recovery of damaged rock salts are analyzed. The wave velocity values of the damaged rock salts increase rapidly during the first 200 h of recovery, and the values gradually increase toward stabilization after 600 h. The recovery of damaged rock salts is subjected to higher initial damage stress. Water is important in damage recovery. The increase in temperature improves damage recovery when water is abundant, but hinders recovery when water evaporates. The presence of residual hydraulic oil blocks the inter-granular role of water and restrains the recovery under triaxial compression. The results indicate that rock salt damage recovery is related to the damage degree, pore pressure, temperature, humidity, and presence of oil due to the sealing integrity of the jacket material. Full article
Open AccessArticle Manufacturing and Characterization of 18Ni Marage 300 Lattice Components by Selective Laser Melting
Materials 2013, 6(8), 3451-3468; doi:10.3390/ma6083451
Received: 7 May 2013 / Revised: 18 July 2013 / Accepted: 6 August 2013 / Published: 13 August 2013
Cited by 1 | PDF Full-text (1504 KB) | HTML Full-text | XML Full-text
Abstract
The spreading use of cellular structures brings the need to speed up manufacturing processes without deteriorating mechanical properties. By using Selective Laser Melting (SLM) to produce cellular structures, the designer has total freedom in defining part geometry and manufacturing is simplified. The [...] Read more.
The spreading use of cellular structures brings the need to speed up manufacturing processes without deteriorating mechanical properties. By using Selective Laser Melting (SLM) to produce cellular structures, the designer has total freedom in defining part geometry and manufacturing is simplified. The paper investigates the suitability of Selective Laser Melting for manufacturing steel cellular lattice structures with characteristic dimensions in the micrometer range. Alternative lattice topologies including reinforcing bars in the vertical direction also are considered. The selected lattice structure topology is shown to be superior over other lattice structure designs considered in literature. Compression tests are carried out in order to evaluate mechanical strength of lattice strut specimens made via SLM. Compressive behavior of samples also is simulated by finite element analysis and numerical results are compared with experimental data in order to assess the constitutive behavior of the lattice structure designs considered in this study. Experimental data show that it is possible to build samples of relative density in the 0.2456–0.4367 range. Compressive strength changes almost linearly with respect to relative density, which in turns depends linearly on the number of vertical reinforces. Specific strength increases with cell and strut edge size. Numerical simulations confirm the plastic nature of the instability phenomena that leads the cellular structures to collapse under compression loading. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
Open AccessArticle Cyclic Deformation of Ultra-Fine Grained Commercial Purity Aluminum Processed by Accumulative Roll-Bonding
Materials 2013, 6(8), 3469-3481; doi:10.3390/ma6083469
Received: 21 May 2013 / Revised: 29 July 2013 / Accepted: 1 August 2013 / Published: 13 August 2013
Cited by 2 | PDF Full-text (3177 KB) | HTML Full-text | XML Full-text
Abstract
Accumulative Roll-Bonding (ARB) is one of the more recently developed techniques capable of producing bulk ultra-fine grained (ufg) metals. There are still many aspects of the behavior of ufg metals that lacks an in-depth understanding, such as a generalized view of the [...] Read more.
Accumulative Roll-Bonding (ARB) is one of the more recently developed techniques capable of producing bulk ultra-fine grained (ufg) metals. There are still many aspects of the behavior of ufg metals that lacks an in-depth understanding, such as a generalized view of the factors that govern the cyclic deformation mechanism(s). This study aims to advance the understanding of the cyclic deformation behavior of ufg metals through the systematic investigation of ARB processed aluminum upon cyclic loading. It was found that the cyclic softening response often reported for ufg metals is largely influenced by the microstructure stability as the cyclic softening response is facilitated by grain coarsening which becomes inhibited with highly stable microstructure. On one hand, shear bands resembling braids of dislocations trespassing multiple grains have been observed to operate for the accommodation of the imposed cyclic strain in cases where grain coarsening is largely restricted. On the other hand, it was found that the microstructure stability can be overcome at higher applied cyclic plastic strain levels, leading to grain coarsening and thus a cyclic softening response. The findings in this study have further confirmed that the cyclic softening behavior found in many ufg metals, which may be detrimental in practical applications, can be inhibited by improvements in the microstructure stability. Full article
(This article belongs to the Section Structure Analysis and Characterization)
Open AccessArticle Study of Radio Frequency Plasma Treatment of PVDF Film Using Ar, O2 and (Ar + O2) Gases for Improved Polypyrrole Adhesion
Materials 2013, 6(8), 3482-3493; doi:10.3390/ma6083482
Received: 3 June 2013 / Revised: 31 July 2013 / Accepted: 1 August 2013 / Published: 13 August 2013
Cited by 4 | PDF Full-text (809 KB) | HTML Full-text | XML Full-text
Abstract
Improvement of the binding of polypyrrole with PVDF (polyvinylidene fluoride) thin film using low pressure plasma was studied. The effects of various plasma gases i.e., Ar, O2 and Ar + O2 gases on surface roughness, surface chemistry and [...] Read more.
Improvement of the binding of polypyrrole with PVDF (polyvinylidene fluoride) thin film using low pressure plasma was studied. The effects of various plasma gases i.e., Ar, O2 and Ar + O2 gases on surface roughness, surface chemistry and hydrophilicity were noted. The topographical change of the PVDF film was observed by means of scanning electron microscopy and chemical changes by X-ray photoelectron spectroscopy, with adhesion of polypyrrole (PPy) by abrasion tests and sheet resistance measurements. Results showed that the increase in roughness and surface functionalization by oxygen functional groups contributed to improved adhesion and Ar + O2 plasma gave better adhesion. Full article
(This article belongs to the Special Issue Advances in Surface Coatings)
Open AccessArticle Effects on the Thermo-Mechanical and Crystallinity Properties of Nylon 6,6 Electrospun Fibres Reinforced with One Dimensional (1D) and Two Dimensional (2D) Carbon
Materials 2013, 6(8), 3494-3513; doi:10.3390/ma6083494
Received: 30 April 2013 / Revised: 30 July 2013 / Accepted: 1 August 2013 / Published: 14 August 2013
Cited by 10 | PDF Full-text (1994 KB) | HTML Full-text | XML Full-text
Abstract
Electrospun one dimensional (1D) and two dimensional (2D) carbon based polymer nanocomposites are studied in order to determine the effect provided by the two differently structured nanofillers on crystallinity and thermo-mechanical properties of the nanofibres. The nanomaterials studied are pristine carbon nanotubes, [...] Read more.
Electrospun one dimensional (1D) and two dimensional (2D) carbon based polymer nanocomposites are studied in order to determine the effect provided by the two differently structured nanofillers on crystallinity and thermo-mechanical properties of the nanofibres. The nanomaterials studied are pristine carbon nanotubes, oxidised carbon nanotubes, reduced graphene oxide and graphene oxide. Functional groups associated with the order structure of the polymers are analysed by infrared and Raman spectroscopies; the morphology is studied by scanning electron microscopy and the crystallinity properties are investigated by differential scanning calorimetry and X-ray diffraction. Differences in crystallisation behaviour between 1D and 2D carbon based nanofibres are shown by their crystallinity degree and their crystal sizes. The nanocomposite crystal sizes perpendicular to the plane (100) decrease with nanofiller content in all cases. The crystallinity trend and crystal sizes are in accordance with storage modulus response. The results also suggest that functionalisation favours interfacial bonding and dispersion of the nanomaterials within the polymer matrix. As a consequence the number of nucleating sites increases which in turn decreases the crystal size in the nanocomposites. These features explain the improved thermo-mechanical properties in the nanocomposites. Full article
(This article belongs to the Special Issue Carbon Nanotubes)
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Open AccessArticle Small-Scale Morphological Features on a Solid Surface Processed by High-Pressure Abrasive Water Jet
Materials 2013, 6(8), 3514-3529; doi:10.3390/ma6083514
Received: 27 May 2013 / Revised: 29 July 2013 / Accepted: 7 August 2013 / Published: 14 August 2013
Cited by 4 | PDF Full-text (1334 KB) | HTML Full-text | XML Full-text
Abstract
Being subjected to a high-pressure abrasive water jet, solid samples will experience an essential variation of both internal stress and physical characteristics, which is closely associated with the kinetic energy attached to the abrasive particles involved in the jet stream. Here, experiments [...] Read more.
Being subjected to a high-pressure abrasive water jet, solid samples will experience an essential variation of both internal stress and physical characteristics, which is closely associated with the kinetic energy attached to the abrasive particles involved in the jet stream. Here, experiments were performed, with particular emphasis being placed on the kinetic energy attenuation and turbulent features in the jet stream. At jet pressure of 260 MPa, mean velocity and root-mean-square (RMS) velocity on two jet-stream sections were acquired by utilizing the phase Doppler anemometry (PDA) technique. A jet-cutting experiment was then carried out with Al-Mg alloy samples being cut by an abrasive water jet. Morphological features and roughness on the cut surface were quantitatively examined through scanning electron microscopy (SEM) and optical profiling techniques. The results indicate that the high-pressure water jet is characterized by remarkably high mean flow velocities and distinct velocity fluctuations. Those irregular pits and grooves on the cut surfaces indicate both the energy attenuation and the development of radial velocity components in the jet stream. When the sample is positioned with different distances from the nozzle outlet, the obtained quantitative surface roughness varies accordingly. A descriptive model highlighting the behaviors of abrasive particles in jet-cutting process is established in light of the experimental results and correlation analysis. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
Open AccessArticle The Influence of Phase Change Materials on the Properties of Self-Compacting Concrete
Materials 2013, 6(8), 3530-3546; doi:10.3390/ma6083530
Received: 14 June 2013 / Revised: 12 July 2013 / Accepted: 5 August 2013 / Published: 15 August 2013
Cited by 7 | PDF Full-text (592 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this paper is to research new thermally-efficient concrete walls, analyzing the mechanical behavior of a self-compacting concrete to manufacture an uncoated solid structural panel, with the incorporation of a micro-encapsulated phase change material as additive. Different dosages are tested [...] Read more.
The aim of this paper is to research new thermally-efficient concrete walls, analyzing the mechanical behavior of a self-compacting concrete to manufacture an uncoated solid structural panel, with the incorporation of a micro-encapsulated phase change material as additive. Different dosages are tested and mechanical properties of the product obtained from the molding of concrete specimens are evaluated, testing mechanical compressive strength, slump flow, and density. The results reveal the optimum percentage of additive in the mixture that enables compliance with the technical specifications required by the product to be manufactured. A test is also performed for measuring the thermal conductivity for the optimal sample obtained and it evidences the reduction thereof. Full article
Open AccessArticle Synthesis, Structural Characterization, and Antitumor Activity of a Ca(II) Coordination Polymer Based on 1,6-Naphthalenedisulfonate and 4,4′-Bipyridyl
Materials 2013, 6(8), 3547-3555; doi:10.3390/ma6083547
Received: 27 June 2013 / Revised: 12 July 2013 / Accepted: 7 August 2013 / Published: 16 August 2013
Cited by 11 | PDF Full-text (343 KB) | HTML Full-text | XML Full-text
Abstract
A novel Ca(II) coordination polymer, [CaL(4,4′-bipyridyl)(H2O)4]n (L = 1,6-naphthalenedisulfonate), was synthesized by reaction of calcium perchlorate with 1,6-naphthalenedisulfonic acid disodium salt and 4,4′-bipyridyl in CH3CH2OH/H2O. It was characterized by elemental analysis, [...] Read more.
A novel Ca(II) coordination polymer, [CaL(4,4′-bipyridyl)(H2O)4]n (L = 1,6-naphthalenedisulfonate), was synthesized by reaction of calcium perchlorate with 1,6-naphthalenedisulfonic acid disodium salt and 4,4′-bipyridyl in CH3CH2OH/H2O. It was characterized by elemental analysis, IR, molar conductivity and thermogravimetric analysis. X-ray crystallography reveals that the Ca(II) coordination polymer belongs to the orthorhombic system, with space group P212121. The geometry of the Ca(II) ion is a distorted CaNO6 pengonal bipyramid, arising from its coordination by four water molecules, one nitrogen atom of 4,4′-bipyridyl molecule, and two oxygen atoms from two L ligands. The complex molecules form a helical chain by self-assembly. The antitumor activity of 1,6-naphthalenedisulfonic acid disodium salt and the Ca(II) coordination polymer against human hepatoma smmc-7721 cell line and human lung adenocarcinoma A549 cell line reveals that the Ca(II) coordination polymer inhibits cell growth of human lung adenocarcinoma A549 cell line with IC50 value of 27 μg/mL, and is more resistive to human lung adenocarcinoma A549 cell line as compared to 1,6-naphthalenedisulfonic acid disodium salt. Full article
(This article belongs to the Section Biomaterials)
Open AccessArticle Periodic Mesoporous Organosilica Functionalized with Sulfonic Acid Groups as Acid Catalyst for Glycerol Acetylation
Materials 2013, 6(8), 3556-3570; doi:10.3390/ma6083556
Received: 11 July 2013 / Revised: 1 August 2013 / Accepted: 13 August 2013 / Published: 16 August 2013
Cited by 7 | PDF Full-text (593 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A Periodic Mesoporous Organosilica (PMO) functionalized with sulfonic acid groups has been successfully synthesized via a sequence of post-synthetic modification steps of a trans-ethenylene bridged PMO material. The double bond is functionalized via a bromination and subsequent substitution obtaining a thiol [...] Read more.
A Periodic Mesoporous Organosilica (PMO) functionalized with sulfonic acid groups has been successfully synthesized via a sequence of post-synthetic modification steps of a trans-ethenylene bridged PMO material. The double bond is functionalized via a bromination and subsequent substitution obtaining a thiol functionality. This is followed by an oxidation towards a sulfonic acid group. After full characterization, the solid acid catalyst is used in the acetylation of glycerol. The catalytic reactivity and reusability of the sulfonic acid modified PMO material is investigated. The catalyst showed a catalytic activity and kinetics that are comparable with the commercially available resin, Amberlyst-15, and furthermore our catalyst can be recycled for several subsequent catalytic runs and retains its catalytic activity. Full article
(This article belongs to the Section Porous Materials)
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Open AccessArticle Study of Lysozyme-Loaded Poly-L-Lactide (PLLA) Porous Microparticles in a Compressed CO2 Antisolvent Process
Materials 2013, 6(8), 3571-3583; doi:10.3390/ma6083571
Received: 5 May 2013 / Revised: 7 July 2013 / Accepted: 14 August 2013 / Published: 19 August 2013
Cited by 3 | PDF Full-text (1072 KB) | HTML Full-text | XML Full-text
Abstract
Lysozyme (LSZ)-loaded poly-L-lactide (PLLA) porous microparticles (PMs) were successfully prepared by a compressed CO2 antisolvent process in combination with a water-in-oil emulsion process using LSZ as a drug model and ammonium bicarbonate as a porogen. The effects of different drug loads [...] Read more.
Lysozyme (LSZ)-loaded poly-L-lactide (PLLA) porous microparticles (PMs) were successfully prepared by a compressed CO2 antisolvent process in combination with a water-in-oil emulsion process using LSZ as a drug model and ammonium bicarbonate as a porogen. The effects of different drug loads (5.0%, 7.5% and 10.0%) on the surface morphology, particle size, porosity, tapped density and drug release profile of the harvested PMs were investigated. The results show that an increase in the amount of LSZ added led to an increase in drug load (DL) but a decrease in encapsulation efficiency. The resulting LSZ-loaded PLLA PMs (LSZ-PLLA PMs) exhibited a porous and uneven morphology, with a density less than 0.1 g·cm−3, a geometric mean diameter of 16.9–18.8 μm, an aerodynamic diameter less than 2.8 μm, a fine particle fraction (FPF) of 59.2%–66.8%, and a porosity of 78.2%–86.3%. According to the results of differential scanning calorimetry, the addition of LSZ improved the thermal stability of PLLA. The Fourier transform infrared spectroscopy analysis and circular dichroism spectroscopy measurement reveal that no significant changes occurred in the molecular structures of LSZ during the fabrication process, which was further confirmed by the evaluation of enzyme activity of LSZ. It is demonstrated that the emulsion-combined precipitation with compressed antisolvent (PCA) process could be a promising technology to develop biomacromolecular drug-loaded inhalable carrier for pulmonary drug delivery. Full article
(This article belongs to the Section Biomaterials)
Open AccessArticle Hydrothermal Growth of Vertically Aligned ZnO Nanorods Using a Biocomposite Seed Layer of ZnO Nanoparticles
Materials 2013, 6(8), 3584-3597; doi:10.3390/ma6083584
Received: 22 July 2013 / Revised: 24 July 2013 / Accepted: 8 August 2013 / Published: 19 August 2013
Cited by 18 | PDF Full-text (1673 KB) | HTML Full-text | XML Full-text
Abstract
Well aligned ZnO nanorods have been prepared by a low temperature aqueous chemical growth method, using a biocomposite seed layer of ZnO nanoparticles prepared in starch and cellulose bio polymers. The effect of different concentrations of biocomposite seed layer on the alignment [...] Read more.
Well aligned ZnO nanorods have been prepared by a low temperature aqueous chemical growth method, using a biocomposite seed layer of ZnO nanoparticles prepared in starch and cellulose bio polymers. The effect of different concentrations of biocomposite seed layer on the alignment of ZnO nanorods has been investigated. ZnO nanorods grown on a gold-coated glass substrate have been characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques. These techniques have shown that the ZnO nanorods are well aligned and perpendicular to the substrate, and grown with a high density and uniformity on the substrate. Moreover, ZnO nanorods can be grown with an orientation along the c-axis of the substrate and exhibit a wurtzite crystal structure with a dominant (002) peak in an XRD spectrum and possessed a high crystal quality. A photoluminescence (PL) spectroscopy study of the ZnO nanorods has revealed a conventional near band edge ultraviolet emission, along with emission in the visible part of the electromagnetic spectrum due to defect emission. This study provides an alternative method for the fabrication of well aligned ZnO nanorods. This method can be helpful in improving the performance of devices where alignment plays a significant role. Full article
(This article belongs to the Section Biomaterials)
Open AccessArticle Drift in Diffusion Gradients
Materials 2013, 6(8), 3598-3609; doi:10.3390/ma6083598
Received: 27 June 2013 / Revised: 23 July 2013 / Accepted: 13 August 2013 / Published: 19 August 2013
Cited by 9 | PDF Full-text (393 KB) | HTML Full-text | XML Full-text
Abstract
The longstanding problem of Brownian transport in a heterogeneous quasi one-dimensional medium with space-dependent self-diffusion coefficient is addressed in the overdamped (zero mass) limit. A satisfactory mesoscopic description is obtained in the Langevin equation formalism by introducing an appropriate drift term, which [...] Read more.
The longstanding problem of Brownian transport in a heterogeneous quasi one-dimensional medium with space-dependent self-diffusion coefficient is addressed in the overdamped (zero mass) limit. A satisfactory mesoscopic description is obtained in the Langevin equation formalism by introducing an appropriate drift term, which depends on the system macroscopic observables, namely the diffuser concentration and current. The drift term is related to the microscopic properties of the medium. The paradoxical existence of a finite drift at zero current suggests the possibility of designing a Maxwell demon operating between two equilibrium reservoirs at the same temperature. Full article
(This article belongs to the Special Issue Diffusion in Micropores and Mesopores 2013)
Open AccessArticle Fabrication of Super-Hydrophobic Microchannels via Strain-Recovery Deformations of Polystyrene and Oxygen Reactive Ion Etch
Materials 2013, 6(8), 3610-3623; doi:10.3390/ma6083610
Received: 26 July 2013 / Revised: 13 August 2013 / Accepted: 14 August 2013 / Published: 19 August 2013
Cited by 7 | PDF Full-text (759 KB) | HTML Full-text | XML Full-text
Abstract
In this article, we report a simple approach to generate micropillars (whose top portions are covered by sub-micron wrinkles) on the inner surfaces of polystyrene (PS) microchannels, as well as on the top surface of the PS substrate, based on strain-recovery deformations [...] Read more.
In this article, we report a simple approach to generate micropillars (whose top portions are covered by sub-micron wrinkles) on the inner surfaces of polystyrene (PS) microchannels, as well as on the top surface of the PS substrate, based on strain-recovery deformations of the PS and oxygen reactive ion etch (ORIE). Using this approach, two types of micropillar-covered microchannels are fabricated. Their widths range from 118 μm to 132 μm, depths vary from 40 μm to 44 μm, and the inclined angles of their sidewalls are from 53° to 64°. The micropillars enable these microchannels to have super-hydrophobic properties. The contact angles observed on the channel-structured surfaces are above 162°, and the tilt angles to make water drops roll off from these channel-structured substrates can be as small as 1°. Full article
(This article belongs to the Special Issue Smart Polymers and Polymeric Structures)
Open AccessArticle The Effect of a Rapid Heating Rate, Mechanical Vibration and Surfactant Chemistry on the Structure–Property Relationships of Epoxy/Clay Nanocomposites
Materials 2013, 6(8), 3624-3640; doi:10.3390/ma6083624
Received: 27 May 2013 / Revised: 6 August 2013 / Accepted: 9 August 2013 / Published: 20 August 2013
Cited by 3 | PDF Full-text (1086 KB) | HTML Full-text | XML Full-text
Abstract
The role of processing conditions and intercalant chemistry in montmorillonite clays on the dispersion, morphology and mechanical properties of two epoxy/clay nanocomposite systems was investigated in this paper. This work highlights the importance of employing complementary techniques (X-ray diffraction, small angle X-ray [...] Read more.
The role of processing conditions and intercalant chemistry in montmorillonite clays on the dispersion, morphology and mechanical properties of two epoxy/clay nanocomposite systems was investigated in this paper. This work highlights the importance of employing complementary techniques (X-ray diffraction, small angle X-ray scattering, optical microscopy and transmission electron microscopy) to correlate nanomorphology to macroscale properties. Materials were prepared using an out of autoclave manufacturing process equipped to generate rapid heating rates and mechanical vibration. The results suggested that the quaternary ammonium surfactant on C30B clay reacted with the epoxy during cure, while the primary ammonium surfactant (I.30E) catalysed the polymerisation reaction. These effects led to important differences in nanocomposite clay morphologies. The use of mechanical vibration at 4 Hz prior to matrix gelation was found to facilitate clay dispersion and to reduce the area fraction of I.30E clay agglomerates in addition to increasing flexural strength by over 40%. Full article
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Open AccessArticle Broadband Luminescence in Rare Earth Doped Sr2SiS4: Relating Energy Levels of Ce3+ and Eu2+
Materials 2013, 6(8), 3663-3675; doi:10.3390/ma6083663
Received: 17 May 2013 / Revised: 17 July 2013 / Accepted: 13 August 2013 / Published: 21 August 2013
Cited by 6 | PDF Full-text (751 KB) | HTML Full-text | XML Full-text
Abstract
Sr2SiS4:Ce3+ is an efficient blue-emitting (460 nm) phosphor, excitable with light of wavelengths up to 420 nm. From the excitation spectrum, we construct the energy level scheme and use it to check the predictive power of the Dorenbos model, relating the positions [...] Read more.
Sr2SiS4:Ce3+ is an efficient blue-emitting (460 nm) phosphor, excitable with light of wavelengths up to 420 nm. From the excitation spectrum, we construct the energy level scheme and use it to check the predictive power of the Dorenbos model, relating the positions of the Ce3+ energy levels with those of Eu2+ in the same host. For strontium thiosilicate, this method gives excellent results and allows us to determine which of two available crystallographic sites is occupied by cerium. We use the Dorenbos method for extracting information on the coordination of Ce3+ from the observed crystal field splitting. Full article
(This article belongs to the Special Issue Luminescent Materials 2013)

Review

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Open AccessReview Surface Stability and Growth Kinetics of Compound Semiconductors: An Ab Initio-Based Approach
Materials 2013, 6(8), 3309-3360; doi:10.3390/ma6083309
Received: 27 June 2013 / Accepted: 30 July 2013 / Published: 6 August 2013
Cited by 11 | PDF Full-text (3553 KB) | HTML Full-text | XML Full-text
Abstract
We review the surface stability and growth kinetics of III-V and III-nitride semiconductors. The theoretical approach used in these studies is based on ab initio calculations and includes gas-phase free energy. With this method, we can investigate the influence of growth conditions, [...] Read more.
We review the surface stability and growth kinetics of III-V and III-nitride semiconductors. The theoretical approach used in these studies is based on ab initio calculations and includes gas-phase free energy. With this method, we can investigate the influence of growth conditions, such as partial pressure and temperature, on the surface stability and growth kinetics. First, we examine the feasibility of this approach by comparing calculated surface phase diagrams of GaAs(001) with experimental results. In addition, the Ga diffusion length on GaAs(001) during molecular beam epitaxy is discussed. Next, this approach is systematically applied to the reconstruction, adsorption and incorporation on various nitride semiconductor surfaces. The calculated results for nitride semiconductor surface reconstructions with polar, nonpolar, and semipolar orientations suggest that adlayer reconstructions generally appear on the polar and the semipolar surfaces. However, the stable ideal surface without adsorption is found on the nonpolar surfaces because the ideal surface satisfies the electron counting rule. Finally, the stability of hydrogen and the incorporation mechanisms of Mg and C during metalorganic vapor phase epitaxy are discussed. Full article
(This article belongs to the Special Issue Compound Semiconductor Materials)
Open AccessReview Progress in Titanium Metal Powder Injection Molding
Materials 2013, 6(8), 3641-3662; doi:10.3390/ma6083641
Received: 29 July 2013 / Revised: 8 August 2013 / Accepted: 9 August 2013 / Published: 20 August 2013
Cited by 12 | PDF Full-text (872 KB) | HTML Full-text | XML Full-text
Abstract
Metal powder injection molding is a shaping technology that has achieved solid scientific underpinnings. It is from this science base that recent progress has occurred in titanium powder injection molding. Much of the progress awaited development of the required particles with specific [...] Read more.
Metal powder injection molding is a shaping technology that has achieved solid scientific underpinnings. It is from this science base that recent progress has occurred in titanium powder injection molding. Much of the progress awaited development of the required particles with specific characteristics of particle size, particle shape, and purity. The production of titanium components by injection molding is stabilized by a good understanding of how each process variable impacts density and impurity level. As summarized here, recent research has isolated the four critical success factors in titanium metal powder injection molding (Ti-MIM) that must be simultaneously satisfied—density, purity, alloying, and microstructure. The critical role of density and impurities, and the inability to remove impurities with sintering, compels attention to starting Ti-MIM with high quality alloy powders. This article addresses the four critical success factors to rationalize Ti-MIM processing conditions to the requirements for demanding applications in aerospace and medical fields. Based on extensive research, a baseline process is identified and reported here with attention to linking mechanical properties to the four critical success factors. Full article
(This article belongs to the Special Issue Progress in Net-shaped PM (Powder Metallurgical) Parts)

Other

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Open AccessConcept Paper A Perspective on the Flame Spray Synthesis of Photocatalyst Nanoparticles
Materials 2013, 6(8), 3194-3212; doi:10.3390/ma6083194
Received: 3 June 2013 / Revised: 6 July 2013 / Accepted: 8 July 2013 / Published: 31 July 2013
Cited by 6 | PDF Full-text (839 KB) | HTML Full-text | XML Full-text
Abstract
The synthesis of functional nanoparticles via one-step flame spray pyrolysis (FSP), especially those of catalytic nature, has attracted the interests of scientists and engineers, as well as industries. The rapid and high temperature continuous synthesis yields nanoparticles with intrinsic features of active [...] Read more.
The synthesis of functional nanoparticles via one-step flame spray pyrolysis (FSP), especially those of catalytic nature, has attracted the interests of scientists and engineers, as well as industries. The rapid and high temperature continuous synthesis yields nanoparticles with intrinsic features of active catalysts, that is, high surface area and surface energetics. For these reasons, FSP finds applications in various thermally inducible catalytic reactions. However, the design and synthesis of photocatalysts by FSP requires a knowledge set which is different from that established for thermal catalysts. Unknown to many, this has resulted in frustrations to those entering the field unprepared, especially since FSP appears to be an elegant tool in synthesising oxide nanoparticles of any elemental construct. From simple oxide to doped-oxide, and mixed metal oxide to the in situ deposition of noble metals, this Perspective gives an overview on the development of photocatalysts made by FSP in the last decade that led to a better understanding of the design criteria. Various challenges and opportunities are also highlighted, especially those beyond simple metal oxides, which perhaps contain the greatest potential for the exploitation of photocatalysts design by FSP. Full article
(This article belongs to the Special Issue Advances in Catalytic Materials)
Open AccessCase Report Optimization of Microwave-Based Heating of Cellulosic Biomass Using Taguchi Method
Materials 2013, 6(8), 3404-3419; doi:10.3390/ma6083404
Received: 15 May 2013 / Revised: 29 July 2013 / Accepted: 1 August 2013 / Published: 9 August 2013
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Abstract
This study discusses the application of microwave-based heating for the pretreatment of biomass material, with Pennisetum purpureum selected for pretreatment. The Taguchi method was used to plan optimization experiments for the pretreatment parameter levels, and to measure the dynamic responses. With a [...] Read more.
This study discusses the application of microwave-based heating for the pretreatment of biomass material, with Pennisetum purpureum selected for pretreatment. The Taguchi method was used to plan optimization experiments for the pretreatment parameter levels, and to measure the dynamic responses. With a low number of experiments, this study analyzed and determined a parameter combination in which Pennisetum purpureum can be rapidly heated to 190 °C. The experimental results suggested that the optimal parameter combination is: vessel capacity of 150 mL (level 2), heating power of 0.5 kW (level 1), and mass of Pennisetum purpureum of 5 g (level 1). The mass of Pennisetum purpureum is a key factor affecting system performance. An eight-order ARX model (Auto-Regressive eXogeneous) was representative of the actual system performance, and the fit was 99.13%. The results proved that microwave-based heating, with the assistance of the Taguchi method for pretreatment of the biomass material, can reduce the parameter combination variations. Full article
(This article belongs to the Special Issue Microwave Processing of Materials)

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