Materials

12 pages, 2988 KiB

Open AccessArticle

Discussion on Microwave-Matter Interaction Mechanisms by In Situ Observation of “Core-Shell” Microstructure during Microwave Sintering

by Wenchao Liu, Feng Xu, Yongcun Li, Xiaofang Hu, Bo Dong and Yu Xiao

Materials 2016, 9(3), 120; https://doi.org/10.3390/ma9030120 - 23 Feb 2016

Cited by 23 | Viewed by 7003

Abstract

This research aims to deepen the understanding of the interaction mechanisms between microwave and matter in a metal-ceramic system based on in situ synchrotron radiation computed tomography. A special internal “core-shell” microstructure was discovered for the first time and used as an indicator [...] Read more.

This research aims to deepen the understanding of the interaction mechanisms between microwave and matter in a metal-ceramic system based on in situ synchrotron radiation computed tomography. A special internal “core-shell” microstructure was discovered for the first time and used as an indicator for the interaction mechanisms between microwave and matter. Firstly, it was proved that the microwave magnetic field acted on metal particles by way of inducing an eddy current in the surface of the metal particles, which led to the formation of a “core-shell” microstructure in the metal particles. On this basis, it was proposed that the ceramic particles could change the microwave field and open a way for the microwave, thereby leading to selective heating in the region around the ceramic particles, which was verified by the fact that all the “core-shell” microstructure was located around ceramic particles. Furthermore, it was indicated that the ceramic particles would gather the microwaves, and might lead to local heating in the metal-ceramic contact region. The focusing of the microwave was proved by the quantitative analysis of the evolution rate of the “core-shell” microstructure in a different region. This study will help to reveal the microwave-matter interaction mechanisms during microwave sintering. Full article

(This article belongs to the Special Issue Microwave Materials Processing)

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8 pages, 2636 KiB

Open AccessArticle

Selective Photophysical Modification on Light-Emitting Polymer Films for Micro- and Nano-Patterning

by Xinping Zhang, Feifei Liu and Hongwei Li

Materials 2016, 9(3), 121; https://doi.org/10.3390/ma9030121 - 23 Feb 2016

Cited by 6 | Viewed by 6335

Abstract

Laser-induced cross-linking in polymeric semiconductors was utilized to achieve micro- and nano-structuring in thin films. Single- and two-photon cross-linking processes led to the reduction in both the refractive index and thickness of the polymer films. The resultant photonic structures combine the features of [...] Read more.

Laser-induced cross-linking in polymeric semiconductors was utilized to achieve micro- and nano-structuring in thin films. Single- and two-photon cross-linking processes led to the reduction in both the refractive index and thickness of the polymer films. The resultant photonic structures combine the features of both relief- and phase-gratings. Selective cross-linking in polymer blend films based on different optical response of different molecular phases enabled “solidification” of the phase-separation scheme, providing a stable template for further photonic structuring. Dielectric and metallic structures are demonstrated for the fabrication methods using cross-linking in polymer films. Selective cross-linking enables direct patterning into polymer films without introducing additional fabrication procedures or additional materials. The diffraction processes of the emission of the patterned polymeric semiconductors may provide enhanced output coupling for light-emitting diodes or distributed feedback for lasers. Full article

(This article belongs to the Special Issue Materials for Display Applications)

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19 pages, 11899 KiB

Open AccessArticle

Effect of Friction Stir Process Parameters on the Mechanical and Thermal Behavior of 5754-H111 Aluminum Plates

by Livia Maria Serio, Davide Palumbo, Luigi Alberto Ciro De Filippis, Umberto Galietti and Antonio Domenico Ludovico

Materials 2016, 9(3), 122; https://doi.org/10.3390/ma9030122 - 23 Feb 2016

Cited by 36 | Viewed by 6511

Abstract

A study of the Friction Stir Welding (FSW) process was carried out in order to evaluate the influence of process parameters on the mechanical properties of aluminum plates (AA5754-H111). The process was monitored during each test by means of infrared cameras in order [...] Read more.

A study of the Friction Stir Welding (FSW) process was carried out in order to evaluate the influence of process parameters on the mechanical properties of aluminum plates (AA5754-H111). The process was monitored during each test by means of infrared cameras in order to correlate temperature information with eventual changes of the mechanical properties of joints. In particular, two process parameters were considered for tests: the welding tool rotation speed and the welding tool traverse speed. The quality of joints was evaluated by means of destructive and non-destructive tests. In this regard, the presence of defects and the ultimate tensile strength (UTS) were investigated for each combination of the process parameters. A statistical analysis was carried out to assess the correlation between the thermal behavior of joints and the process parameters, also proving the capability of Infrared Thermography for on-line monitoring of the quality of joints. Full article

(This article belongs to the Section Manufacturing Processes and Systems)

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13 pages, 2867 KiB

Open AccessFeature PaperReview

Crystal Structure Formation of CH₃NH₃PbI_3-xCl_x Perovskite

by Shiqiang Luo and Walid A. Daoud

Materials 2016, 9(3), 123; https://doi.org/10.3390/ma9030123 - 24 Feb 2016

Cited by 93 | Viewed by 26663

Abstract

Inorganic-organic hydride perovskites bring the hope for fabricating low-cost and large-scale solar cells. At the beginning of the research, two open questions were raised: the hysteresis effect and the role of chloride. The presence of chloride significantly improves the crystallization and charge transfer [...] Read more.

Inorganic-organic hydride perovskites bring the hope for fabricating low-cost and large-scale solar cells. At the beginning of the research, two open questions were raised: the hysteresis effect and the role of chloride. The presence of chloride significantly improves the crystallization and charge transfer property of the perovskite. However, though the long held debate over of the existence of chloride in the perovskite seems to have now come to a conclusion, no prior work has been carried out focusing on the role of chloride on the electronic performance and the crystallization of the perovskite. Furthermore, current reports on the crystal structure of the perovskite are rather confusing. This article analyzes the role of chloride in CH₃NH₃PbI_3-xCl_x on the crystal orientation and provides a new explanation about the (110)-oriented growth of CH₃NH₃PbI₃ and CH₃NH₃PbI_3-xCl_x. Full article

(This article belongs to the Special Issue Photovoltaic Materials and Electronic Devices)

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37 pages, 9408 KiB

Open AccessReview

Recent Progress in Fabrication and Applications of Superhydrophobic Coating on Cellulose-Based Substrates

by Hui Liu, Shou-Wei Gao, Jing-Sheng Cai, Cheng-Lin He, Jia-Jun Mao, Tian-Xue Zhu, Zhong Chen, Jian-Ying Huang, Kai Meng, Ke-Qin Zhang, Salem S. Al-Deyab and Yue-Kun Lai

Materials 2016, 9(3), 124; https://doi.org/10.3390/ma9030124 - 25 Feb 2016

Cited by 127 | Viewed by 21722

Abstract

Multifuntional fabrics with special wettability have attracted a lot of interest in both fundamental research and industry applications over the last two decades. In this review, recent progress of various kinds of approaches and strategies to construct super-antiwetting coating on cellulose-based substrates (fabrics [...] Read more.

Multifuntional fabrics with special wettability have attracted a lot of interest in both fundamental research and industry applications over the last two decades. In this review, recent progress of various kinds of approaches and strategies to construct super-antiwetting coating on cellulose-based substrates (fabrics and paper) has been discussed in detail. We focus on the significant applications related to artificial superhydrophobic fabrics with special wettability and controllable adhesion, e.g., oil-water separation, self-cleaning, asymmetric/anisotropic wetting for microfluidic manipulation, air/liquid directional gating, and micro-template for patterning. In addition to the anti-wetting properties and promising applications, particular attention is paid to coating durability and other incorporated functionalities, e.g., air permeability, UV-shielding, photocatalytic self-cleaning, self-healing and patterned antiwetting properties. Finally, the existing difficulties and future prospects of this traditional and developing field are briefly proposed and discussed. Full article

(This article belongs to the Special Issue Superhydrophobicity of Materials)

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12 pages, 1250 KiB

Open AccessArticle

Acid Neutralizing Ability and Shear Bond Strength Using Orthodontic Adhesives Containing Three Different Types of Bioactive Glass

by Song-Yi Yang, Seong-Hwan Kim, Se-Young Choi and Kwang-Mahn Kim

Materials 2016, 9(3), 125; https://doi.org/10.3390/ma9030125 - 24 Feb 2016

Cited by 78 | Viewed by 6257

Abstract

The objective of the study was to compare the acid neutralizing ability and shear bond strength (SBS) of three different types of orthodontic adhesives containing bioactive glasses (BAGs). 45S5, 45S5F and S53P4 BAGs were prepared using the melting technique and ground to fine [...] Read more.

The objective of the study was to compare the acid neutralizing ability and shear bond strength (SBS) of three different types of orthodontic adhesives containing bioactive glasses (BAGs). 45S5, 45S5F and S53P4 BAGs were prepared using the melting technique and ground to fine particles. Orthodontic adhesives containing three types of BAGs were prepared as follows: 52.5% 45S5 BAG + 17.5% glass (45S5_A); 61.25% 45S5 BAG + 8.75% glass (45S5_B); 52.5% 45S5F BAG + 17.5% glass (45S5F_A); 61.25% 45S5F BAG + 8.75% glass (45S5F_B); 52.5% S53P4 BAG + 17.5% glass (S53P4_A); 61.25% S53P4 BAG + 8.75% glass (S53P4_B); and 70.0% glass (BAG_0). To evaluate the acid neutralizing properties, specimens were immersed in lactic acid solution, and pH changes were measured. SBS was measured with a universal testing machine. For all of the BAG-containing adhesives, the one with 61.25% of BAG showed a significantly greater increase of pH than the one with 52.5% of BAG (p < 0.05). Groups with 61.25% of BAG showed lower SBS than samples with 52.5% of BAG. 45S5F_A showed no significant difference of SBS compared to BAG_0 (p > 0.05). The adhesive containing 61.25% of 45S5F BAG exhibited clinically acceptable SBS and acid neutralizing properties. Therefore, this composition is a suitable candidate to prevent white spot lesions during orthodontic treatment. Full article

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13 pages, 5334 KiB

Open AccessArticle

The Effect of Bi-Sr and Ca-Sr Interactions on the Microstructure and Tensile Properties of Al-Si-Based Alloys

by Agnes M. Samuel, Herbert W. Doty, Salvador Valtierra Gallardo and Fawzy H. Samuel

Materials 2016, 9(3), 126; https://doi.org/10.3390/ma9030126 - 25 Feb 2016

Cited by 14 | Viewed by 5204

Abstract

The effect of bismuth and calcium additions on the microstructural characteristics and the tensile properties of the modified and grain-refined Al-Si based B319 alloys were studied in this paper. Based on the results obtained, it has been concluded that Bi reacts with both [...] Read more.

The effect of bismuth and calcium additions on the microstructural characteristics and the tensile properties of the modified and grain-refined Al-Si based B319 alloys were studied in this paper. Based on the results obtained, it has been concluded that Bi reacts with both Sr and Mg, leading to severe demodification of the eutectic Si at Bi levels of 0.15%–0.6% Bi. Bismuth causes a decrease of the yield and tensile strengths for the as-cast and artificially aged conditions and an increase of yield strength in the solution heat-treated condition. The elongation increases with the Bi in the solution heat-treated condition. Based on this, Bi is found to be an efficient solid-solution strengthening element for these alloys. Thus, solution heat treatment, rather than the artificial aging, may be recommended for alloys containing about 1.0% Bi. Calcium has no significant demodification effect on the Sr-modified Si particles at 100–400 ppm Ca, and has a modifying effect at ~600 ppm Ca. The elongation increases with the Ca level at all conditions (as-cast, solution heat-treated, and artificially aged). A slight increase of the tensile strength in the heat-treated conditions was also observed. The lowest tensile properties either in the as-cast or the heat-treated conditions correspond to the most demodified-Si condition obtained at 408 ppm Ca. Calcium is, therefore, not as detrimental to the tensile properties as Bi. Full article

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17 pages, 3714 KiB

Open AccessFeature PaperArticle

Lignin as a Binder Material for Eco-Friendly Li-Ion Batteries

by Huiran Lu, Ann Cornell, Fernando Alvarado, Mårten Behm, Simon Leijonmarck, Jiebing Li, Per Tomani and Göran Lindbergh

Materials 2016, 9(3), 127; https://doi.org/10.3390/ma9030127 - 25 Feb 2016

Cited by 68 | Viewed by 11522

Abstract

The industrial lignin used here is a byproduct from Kraft pulp mills, extracted from black liquor. Since lignin is inexpensive, abundant and renewable, its utilization has attracted more and more attention. In this work, lignin was used for the first time as binder [...] Read more.

The industrial lignin used here is a byproduct from Kraft pulp mills, extracted from black liquor. Since lignin is inexpensive, abundant and renewable, its utilization has attracted more and more attention. In this work, lignin was used for the first time as binder material for LiFePO₄ positive and graphite negative electrodes in Li-ion batteries. A procedure for pretreatment of lignin, where low-molecular fractions were removed by leaching, was necessary to obtain good battery performance. The lignin was analyzed for molecular mass distribution and thermal behavior prior to and after the pretreatment. Electrodes containing active material, conductive particles and lignin were cast on metal foils, acting as current collectors and characterized using scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge cycles. Good reversible capacities were obtained, 148 mAh·g⁻¹ for the positive electrode and 305 mAh·g⁻¹ for the negative electrode. Fairly good rate capabilities were found for both the positive electrode with 117 mAh·g⁻¹ and the negative electrode with 160 mAh·g⁻¹ at 1C. Low ohmic resistance also indicated good binder functionality. The results show that lignin is a promising candidate as binder material for electrodes in eco-friendly Li-ion batteries. Full article

(This article belongs to the Special Issue Electrode Materials)

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23 pages, 4159 KiB

Open AccessFeature PaperArticle

Spectroscopic Ellipsometry Studies of n-i-p Hydrogenated Amorphous Silicon Based Photovoltaic Devices

by Laxmi Karki Gautam, Maxwell M. Junda, Hamna F. Haneef, Robert W. Collins and Nikolas J. Podraza

Materials 2016, 9(3), 128; https://doi.org/10.3390/ma9030128 - 25 Feb 2016

Cited by 11 | Viewed by 7797

Abstract

Optimization of thin film photovoltaics (PV) relies on characterizing the optoelectronic and structural properties of each layer and correlating these properties with device performance. Growth evolution diagrams have been used to guide production of materials with good optoelectronic properties in the full hydrogenated [...] Read more.

Optimization of thin film photovoltaics (PV) relies on characterizing the optoelectronic and structural properties of each layer and correlating these properties with device performance. Growth evolution diagrams have been used to guide production of materials with good optoelectronic properties in the full hydrogenated amorphous silicon (a-Si:H) PV device configuration. The nucleation and evolution of crystallites forming from the amorphous phase were studied using in situ near-infrared to ultraviolet spectroscopic ellipsometry during growth of films prepared as a function of hydrogen to reactive gas flow ratio R = [H₂]/[SiH₄]. In conjunction with higher photon energy measurements, the presence and relative absorption strength of silicon-hydrogen infrared modes were measured by infrared extended ellipsometry measurements to gain insight into chemical bonding. Structural and optical models have been developed for the back reflector (BR) structure consisting of sputtered undoped zinc oxide (ZnO) on top of silver (Ag) coated glass substrates. Characterization of the free-carrier absorption properties in Ag and the ZnO + Ag interface as well as phonon modes in ZnO were also studied by spectroscopic ellipsometry. Measurements ranging from 0.04 to 5 eV were used to extract layer thicknesses, composition, and optical response in the form of complex dielectric function spectra (ε = ε₁ + iε₂) for Ag, ZnO, the ZnO + Ag interface, and undoped a-Si:H layer in a substrate n-i-p a-Si:H based PV device structure. Full article

(This article belongs to the Special Issue Photovoltaic Materials and Electronic Devices)

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11 pages, 3961 KiB

Open AccessArticle

Microstructure and Characteristic of BiVO₄ Prepared under Different pH Values: Photocatalytic Efficiency and Antibacterial Activity

by Zhengyao Qu, Peng Liu, Xiaoyu Yang, Fazhou Wang, Wenqin Zhang and Chenggang Fei

Materials 2016, 9(3), 129; https://doi.org/10.3390/ma9030129 - 25 Feb 2016

Cited by 39 | Viewed by 8147

Abstract

In the present study, BiVO₄ sample was prepared under different pH 0.5–13 without capping agent. Different morphology characteristics were observed, such as sheet crystal structure, cross crystal structure and branching crystal structure. The mechanism of the formation of BiVO₄ nanostructure was [...] Read more.

In the present study, BiVO₄ sample was prepared under different pH 0.5–13 without capping agent. Different morphology characteristics were observed, such as sheet crystal structure, cross crystal structure and branching crystal structure. The mechanism of the formation of BiVO₄ nanostructure was discussed. Under acid condition, sheet crystal structure was obtained. The phenomenon could be attributed to polymerization of vanadate in the presence of H⁺. In the weak alkaline solution, across structure and branching type morphology was obtained. The photocatalytic efficiency for the samples ranked as pH 5 > pH 3 > pH 7 > pH 9 > pH 1 > pH 11 > pH 13 > blank, which is in good agreement with X-ray diffraction (XRD) result. E. coli envelop was damaged in the presence of BiVO₄ under visible light. The protrusion on envelop was diminished by BiVO₄. Attenuated Total Reflection Fourier transformed Infrared Spectroscopy (ATR-FTIR) results suggested the intensity was weakened for the amide, phosphoric, –COO⁻ group and C-H bond in lipopolysaccharides (LPS), peptidoglycan and periplasm molecules. Full article

(This article belongs to the Special Issue Advancement of Photocatalytic Materials 2016)

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14 pages, 5025 KiB

Open AccessFeature PaperArticle

Residual Ductility and Microstructural Evolution in Continuous-Bending-under-Tension of AA-6022-T4

by Milovan Zecevic, Timothy J. Roemer, Marko Knezevic, Yannis P. Korkolis and Brad L. Kinsey

Materials 2016, 9(3), 130; https://doi.org/10.3390/ma9030130 - 26 Feb 2016

Cited by 55 | Viewed by 7572

Abstract

A ubiquitous experiment to characterize the formability of sheet metal is the simple tension test. Past research has shown that if the material is repeatedly bent and unbent during this test (i.e., Continuous-Bending-under-Tension, CBT), the percent elongation at failure can significantly [...] Read more.

A ubiquitous experiment to characterize the formability of sheet metal is the simple tension test. Past research has shown that if the material is repeatedly bent and unbent during this test (i.e., Continuous-Bending-under-Tension, CBT), the percent elongation at failure can significantly increase. In this paper, this phenomenon is evaluated in detail for AA-6022-T4 sheets using a custom-built CBT device. In particular, the residual ductility of specimens that are subjected to CBT processing is investigated. This is achieved by subjecting a specimen to CBT processing and then creating subsize tensile test and microstructural samples from the specimens after varying numbers of CBT cycles. Interestingly, the engineering stress initially increases after CBT processing to a certain number of cycles, but then decreases with less elongation achieved for increasing numbers of CBT cycles. Additionally, a detailed microstructure and texture characterization are performed using standard scanning electron microscopy and electron backscattered diffraction imaging. The results show that the material under CBT preserves high integrity to large plastic strains due to a uniform distribution of damage formation and evolution in the material. The ability to delay ductile fracture during the CBT process to large plastic strains, results in formation of a strong <111> fiber texture throughout the material. Full article

(This article belongs to the Special Issue Forming of Light Weight Materials)

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15 pages, 6956 KiB

Open AccessArticle

Effectiveness of Fiber Reinforcement on the Mechanical Properties and Shrinkage Cracking of Recycled Fine Aggregate Concrete

by Jeongsoo Nam, Gyuyong Kim, Jaechul Yoo, Gyeongcheol Choe, Hongseop Kim, Hyeonggil Choi and Youngduck Kim

Materials 2016, 9(3), 131; https://doi.org/10.3390/ma9030131 - 26 Feb 2016

Cited by 54 | Viewed by 7817

Abstract

This paper presents an experimental study conducted to investigate the effect of fiber reinforcement on the mechanical properties and shrinkage cracking of recycled fine aggregate concrete (RFAC) with two types of fiber—polyvinyl alcohol (PVA) and nylon. A small fiber volume fraction, such as [...] Read more.

This paper presents an experimental study conducted to investigate the effect of fiber reinforcement on the mechanical properties and shrinkage cracking of recycled fine aggregate concrete (RFAC) with two types of fiber—polyvinyl alcohol (PVA) and nylon. A small fiber volume fraction, such as 0.05% or 0.1%, in RFAC with polyvinyl alcohol or nylon fibers was used for optimum efficiency in minimum quantity. Additionally, to make a comparative evaluation of the mechanical properties and shrinkage cracking, we examined natural fine aggregate concrete as well. The test results revealed that the addition of fibers and fine aggregates plays an important role in improving the mechanical performance of the investigated concrete specimens as well as controlling their cracking behavior. The mechanical properties such as compressive strength, splitting tensile strength, and flexural strength of fiber-reinforced RFAC were slightly better than those of non-fiber-reinforced RFAC. The shrinkage cracking behavior was examined using plat-ring-type and slab-type tests. The fiber-reinforced RFAC showed a greater reduction in the surface cracks than non-fiber-reinforced concrete. The addition of fibers at a small volume fraction in RFAC is more effective for drying shrinkage cracks than for improving mechanical performance. Full article

(This article belongs to the Special Issue Utilisation of By-Product Materials in Concrete)

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9 pages, 2025 KiB

Open AccessArticle

Discussion on Local Spark Sintering of a Ceramic-Metal System in an SR-CT Experiment during Microwave Processing

by Yongcun Li, Feng Xu, Xiaofang Hu, Bo Dong, Yunbo Luan and Yu Xiao

Materials 2016, 9(3), 132; https://doi.org/10.3390/ma9030132 - 26 Feb 2016

Cited by 2 | Viewed by 5918

Abstract

In this paper, local spark sintering of a ceramic-metal system (SiO₂-Sn) during microwave processing was examinedby means of synchrotron-radiation-computed tomography technology. From the reconstructed 3-D and cross-section images of the specimen, adensification process was observed below the melting point of Sn, [...] Read more.

In this paper, local spark sintering of a ceramic-metal system (SiO₂-Sn) during microwave processing was examinedby means of synchrotron-radiation-computed tomography technology. From the reconstructed 3-D and cross-section images of the specimen, adensification process was observed below the melting point of Sn, and then the specimen came into a rapid densification stage. These results may be due to the local spark sintering induced by the high-frequency alternating microwave electric fields. As the metallic particles Sn were introduced, the microstructure of “ceramic-metal” will lead to a non-uniform distribution and micro-focusing effect from electric fields in some regions (e.g., the neck). This will result in high-intensity electric fields and then induce rapid spark sintering within the micro-region. However, in the subsequent stage, the densification rate declined even when the specimen was not dense enough. The explanation for this is that as the liquid Sn permeated the gaps between SiO₂, the specimen became dense and the micro-focusing effect of electric fields decreased. This may result in the decrease or disappearance of spark sintering. These results will contribute to the understanding of microwave sintering mechanisms and the improvement of microwave processing methods. Full article

(This article belongs to the Collection Spark-Plasma Sintering and Related Field-Assisted Powder Consolidation Technologies)

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14 pages, 966 KiB

Open AccessReview

Newly Developed Techniques on Polycondensation, Ring-Opening Polymerization and Polymer Modification: Focus on Poly(Lactic Acid)

by Yunzi Hu, Walid A. Daoud, Kevin Ka Leung Cheuk and Carol Sze Ki Lin

Materials 2016, 9(3), 133; https://doi.org/10.3390/ma9030133 - 26 Feb 2016

Cited by 158 | Viewed by 26100

Abstract

Polycondensation and ring-opening polymerization are two important polymer synthesis methods. Poly(lactic acid), the most typical biodegradable polymer, has been researched extensively from 1900s. It is of significant importance to have an up-to-date review on the recent improvement in techniques for biodegradable polymers. This [...] Read more.

Polycondensation and ring-opening polymerization are two important polymer synthesis methods. Poly(lactic acid), the most typical biodegradable polymer, has been researched extensively from 1900s. It is of significant importance to have an up-to-date review on the recent improvement in techniques for biodegradable polymers. This review takes poly(lactic acid) as the example to present newly developed polymer synthesis techniques on polycondensation and ring-opening polymerization reported in the recent decade (2005–2015) on the basis of industrial technique modifications and advanced laboratory research. Different polymerization methods, including various solvents, heating programs, reaction apparatus and catalyst systems, are summarized and compared with the current industrial production situation. Newly developed modification techniques for polymer properties improvement are also discussed based on the case of poly(lactic acid). Full article

(This article belongs to the Special Issue Biodegradable and Bio-Based Polymers)

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21 pages, 4663 KiB

Open AccessFeature PaperArticle

Reinforcing Low-Volume Fraction Nano-TiN Particulates to Monolithical, Pure Mg for Enhanced Tensile and Compressive Response

by Ganesh Kumar Meenashisundaram, Mui Hoon Nai, Abdulhakim Almajid and Manoj Gupta

Materials 2016, 9(3), 134; https://doi.org/10.3390/ma9030134 - 26 Feb 2016

Cited by 14 | Viewed by 4840

Abstract

Novel Mg (0.58, 0.97, 1.98 and 2.5) vol. % TiN nanocomposites containing titanium nitride (TiN) nanoparticulates of ~20 nm size are successfully synthesized by a disintegrated melt deposition technique followed by hot extrusion. Microstructural characterization of Mg-TiN nanocomposites indicate significant grain refinement with [...] Read more.

Novel Mg (0.58, 0.97, 1.98 and 2.5) vol. % TiN nanocomposites containing titanium nitride (TiN) nanoparticulates of ~20 nm size are successfully synthesized by a disintegrated melt deposition technique followed by hot extrusion. Microstructural characterization of Mg-TiN nanocomposites indicate significant grain refinement with Mg 2.5 vol. % TiN exhibiting a minimum grain size of ~11 μm. X-ray diffraction studies of Mg-TiN nanocomposites indicate that addition of up to 1.98 vol. % TiN nanoparticulates aids in modifying the strong basal texture of pure Mg. An attempt is made to study the effects of the type of titanium (metal or ceramic), size, and volume fraction addition of nanoparticulates on the microstructural and mechanical properties of pure magnesium. Among the major strengthening mechanisms contributing to the strength of Mg-Ti-based nanocomposites, Hall-Petch strengthening was found to play a vital role. The synthesized Mg-TiN nanocomposites exhibited superior tensile and compression properties indicating significant improvement in the fracture strain values of pure magnesium under loading. Under tensile and compression loading the presence of titanium (metal or ductile phase) nanoparticulates were found to contribute more towards the strengthening, whereas ceramics of titanium (brittle phases) contribute more towards the ductility of pure magnesium. Full article

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12 pages, 1971 KiB

Open AccessFeature PaperArticle

Alendronate Functionalized Mesoporous Bioactive Glass Nanospheres

by Elisa Boanini, Silvia Panseri, Fabiola Arroyo, Monica Montesi, Katia Rubini, Anna Tampieri, Cristian Covarrubias and Adriana Bigi

Materials 2016, 9(3), 135; https://doi.org/10.3390/ma9030135 - 26 Feb 2016

Cited by 21 | Viewed by 6421

Abstract

In this work we synthesized mesoporous bioactive glass nanospheres (nMBG) with the aim to utilize them as substrates for loading one of the most potent amino-bisphosphonates, alendronate (AL). The results of the chemical and structural characterization show that the nMBG display a relatively [...] Read more.

In this work we synthesized mesoporous bioactive glass nanospheres (nMBG) with the aim to utilize them as substrates for loading one of the most potent amino-bisphosphonates, alendronate (AL). The results of the chemical and structural characterization show that the nMBG display a relatively high surface area (528 m²/g) and a mean pore volume of 0.63 cm³/g, both of which decrease on increasing alendronate content. It is possible to modulate the amount of AL loaded into the nanospheres up to a maximum value of about 17 wt %. In vitro tests were performed using a human osteosarcoma cell line (MG63) and a murine monocyte/macrophage cell line as osteoclast model (RAW 264.7). The results indicate that even the lower concentration of alendronate provokes decreased tumor cell viability, and that osteoclast activity exhibits an alendronate dose-dependent inhibition. The data suggest that nMBG can act as a suitable support for the local delivery of alendronate, and that the antiresorptive and antitumor properties of the functionalized mesoporous nanospheres can be modulated by varying the amount of alendronate loading. Full article

(This article belongs to the Special Issue Bioactive Glasses)

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12 pages, 7486 KiB

Open AccessArticle

Development of Hybrid Surfaces with Tunable Wettability by Selective Surface Modifications

by Hyun-Joong Lee and Keun Park

Materials 2016, 9(3), 136; https://doi.org/10.3390/ma9030136 - 26 Feb 2016

Cited by 8 | Viewed by 5526

Abstract

Recent advances in micro/nano technology have driven artificial modifications of surface wettability by mimicking biological surfaces, such as superhydrophobic and water-harvesting surfaces. In this study, surface wettability of polycarbonate (PC) films was modified using various surface treatments: micropatterning using ultrasonic imprint lithography, fluorinate [...] Read more.

Recent advances in micro/nano technology have driven artificial modifications of surface wettability by mimicking biological surfaces, such as superhydrophobic and water-harvesting surfaces. In this study, surface wettability of polycarbonate (PC) films was modified using various surface treatments: micropatterning using ultrasonic imprint lithography, fluorinate silane coating, and electron beam irradiation. To modify surface wettability selectively in a specified region, these three treatments were performed using profiled masks with the corresponding shapes. Various combinations of these treatments were investigated in terms of wettability changes, by measuring contact angle (CA). The semi-hydrophobic PC film (CA: 89.2°) was modified to create a super- hydrophobic state (CA: 155.9°) by virtue of the selective micropatterning and coating. The electron beam irradiation had an opposite effect, reducing the CA (48.2°), so that the irradiated region was modified to create a hydrophilic state. Two combinations of the proposed surface modifications made it possible to have a great difference in CA on a single surface (107.7°), and to have four different wetting states on a single surface. Various water-drop experiments proved that the developed hybrid surfaces were selectively wettable and showed water-collecting capability. Full article

(This article belongs to the Special Issue Superhydrophobicity of Materials)

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37 pages, 15970 KiB

Open AccessReview

Terpyridine and Quaterpyridine Complexes as Sensitizers for Photovoltaic Applications

by Davide Saccone, Claudio Magistris, Nadia Barbero, Pierluigi Quagliotto, Claudia Barolo and Guido Viscardi

Materials 2016, 9(3), 137; https://doi.org/10.3390/ma9030137 - 27 Feb 2016

Cited by 57 | Viewed by 11608

Abstract

Terpyridine and quaterpyridine-based complexes allow wide light harvesting of the solar spectrum. Terpyridines, with respect to bipyridines, allow for achieving metal-complexes with lower band gaps in the metal-to-ligand transition (MLCT), thus providing a better absorption at lower energy wavelengths resulting in an enhancement [...] Read more.

Terpyridine and quaterpyridine-based complexes allow wide light harvesting of the solar spectrum. Terpyridines, with respect to bipyridines, allow for achieving metal-complexes with lower band gaps in the metal-to-ligand transition (MLCT), thus providing a better absorption at lower energy wavelengths resulting in an enhancement of the solar light-harvesting ability. Despite the wider absorption of the first tricarboxylate terpyridyl ligand-based complex, Black Dye (BD), dye-sensitized solar cell (DSC) performances are lower if compared with N719 or other optimized bipyridine-based complexes. To further improve BD performances several modifications have been carried out in recent years affecting each component of the complexes: terpyridines have been replaced by quaterpyridines; other metals were used instead of ruthenium, and thiocyanates have been replaced by different pinchers in order to achieve cyclometalated or heteroleptic complexes. The review provides a summary on design strategies, main synthetic routes, optical and photovoltaic properties of terpyridine and quaterpyridine ligands applied to photovoltaic, and focuses on n-type DSCs. Full article

(This article belongs to the Special Issue Photovoltaic Materials and Electronic Devices)

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13 pages, 5242 KiB

Open AccessArticle

Transition Behaviors of Configurations of Colloidal Particles at a Curved Oil-Water Interface

by Mina Lee, Ming Xia and Bum Jun Park

Materials 2016, 9(3), 138; https://doi.org/10.3390/ma9030138 - 26 Feb 2016

Cited by 14 | Viewed by 5790

Abstract

We studied the transition behaviors of colloidal arrangements confined at a centro-symmetrically curved oil-water interface. We found that assemblies composed of several colloidal particles at the curved interface exhibit at least two unique patterns that can be attributed to two factors: heterogeneity of [...] Read more.

We studied the transition behaviors of colloidal arrangements confined at a centro-symmetrically curved oil-water interface. We found that assemblies composed of several colloidal particles at the curved interface exhibit at least two unique patterns that can be attributed to two factors: heterogeneity of single-colloid self-potential and assembly kinetics. The presence of the two assembly structures indicates that an essential energy barrier between the two structures exists and that one of the structures is kinetically stable. This energy barrier can be overcome via external stimuli (e.g., convection and an optical force), leading to dynamic transitions of the assembly patterns. Full article

(This article belongs to the Special Issue Pickering Emulsion and Derived Materials)

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17 pages, 4771 KiB

Open AccessArticle

A Dissipative Connector for CLT Buildings: Concept, Design and Testing

by Roberto Scotta, Luca Marchi, Davide Trutalli and Luca Pozza

Materials 2016, 9(3), 139; https://doi.org/10.3390/ma9030139 - 26 Feb 2016

Cited by 48 | Viewed by 6274

Abstract

This paper deals with the conception and characterization of an innovative connection for cross-laminated timber (CLT) panels. The connection is designed to provide an adequate level of dissipative capacity to CLT structures also when realized with large horizontal panels and therefore prone to [...] Read more.

This paper deals with the conception and characterization of an innovative connection for cross-laminated timber (CLT) panels. The connection is designed to provide an adequate level of dissipative capacity to CLT structures also when realized with large horizontal panels and therefore prone to fragile shear sliding failure. The connector, named X-bracket, has been theorized and designed by means of numerical parametric analyses. Furthermore, its cyclic behavior has been verified with experimental tests and compared to that of traditional connectors. Numerical simulations of cyclic tests of different CLT walls anchored to the foundation with X-brackets were also performed to assess their improved seismic performances. Finally, the analysis of the response of a 6 m × 3 m squat wall demonstrates that the developed connection provides good ductility and dissipation capacities also to shear walls realized with a single CLT panel. Full article

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9 pages, 2323 KiB

Open AccessArticle

Nanomechanical Behavior of Multi-Walled Carbon Nanotubes Particulate Reinforced Aluminum Nanocomposites Prepared by Ball Milling

by Farhad Ostovan, Khamirul Amin Matori, Meysam Toozandehjani, Arshin Oskoueian, Hamdan Mohamed Yusoff, Robiah Yunus and Azmah Hanim Mohamed Ariff

Materials 2016, 9(3), 140; https://doi.org/10.3390/ma9030140 - 26 Feb 2016

Cited by 35 | Viewed by 4692

Abstract

The nanomechanical properties of carbon nanotubes particulate-reinforced aluminum matrix nanocomposites (Al-CNTs) have been characterized using nanoindentation. Bulk nanocomposite specimens containing 2 wt % multiwalled CNTs (MWCNTs) were synthesized by a combination of ball milling and powder metallurgy route. It has been tried to [...] Read more.

The nanomechanical properties of carbon nanotubes particulate-reinforced aluminum matrix nanocomposites (Al-CNTs) have been characterized using nanoindentation. Bulk nanocomposite specimens containing 2 wt % multiwalled CNTs (MWCNTs) were synthesized by a combination of ball milling and powder metallurgy route. It has been tried to understand the correlation between microstructural evolution particularly carbon nanotubes (CNTs) dispersion during milling and mechanical properties of Al-2 wt % nanocomposites. Maximum enhancement of +23% and +44% has been found in Young’s modulus and hardness respectively, owing to well homogenous dispersion of CNTs within the aluminum matrix at longer milling time. Full article

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12 pages, 20215 KiB

Open AccessArticle

Surface Characterizations of Fretting Fatigue Damage in Aluminum Alloy 7075-T6 Clamped Joints: The Beneficial Role of Ni–P Coatings

by Reza H. Oskouei, Mohammad Reza Barati and Raafat N. Ibrahim

Materials 2016, 9(3), 141; https://doi.org/10.3390/ma9030141 - 27 Feb 2016

Cited by 15 | Viewed by 8849

Abstract

This paper aims to characterize the surface damage as a consequence of fretting fatigue in aluminum alloy 7075-T6 plates in double-lap bolted joints through XRD, surface profilometry, and SEM analyses. The main focus was on the surface roughness and chemical phase composition of [...] Read more.

This paper aims to characterize the surface damage as a consequence of fretting fatigue in aluminum alloy 7075-T6 plates in double-lap bolted joints through XRD, surface profilometry, and SEM analyses. The main focus was on the surface roughness and chemical phase composition of the damaged zone along with the identification of fretting fatigue crack initiations over the surface of the material. The surface roughness of the fretted zone was found to increase when the joint was clamped with a higher tightening torque and tested under the same cyclic loading. Additionally, MgZn₂ (η/ή) precipitates and ZnO phase were found to form onto the surface of uncoated aluminum plate in the fretted and worn zones. The formation of the ZnO phase was understood to be a result of frictional heat induced between the surface of contacting uncoated Al 7075-T6 plates during cyclic loading and exposure to the air. The beneficial role of electroless nickel-phosphorous (Ni–P) coatings in minimizing the fretting damage and thus improving the fretting fatigue life of the aluminum plates was also studied. The results showed that the surface roughness decreased by approximately 40% after applying Ni–P coatings to the Al 7075-T6 plates. Full article

(This article belongs to the Special Issue Surface Modification Methods to Improve Fatigue, Fretting Fatigue, and Fretting Wear Behavior of Materials)

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27 pages, 11058 KiB

Open AccessFeature PaperReview

Sustainable Materials for Sustainable Energy Storage: Organic Na Electrodes

by Viorica-Alina Oltean, Stéven Renault, Mario Valvo and Daniel Brandell

Materials 2016, 9(3), 142; https://doi.org/10.3390/ma9030142 - 1 Mar 2016

Cited by 62 | Viewed by 11542

Abstract

In this review, we summarize research efforts to realize Na-based organic materials for novel battery chemistries. Na is a more abundant element than Li, thereby contributing to less costly materials with limited to no geopolitical constraints while organic electrode materials harvested from biomass [...] Read more.

In this review, we summarize research efforts to realize Na-based organic materials for novel battery chemistries. Na is a more abundant element than Li, thereby contributing to less costly materials with limited to no geopolitical constraints while organic electrode materials harvested from biomass resources provide the possibility of achieving renewable battery components with low environmental impact during processing and recycling. Together, this can form the basis for truly sustainable electrochemical energy storage. We explore the efforts made on electrode materials of organic salts, primarily carbonyl compounds but also Schiff bases, unsaturated compounds, nitroxides and polymers. Moreover, sodiated carbonaceous materials derived from biomasses and waste products are surveyed. As a conclusion to the review, some shortcomings of the currently investigated materials are highlighted together with the major limitations for future development in this field. Finally, routes to move forward in this direction are suggested. Full article

(This article belongs to the Special Issue Electrode Materials)

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15 pages, 4467 KiB

Open AccessFeature PaperArticle

Electrospun Nafion^®/Polyphenylsulfone Composite Membranes for Regenerative Hydrogen Bromine Fuel Cells

by Jun Woo Park, Ryszard Wycisk, Peter N. Pintauro, Venkata Yarlagadda and Trung Van Nguyen

Materials 2016, 9(3), 143; https://doi.org/10.3390/ma9030143 - 29 Feb 2016

Cited by 30 | Viewed by 9298

Abstract

The regenerative H₂/Br₂-HBr fuel cell, utilizing an oxidant solution of Br₂ in aqueous HBr, shows a number of benefits for grid-scale electricity storage. The membrane-electrode assembly, a key component of a fuel cell, contains a proton-conducting membrane, typically [...] Read more.

The regenerative H₂/Br₂-HBr fuel cell, utilizing an oxidant solution of Br₂ in aqueous HBr, shows a number of benefits for grid-scale electricity storage. The membrane-electrode assembly, a key component of a fuel cell, contains a proton-conducting membrane, typically based on the perfluorosulfonic acid (PFSA) ionomer. Unfortunately, the high cost of PFSA membranes and their relatively high bromine crossover are serious drawbacks. Nanofiber composite membranes can overcome these limitations. In this work, composite membranes were prepared from electrospun dual-fiber mats containing Nafion^® PFSA ionomer for facile proton transport and an uncharged polymer, polyphenylsulfone (PPSU), for mechanical reinforcement, and swelling control. After electrospinning, Nafion/PPSU mats were converted into composite membranes by softening the PPSU fibers, through exposure to chloroform vapor, thus filling the voids between ionomer nanofibers. It was demonstrated that the relative membrane selectivity, referenced to Nafion^® 115, increased with increasing PPSU content, e.g., a selectivity of 11 at 25 vol% of Nafion fibers. H₂-Br₂ fuel cell power output with a 65 μm thick membrane containing 55 vol% Nafion fibers was somewhat better than that of a 150 μm Nafion^® 115 reference, but its cost advantage due to a four-fold decrease in PFSA content and a lower bromine species crossover make it an attractive candidate for use in H₂/Br₂-HBr systems. Full article

(This article belongs to the Special Issue Electrospun Materials)

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23 pages, 4572 KiB

Open AccessFeature PaperArticle

The Role of Grain Size on Neutron Irradiation Response of Nanocrystalline Copper

by Walid Mohamed, Brandon Miller, Douglas Porter and Korukonda Murty

Materials 2016, 9(3), 144; https://doi.org/10.3390/ma9030144 - 1 Mar 2016

Cited by 19 | Viewed by 8339

Abstract

The role of grain size on the developed microstructure and mechanical properties of neutron irradiated nanocrystalline copper was investigated by comparing the radiation response of material to the conventional micrograined counterpart. Nanocrystalline (nc) and micrograined (MG) copper samples were subjected to a range [...] Read more.

The role of grain size on the developed microstructure and mechanical properties of neutron irradiated nanocrystalline copper was investigated by comparing the radiation response of material to the conventional micrograined counterpart. Nanocrystalline (nc) and micrograined (MG) copper samples were subjected to a range of neutron exposure levels from 0.0034 to 2 dpa. At all damage levels, the response of MG-copper was governed by radiation hardening manifested by an increase in strength with accompanying ductility loss. Conversely, the response of nc-copper to neutron irradiation exhibited a dependence on the damage level. At low damage levels, grain growth was the primary response, with radiation hardening and embrittlement becoming the dominant responses with increasing damage levels. Annealing experiments revealed that grain growth in nc-copper is composed of both thermally-activated and irradiation-induced components. Tensile tests revealed minimal change in the source hardening component of the yield stress in MG-copper, while the source hardening component was found to decrease with increasing radiation exposure in nc-copper. Full article

(This article belongs to the Special Issue Nuclear Materials 2015)

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23 pages, 3426 KiB

Open AccessFeature PaperArticle

Effect of Ionic Correlations on the Surface Forces in Thin Liquid Films: Influence of Multivalent Coions and Extended Theory

by Krassimir D. Danov, Elka S. Basheva and Peter A. Kralchevsky

Materials 2016, 9(3), 145; https://doi.org/10.3390/ma9030145 - 1 Mar 2016

Cited by 12 | Viewed by 5567

Abstract

Experimental data for the disjoining pressure of foam films stabilized by anionic surfactant in the presence of 1:1, 1:2, 1:3, and 2:2 electrolytes: NaCl, Na₂SO₄, Na₃Citrate, and MgSO₄ are reported. The disjoining pressure predicted by the [...] Read more.

Experimental data for the disjoining pressure of foam films stabilized by anionic surfactant in the presence of 1:1, 1:2, 1:3, and 2:2 electrolytes: NaCl, Na₂SO₄, Na₃Citrate, and MgSO₄ are reported. The disjoining pressure predicted by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory coincides with the experimental data in the case of a 1:1 electrolyte, but it is considerably greater than the measured pressure in all other cases. The theory is extended to account for the effects of ionic correlations and finite ionic radii. Original analytical expressions are derived for the local activity coefficient, electrostatic disjoining pressure, and asymptotic screening parameter. With the same parameter of counterion binding as for a 1:1 electrolyte, the curves predicted by the extended theory are in perfect agreement with the experimental data for 1:2 and 1:3 electrolytes. In comparison with the DLVO theory, the effect of ionic correlations leads to more effective screening of electrostatic interactions, and lower electric potential and counterion concentrations in the film’s midplane, resulting in lower disjoining pressure, as experimentally observed. The developed theory is applicable to both multivalent coions and multivalent counterions. Its application could remove some discrepancies between theory and experiment observed in studies with liquid films from electrolyte solutions. Full article

(This article belongs to the Special Issue Surface Forces and Thin Liquid Films)

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14 pages, 4969 KiB

Open AccessArticle

Pozzolanic Reactivity of Silica Fume and Ground Rice Husk Ash as Reactive Silica in a Cementitious System: A Comparative Study

by Weiting Xu, Tommy Yiu Lo, Weilun Wang, Dong Ouyang, Penggang Wang and Feng Xing

Materials 2016, 9(3), 146; https://doi.org/10.3390/ma9030146 - 1 Mar 2016

Cited by 81 | Viewed by 8173

Abstract

This study comparably assessed the pozzolanic effect of silica fume (SF) and ground rice husk ash (RHA) as supplementary cementing materials on the properties of blended cement pastes and concretes. A commonly commercial silica fume (SF) and locally-produced rice husk ash (RHA) samples [...] Read more.

This study comparably assessed the pozzolanic effect of silica fume (SF) and ground rice husk ash (RHA) as supplementary cementing materials on the properties of blended cement pastes and concretes. A commonly commercial silica fume (SF) and locally-produced rice husk ash (RHA) samples with two finenesses (one with larger size than cement and the other with smaller size than cement) were used in this study. Material properties of SF and RHA were experimentally characterized. Hydration and mechanical properties of cement pastes incorporating SF and RHA were determined by thermogravimetric analysis (TGA) and compressive strength tests, respectively. Properties of concretes regarding workability, mechanical property, durability, and microstructure were evaluated. Results showed that, although the finely ground RHA used in this study possessed lower SiO₂ content and higher particle size compared to SF, it exhibited comparable pozzolanic reactivity with SF due to the nano-scale pores on its each single particle, leading to a higher specific surface area. The optimal replacement levels of SF and RHA were 10% by weight of cement in pastes and concretes. Although addition of SF and RHA led to a significant reduction in slump for the fresh mixtures, inclusion of up to 30% of SF or 15% of ground RHA did not adversely affect the strength of concretes. At the same mix, incorporation of finely-ground RHA in cement composites provided comparable mechanical properties, hydration degree, and durability with SF blended cement composites, owing to the porous structure and high specific surface area of RHA particles. Microstructure morphology analysis of concretes explored by scanning electron microscopy (SEM) further validated the strength and the durability test results. Full article

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11 pages, 2337 KiB

Open AccessArticle

Effect of Admixtures on the Yield Stresses of Cement Pastes under High Hydrostatic Pressures

by Hong Jae Yim, Jae Hong Kim and Seung Hee Kwon

Materials 2016, 9(3), 147; https://doi.org/10.3390/ma9030147 - 2 Mar 2016

Cited by 17 | Viewed by 5394

Abstract

When cement-based materials are transported at a construction site, they undergo high pressures during the pumping process. The rheological properties of the materials under such high pressures are unknown, and estimating the workability of the materials after pumping is a complex problem. Among [...] Read more.

When cement-based materials are transported at a construction site, they undergo high pressures during the pumping process. The rheological properties of the materials under such high pressures are unknown, and estimating the workability of the materials after pumping is a complex problem. Among various influential factors on the rheology of concrete, this study investigated the effect of mineral and chemical admixtures on the high-pressure rheology. A rheometer was fabricated that could measure the rheological properties while maintaining a high pressure to simulate the pumping process. The effects of superplasticizer, silica fume, nanoclay, fly ash, or ground granulated blast furnace slag were investigated when mixed with two control cement pastes. The water-to-cement ratios were 0.35 and 0.50. Full article

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25 pages, 16756 KiB

Open AccessArticle

Seismic Performance of Composite Shear Walls Constructed Using Recycled Aggregate Concrete and Different Expandable Polystyrene Configurations

by Wenchao Liu, Wanlin Cao, Jianwei Zhang, Qiyun Qiao and Heng Ma

Materials 2016, 9(3), 148; https://doi.org/10.3390/ma9030148 - 2 Mar 2016

Cited by 19 | Viewed by 7456

Abstract

The seismic performance of recycled aggregate concrete (RAC) composite shear walls with different expandable polystyrene (EPS) configurations was investigated. Six concrete shear walls were designed and tested under cyclic loading to evaluate the effect of fine RAC in designing earthquake-resistant structures. Three of [...] Read more.

The seismic performance of recycled aggregate concrete (RAC) composite shear walls with different expandable polystyrene (EPS) configurations was investigated. Six concrete shear walls were designed and tested under cyclic loading to evaluate the effect of fine RAC in designing earthquake-resistant structures. Three of the six specimens were used to construct mid-rise walls with a shear-span ratio of 1.5, and the other three specimens were used to construct low-rise walls with a shear-span ratio of 0.8. The mid-rise and low-rise shear walls consisted of an ordinary recycled concrete shear wall, a composite wall with fine aggregate concrete (FAC) protective layer (EPS modules as the external insulation layer), and a composite wall with sandwiched EPS modules as the insulation layer. Several parameters obtained from the experimental results were compared and analyzed, including the load-bearing capacity, stiffness, ductility, energy dissipation, and failure characteristics of the specimens. The calculation formula of load-bearing capacity was obtained by considering the effect of FAC on composite shear walls as the protective layer. The damage process of the specimen was simulated using the ABAQUS Software, and the results agreed quite well with those obtained from the experiments. The results show that the seismic resistance behavior of the EPS module composite for shear walls performed better than ordinary recycled concrete for shear walls. Shear walls with sandwiched EPS modules had a better seismic performance than those with EPS modules lying outside. Although the FAC protective layer slightly improved the seismic performance of the structure, it undoubtedly slowed down the speed of crack formation and the stiffness degradation of the walls. Full article

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7 pages, 3365 KiB

Open AccessArticle

Synthesis, Characterization and Cytotoxicity of Novel Multifunctional Fe₃O₄@SiO₂@GdVO₄:Dy³⁺ Core-Shell Nanocomposite as a Drug Carrier

by Bo Li, Huitao Fan, Qiang Zhao and Congcong Wang

Materials 2016, 9(3), 149; https://doi.org/10.3390/ma9030149 - 2 Mar 2016

Cited by 19 | Viewed by 7281

Abstract

In this study, multifunctional Fe₃O₄@SiO₂@GdVO₄:Dy³⁺ nanocomposites were successfully synthesized via a two-step method. Their structure, luminescence and magnetic properties were characterized by X-ray diffraction (XRD), scanning electronic microscope (SEM), transmission electron microscopy (TEM), photoluminescence [...] Read more.

In this study, multifunctional Fe₃O₄@SiO₂@GdVO₄:Dy³⁺ nanocomposites were successfully synthesized via a two-step method. Their structure, luminescence and magnetic properties were characterized by X-ray diffraction (XRD), scanning electronic microscope (SEM), transmission electron microscopy (TEM), photoluminescence (PL) spectra and vibrating sample magnetometer (VSM). The results indicated that the as-prepared multifunctional composites displayed a well-defined core-shell structure. The composites show spherical morphology with a size distribution of around 360 nm. Additionally, the composites exhibit high saturation magnetization (20.40 emu/g) and excellent luminescence properties. The inner Fe₃O₄ cores and the outer GdVO₄:Dy³⁺ layers endow the composites with good responsive magnetic properties and strong fluorescent properties, which endow the nanoparticles with great potential applications in drug delivery, magnetic resonance imaging, and marking and separating of cells in vitro. Full article

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9 pages, 4566 KiB

Open AccessFeature PaperArticle

Differential Effects of Coating Materials on Viability and Migration of Schwann Cells

by Silvan Klein, Lukas Prantl, Jody Vykoukal, Markus Loibl and Oliver Felthaus

Materials 2016, 9(3), 150; https://doi.org/10.3390/ma9030150 - 3 Mar 2016

Cited by 17 | Viewed by 4874

Abstract

Synthetic nerve conduits have emerged as an alternative to guide axonal regeneration in peripheral nerve gap injuries. Migration of Schwann cells (SC) from nerve stumps has been demonstrated as one essential factor for nerve regeneration in nerve defects. In this experiment, SC viability [...] Read more.

Synthetic nerve conduits have emerged as an alternative to guide axonal regeneration in peripheral nerve gap injuries. Migration of Schwann cells (SC) from nerve stumps has been demonstrated as one essential factor for nerve regeneration in nerve defects. In this experiment, SC viability and migration were investigated for various materials to determine the optimal conditions for nerve regeneration. Cell viability and SC migration assays were conducted for collagen I, laminin, fibronectin, lysine and ornithine. The highest values for cell viability were detected for collagen I, whereas fibronectin was most stimulatory for SC migration. At this time, clinically approved conduits are based on single-material structures. In contrast, the results of this experiment suggest that material compounds such as collagen I in conjunction with fibronectin should be considered for optimal nerve healing. Full article

(This article belongs to the Special Issue Regenerative Materials)

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27 pages, 6077 KiB

Open AccessReview

Recent Advances in Superhydrophobic Electrodeposits

by Jason Tam, Gino Palumbo and Uwe Erb

Materials 2016, 9(3), 151; https://doi.org/10.3390/ma9030151 - 3 Mar 2016

Cited by 77 | Viewed by 10396

Abstract

In this review, we present an extensive summary of research on superhydrophobic electrodeposits reported in the literature over the past decade. As a synthesis technique, electrodeposition is a simple and scalable process to produce non-wetting metal surfaces. There are three main categories of [...] Read more.

In this review, we present an extensive summary of research on superhydrophobic electrodeposits reported in the literature over the past decade. As a synthesis technique, electrodeposition is a simple and scalable process to produce non-wetting metal surfaces. There are three main categories of superhydrophobic surfaces made by electrodeposition: (i) electrodeposits that are inherently non-wetting due to hierarchical roughness generated from the process; (ii) electrodeposits with plated surface roughness that are further modified with low surface energy material; (iii) composite electrodeposits with co-deposited inert and hydrophobic particles. A recently developed strategy to improve the durability during the application of superhydrophobic electrodeposits by controlling the microstructure of the metal matrix and the co-deposition of hydrophobic ceramic particles will also be addressed. Full article

(This article belongs to the Special Issue Superhydrophobicity of Materials)

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17 pages, 8366 KiB

Open AccessArticle

Preparation and Properties of Melamine Urea-Formaldehyde Microcapsules for Self-Healing of Cementitious Materials

by Wenting Li, Xujing Zhu, Nan Zhao and Zhengwu Jiang

Materials 2016, 9(3), 152; https://doi.org/10.3390/ma9030152 - 3 Mar 2016

Cited by 107 | Viewed by 13026

Abstract

Self-healing microcapsules were synthesized by in situ polymerization with a melamine urea-formaldehyde resin shell and an epoxy resin adhesive. The effects of the key factors, i.e., core–wall ratio, reaction temperature, pH and stirring rate, were investigated by characterizing microcapsule morphology, shell thickness, [...] Read more.

Self-healing microcapsules were synthesized by in situ polymerization with a melamine urea-formaldehyde resin shell and an epoxy resin adhesive. The effects of the key factors, i.e., core–wall ratio, reaction temperature, pH and stirring rate, were investigated by characterizing microcapsule morphology, shell thickness, particle size distribution, mechanical properties and chemical nature. Microcapsule healing mechanisms in cement paste were evaluated based on recovery strength and healing microstructure. The results showed that the encapsulation ability, the elasticity modulus and hardness of the capsule increased with an increase of the proportion of shell material. Increased polymerization temperatures were beneficial to the higher degree of shell condensation polymerization, higher resin particles deposition on microcapsule surfaces and enhanced mechanical properties. For relatively low pH values, the less porous three-dimensional structure led to the increased elastic modulus of shell and the more stable chemical structure. Optimized microcapsules were produced at a temperature of 60 °C, a core-wall ratio of 1:1, at pH 2~3 and at a stirring rate of 300~400 r/min. The best strength restoration was observed in the cement paste pre-damaged by 30% f_max and incorporating 4 wt % of capsules. Full article

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8 pages, 1521 KiB

Open AccessArticle

Preparation and Characterization of Ni Spines Grown on the Surface of Cubic Boron Nitride Grains by Electroplating Method

by Yanghai Gui, Jianbo Zhao, Jingbo Chen and Yuanli Jiang

Materials 2016, 9(3), 153; https://doi.org/10.3390/ma9030153 - 4 Mar 2016

Cited by 5 | Viewed by 5812

Abstract

Cubic boron nitride (cBN) is widely applied in cutting and grinding tools. cBN grains plated by pure Ni and Ni/SiC composite were produced under the same conditions from an additive-free nickel Watts type bath. The processed electroplating products were characterized by the techniques [...] Read more.

Cubic boron nitride (cBN) is widely applied in cutting and grinding tools. cBN grains plated by pure Ni and Ni/SiC composite were produced under the same conditions from an additive-free nickel Watts type bath. The processed electroplating products were characterized by the techniques of scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermoanalysis (TG-DTA). Due to the presence of SiC particles, there are some additional nodules on the surface of Ni/SiC plated cBN compared with the pure Ni plated cBN. The unique morphology of Ni/SiC plated cBN should attain greater retention force in resin bond. Moreover, the coating weight of cBN grains could be controlled by regulating the plating time. cBN grains with 60% coating weight possess the optimum grinding performance due to their roughest and spiniest surface. In addition, Ni spines plated cBN grains show good thermal stability when temperature is lower than 464 °C. Therefore, the plated cBN grains are more stable and suitable for making resin bond abrasive tools below 225 °C. Finally, the formation mechanism of electroplating products is also discussed. Full article

(This article belongs to the Section Advanced Materials Characterization)

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18 pages, 5559 KiB

Open AccessArticle

Effect of A-Site Cation Ordering on Chemical Stability, Oxygen Stoichiometry and Electrical Conductivity in Layered LaBaCo₂O_5+δ Double Perovskite

by Carlos Bernuy-Lopez, Kristin Høydalsvik, Mari-Ann Einarsrud and Tor Grande

Materials 2016, 9(3), 154; https://doi.org/10.3390/ma9030154 - 3 Mar 2016

Cited by 59 | Viewed by 9139

Abstract

The effect of the A-site cation ordering on the chemical stability, oxygen stoichiometry and electrical conductivity in layered LaBaCo₂O_5+δ double perovskite was studied as a function of temperature and partial pressure of oxygen. Tetragonal A-site cation ordered layered LaBaCo₂ [...] Read more.

The effect of the A-site cation ordering on the chemical stability, oxygen stoichiometry and electrical conductivity in layered LaBaCo₂O_5+δ double perovskite was studied as a function of temperature and partial pressure of oxygen. Tetragonal A-site cation ordered layered LaBaCo₂O_5+δ double perovskite was obtained by annealing cubic A-site cation disordered La_0.5Ba_0.5CoO_3-δ perovskite at 1100 °C in N₂. High temperature X-ray diffraction between room temperature (RT) and 800 °C revealed that LaBaCo₂O_5+δ remains tetragonal during heating in oxidizing atmosphere, but goes through two phase transitions in N₂ and between 450 °C and 675 °C from tetragonal P4/mmm to orthorhombic Pmmm and back to P4/mmm due to oxygen vacancy ordering followed by disordering of the oxygen vacancies. An anisotropic chemical and thermal expansion of LaBaCo₂O_5+δ was demonstrated. La_0.5Ba_0.5CoO_3-δ remained cubic at the studied temperature irrespective of partial pressure of oxygen. LaBaCo₂O_5+δ is metastable with respect to La_0.5Ba_0.5CoO_3-δ at oxidizing conditions inferred from the thermal evolution of the oxygen deficiency and oxidation state of Co in the two materials. The oxidation state of Co is higher in La_0.5Ba_0.5CoO_3-δ resulting in a higher electrical conductivity relative to LaBaCo₂O_5+δ. The conductivity in both materials was reduced with decreasing partial pressure of oxygen pointing to a p-type semiconducting behavior. Full article

(This article belongs to the Section Advanced Materials Characterization)

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14 pages, 4143 KiB

Open AccessArticle

Inhibited Bacterial Adhesion and Biofilm Formation on Quaternized Chitosan-Loaded Titania Nanotubes with Various Diameters

by Wen-tao Lin, Yi-yuan Zhang, Hong-lue Tan, Hai-yong Ao, Zhao-ling Duan, Guo He and Ting-ting Tang

Materials 2016, 9(3), 155; https://doi.org/10.3390/ma9030155 - 3 Mar 2016

Cited by 33 | Viewed by 7043

Abstract

Titania nanotube-based local drug delivery is an attractive strategy for combating implant-associated infection. In our previous study, we demonstrated that the gentamicin-loaded nanotubes could dramatically inhibit bacterial adhesion and biofilm formation on implant surfaces. Considering the overuse of antibiotics may lead to the [...] Read more.

Titania nanotube-based local drug delivery is an attractive strategy for combating implant-associated infection. In our previous study, we demonstrated that the gentamicin-loaded nanotubes could dramatically inhibit bacterial adhesion and biofilm formation on implant surfaces. Considering the overuse of antibiotics may lead to the evolution of antibiotic-resistant bacteria, we synthesized a new quaternized chitosan derivative (hydroxypropyltrimethyl ammonium chloride chitosan, HACC) with a 27% degree of substitution (DS; referred to as 27% HACC) that had a strong antibacterial activity and simultaneously good biocompatibility with osteogenic cells. Titania nanotubes with various diameters (80, 120, 160, and 200 nm) and 200 nm length were loaded with 2 mg of HACC using a lyophilization method and vacuum drying. Two standard strain, methicillin-resistant Staphylococcus aureus (American Type Culture Collection 43300) and Staphylococcus epidermidis (American Type Culture Collection 35984), and two clinical isolates, S. aureus 376 and S. epidermidis 389, were selected to investigate the bacterial adhesion at 6 h and biofilm formation at 24, 48, and 72 h on the HACC-loaded nanotubes (NT-H) using the spread plate method, confocal laser scanning microscopy (CLSM), and scanning electron microscopy (SEM). Smooth titanium (Smooth Ti) was also investigated and compared. We found that NT-H could significantly inhibit bacterial adhesion and biofilm formation on its surface compared with Smooth Ti, and the NT-H with 160 nm and 200 nm diameters had stronger antibacterial activity because of the extended HACC release time of NT-H with larger diameters. Therefore, NT-H can significantly improve the antibacterial ability of orthopedic implants and provide a promising strategy to prevent implant-associated infections. Full article

(This article belongs to the Special Issue Biofilm and Materials Science)

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12 pages, 1671 KiB

Open AccessArticle

Evaluation of the Influence of Specific Surface Treatments of RBA on a Set of Properties of Concrete

by Marcela Ondova and Alena Sicakova

Materials 2016, 9(3), 156; https://doi.org/10.3390/ma9030156 - 3 Mar 2016

Cited by 16 | Viewed by 4121

Abstract

High water absorption of recycled brick aggregate (RBA) is one of the most discussed parameters in terms of its application in the production of concrete—its influence on the amount of mixing water and, hence, the quality of the concrete, is usually considered negative. [...] Read more.

High water absorption of recycled brick aggregate (RBA) is one of the most discussed parameters in terms of its application in the production of concrete—its influence on the amount of mixing water and, hence, the quality of the concrete, is usually considered negative. In this paper, different methods of decreasing the absorption of RBA and, consequently, the impact on the properties of concrete, are described. The RBA has been treated to decrease the water absorption capacity by impregnation approach using specific impregnators. Afterwards, the RBA samples have been dried at two different temperatures in the laboratory oven—20 and 90 °C. Concretes using 4/8 fraction of the treated RBA instead of natural aggregate (NA) have been mixed and tested. The effectiveness of the RBA treatments have been evaluated on the basis of their influence on the properties of the hardened concrete; by means of the following tests: flexural strength, compressive strength, capillarity, total water absorption capacity, depth of water penetration under pressure, and frost resistance. The method of ranking by ordinal scale has been used as it is suitable for the comparison of a large set of results, while results have been analyzed in terms of the most important technological parameter that influences the quality of the concrete-effective water content. Out of all the tested surface-treatments of RBA, treatment by sodium water glass has the best potential for reduction of the water/cement (w/c) ratio. When the effective w/c ratio is kept within standard limits, concretes containing treated RBA are possible to be specified for various exposure classes and manufacturing in practice. The experiment confirms that at a constant amount of mixing water, with decreasing water absorption of RBA, the effective amount of water in the concrete increases and, hence, the final properties of the concrete decrease (get worse). As the water absorption of the RBA declines, there is a potential for the reduction of the w/c ratio and improvement in the quality of the concrete. Full article

(This article belongs to the Section Advanced Composites)

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8 pages, 4108 KiB

Open AccessArticle

Effects of Complex Modification by Sr–Sb on the Microstructures and Mechanical Properties of Al–18 wt % Mg₂Si–4.5Cu Alloys

by Youhong Sun, Shaoming Ma, Huiyuan Wang, Lei Chen, Ke Gao, Yinlong Ma and Baochang Liu

Materials 2016, 9(3), 157; https://doi.org/10.3390/ma9030157 - 4 Mar 2016

Cited by 13 | Viewed by 4803

Abstract

This research was carried out to investigate the influence of Sr–Sb on the microstructures and mechanical properties of Al–18 wt % Mg₂Si–4.5Cu alloys. After the addition of 0.2 wt % Sr–Sb, the morphologies of primary Mg₂Si transformed from equiaxed [...] Read more.

This research was carried out to investigate the influence of Sr–Sb on the microstructures and mechanical properties of Al–18 wt % Mg₂Si–4.5Cu alloys. After the addition of 0.2 wt % Sr–Sb, the morphologies of primary Mg₂Si transformed from equiaxed dendrite to cube in as-cast alloys and the average size of primary Mg₂Si decreased from ~50 to ~20 μm. The shape of eutectic Mg₂Si changed from Chinese script to short rod. After extrusion and T6 heat treatment, the ultimate tensile strength of modified alloy at room temperature (RT) and 100 °C increased respectively from 229 to 288 MPa, and from 231 to 272 MPa. The elongation-to-failure only slightly improved from 2.9% to 3.8% and from 3.3% to 3.7% at RT and 100 °C, respectively. The tensile fracture surface revealed a transition from brittle fracture to ductile fracture after modifying by 0.2 wt % Sr–Sb. Full article

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16 pages, 3010 KiB

Open AccessArticle

Microstructural and Mechanical Properties of Alkali Activated Colombian Raw Materials

by Maria Criado, Willian Aperador and Isabel Sobrados

Materials 2016, 9(3), 158; https://doi.org/10.3390/ma9030158 - 5 Mar 2016

Cited by 145 | Viewed by 8334

Abstract

Microstructural and mechanical properties of alkali activated binders based on blends of Colombian granulated blast furnace slag (GBFS) and fly ash (FA) were investigated. The synthesis of alkali activated binders was conducted at 85 °C for 24 h with different slag/fly ash ratios [...] Read more.

Microstructural and mechanical properties of alkali activated binders based on blends of Colombian granulated blast furnace slag (GBFS) and fly ash (FA) were investigated. The synthesis of alkali activated binders was conducted at 85 °C for 24 h with different slag/fly ash ratios (100:0, 80:20, 60:40, 40:60, 20:80, and 0:100). Mineralogical and microstructural characterization was carried out by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) and Nuclear magnetic resonance (NMR). Mechanical properties were evaluated through the compressive strength, modulus of elasticity and Poisson’s ratio. The results show that two different reaction products were detected in the slag/fly ash mixtures, a calcium silicate hydrate with Al in its structure (C-A-S-H gel) and a sodium aluminosilicate hydrate (N-A-S-H gel) with higher number of polymerized species and low content in Ca. It was found that with the increase of the amount of added slag, the amount of C-A-S-H gel increased and the amount of N-A-S-H gel decreased. The matrix was more dense and compact with almost absence of pores. The predominance of slag affected positively the compressive strength, Young’s modulus and Poisson’s ratio, with 80% slag and 20% fly ash concrete being the best mechanical performance blend. Full article

(This article belongs to the Special Issue Advances in Geopolymers and Alkali-Activated Materials)

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15 pages, 5182 KiB

Open AccessArticle

Lamellae Evolution of Stereocomplex-Type Poly(Lactic Acid)/Organically-Modified Layered Zinc Phenylphosphonate Nanocomposites Induced by Isothermal Crystallization

by Yi-An Chen, Erh-Chiang Chen and Tzong-Ming Wu

Materials 2016, 9(3), 159; https://doi.org/10.3390/ma9030159 - 4 Mar 2016

Cited by 16 | Viewed by 5635

Abstract

Stereocomplex-type poly(lactic acid) (SC-PLA)/oleylamine-modified layered zinc phenylphosphonate (SC-PLA/m-PPZn) nanocomposites are successfully fabricated using a solution mixing process. Wide-angle X-ray diffraction (WAXD) analysis reveals that the structural arrangement of the oleylamine-modified PPZn exhibits a large interlayer spacing of 30.3 Å. In addition, we investigate [...] Read more.

Stereocomplex-type poly(lactic acid) (SC-PLA)/oleylamine-modified layered zinc phenylphosphonate (SC-PLA/m-PPZn) nanocomposites are successfully fabricated using a solution mixing process. Wide-angle X-ray diffraction (WAXD) analysis reveals that the structural arrangement of the oleylamine-modified PPZn exhibits a large interlayer spacing of 30.3 Å. In addition, we investigate the temperature effect on the real-time structural arrangement of PPZn and m-PPZn. The results indicated that the lattice expansion of m-PPZn with increasing temperature leads to an increase in the interlayer spacing from 30.3 to 37.1 Å as the temperature increases from 30 to 150 °C. The interlayer spacing decreases slightly as the temperature further increases to 210 °C. This behavior might be attributed to interlayer oleylamine elimination, which results in hydrogen bonding destruction between the hydroxide sheets and water molecules. As the temperature reaches 240 °C, the in situ WAXD patterns show the coexistence of m-PPZn and PPZn. However, the layered structures of m-PPZn at 300 °C are almost the same as those of PPZn, after the complete degradation temperature of oleylamine. The morphology of the SC-PLA/m-PPZn nanocomposites characterized using WAXD and transmission electron microscopy (TEM) demonstrates that most partial delamination layered materials are randomly dispersed in the SC-PLA matrix. Small-angle X-ray scattering reveals that higher crystal layer thickness and lower surface free energy is achieved in 0.25 wt% SC-PLA/m-PPZn nanocomposites. These results indicate that the introduction of 0.25 wt% m-PPZn into SC-PLA reduces the surface free energy, thereby increasing the polymer chain mobility. Full article

(This article belongs to the Section Advanced Materials Characterization)

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14 pages, 2751 KiB

Open AccessArticle

Preparation of a Microspherical Silver-Reduced Graphene Oxide-Bismuth Vanadate Composite and Evaluation of Its Photocatalytic Activity

by Mao Du, Shimin Xiong, Tianhui Wu, Deqiang Zhao, Qian Zhang, Zihong Fan, Yao Zeng, Fangying Ji, Qiang He and Xuan Xu

Materials 2016, 9(3), 160; https://doi.org/10.3390/ma9030160 - 4 Mar 2016

Cited by 33 | Viewed by 10563

Abstract

A novel Ag-reduced graphene oxide (rGO)-bismuth vanadate (BiVO₄) (AgGB) ternary composite was successfully synthesized via a one-step method. The prepared composite was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Brunauer-Emmett-Teller (BET) [...] Read more.

A novel Ag-reduced graphene oxide (rGO)-bismuth vanadate (BiVO₄) (AgGB) ternary composite was successfully synthesized via a one-step method. The prepared composite was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Brunauer-Emmett-Teller (BET) surface area measurement, Raman scattering spectroscopy, and ultraviolet-visible diffuse-reflection spectroscopy (UV-vis DRS). The results showed that bulk monoclinic needle-like BiVO₄ and Ag nanoparticles with a diameter of approximately 40 nm formed microspheres (diameter, 5–8 μm) with a uniform size distribution that could be loaded on rGO sheets to facilitate the transport of electrons photogenerated in BiVO₄, thereby reducing the rate of recombination of photogenerated charge carriers in the coupled AgGB composite system. Ag nanoparticles were dispersed on the surface of the rGO sheets, which exhibited a localized surface plasmon resonance phenomenon and enhanced visible light absorption. The removal efficiency of rhodamine B dye by AgGB (80.2%) was much higher than that of pure BiVO₄ (51.6%) and rGO-BiVO₄ (58.3%) under visible light irradiation. Recycle experiments showed that the AgGB composite still presented significant photocatalytic activity after five successive cycles. Finally, we propose a possible pathway and mechanism for the photocatalytic degradation of rhodamine B dye using the composite photocatalyst under visible light irradiation. Full article

(This article belongs to the Special Issue Advancement of Photocatalytic Materials 2016)

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11 pages, 3355 KiB

Open AccessArticle

Compressibility of 304 Stainless Steel Powder Metallurgy Materials Reinforced with 304 Short Stainless Steel Fibers

by Bibo Yao, Zhaoyao Zhou, Liuyang Duan and Zhiyu Xiao

Materials 2016, 9(3), 161; https://doi.org/10.3390/ma9030161 - 4 Mar 2016

Cited by 17 | Viewed by 7075

Abstract

Powder metallurgy (P/M) technique is usually used for manufacturing porous metal materials. However, some P/M materials are limitedly used in engineering for their performance deficiency. A novel 304 stainless steel P/M material was produced by a solid-state sintering of 304 stainless steel powders [...] Read more.

Powder metallurgy (P/M) technique is usually used for manufacturing porous metal materials. However, some P/M materials are limitedly used in engineering for their performance deficiency. A novel 304 stainless steel P/M material was produced by a solid-state sintering of 304 stainless steel powders and 304 short stainless steel fibers, which were alternately laid in layers according to mass ratio. In this paper, the compressive properties of the P/M materials were characterized by a series of uniaxial compression tests. The effects of fiber content, compaction pressure and high temperature nitriding on compressive properties were investigated. The results indicated that, without nitriding, the samples changed from cuboid to cydariform without damage in the process of compression. The compressive stress was enhanced with increasing fiber content ranging from 0 to 8 wt.%. For compaction pressure from 55 to 75 MPa, greater compaction pressure improved compressive stress. Moreover, high temperature nitriding was able to significantly improve the yield stress, but collapse failure eventually occurred. Full article

(This article belongs to the Section Porous Materials)

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16 pages, 6228 KiB

Open AccessFeature PaperArticle

Finite Element Analysis of Aluminum Honeycombs Subjected to Dynamic Indentation and Compression Loads

by A.S.M. Ayman Ashab, Dong Ruan, Guoxing Lu and Arafat A. Bhuiyan

Materials 2016, 9(3), 162; https://doi.org/10.3390/ma9030162 - 4 Mar 2016

Cited by 25 | Viewed by 7715

Abstract

The mechanical behavior of aluminum hexagonal honeycombs subjected to out-of-plane dynamic indentation and compression loads has been investigated numerically using ANSYS/LS-DYNA in this paper. The finite element (FE) models have been verified by previous experimental results in terms of deformation pattern, stress-strain curve, [...] Read more.

The mechanical behavior of aluminum hexagonal honeycombs subjected to out-of-plane dynamic indentation and compression loads has been investigated numerically using ANSYS/LS-DYNA in this paper. The finite element (FE) models have been verified by previous experimental results in terms of deformation pattern, stress-strain curve, and energy dissipation. The verified FE models have then been used in comprehensive numerical analysis of different aluminum honeycombs. Plateau stress, σ_pl, and dissipated energy (E_I for indentation and E_C for compression) have been calculated at different strain rates ranging from 10² to 10⁴ s⁻¹. The effects of strain rate and t/l ratio on the plateau stress, dissipated energy, and tearing energy have been discussed. An empirical formula is proposed to describe the relationship between the tearing energy per unit fracture area, relative density, and strain rate for honeycombs. Moreover, it has been found that a generic formula can be used to describe the relationship between tearing energy per unit fracture area and relative density for both aluminum honeycombs and foams. Full article

(This article belongs to the Special Issue Cellular Materials: Design and Optimisation)

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15 pages, 6651 KiB

Open AccessArticle

Polyamide Fiber Reinforced Shotcrete for Tunnel Application

by Joong Kyu Jeon, WooSeok Kim, Gyu Yong Kim and Chan Ki Jeon

Materials 2016, 9(3), 163; https://doi.org/10.3390/ma9030163 - 5 Mar 2016

Cited by 26 | Viewed by 6280

Abstract

This study intends to establish the mechanical properties of polyamide fiber reinforced shotcrete (PAFRS) in terms of compressive and flexural strengths, in accordance with ASTM C1609/C1609M-12. The mechanical properties identified the influence of polyamide fiber content on the PAFRS strength. This study evaluated [...] Read more.

This study intends to establish the mechanical properties of polyamide fiber reinforced shotcrete (PAFRS) in terms of compressive and flexural strengths, in accordance with ASTM C1609/C1609M-12. The mechanical properties identified the influence of polyamide fiber content on the PAFRS strength. This study evaluated the toughness of PAFRS and proposed additional toughness level criteria to better represent organic fiber performance. In addition, the fiber rebounding rate and PAFRS performance in tunneling application were evaluated based on a tunnel application in Korea. PAFRS with 0.6%~0.8% volume content in tunneling shotcrete could significantly improve flexural ductility, toughness, and ultimate load capacity. Fiber rebounding tests exhibited a low rebounding rate (8.5%) and low fiber drop (63.5%). Therefore, PAFRS applied to a tunnel exhibited stability and constructability. Full article

(This article belongs to the Section Advanced Materials Characterization)

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9 pages, 2022 KiB

Open AccessArticle

Electronic Structure and Optical Property Analysis of Al/Ga-Codoped ZnO through First-Principles Calculations

by Chieh-Cheng Chen and Hsuan-Chung Wu

Materials 2016, 9(3), 164; https://doi.org/10.3390/ma9030164 - 4 Mar 2016

Cited by 25 | Viewed by 4797

Abstract

Using density functional theory and the Hubbard U method, we investigated the geometric structure, electronic structure, and optical property of Al/Ga-codoped ZnO. A 3 × 3 × 3 ZnO supercell was used to construct Al- and Ga-monodoped ZnO structures and Al/Ga-codoped ZnO (AGZO) [...] Read more.

Using density functional theory and the Hubbard U method, we investigated the geometric structure, electronic structure, and optical property of Al/Ga-codoped ZnO. A 3 × 3 × 3 ZnO supercell was used to construct Al- and Ga-monodoped ZnO structures and Al/Ga-codoped ZnO (AGZO) structures. All three structures showed n-type conduction, and the optical band gaps were larger than that of pure ZnO. For a given impurity concentration, Ga impurities contribute more free carriers than Al impurities in AGZO. However, the presence of Al impurities improves the transmittance. These results can theoretically explain the factors that influence the electrical and optical properties. Full article

(This article belongs to the Special Issue Transparent Conducting Oxide Nanoparticles)

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15 pages, 5039 KiB

Open AccessArticle

Experimental Study on Conductivity Anisotropy of Limestone Considering the Bedding Directional Effect in the Whole Process of Uniaxial Compression

by Xinji Xu, Bin Liu, Shucai Li, Lei Yang, Jie Song, Ming Li and Jie Mei

Materials 2016, 9(3), 165; https://doi.org/10.3390/ma9030165 - 4 Mar 2016

Cited by 20 | Viewed by 4663

Abstract

Experimental studies were conducted on the changes of the potential differences in different directions during the uniaxial compression on limestone samples parallel and normal to the bedding plane. In the test, electric current was supplied at both ends of the samples, and concurrent [...] Read more.

Experimental studies were conducted on the changes of the potential differences in different directions during the uniaxial compression on limestone samples parallel and normal to the bedding plane. In the test, electric current was supplied at both ends of the samples, and concurrent measurement was conducted in four measuring lines at a 45-degree angle to each other. First, the change laws of the potential differences in different directions and the similarities and differences of rock samples were summarized. In regards to the uniaxial compression properties and crack growth, the above-mentioned similarities and differences were further analyzed. Then, the anisotropy factor was introduced to further explore the response characteristics. It was found that the anisotropic changes of rock samples went through three stages during the uniaxial compression process, providing a reference for describing the properties in different failure stages of rock samples and obtaining precursory information about the fracture. Besides, the relationship between the peak stress and initial potential difference in a direction normal to the current direction was obtained by means of data fitting, providing a new method of predicting the uniaxial compressive strength of rock samples. According to the preceding analysis, this paper studied rock anisotropy by considering the bedding directional effect in terms of conductivity and provided a reference for subsequent study on rock materials’ properties and engineering practices. Full article

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12 pages, 7182 KiB

Open AccessArticle

Cyclic Behavior of Mortarless Brick Joints with Different Interlocking Shapes

by Hongjun Liu, Peng Liu, Kun Lin and Sai Zhao

Materials 2016, 9(3), 166; https://doi.org/10.3390/ma9030166 - 4 Mar 2016

Cited by 32 | Viewed by 10074

Abstract

The framed structure infilled with a mortarless brick (MB) panel exhibits considerable in-plane energy dissipation because of the relative sliding between bricks and good out-of-plane stability resulting from the use of interlocking mechanisms. The cyclic behaviors of MB are investigated experimentally in this [...] Read more.

The framed structure infilled with a mortarless brick (MB) panel exhibits considerable in-plane energy dissipation because of the relative sliding between bricks and good out-of-plane stability resulting from the use of interlocking mechanisms. The cyclic behaviors of MB are investigated experimentally in this study. Two different types of bricks, namely non-interlocking mortarless brick (N-IMB) and interlocking mortarless brick (IMB), are examined experimentally. The cyclic behavior of all of the joints (N-IMB and IMB) are investigated in consideration of the effects of interlocking shapes, loading compression stress levels and loading cycles. The hysteretic loops of N-IMB and IMB joints are obtained, according to which a mechanical model is developed. The Mohr–Coulomb failure criterion is employed to describe the shear failure modes of all of the investigated joints. A typical frictional behavior is observed for the N-IMB joints, and a significant stiffening effect is observed for the IMB joints during their sliding stage. The friction coefficients of all of the researched joints increase with the augmentation of the compression stress level and improvement of the smoothness of the interlocking surfaces. An increase in the loading cycle results in a decrease in the friction coefficients of all of the joints. The degradation rate (DR) of the friction coefficients increases with the reduction in the smoothness of the interlocking surface. Full article

(This article belongs to the Section Advanced Materials Characterization)

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15 pages, 2075 KiB

Open AccessArticle

Nanostructured Thin Films Obtained from Fischer Aminocarbene Complexes

by Rosa E. Lazo-Jiménez, M. Carmen Ortega-Alfaro, José G. López-Cortés, Cecilio Alvarez-Toledano, José Á. Chávez-Carvayar, Jordi Ignés-Mullol, Maykel González-Torres and Pilar Carreón-Castro

Materials 2016, 9(3), 167; https://doi.org/10.3390/ma9030167 - 4 Mar 2016

Cited by 3 | Viewed by 5734

Abstract

The synthesis of four amphiphilic organometallic complexes with the general formula RC = M(CO)₅NH(CH₂)₁₅CH₃, where R is a ferrocenyl 2(a-b) or a phenyl 4(a-b) group as a donor moiety and a Fischer carbene of chromium [...] Read more.

The synthesis of four amphiphilic organometallic complexes with the general formula RC = M(CO)₅NH(CH₂)₁₅CH₃, where R is a ferrocenyl 2(a-b) or a phenyl 4(a-b) group as a donor moiety and a Fischer carbene of chromium (0) or tungsten (0) as an acceptor group, are reported. These four push-pull systems formed Langmuir (L) monolayers at the air-water interface, which were characterized by isotherms of surface pressure versus molecular area and compression/expansion cycles (hysteresis curves); Brewster angle microscopic images were also obtained. By using the Langmuir–Blodgett (LB) method, molecular monolayers were transferred onto glass substrates forming Z-type multilayers. LB films were characterized through ultraviolet-visible spectroscopy, atomic force microscopy and X-ray diffraction techniques. Results indicated that films obtained from 2b complex [(Ferrocenyl)(hexadecylamine)methylidene] pentacarbonyl tungsten (0) are the most stable and homogeneous; due to their properties, these materials may be incorporated into organic electronic devices. Full article

(This article belongs to the Section Advanced Materials Characterization)

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17 pages, 7894 KiB

Open AccessArticle

Experimental Study of Fire Hazards of Thermal-Insulation Material in Diesel Locomotive: Aluminum-Polyurethane

by Taolin Zhang, Xiaodong Zhou and Lizhong Yang

Materials 2016, 9(3), 168; https://doi.org/10.3390/ma9030168 - 5 Mar 2016

Cited by 9 | Viewed by 6027

Abstract

This work investigated experimentally and theoretically the fire hazards of thermal-insulation materials used in diesel locomotives under different radiation heat fluxes. Based on the experimental results, the critical heat flux for ignition was determined to be 6.15 kW/m² and 16.39 kW/m² [...] Read more.

This work investigated experimentally and theoretically the fire hazards of thermal-insulation materials used in diesel locomotives under different radiation heat fluxes. Based on the experimental results, the critical heat flux for ignition was determined to be 6.15 kW/m² and 16.39 kW/m² for pure polyurethane and aluminum-polyurethane respectively. A theoretical model was established for both to predict the fire behaviors under different circumstances. The fire behavior of the materials was evaluated based on the flashover and the total heat release rate (HRR). The fire hazards levels were classified based on different experimental results. It was found that the fire resistance performance of aluminum-polyurethane is much better than that of pure-polyurethane under various external heat fluxes. The concentration of toxic pyrolysis volatiles generated from aluminum-polyurethane materials is much higher than that of pure polyurethane materials, especially when the heat flux is below 50 kW/m². The hazard index HI during peak width time was proposed based on the comprehensive impact of time and concentrations. The predicted HI in this model coincides with the existed N-gas and FED models which are generally used to evaluate the fire gas hazard in previous researches. The integrated model named HNF was proposed as well to estimate the fire hazards of materials by interpolation and weighted average calculation. Full article

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9 pages, 1372 KiB

Open AccessArticle

Control of Magnetic Properties of NiMn₂O₄ by a Microwave Magnetic Field under Air

by Hiroshi Goto, Jun Fukushima and Hirotsugu Takizawa

Materials 2016, 9(3), 169; https://doi.org/10.3390/ma9030169 - 4 Mar 2016

Cited by 10 | Viewed by 8545

Abstract

NiMn₂O₄ prepared by conventional heating was irradiated with a microwave H-field using a single-mode cavity under air and magnetic properties of the microwave-irradiated material were investigated. X-ray diffraction and transmission electron microscopy demonstrated that the phase and microstructure are not [...] Read more.

NiMn₂O₄ prepared by conventional heating was irradiated with a microwave H-field using a single-mode cavity under air and magnetic properties of the microwave-irradiated material were investigated. X-ray diffraction and transmission electron microscopy demonstrated that the phase and microstructure are not affected by H-field irradiation. Measurements of the magnetization as a function of temperature revealed that the antiferromagnetic sublattice disappeared and electron spin resonance showed the existence of Mn²⁺, suggesting that Mn³⁺ is partially reduced. Moreover, the magnetization of NiMn₂O₄ was controlled from 35.3 to 18.2 emu/g and the coercivity from 140 to 750 Oe by changing the sample temperature during microwave irradiation. The reduction reaction of NiMn₂O₄ is controlled by microwave H-field irradiation, resulting in control over the magnetic properties. Full article

(This article belongs to the Special Issue Microwave Materials Processing)

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16 pages, 8109 KiB

Open AccessArticle

Silica-Gentamicin Nanohybrids: Synthesis and Antimicrobial Action

by Dina Ahmed Mosselhy, Yanling Ge, Michael Gasik, Katrina Nordström, Olli Natri and Simo-Pekka Hannula

Materials 2016, 9(3), 170; https://doi.org/10.3390/ma9030170 - 5 Mar 2016

Cited by 28 | Viewed by 7700

Abstract

Orthopedic applications commonly require the administration of systemic antibiotics. Gentamicin is one of the most commonly used aminoglycosides in the treatment and prophylaxis of infections associated with orthopedic applications, but gentamicin has a short half-life. However, silica nanoparticles (SiO₂ NPs) can be [...] Read more.

Orthopedic applications commonly require the administration of systemic antibiotics. Gentamicin is one of the most commonly used aminoglycosides in the treatment and prophylaxis of infections associated with orthopedic applications, but gentamicin has a short half-life. However, silica nanoparticles (SiO₂ NPs) can be used as elegant carriers for antibiotics to prolong their release. Our goal is the preparation and characterization of SiO₂-gentamicin nanohybrids for their potential antimicrobial administration in orthopedic applications. In vitro gentamicin release profile from the nanohybrids (gentamicin-conjugated SiO₂ NPs) prepared by the base-catalyzed precipitation exhibited fast release (21.4%) during the first 24 h and further extension with 43.9% release during the five-day experiment. Antimicrobial studies of the SiO₂-gentamicin nanohybrids versus native SiO₂ NPs and free gentamicin were performed against Bacillus subtilis (B. subtilis), Pseudomonas fluorescens (P. fluorescens) and Escherichia coli (E. coli). SiO₂-gentamicin nanohybrids were most effective against B. subtilis. SiO₂ NPs play no antimicrobial role. Parallel antimicrobial studies for the filter-sterilized gentamicin were performed to assess the effect of ultraviolet (UV)-irradiation on gentamicin. In summary, the initial fast gentamicin release fits the need for high concentration of antibiotics after orthopedic surgical interventions. Moreover, the extended release justifies the promising antimicrobial administration of the nanohybrids in bone applications. Full article

(This article belongs to the Special Issue Advances and Applications of Nano-antimicrobial Treatments)

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9 pages, 1984 KiB

Open AccessArticle

Integrated Effects of Two Additives on the Enhanced Performance of PTB7:PC₇₁BM Polymer Solar Cells

by Lin Wang, Suling Zhao, Zheng Xu, Jiao Zhao, Di Huang and Ling Zhao

Materials 2016, 9(3), 171; https://doi.org/10.3390/ma9030171 - 5 Mar 2016

Cited by 18 | Viewed by 6829

Abstract

Organic photovoltaics (OPVs) are fabricated with blended active layers of poly [[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl]]: [6,6]-phenylC71-butyric acid methyl ester (PTB7:PC₇₁BM). The active layers are prepared in chlorobenzene (CB) added different additives of 1, 8-Diiodooctane (DIO) and polystyrene (PS) with different concentrations by spin [...] Read more.

Organic photovoltaics (OPVs) are fabricated with blended active layers of poly [[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl]]: [6,6]-phenylC71-butyric acid methyl ester (PTB7:PC₇₁BM). The active layers are prepared in chlorobenzene (CB) added different additives of 1, 8-Diiodooctane (DIO) and polystyrene (PS) with different concentrations by spin coating. A small addition, 0.5%–5% by weight relative to the BHJ components, of inert high molecular weight PS is used to increase the solution viscosity and film thickness without sacrificing desirable phase separation and structural order. The effects of the PS are studied with respect of photovoltaic parameters such as fill factor, short circuit current density, and power conversion efficiency. Together with DIO, the device with 3.0 v% DIO and 1 wt % PS shows a high power conversion efficiency (PCE) of 8.92% along with an open-circuit voltage (V_oc) of 0.76 V, a short-circuit current (J_sc) of 16.37 mA/cm², and a fill factor (FF) of 71.68%. The absorption and surface morphology of the active layers are investigated by UV-visible spectroscopy, atomic force microscopy (AFM) respectively. The positive effect of DIO and PS additives on the performance of the OPVs is attributed to the increased absorption and the charge carrier transport and collection. Full article

(This article belongs to the Special Issue Photovoltaic Materials and Electronic Devices)

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12 pages, 4093 KiB

Open AccessArticle

Experimental Investigation of the Mechanical and Durability Properties of Crumb Rubber Concrete

by Hanbing Liu, Xianqiang Wang, Yubo Jiao and Tao Sha

Materials 2016, 9(3), 172; https://doi.org/10.3390/ma9030172 - 7 Mar 2016

Cited by 158 | Viewed by 9823

Abstract

Recycling waste tire rubber by incorporating it into concrete has become the preferred solution to dispose of waste tires. In this study, the effect of the volume content of crumb rubber and pretreatment methods on the performances of concrete was evaluated. Firstly, the [...] Read more.

Recycling waste tire rubber by incorporating it into concrete has become the preferred solution to dispose of waste tires. In this study, the effect of the volume content of crumb rubber and pretreatment methods on the performances of concrete was evaluated. Firstly, the fine aggregate and mixture were partly replaced by crumb rubber to produce crumb rubber concrete. Secondly, the mechanical and durability properties of crumb rubber concrete with different replacement forms and volume contents had been investigated. Finally, the crumb rubber after pretreatment by six modifiers was introduced into the concrete mixture. Corresponding tests were conducted to verify the effectiveness of pretreatment methods as compared to the concrete containing untreated crumb rubber. It was observed that the mechanical strength of crumb rubber concrete was reduced, while durability was improved with the increasing of crumb rubber content. 20% replacement of fine aggregate and 5% replacement of the total mixture exhibited acceptable properties for practical applications. In addition, the results indicated that the modifiers had a positive impact on the mechanical and durability properties of crumb rubber concrete. It avoided the disadvantage of crumb rubber concrete having lower strength and provides a reference for the production of modified crumb rubber concrete. Full article

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15 pages, 5527 KiB

Open AccessArticle

Effect of Initial Aluminum Alloy Particle Size on the Damage of Carbon Nanotubes during Ball Milling

by Xian Zhu, Yu Guang Zhao, Min Wu, Hui Yuan Wang and Qi Chuan Jiang

Materials 2016, 9(3), 173; https://doi.org/10.3390/ma9030173 - 8 Mar 2016

Cited by 12 | Viewed by 6841

Abstract

Damage to carbon nanotubes (CNTs) during the fabrication process of CNT reinforced composites has great influence on their mechanical properties. In this study, the 2014 Al with powder sizes of 20, 9 and 5 μm was selected to study the effect of initial [...] Read more.

Damage to carbon nanotubes (CNTs) during the fabrication process of CNT reinforced composites has great influence on their mechanical properties. In this study, the 2014 Al with powder sizes of 20, 9 and 5 μm was selected to study the effect of initial particle size on the damage to carbon nanotubes (CNTs) during ball milling. The result shows that for CNTs in the ball milled CNT/Al (with powder size of 20 and 9 μm) mixtures, the intensity ratio of the D band and the G band (ID/IG) first increased and then reached a plateau, mainly because most of the CNTs are embedded, to a certain extent, in the aluminum powder after milling, which could protect the CNTs from damage during further milling. While for CNTs in the ball milled CNT/Al (with powder size of 5 μm) mixture, the ID/IG ratio continues to climb from 1.31 to 2.33 with time, indicating continuous damage to the CNTs occurs during the milling. Differential scanning calorimetry (DSC) analysis demonstrates that the chemical instability increased with an increase in the damage level of CNTs, resulting in the formation of aluminum carbide (Al₄C₃) at a lower temperature before the melting of aluminum, which is detrimental to their mechanical properties. Full article

(This article belongs to the Section Advanced Composites)

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14 pages, 6746 KiB

Open AccessArticle

Reactivation of a Retarded Suspension of Ground Granulated Blast-Furnace Slag

by Nick Schneider and Dietmar Stephan

Materials 2016, 9(3), 174; https://doi.org/10.3390/ma9030174 - 7 Mar 2016

Cited by 7 | Viewed by 6901

Abstract

An effective retarded suspension of ground granulated blast-furnace slag (GGBFS) needs a strong activator to reactivate the hydration. In this research study, sodium hydroxide (NaOH) as an alkali activator in two different concentrations (30 and 50 wt.%) was used to overcome the retardation [...] Read more.

An effective retarded suspension of ground granulated blast-furnace slag (GGBFS) needs a strong activator to reactivate the hydration. In this research study, sodium hydroxide (NaOH) as an alkali activator in two different concentrations (30 and 50 wt.%) was used to overcome the retardation and give the hardened GGBFS the reasonable strength. The study was carried out with a mixture of GGBFS, a solution of 1.0 wt.% d-gluconic acid (C₆H₁₂O₇) as a retarder in the mixing water and a methyl cellulose as a stabilizer. The reactivation was executed after seven different periods (up to 28 days) after the system was retarded. The following investigations were performed: slump test, measurement of ultrasonic (US) velocity, compressive strength and gross density, thermogravimetry (TG) and scanning electron microscopy (SEM). The analyses of the hardened samples were carried out seven, 28 and 90 days after the reactivation. The result of the study is an effective reactivation of a retarded suspension. In this case, the activator with 50 wt.% NaOH shows a very high performance. The setting time of the reactivated binders is much longer compared to the reference, but, in the longer term, the compressive strength and the progress of the hydration exceed the performance of the reference. Full article

(This article belongs to the Section Advanced Composites)

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12 pages, 3787 KiB

Open AccessArticle

Preparation and Evaluation of Dexamethasone-Loaded Electrospun Nanofiber Sheets as a Sustained Drug Delivery System

by Jin Woo Lee, Hye Yun Lee, Seung Hun Park, Ji Hoon Park, Jae Ho Kim, Byoung Hyun Min and Moon Suk Kim

Materials 2016, 9(3), 175; https://doi.org/10.3390/ma9030175 - 8 Mar 2016

Cited by 17 | Viewed by 9120

Abstract

Recently, electrospinning technology has been widely used as a processing method to make nanofiber sheets (NS) for biomedical applications because of its unique features, such as ease of fabrication and high surface area. To develop a sustained dexamethasone (Dex) delivery system, in this [...] Read more.

Recently, electrospinning technology has been widely used as a processing method to make nanofiber sheets (NS) for biomedical applications because of its unique features, such as ease of fabrication and high surface area. To develop a sustained dexamethasone (Dex) delivery system, in this work, poly(ε-caprolactone-co-l-lactide) (PCLA) copolymer with controllable biodegradability was synthesized and further utilized to prepare electrospun Dex-loaded NS using water-insoluble Dex (Dex(b)) or water-soluble Dex (Dex(s)). The Dex-NS obtained by electrospinning exhibited randomly oriented and interconnected fibrillar structures. The in vitro and in vivo degradation of Dex-NS was confirmed over a period of a few weeks by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR). The evaluation of in vitro and in vivo Dex(b) and Dex(s) release from Dex-NS showed an initial burst of Dex(b) at day 1 and, thereafter, almost the same amount of release as Dex(b) for up to 28 days. In contrast, Dex(s)-NS exhibited a small initial burst of Dex(s) and a first-order releasing profile from Dex-NS. In conclusion, Dex-NS exhibited sustained in vitro and in vivo Dex(s) release for a prolonged period, as well as controlled biodegradation of the NS over a defined treatment period. Full article

(This article belongs to the Special Issue Electrospun Materials)

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14 pages, 27691 KiB

Open AccessFeature PaperArticle

Revealing the Dark Side of Portlandite Clusters in Cement Paste by Circular Polarization Microscopy

by Oğuzhan Çopuroğlu

Materials 2016, 9(3), 176; https://doi.org/10.3390/ma9030176 - 8 Mar 2016

Cited by 14 | Viewed by 7906

Abstract

Plane and crossed polarization are the two standard light modes in polarized light microscopy that are widely used to characterize crystalline and amorphous phases in cement-based materials. However, the use of the crossed polarized light mode has been found to be restrictive for [...] Read more.

Plane and crossed polarization are the two standard light modes in polarized light microscopy that are widely used to characterize crystalline and amorphous phases in cement-based materials. However, the use of the crossed polarized light mode has been found to be restrictive for studying birefringent phases quantitatively due to the extinction phenomenon that arises depending on the crystal orientation. This paper introduces circular polarization microscopy as an alternative technique to overcome the extinction problem during the examination of cementitious materials’ microstructure with optical microscopy. In order to evaluate the feasibility of this technique, selected optical and micromorphological features of portlandite clusters were investigated in cement paste. Image analysis results showed that compared to the conventional crossed polarization technique, circular polarization offers significant advantages when portlandite quantification is of interest, and it stands out as a promising low-cost alternative to backscattered electron microscopy. Full article

(This article belongs to the Special Issue Image Analysis and Processing for Cement-based Materials)

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13 pages, 1830 KiB

Open AccessFeature PaperArticle

Image Charge Effects in the Wetting Behavior of Alkanes on Water with Accounting for Water Solubility

by Kirill A. Emelyanenko, Alexandre M. Emelyanenko and Ludmila B. Boinovich

Materials 2016, 9(3), 177; https://doi.org/10.3390/ma9030177 - 8 Mar 2016

Cited by 5 | Viewed by 5553

Abstract

Different types of surface forces, acting in the films of pentane, hexane, and heptane on water are discussed. It is shown that an important contribution to the surface forces originates from the solubility of water in alkanes. The equations for the distribution of [...] Read more.

Different types of surface forces, acting in the films of pentane, hexane, and heptane on water are discussed. It is shown that an important contribution to the surface forces originates from the solubility of water in alkanes. The equations for the distribution of electric potential inside the film are derived within the Debye-Hückel approximation, taking into account the polarization of the film boundaries by discrete charges at water-alkane interface and by the dipoles of water molecules dissolved in the film. On the basis of above equations we estimate the image charge contribution to the surface forces, excess free energy, isotherms of water adsorption in alkane film, and the total isotherms of disjoining pressure in alkane film. The results indicate the essential influence of water/alkane interface charging on the disjoining pressure in alkane films, and the wettability of water surface by different alkanes is discussed. Full article

(This article belongs to the Special Issue Surface Forces and Thin Liquid Films)

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15 pages, 5627 KiB

Open AccessArticle

Effects of Ca Content on Formation and Photoluminescence Properties of CaAlSiN₃:Eu²⁺ Phosphor by Combustion Synthesis

by Shyan-Lung Chung and Shu-Chi Huang

Materials 2016, 9(3), 178; https://doi.org/10.3390/ma9030178 - 8 Mar 2016

Cited by 9 | Viewed by 5733

Abstract

Effects of Ca content (in the reactant mixture) on the formation and the photoluminescence properties of CaAlSiN₃:Eu²⁺ phosphor (CASIN) were investigated by a combustion synthesis method. Ca, Al, Si, Eu₂O₃, NaN₃, NH₄Cl [...] Read more.

Effects of Ca content (in the reactant mixture) on the formation and the photoluminescence properties of CaAlSiN₃:Eu²⁺ phosphor (CASIN) were investigated by a combustion synthesis method. Ca, Al, Si, Eu₂O₃, NaN₃, NH₄Cl and Si₃N₄ powders were used as the starting materials and they were mixed and pressed into a compact which was then wrapped up with an igniting agent (i.e., Mg + Fe₃O₄). The compact was ignited by electrical heating under a N₂ pressure of ≤1.0 MPa. By keeping the molar ratios of Al and Si (including the Si powder and the Si in Si₃N₄ powder) both at 1.00 and that of Eu₂O₃ at 0.02, XRD (X-ray diffraction) coupled with TEM-EDS (transmission electron microscope equipped with an energy-dispersive X-ray spectroscope) and SAED (selected area electron diffraction) measurements show that AlN:Eu²⁺ and Ca-α-SiAlON:Eu²⁺ are formed as the major phosphor products when the Ca molar ratio (denoted by Y) is equal to 0.25 and AlN:Eu²⁺ and Ca-α-SiAlON:Eu²⁺ could not be detected at Y ≥ 0.75 and ≥1.00, respectively. CASIN (i.e., CaAlSiN₃:Eu²⁺) becomes the only phosphor product as Y is increased to 1.00 and higher. The extent of formation of CASIN increases with increasing Y up to 1.50 and begins to decrease as Y is further increased to 1.68. While the excitation wavelength regions are similar at various Y, the emission wavelength regions vary significantly as Y is increased from 0.25 to 1.00 due to different combinations of phosphor phases formed at different Y. The emission intensity of CASIN was found to vary with Y in a similar trend to its extent of formation. The Ca and Eu contents (expressed as molar ratios) in the synthesized products were found to increase roughly with increasing Y but were both lower than the respective Ca and Eu contents in the reactant mixtures. Full article

(This article belongs to the Special Issue Selected Papers from ICBEI2015)

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12 pages, 3676 KiB

Open AccessFeature PaperArticle

Compositional Design of Dielectric, Ferroelectric and Piezoelectric Properties of (K, Na)NbO₃ and (Ba, Na)(Ti, Nb)O₃ Based Ceramics Prepared by Different Sintering Routes

by José A. Eiras, Rosimeire B. Z. Gerbasi, Jaciele M. Rosso, Daniel M. Silva, Luiz F. Cótica, Ivair A. Santos, Camila A. Souza and Manuel H. Lente

Materials 2016, 9(3), 179; https://doi.org/10.3390/ma9030179 - 8 Mar 2016

Cited by 25 | Viewed by 7245

Abstract

Lead free piezoelectric materials are being intensively investigated in order to substitute lead based ones, commonly used in many different applications. Among the most promising lead-free materials are those with modified NaNbO₃, such as (K, Na)NbO₃ (KNN) and (Ba, Na)(Ti, [...] Read more.

Lead free piezoelectric materials are being intensively investigated in order to substitute lead based ones, commonly used in many different applications. Among the most promising lead-free materials are those with modified NaNbO₃, such as (K, Na)NbO₃ (KNN) and (Ba, Na)(Ti, Nb)O₃ (BTNN) families. From a ceramic processing point of view, high density single phase KNN and BTNN ceramics are very difficult to sinter due to the volatility of the alkaline elements, the narrow sintering temperature range and the anomalous grain growth. In this work, Spark Plasma Sintering (SPS) and high-energy ball milling (HEBM), following heat treatments (calcining and sintering), in oxidative (O₂) atmosphere have been used to prepare single phase highly densified KNN (“pure” and Cu²⁺ or Li¹⁺ doped), with theoretical densities ρ_th > 97% and BTNN ceramics (ρ_th - 90%), respectively. Using BTTN ceramics with a P4mm perovskite-like structure, we showed that by increasing the NaNbO₃ content, the ferroelectric properties change from having a relaxor effect to an almost “normal” ferroelectric character, while the tetragonality and grain size increase and the shear piezoelectric coefficients (k₁₅, g₁₅ and d₁₅) improve. For KNN ceramics, the results reveal that the values for remanent polarization as well as for most of the coercive field are quite similar among all compositions. These facts evidenced that Cu²⁺ may be incorporated into the A and/or B sites of the perovskite structure, having both hardening and softening effects. Full article

(This article belongs to the Special Issue Piezoelectric Materials)

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13 pages, 1249 KiB

Open AccessArticle

Influence of Specimen Preparation and Test Methods on the Flexural Strength Results of Monolithic Zirconia Materials

by Christine Schatz, Monika Strickstrock, Malgorzata Roos, Daniel Edelhoff, Marlis Eichberger, Isabella-Maria Zylla and Bogna Stawarczyk

Materials 2016, 9(3), 180; https://doi.org/10.3390/ma9030180 - 9 Mar 2016

Cited by 35 | Viewed by 7085

Abstract

The aim of this work was to evaluate the influence of specimen preparation and test method on the flexural strength results of monolithic zirconia. Different monolithic zirconia materials (Ceramill Zolid (Amann Girrbach, Koblach, Austria), Zenostar ZrTranslucent (Wieland Dental, Pforzheim, Germany), and DD Bio [...] Read more.

The aim of this work was to evaluate the influence of specimen preparation and test method on the flexural strength results of monolithic zirconia. Different monolithic zirconia materials (Ceramill Zolid (Amann Girrbach, Koblach, Austria), Zenostar ZrTranslucent (Wieland Dental, Pforzheim, Germany), and DD Bio zx² (Dental Direkt, Spenge, Germany)) were tested with three different methods: 3-point, 4-point, and biaxial flexural strength. Additionally, different specimen preparation methods were applied: either dry polishing before sintering or wet polishing after sintering. Each subgroup included 40 specimens. The surface roughness was assessed using scanning electron microscopy (SEM) and a profilometer whereas monoclinic phase transformation was investigated with X-ray diffraction. The data were analyzed using a three-way Analysis of Variance (ANOVA) with respect to the three factors: zirconia, specimen preparation, and test method. One-way ANOVA was conducted for the test method and zirconia factors within the combination of two other factors. A 2-parameter Weibull distribution assumption was applied to analyze the reliability under different testing conditions. In general, values measured using the 4-point test method presented the lowest flexural strength values. The flexural strength findings can be grouped in the following order: 4-point < 3-point < biaxial. Specimens prepared after sintering showed significantly higher flexural strength values than prepared before sintering. The Weibull moduli ranged from 5.1 to 16.5. Specimens polished before sintering showed higher surface roughness values than specimens polished after sintering. In contrast, no strong impact of the polishing procedures on the monoclinic surface layer was observed. No impact of zirconia material on flexural strength was found. The test method and the preparation method significantly influenced the flexural strength values. Full article

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18 pages, 3631 KiB

Open AccessArticle

The Influence of Conjugated Polymer Side Chain Manipulation on the Efficiency and Stability of Polymer Solar Cells

by Ilona M. Heckler, Jurgen Kesters, Maxime Defour, Morten V. Madsen, Huguette Penxten, Jan D’Haen, Bruno Van Mele, Wouter Maes and Eva Bundgaard

Materials 2016, 9(3), 181; https://doi.org/10.3390/ma9030181 - 9 Mar 2016

Cited by 15 | Viewed by 6590

Abstract

The stability of polymer solar cells (PSCs) can be influenced by the introduction of particular moieties on the conjugated polymer side chains. In this study, two series of donor-acceptor copolymers, based on bis(thienyl)dialkoxybenzene donor and benzo[c][1,2,5]thiadiazole (BT) or thiazolo[5,4-d]thiazole [...] Read more.

The stability of polymer solar cells (PSCs) can be influenced by the introduction of particular moieties on the conjugated polymer side chains. In this study, two series of donor-acceptor copolymers, based on bis(thienyl)dialkoxybenzene donor and benzo[c][1,2,5]thiadiazole (BT) or thiazolo[5,4-d]thiazole (TzTz) acceptor units, were selected toward effective device scalability by roll-coating. The influence of the partial exchange (5% or 10%) of the solubilizing 2-hexyldecyloxy by alternative 2-phenylethoxy groups on efficiency and stability was investigated. With an increasing 2-phenylethoxy ratio, a decrease in solar cell efficiency was observed for the BT-based series, whereas the efficiencies for the devices based on the TzTz polymers remained approximately the same. The photochemical degradation rate for PSCs based on the TzTz polymers decreased with an increasing 2-phenylethoxy ratio. Lifetime studies under constant sun irradiance showed a diminishing initial degradation rate for the BT-based devices upon including the alternative side chains, whereas the (more stable) TzTz-based devices degraded at a faster rate from the start of the experiment upon partly exchanging the side chains. No clear trends in the degradation behavior, linked to the copolymer structural changes, could be established at this point, evidencing the complex interplay of events determining PSCs’ lifetime. Full article

(This article belongs to the Special Issue Electroactive Polymers)

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16 pages, 10175 KiB

Open AccessFeature PaperReview

Imaging Water Thin Films in Ambient Conditions Using Atomic Force Microscopy

by Sergio Santos and Albert Verdaguer

Materials 2016, 9(3), 182; https://doi.org/10.3390/ma9030182 - 9 Mar 2016

Cited by 29 | Viewed by 7945

Abstract

All surfaces exposed to ambient conditions are covered by a thin film of water. Other than at high humidity conditions, i.e., relative humidity higher than 80%, those water films have nanoscale thickness. Nevertheless, even the thinnest film can profoundly affect the physical [...] Read more.

All surfaces exposed to ambient conditions are covered by a thin film of water. Other than at high humidity conditions, i.e., relative humidity higher than 80%, those water films have nanoscale thickness. Nevertheless, even the thinnest film can profoundly affect the physical and chemical properties of the substrate. Information on the structure of these water films can be obtained from spectroscopic techniques based on photons, but these usually have poor lateral resolution. When information with nanometer resolution in the three dimensions is needed, for example for surfaces showing heterogeneity in water affinity at the nanoscale, Atomic Force Microscopy (AFM) is the preferred tool since it can provide such resolution while being operated in ambient conditions. A complication in the interpretation of the data arises when using AFM, however, since, in most cases, direct interaction between a solid probe and a solid surface occurs. This induces strong perturbations of the liquid by the probe that should be controlled or avoided. The aim of this review is to provide an overview of different AFM methods developed to overcome this problem, measuring different interactions between the AFM probe and the water films, and to discuss the type of information about the water film that can be obtained from these interactions. Full article

(This article belongs to the Special Issue Surface Forces and Thin Liquid Films)

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10 pages, 4625 KiB

Open AccessArticle

Biosynthesis of Bacterial Cellulose/Carboxylic Multi-Walled Carbon Nanotubes for Enzymatic Biofuel Cell Application

by Pengfei Lv, Quan Feng, Qingqing Wang, Guohui Li, Dawei Li and Qufu Wei

Materials 2016, 9(3), 183; https://doi.org/10.3390/ma9030183 - 9 Mar 2016

Cited by 44 | Viewed by 7664

Abstract

Novel nanocomposites comprised of bacterial cellulose (BC) with carboxylic multi-walled carbon nanotubes (c-MWCNTs) incorporated into the BC matrix were prepared through a simple method of biosynthesis. The biocathode and bioanode for the enzyme biological fuel cell (EBFC) were prepared using BC/c-MWCNTs composite injected [...] Read more.

Novel nanocomposites comprised of bacterial cellulose (BC) with carboxylic multi-walled carbon nanotubes (c-MWCNTs) incorporated into the BC matrix were prepared through a simple method of biosynthesis. The biocathode and bioanode for the enzyme biological fuel cell (EBFC) were prepared using BC/c-MWCNTs composite injected by laccase (Lac) and glucose oxidase (GOD) with the aid of glutaraldehyde (GA) crosslinking. Biosynthesis of BC/c-MWCNTs composite was characterized by digital photos, scanning electron microscope (SEM), and Fourier Transform Infrared (FTIR). The experimental results indicated the successful incorporation of c-MWCNTs into the BC. The electrochemical and biofuel performance were evaluated by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The power density and current density of EBFCs were recorded at 32.98 µW/cm³ and 0.29 mA/cm³, respectively. Additionally, the EBFCs also showed acceptable stability. Preliminary tests on double cells indicated that renewable BC have great potential in the application field of EBFCs. Full article

(This article belongs to the Section Biomaterials)

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8 pages, 3447 KiB

Open AccessArticle

Rapid Synthesis of Carbon Dots by Hydrothermal Treatment of Lignin

by Wenxin Chen, Chaofan Hu, Yunhua Yang, Jianghu Cui and Yingliang Liu

Materials 2016, 9(3), 184; https://doi.org/10.3390/ma9030184 - 9 Mar 2016

Cited by 153 | Viewed by 13969

Abstract

A rapid approach has been developed for the fluorescent carbon dots (CDs) by the hydrothermal treatment of lignin in the presence of H₂O₂. The as-synthesized CDs were found to emit blue photoluminescence with excellent photostability. Moreover, the CDs displayed [...] Read more.

A rapid approach has been developed for the fluorescent carbon dots (CDs) by the hydrothermal treatment of lignin in the presence of H₂O₂. The as-synthesized CDs were found to emit blue photoluminescence with excellent photostability. Moreover, the CDs displayed biocompatibility, low cytotoxicity, and high water solubility properties. Finally, the as-resulted CDs were demonstrated to be excellent probes for bioimaging and biosensing applications. Full article

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11 pages, 2338 KiB

Open AccessArticle

Strength Development and Hydration Behavior of Self-Activation of Commercial Ground Granulated Blast-Furnace Slag Mixed with Purified Water

by Hyeoneun Park, Yeonung Jeong, Jae-Hong Jeong and Jae Eun Oh

Materials 2016, 9(3), 185; https://doi.org/10.3390/ma9030185 - 10 Mar 2016

Cited by 29 | Viewed by 6703

Abstract

In this study, ground granulated blast-furnace slag (GGBFS) samples from Singapore, Korea, and the United Arab Emirates were hydrated with purified water to estimate the cementing capabilities without activators. Raw GGBFS samples and hardened pastes were characterized to provide rational explanations for the [...] Read more.

In this study, ground granulated blast-furnace slag (GGBFS) samples from Singapore, Korea, and the United Arab Emirates were hydrated with purified water to estimate the cementing capabilities without activators. Raw GGBFS samples and hardened pastes were characterized to provide rational explanations for the strengths and hydration products. The slag characteristics that influenced the best strength of raw GGBFS were identified. Although it is widely recognized that GGBFS alone generally shows little cementing capability when hydrated with water, the GGBFSs examined in this study demonstrated various strength developments and hydration behaviors; one of the GGBFS samples even produced a high strength comparable to that of alkali- or Ca(OH)₂-activated GGBFS. In particular, as the GGBFS exhibited a greater number of favorable slag characteristics for hydraulic reactivity, it produced more C-S-H and ettringite. The results demonstrated a reasonable potential for commercial GGBFS with calcium sulfates to function as an independent cementitious binder without activators. Full article

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22 pages, 4051 KiB

Open AccessArticle

Topological Design of Cellular Phononic Band Gap Crystals

by Yang Fan Li, Xiaodong Huang and Shiwei Zhou

Materials 2016, 9(3), 186; https://doi.org/10.3390/ma9030186 - 10 Mar 2016

Cited by 65 | Viewed by 8115

Abstract

This paper systematically investigated the topological design of cellular phononic crystals with a maximized gap size between two adjacent bands. Considering that the obtained structures may sustain a certain amount of static loadings, it is desirable to ensure the optimized designs to have [...] Read more.

This paper systematically investigated the topological design of cellular phononic crystals with a maximized gap size between two adjacent bands. Considering that the obtained structures may sustain a certain amount of static loadings, it is desirable to ensure the optimized designs to have a relatively high stiffness. To tackle this issue, we conducted a multiple objective optimization to maximize band gap size and bulk or shear modulus simultaneously with a prescribed volume fraction of solid material so that the resulting structures can be lightweight, as well. In particular, we first conducted the finite element analysis of the phononic band gap crystals and then adapted a very efficient optimization procedure to resolve this problem based on bi-directional evolutionary structure optimization (BESO) algorithm in conjunction with the homogenization method. A number of optimization results for maximizing band gaps with bulk and shear modulus constraints are presented for out-of-plane and in-plane modes. Numerical results showed that the optimized structures are similar to those obtained for composite case, except that additional slim connections are added in the cellular case to support the propagation of shear wave modes and meanwhile to satisfy the prescribed bulk or shear modulus constraints. Full article

(This article belongs to the Special Issue Cellular Materials: Design and Optimisation)

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10 pages, 2027 KiB

Open AccessArticle

PEEK Primary Crowns with Cobalt-Chromium, Zirconia and Galvanic Secondary Crowns with Different Tapers—A Comparison of Retention Forces

by Veronika Stock, Patrick R. Schmidlin, Susanne Merk, Christina Wagner, Malgorzata Roos, Marlis Eichberger and Bogna Stawarczyk

Materials 2016, 9(3), 187; https://doi.org/10.3390/ma9030187 - 10 Mar 2016

Cited by 39 | Viewed by 8039

Abstract

In prosthetic dentistry, double crown systems have proved their suitability as retainers for removable partial dentures. However, investigations in this context, regarding polyetheretherketone, are scarce. Therefore, the aim of this study was to test the retention force (RF) between polyetheretherketone (PEEK) primary and [...] Read more.

In prosthetic dentistry, double crown systems have proved their suitability as retainers for removable partial dentures. However, investigations in this context, regarding polyetheretherketone, are scarce. Therefore, the aim of this study was to test the retention force (RF) between polyetheretherketone (PEEK) primary and cobalt-chromium (CoCr), zirconia (ZrO₂) and galvanic (GAL) secondary crowns with three different tapers. Primary PEEK-crowns were milled with the tapers 0°, 1°, and 2° (n = 10/taper, respectively). Afterwards, 90 secondary crowns were fabricated: (i) 30 CoCr-crowns milled from Ceramill Sintron (AmannGirrbach, Koblach, Austria) (n = 10/taper), (ii) 30 ZrO₂-crowns milled from Ceramill ZI (AmannGirrbach, Koblach, Austria) (n = 10/taper), and (iii) 30 GAL-crowns made using electroforming (n = 10/taper). RF was measured in a pull-off test (20 pull-offs/specimen) and data were analyzed using 2-/1-way Analysis of Variance (ANOVA) followed by the Tukey-Honestly Significant Difference (HSD) post hoc test and linear regression analyses (p < 0.05). The measured mean RF values ranged between 9.6 and 38.2 N. With regard to the 0°, 1°, and 2° tapered crowns, no statistically significant differences between CoCr and ZrO₂ were observed (p > 0.141). At 0° taper, no differences in retention forces between GAL, CrCr, and ZrO₂ crowns were found (p = 0.075). However, at 1° and 2° taper, lower RF for GAL-crowns were observed (p < 0.009, p < 0.001, respectively). According to this laboratory study, PEEK might be a suitable material for primary crowns, regardless of the taper and the material of secondary crown. Long-term results, however, are still necessary. Full article

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16 pages, 1888 KiB

Open AccessFeature PaperArticle

Spatial Frequency Responses of Anisotropic Refractive Index Gratings Formed in Holographic Polymer Dispersed Liquid Crystals

by Yoshiaki Fukuda and Yasuo Tomita

Materials 2016, 9(3), 188; https://doi.org/10.3390/ma9030188 - 10 Mar 2016

Cited by 7 | Viewed by 6773

Abstract

We report on an experimental investigation of spatial frequency responses of anisotropic transmission refractive index gratings formed in holographic polymer dispersed liquid crystals (HPDLCs). We studied two different types of HPDLC materials employing two different monomer systems: one with acrylate monomer capable of [...] Read more.

We report on an experimental investigation of spatial frequency responses of anisotropic transmission refractive index gratings formed in holographic polymer dispersed liquid crystals (HPDLCs). We studied two different types of HPDLC materials employing two different monomer systems: one with acrylate monomer capable of radical mediated chain-growth polymerizations and the other with thiol-ene monomer capable of step-growth polymerizations. It was found that the photopolymerization kinetics of the two HPDLC materials could be well explained by the autocatalytic model. We also measured grating-spacing dependences of anisotropic refractive index gratings at a recording wavelength of 532 nm. It was found that the HPDLC material with the thiol-ene monomer gave higher spatial frequency responses than that with the acrylate monomer. Statistical thermodynamic simulation suggested that such a spatial frequency dependence was attributed primarily to a difference in the size of formed liquid crystal droplets due to different photopolymerization mechanisms. Full article

(This article belongs to the Special Issue Photopolymers for Holographic Applications)

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8 pages, 2373 KiB

Open AccessArticle

Thermal Mechanical Processing Effects on Microstructure Evolution and Mechanical Properties of the Sintered Ti-22Al-25Nb Alloy

by Yuanxin Wang, Zhen Lu, Kaifeng Zhang and Dalin Zhang

Materials 2016, 9(3), 189; https://doi.org/10.3390/ma9030189 - 11 Mar 2016

Cited by 7 | Viewed by 5297

Abstract

This work illustrates the effect of thermal mechanical processing parameters on the microstructure and mechanical properties of the Ti-22Al-25Nb alloy prepared by reactive sintering with element powders, consisting of O, B2 and Ti₃Al phases. Tensile and plane strain fracture toughness tests [...] Read more.

This work illustrates the effect of thermal mechanical processing parameters on the microstructure and mechanical properties of the Ti-22Al-25Nb alloy prepared by reactive sintering with element powders, consisting of O, B2 and Ti₃Al phases. Tensile and plane strain fracture toughness tests were carried out at room temperature to understand the mechanical behavior of the alloys and its correlation with the microstructural features characterized by scanning and transmission electron microscopy. The results show that the increased tensile strength (from 340 to 500 MPa) and elongation (from 3.6% to 4.2%) is due to the presence of lamellar O/B2 colony and needle-like O phase in B2 matrix in the as-processed Ti-22Al-25Nb alloys, as compared to the coarse lath O adjacent to B2 in the sintered alloys. Changes in morphologies of O phase improve the fracture toughness (K_IC) of the sintered alloys from 7 to 15 MPa·m^−1/2. Additionally, the fracture mechanism shifts from cleavage fracture in the as-sintered alloys to quasi-cleavage fracture in the as-processed alloys. Full article

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11 pages, 580 KiB

Open AccessReview

Repopulating Decellularized Kidney Scaffolds: An Avenue for Ex Vivo Organ Generation

by Robert A. McKee and Rebecca A. Wingert

Materials 2016, 9(3), 190; https://doi.org/10.3390/ma9030190 - 11 Mar 2016

Cited by 19 | Viewed by 7650

Abstract

Recent research has shown that fully developed organs can be decellularized, resulting in a complex scaffold and extracellular matrix (ECM) network capable of being populated with other cells. This work has resulted in a growing field in bioengineering focused on the isolation, characterization, [...] Read more.

Recent research has shown that fully developed organs can be decellularized, resulting in a complex scaffold and extracellular matrix (ECM) network capable of being populated with other cells. This work has resulted in a growing field in bioengineering focused on the isolation, characterization, and modification of organ derived acellular scaffolds and their potential to sustain and interact with new cell populations, a process termed reseeding. In this review, we cover contemporary advancements in the bioengineering of kidney scaffolds including novel work showing that reseeded donor scaffolds can be transplanted and can function in recipients using animal models. Several major areas of the field are taken into consideration, including the decellularization process, characterization of acellular and reseeded scaffolds, culture conditions, and cell sources. Finally, we discuss future avenues based on the advent of 3D bioprinting and recent developments in kidney organoid cultures as well as animal models of renal genesis. The ongoing mergers and collaborations between these fields hold the potential to produce functional kidneys that can be generated ex vivo and utilized for kidney transplantations in patients suffering with renal disease. Full article

(This article belongs to the Special Issue Regenerative Materials)

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15 pages, 5030 KiB

Open AccessArticle

A Novel HA/β-TCP-Collagen Composite Enhanced New Bone Formation for Dental Extraction Socket Preservation in Beagle Dogs

by Ko-Ning Ho, Eisner Salamanca, Kuo-Chi Chang, Tsai-Chin Shih, Yu-Chi Chang, Haw-Ming Huang, Nai-Chia Teng, Che-Tong Lin, Sheng-Wei Feng and Wei-Jen Chang

Materials 2016, 9(3), 191; https://doi.org/10.3390/ma9030191 - 11 Mar 2016

Cited by 20 | Viewed by 8399

Abstract

Past studies in humans have demonstrated horizontal and vertical bone loss after six months following tooth extraction. Many biomaterials have been developed to preserve bone volume after tooth extraction. Type I collagen serves as an excellent delivery system for growth factors and promotes [...] Read more.

Past studies in humans have demonstrated horizontal and vertical bone loss after six months following tooth extraction. Many biomaterials have been developed to preserve bone volume after tooth extraction. Type I collagen serves as an excellent delivery system for growth factors and promotes angiogenesis. Calcium phosphate ceramics have also been investigated because their mineral chemistry resembles human bone. The aim of this study was to compare the performance of a novel bioresorbable purified fibrillar collagen and hydroxyapatite/β-tricalcium phosphate (HA/β-TCP) ceramic composite versus collagen alone and a bovine xenograft-collagen composite in beagles. Collagen plugs, bovine graft-collagen composite and HA/β-TCP-collagen composite were implanted into the left and right first, second and third mandibular premolars, and the fourth molar was left empty for natural healing. In total, 20 male beagle dogs were used, and quantitative and histological analyses of the extraction ridge was done. The smallest width reduction was 19.09% ± 8.81% with the HA/β-TCP-collagen composite at Week 8, accompanied by new bone formation at Weeks 4 and 8. The HA/β-TCP-collagen composite performed well, as a new osteoconductive and biomimetic composite biomaterial, for socket bone preservation after tooth extraction. Full article

(This article belongs to the Special Issue Biodegradable and Bio-Based Polymers)

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26 pages, 7100 KiB

Open AccessArticle

Molecular Mobility in Hyperbranched Polymers and Their Interaction with an Epoxy Matrix

by Frida Román, Pere Colomer, Yolanda Calventus and John M. Hutchinson

Materials 2016, 9(3), 192; https://doi.org/10.3390/ma9030192 - 15 Mar 2016

Cited by 19 | Viewed by 6135

Abstract

The molecular mobility related to the glass transition and secondary relaxations in a hyperbranched polyethyleneimine, HBPEI, and its relaxation behaviour when incorporated into an epoxy resin matrix are investigated by dielectric relaxation spectroscopy (DRS) and dynamic mechanical analysis (DMA). Three systems are analysed: [...] Read more.

The molecular mobility related to the glass transition and secondary relaxations in a hyperbranched polyethyleneimine, HBPEI, and its relaxation behaviour when incorporated into an epoxy resin matrix are investigated by dielectric relaxation spectroscopy (DRS) and dynamic mechanical analysis (DMA). Three systems are analysed: HBPEI, epoxy and an epoxy/HBPEI mixture, denoted ELP. The DRS behaviour is monitored in the ELP system in three stages: prior to curing, during curing, and in the fully cured system. In the stage prior to curing, DRS measurements show three dipolar relaxations: γ, β and α, for all systems (HBPEI, epoxy and ELP). The α-relaxation for the ELP system deviates significantly from that for HBPEI, but superposes on that for the epoxy resin. The fully cured thermoset displays both β- and α-relaxations. In DMA measurements, both α- and β-relaxations are observed in all systems and in both the uncured and fully cured systems, similar to the behaviour identified by DRS. Full article

(This article belongs to the Section Advanced Materials Characterization)

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11 pages, 3195 KiB

Open AccessArticle

Preparation and Characterization of All-Biomass Soy Protein Isolate-Based Films Enhanced by Epoxy Castor Oil Acid Sodium and Hydroxypropyl Cellulose

by La Wang, Jianzhang Li, Shifeng Zhang and Junyou Shi

Materials 2016, 9(3), 193; https://doi.org/10.3390/ma9030193 - 15 Mar 2016

Cited by 31 | Viewed by 6548

Abstract

All-biomass soy protein-based films were prepared using soy protein isolate (SPI), glycerol, hydroxypropyl cellulose (HPC) and epoxy castor oil acid sodium (ECOS). The effect of the incorporated HPC and ECOS on the properties of the SPI film was investigated. The experimental results showed [...] Read more.

All-biomass soy protein-based films were prepared using soy protein isolate (SPI), glycerol, hydroxypropyl cellulose (HPC) and epoxy castor oil acid sodium (ECOS). The effect of the incorporated HPC and ECOS on the properties of the SPI film was investigated. The experimental results showed that the tensile strength of the resultant films increased from 2.84 MPa (control) to 4.04 MPa and the elongation at break increased by 22.7% when the SPI was modified with 2% HPC and 10% ECOS. The increased tensile strength resulted from the reaction between the ECOS and SPI, which was confirmed by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). It was found that ECOS and HPC effectively improved the performance of SPI-based films, which can provide a new method for preparing environmentally-friendly polymer films for a number of commercial applications. Full article

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13 pages, 2081 KiB

Open AccessFeature PaperArticle

Influence of 4,4’-azobis (4-cyanopentanoic acid) in Transmission and Reflection Gratings Stored in a PVA/AA Photopolymer

by Elena Fernandez, Rosa Fuentes, Augusto Belendez and Inmaculada Pascual

Materials 2016, 9(3), 194; https://doi.org/10.3390/ma9030194 - 15 Mar 2016

Cited by 4 | Viewed by 4588

Abstract

Holographic transmission gratings with a spatial frequency of 2658 lines/mm and reflection gratings with a spatial frequency of 4553 lines/mm were stored in a polyvinyl alcohol (PVA)/acrylamide (AA) based photopolymer. This material can reach diffraction efficiencies close to 100% for spatial frequencies about [...] Read more.

Holographic transmission gratings with a spatial frequency of 2658 lines/mm and reflection gratings with a spatial frequency of 4553 lines/mm were stored in a polyvinyl alcohol (PVA)/acrylamide (AA) based photopolymer. This material can reach diffraction efficiencies close to 100% for spatial frequencies about 1000 lines/mm. However, for higher spatial frequencies, the diffraction efficiency decreases considerably as the spatial frequency increases. To enhance the material response at high spatial frequencies, a chain transfer agent, the 4,4’-azobis (4-cyanopentanoic acid), ACPA, is added to the composition of the material. Different concentrations of ACPA are incorporated into the main composition of the photopolymer to find the concentration value that provides the highest diffraction efficiency. Moreover, the refractive index modulation and the optical thickness of the transmission and reflection gratings were obtained, evaluated and compared to procure more information about the influence of the ACPA on them. Full article

(This article belongs to the Special Issue Photopolymers for Holographic Applications)

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12 pages, 2689 KiB

Open AccessFeature PaperArticle

Blazed Gratings Recorded in Absorbent Photopolymers

by Roberto Fernández, Sergi Gallego, Andrés Márquez, Víctor Navarro-Fuster and Augusto Beléndez

Materials 2016, 9(3), 195; https://doi.org/10.3390/ma9030195 - 15 Mar 2016

Cited by 12 | Viewed by 5023

Abstract

Phase diffractive optical elements, which have many interesting applications, are usually fabricated using a photoresist. In this paper, they were made using a hybrid optic-digital system and a photopolymer as recording medium. We analyzed the characteristics of the input and recording light and [...] Read more.

Phase diffractive optical elements, which have many interesting applications, are usually fabricated using a photoresist. In this paper, they were made using a hybrid optic-digital system and a photopolymer as recording medium. We analyzed the characteristics of the input and recording light and then simulated the generation of blazed gratings with different spatial periods in different types of photopolymers using a diffusion model. Finally, we analyzed the output and diffraction efficiencies of the 0 and 1st order so as to compare the simulated values with those measured experimentally. We evaluated the effects of index matching in a standard PVA/AA photopolymer, and in a variation of Biophotopol, a more biocompatible photopolymer. Diffraction efficiencies near 70%, for a wavelength of 633 nm, were achieved for periods longer than 300 µm in this kind of materials. Full article

(This article belongs to the Special Issue Photopolymers for Holographic Applications)

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11 pages, 2825 KiB

Open AccessArticle

Nanotextured Shrink Wrap Superhydrophobic Surfaces by Argon Plasma Etching

by Jolie M. Nokes, Himanshu Sharma, Roger Tu, Monica Y. Kim, Michael Chu, Ali Siddiqui and Michelle Khine

Materials 2016, 9(3), 196; https://doi.org/10.3390/ma9030196 - 14 Mar 2016

Cited by 18 | Viewed by 8459

Abstract

We present a rapid, simple, and scalable approach to achieve superhydrophobic (SH) substrates directly in commodity shrink wrap film utilizing Argon (Ar) plasma. Ar plasma treatment creates a stiff skin layer on the surface of the shrink film. When the film shrinks, the [...] Read more.

We present a rapid, simple, and scalable approach to achieve superhydrophobic (SH) substrates directly in commodity shrink wrap film utilizing Argon (Ar) plasma. Ar plasma treatment creates a stiff skin layer on the surface of the shrink film. When the film shrinks, the mismatch in stiffness between the stiff skin layer and bulk shrink film causes the formation of multiscale hierarchical wrinkles with nano-textured features. Scanning electron microscopy (SEM) images confirm the presence of these biomimetic structures. Contact angle (CA) and contact angle hysteresis (CAH) measurements, respectively, defined as values greater than 150° and less than 10°, verified the SH nature of the substrates. Furthermore, we demonstrate the ability to reliably pattern hydrophilic regions onto the SH substrates, allowing precise capture and detection of proteins in urine. Finally, we achieved self-driven microfluidics via patterning contrasting superhydrophilic microchannels on the SH Ar substrates to induce flow for biosensing. Full article

(This article belongs to the Special Issue Bioinspired and Biomimetic Materials)

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19 pages, 9466 KiB

Open AccessArticle

Post Processing and Biological Evaluation of the Titanium Scaffolds for Bone Tissue Engineering

by Bartłomiej Wysocki, Joanna Idaszek, Karol Szlązak, Karolina Strzelczyk, Tomasz Brynk, Krzysztof J. Kurzydłowski and Wojciech Święszkowski

Materials 2016, 9(3), 197; https://doi.org/10.3390/ma9030197 - 15 Mar 2016

Cited by 95 | Viewed by 11718

Abstract

Nowadays, post-surgical or post-accidental bone loss can be substituted by custom-made scaffolds fabricated by additive manufacturing (AM) methods from metallic powders. However, the partially melted powder particles must be removed in a post-process chemical treatment. The aim of this study was to investigate [...] Read more.

Nowadays, post-surgical or post-accidental bone loss can be substituted by custom-made scaffolds fabricated by additive manufacturing (AM) methods from metallic powders. However, the partially melted powder particles must be removed in a post-process chemical treatment. The aim of this study was to investigate the effect of the chemical polishing with various acid baths on novel scaffolds’ morphology, porosity and mechanical properties. In the first stage, Magics software (Materialise NV, Leuven, Belgium) was used to design a porous scaffolds with pore size equal to (A) 200 µm, (B) 500 µm and (C) 200 + 500 µm, and diamond cell structure. The scaffolds were fabricated from commercially pure titanium powder (CP Ti) using a SLM50 3D printing machine (Realizer GmbH, Borchen, Germany). The selective laser melting (SLM) process was optimized and the laser beam energy density in range of 91–151 J/mm³ was applied to receive 3D structures with fully dense struts. To remove not fully melted titanium particles the scaffolds were chemically polished using various HF and HF-HNO₃ acid solutions. Based on scaffolds mass loss and scanning electron (SEM) observations, baths which provided most uniform surface cleaning were proposed for each porosity. The pore and strut size after chemical treatments was calculated based on the micro-computed tomography (µ-CT) and SEM images. The mechanical tests showed that the treated scaffolds had Young’s modulus close to that of compact bone. Additionally, the effect of pore size of chemically polished scaffolds on cell retention, proliferation and differentiation was studied using human mesenchymal stem cells. Small pores yielded higher cell retention within the scaffolds, which then affected their growth. This shows that in vitro cell performance can be controlled to certain extent by varying pore sizes. Full article

(This article belongs to the Special Issue Metallic Scaffolds for Bone Regeneration)

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11 pages, 3078 KiB

Open AccessArticle

Development and Characterization of a Bioinspired Bone Matrix with Aligned Nanocrystalline Hydroxyapatite on Collagen Nanofibers

by Hsi-Chin Wu, Tzu-Wei Wang, Jui-Sheng Sun, Yi-Hsuan Lee, Meng-Han Shen, Zong-Ruei Tsai, Chih-Yu Chen and Horng-Chaung Hsu

Materials 2016, 9(3), 198; https://doi.org/10.3390/ma9030198 - 15 Mar 2016

Cited by 25 | Viewed by 6741

Abstract

Various kinds of three-dimensional (3D) scaffolds have been designed to mimic the biological spontaneous bone formation characteristics by providing a suitable microenvironment for osteogenesis. In view of this, a natural bone-liked composite scaffold, which was combined with inorganic (hydroxyapatite, Hap) and organic (type [...] Read more.

Various kinds of three-dimensional (3D) scaffolds have been designed to mimic the biological spontaneous bone formation characteristics by providing a suitable microenvironment for osteogenesis. In view of this, a natural bone-liked composite scaffold, which was combined with inorganic (hydroxyapatite, Hap) and organic (type I collagen, Col) phases, has been developed through a self-assembly process. This 3D porous scaffold consisting of a c-axis of Hap nanocrystals (nHap) aligning along Col fibrils arrangement is similar to natural bone architecture. A significant increase in mechanical strength and elastic modulus of nHap/Col scaffold is achieved through biomimetic mineralization process when compared with simple mixture of collagen and hydroxyapatite method. It is suggested that the self-organization of Hap and Col produced in vivo could also be achieved in vitro. The oriented nHap/Col composite not only possesses bone-like microstructure and adequate mechanical properties but also enhances the regeneration and reorganization abilities of bone tissue. These results demonstrated that biomimetic nHap/Col can be successfully reconstructed as a bone graft substitute in bone tissue engineering. Full article

(This article belongs to the Section Biomaterials)

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17 pages, 10376 KiB

Open AccessArticle

Semisolid Microstructural Evolution during Partial Remelting of a Bulk Alloy Prepared by Cold Pressing of the Ti-Al-2024Al Powder Mixture

by Yahong Qin, Tijun Chen, Yingjun Wang, Xuezheng Zhang and Pubo Li

Materials 2016, 9(3), 199; https://doi.org/10.3390/ma9030199 - 16 Mar 2016

Cited by 14 | Viewed by 4837

Abstract

A new method, powder thixoforming, has been proposed to fabricate an in situ Al₃Ti_p/2024Al composite. During partial remelting, the microstructural evolution of the bulk alloy prepared by cold pressing of the Ti, Al, 2024Al powder mixture was investigated, and [...] Read more.

A new method, powder thixoforming, has been proposed to fabricate an in situ Al₃Ti_p/2024Al composite. During partial remelting, the microstructural evolution of the bulk alloy prepared by cold pressing of the Ti, Al, 2024Al powder mixture was investigated, and the formation mechanism of the Al₃Ti particles produced by the reaction between the Ti powder and the Al alloy melt is also discussed in detail. The results indicate that the microstructural evolution of the 2024 alloy matrix can be divided into three stages: a rapid coarsening of the powder grains; a formation of primary α-Al particles surrounded with a continuous liquid film; and a slight coarsening of the primary α-Al particles. Simultaneously, a reaction layer of Al₃Ti can be formed on the Ti powder surface when the bulk is heated for 10 min at 640 °C The thickness (X) of the reaction layer increases with the time according to the parabolic law of (X = -0.43t^{2} + 4.21t + 0.17). The stress generated in the reaction layer due to the volume dilatation can be calculated by using the equationσ (sigma_{Al_{3}Ti} = -frac{ E_{Al_{3}Ti} }{6(1-v{Al_{3}Ti})} frac{ t^{3}_{Al_{3}Ti} }{t_{Ti}} left(frac{1}{R} - frac{1}{R_{0}} ight) ). Comparing the obtained data with the results of the drip experiment, the reaction rate for the Ti powder and Al powder mixture is greater than that for the Ti plate and Al alloy mixture, respectively. Full article

(This article belongs to the Section Advanced Materials Characterization)

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14 pages, 7075 KiB

Open AccessArticle

Effect of Chromium on Corrosion Behavior of P110 Steels in CO₂-H₂S Environment with High Pressure and High Temperature

by Jianbo Sun, Chong Sun, Xueqiang Lin, Xiangkun Cheng and Huifeng Liu

Materials 2016, 9(3), 200; https://doi.org/10.3390/ma9030200 - 16 Mar 2016

Cited by 50 | Viewed by 7310

Abstract

The novel Cr-containing low alloy steels have exhibited good corrosion resistance in CO₂ environment, mainly owing to the formation of Cr-enriched corrosion film. In order to evaluate whether it is applicable to the CO₂ and H₂S coexistence conditions, the [...] Read more.

The novel Cr-containing low alloy steels have exhibited good corrosion resistance in CO₂ environment, mainly owing to the formation of Cr-enriched corrosion film. In order to evaluate whether it is applicable to the CO₂ and H₂S coexistence conditions, the corrosion behavior of low-chromium steels in CO₂-H₂S environment with high pressure and high temperature was investigated using weight loss measurement and surface characterization. The results showed that P110 steel suffered localized corrosion and both 3Cr-P110 and 5Cr-P110 steels exhibited general corrosion. However, the corrosion rate of 5Cr-P110 was the highest among them. The corrosion process of the steels was simultaneously governed by CO₂ and H₂S. The outer scales on the three steels mainly consisted of FeS_1−x crystals, whereas the inner scales on Cr-containing steels comprised of amorphous FeS_1−x, Cr(OH)₃ and FeCO₃, in contrast with the amorphous FeS_1−x and FeCO₃ mixture film of P110 steel. The more chromium the steel contains, the more chromium compounds the corrosion products contain. The addition of chromium in steels increases the uniformity of the Cr-enriched corrosion scales, eliminates the localized corrosion, but cannot decrease the general corrosion rates. The formation of FeS_1−x may interfere with Cr-enriched corrosion scales and lowering the corrosion performance of 3Cr-P110 and 5Cr-P110 steels. Full article

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13 pages, 4450 KiB

Open AccessFeature PaperArticle

Controlled Photocatalytic Synthesis of Core–Shell SiC/Polyaniline Hybrid Nanostructures

by Attila Kormányos, Balázs Endrődi, Róbert Ondok, András Sápi and Csaba Janáky

Materials 2016, 9(3), 201; https://doi.org/10.3390/ma9030201 - 16 Mar 2016

Cited by 18 | Viewed by 7377

Abstract

Hybrid materials of electrically conducting polymers and inorganic semiconductors form an exciting class of functional materials. To fully exploit the potential synergies of the hybrid formation, however, sophisticated synthetic methods are required that allow for the fine-tuning of the nanoscale structure of the [...] Read more.

Hybrid materials of electrically conducting polymers and inorganic semiconductors form an exciting class of functional materials. To fully exploit the potential synergies of the hybrid formation, however, sophisticated synthetic methods are required that allow for the fine-tuning of the nanoscale structure of the organic/inorganic interface. Here we present the photocatalytic deposition of a conducting polymer (polyaniline) on the surface of silicon carbide (SiC) nanoparticles. The polymerization is facilitated on the SiC surface, via the oxidation of the monomer molecules by ultraviolet-visible (UV-vis) light irradiation through the photogenerated holes. The synthesized core–shell nanostructures were characterized by UV-vis, Raman, and Fourier Transformed Infrared (FT-IR) Spectroscopy, thermogravimetric analysis, transmission and scanning electron microscopy, and electrochemical methods. It was found that the composition of the hybrids can be varied by simply changing the irradiation time. In addition, we proved the crucial importance of the irradiation wavelength in forming conductive polyaniline, instead of its overoxidized, insulating counterpart. Overall, we conclude that photocatalytic deposition is a promising and versatile approach for the synthesis of conducting polymers with controlled properties on semiconductor surfaces. The presented findings may trigger further studies using photocatalysis as a synthetic strategy to obtain nanoscale hybrid architectures of different semiconductors. Full article

(This article belongs to the Special Issue Advancement of Photocatalytic Materials 2016)

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13 pages, 3460 KiB

Open AccessFeature PaperArticle

Study of Polydiacetylene-Poly (Ethylene Oxide) Electrospun Fibers Used as Biosensors

by A K M Mashud Alam, Janet P. Yapor, Melissa M. Reynolds and Yan Vivian Li

Materials 2016, 9(3), 202; https://doi.org/10.3390/ma9030202 - 16 Mar 2016

Cited by 28 | Viewed by 8284

Abstract

Polydiacetylene (PDA) is an attractive conjugated material for use in biosensors due to its unique characteristic of undergoing a blue-to-red color change in response to external stimuli. 10,12-Pentacosadiynoic acid (PCDA) and poly (ethylene oxide) (PEO) were used in this study to develop fiber [...] Read more.

Polydiacetylene (PDA) is an attractive conjugated material for use in biosensors due to its unique characteristic of undergoing a blue-to-red color change in response to external stimuli. 10,12-Pentacosadiynoic acid (PCDA) and poly (ethylene oxide) (PEO) were used in this study to develop fiber composites via an electrospinning method at various mass ratios of PEO to PCDA, solution concentrations, and injection speeds. The PEO-PDA fibers in blue phase were obtained via photo-polymerization upon UV-light irritation. High mass ratios of PEO to PCDA, low polymer concentrations of spinning solution, and low injection speeds promoted fine fibers with small diameters and smooth surfaces. The colorimetric transition of the fibers was investigated when the fibers were heated at temperatures ranging from 25 °C to 120 °C. A color switch from blue to red in the fibers was observed when the fibers were heated at temperatures greater than 60 °C. The color transition was more sensitive in the fibers made with a low mass ratio of PEO to PCDA due to high fraction of PDA in the fibers. The large diameter fibers also promoted the color switch due to high reflectance area in the fibers. All of the fibers were analyzed using Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC) and compared before and after the color change occurred. The colorimetric transitional mechanism is proposed to occur due to conformational changes in the PDA macromolecules. Full article

(This article belongs to the Section Advanced Composites)

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8 pages, 892 KiB

Open AccessArticle

Surface Morphology and Tooth Adhesion of a Novel Nanostructured Dental Restorative Composite

by Marco Salerno, Patrizia Loria, Giunio Matarazzo, Francesco Tomè, Alberto Diaspro and Roberto Eggenhöffner

Materials 2016, 9(3), 203; https://doi.org/10.3390/ma9030203 - 16 Mar 2016

Cited by 21 | Viewed by 4859

Abstract

Recently, a novel dental restorative composite based on nanostructured micro-fillers of anodic porous alumina has been proposed. While its bulk properties are promising thanks to decreased aging and drug delivery capabilities, its surface properties are still unknown. Here we investigated the surface morphology [...] Read more.

Recently, a novel dental restorative composite based on nanostructured micro-fillers of anodic porous alumina has been proposed. While its bulk properties are promising thanks to decreased aging and drug delivery capabilities, its surface properties are still unknown. Here we investigated the surface morphology and the adhesion to tooth dentin of this composite as prepared. For comparison, we used two commercial composites: Tetric EVO Flow (Ivoclar) and Enamel HRi Plus (Micerium). The surface morphology was characterized by atomic force microscopy and the adhesion strength by tensile tests. The experimental composite is rougher than the commercial composites, with root mean square roughness of ~549 nm against 170–511 nm, and presents an adhesion strength of ~15 MPa against 19–21 MPa. These results show at the same time some proximity to the commercial composites, but also the need for optimization of the experimental material formulation. Full article

(This article belongs to the Section Biomaterials)

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11 pages, 4889 KiB

Open AccessArticle

Cavitation Erosion of Cermet-Coated Aluminium Bronzes

by Ion Mitelea, Octavian Oancă, Ilare Bordeaşu and Corneliu M. Crăciunescu

Materials 2016, 9(3), 204; https://doi.org/10.3390/ma9030204 - 17 Mar 2016

Cited by 7 | Viewed by 5759

Abstract

The cavitation erosion resistance of CuAl10Ni5Fe2.5Mn1 following plasma spraying with Al₂O₃·30(Ni₂₀Al) powder and laser re-melting was analyzed in view of possible improvements of the lifetime of components used in hydraulic environments. The cavitation erosion resistance was substantially [...] Read more.

The cavitation erosion resistance of CuAl10Ni5Fe2.5Mn1 following plasma spraying with Al₂O₃·30(Ni₂₀Al) powder and laser re-melting was analyzed in view of possible improvements of the lifetime of components used in hydraulic environments. The cavitation erosion resistance was substantially improved compared with the one of the base material. The thickness of the re-melted layer was in the range of several hundred micrometers, with a surface microhardness increasing from 250 to 420 HV 0.2. Compositional, structural, and microstructural explorations showed that the microstructure of the re-melted and homogenized layer, consisting of a cubic Al₂O₃ matrix with dispersed Ni-based solid solution is associated with the hardness increase and consequently with the improvement of the cavitation erosion resistance. Full article

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21 pages, 4835 KiB

Open AccessFeature PaperArticle

Computational Study of the Effect of Cortical Porosity on Ultrasound Wave Propagation in Healthy and Osteoporotic Long Bones

by Vassiliki T. Potsika, Konstantinos N. Grivas, Theodoros Gortsas, Gianluca Iori, Vasilios C. Protopappas, Kay Raum, Demosthenes Polyzos and Dimitrios I. Fotiadis

Materials 2016, 9(3), 205; https://doi.org/10.3390/ma9030205 - 17 Mar 2016

Cited by 6 | Viewed by 5866

Abstract

Computational studies on the evaluation of bone status in cases of pathologies have gained significant interest in recent years. This work presents a parametric and systematic numerical study on ultrasound propagation in cortical bone models to investigate the effect of changes in cortical [...] Read more.

Computational studies on the evaluation of bone status in cases of pathologies have gained significant interest in recent years. This work presents a parametric and systematic numerical study on ultrasound propagation in cortical bone models to investigate the effect of changes in cortical porosity and the occurrence of large basic multicellular units, simply called non-refilled resorption lacunae (RL), on the velocity of the first arriving signal (FAS). Two-dimensional geometries of cortical bone are established for various microstructural models mimicking normal and pathological tissue states. Emphasis is given on the detection of RL formation which may provoke the thinning of the cortical cortex and the increase of porosity at a later stage of the disease. The central excitation frequencies 0.5 and 1 MHz are examined. The proposed configuration consists of one point source and multiple successive receivers in order to calculate the FAS velocity in small propagation paths (local velocity) and derive a variation profile along the cortical surface. It was shown that: (a) the local FAS velocity can capture porosity changes including the occurrence of RL with different number, size and depth of formation; and (b) the excitation frequency 0.5 MHz is more sensitive for the assessment of cortical microstructure. Full article

(This article belongs to the Special Issue Acoustic Waves in Advanced Materials)

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11 pages, 2099 KiB

Open AccessArticle

Nitric Acid-Treated Carbon Fibers with Enhanced Hydrophilicity for Candida tropicalis Immobilization in Xylitol Fermentation

by Le Wang, Na Liu, Zheng Guo, Dapeng Wu, Weiwei Chen, Zheng Chang, Qipeng Yuan, Ming Hui and Jinshui Wang

Materials 2016, 9(3), 206; https://doi.org/10.3390/ma9030206 - 17 Mar 2016

Cited by 47 | Viewed by 8053

Abstract

Nitric acid (HNO₃)-treated carbon fiber (CF) rich in hydrophilic groups was applied as a cell-immobilized carrier for xylitol fermentation. Using scanning electron microscopy, we characterized the morphology of the HNO₃-treated CF. Additionally, we evaluated the immobilized efficiency (IE) of [...] Read more.

Nitric acid (HNO₃)-treated carbon fiber (CF) rich in hydrophilic groups was applied as a cell-immobilized carrier for xylitol fermentation. Using scanning electron microscopy, we characterized the morphology of the HNO₃-treated CF. Additionally, we evaluated the immobilized efficiency (IE) of Candida tropicalis and xylitol fermentation yield by investigating the surface properties of nitric acid treated CF, specifically, the acidic group content, zero charge point, degree of moisture and contact angle. We found that adhesion is the major mechanism for cell immobilization and that it is greatly affected by the hydrophilic–hydrophilic surface properties. In our experiments, we found 3 hto be the optimal time for treating CF with nitric acid, resulting in an improved IE of Candida tropicalis of 0.98 g∙g⁻¹ and the highest xylitol yield and volumetric productivity (70.13% and 1.22 g∙L⁻¹∙h⁻¹, respectively). The HNO₃-treated CF represents a promising method for preparing biocompatible biocarriers for multi-batch fermentation. Full article

(This article belongs to the Section Biomaterials)

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23 pages, 8933 KiB

Open AccessArticle

Fatigue Life Prediction of Fiber-Reinforced Ceramic-Matrix Composites with Different Fiber Preforms at Room and Elevated Temperatures

by Longbiao Li

Materials 2016, 9(3), 207; https://doi.org/10.3390/ma9030207 - 17 Mar 2016

Cited by 17 | Viewed by 6339

Abstract

In this paper, the fatigue life of fiber-reinforced ceramic-matrix composites (CMCs) with different fiber preforms, i.e., unidirectional, cross-ply, 2D (two dimensional), 2.5D and 3D CMCs at room and elevated temperatures in air and oxidative environments, has been predicted using the micromechanics approach. [...] Read more.

In this paper, the fatigue life of fiber-reinforced ceramic-matrix composites (CMCs) with different fiber preforms, i.e., unidirectional, cross-ply, 2D (two dimensional), 2.5D and 3D CMCs at room and elevated temperatures in air and oxidative environments, has been predicted using the micromechanics approach. An effective coefficient of the fiber volume fraction along the loading direction (ECFL) was introduced to describe the fiber architecture of preforms. The statistical matrix multicracking model and fracture mechanics interface debonding criterion were used to determine the matrix crack spacing and interface debonded length. Under cyclic fatigue loading, the fiber broken fraction was determined by combining the interface wear model and fiber statistical failure model at room temperature, and interface/fiber oxidation model, interface wear model and fiber statistical failure model at elevated temperatures, based on the assumption that the fiber strength is subjected to two-parameter Weibull distribution and the load carried by broken and intact fibers satisfies the Global Load Sharing (GLS) criterion. When the broken fiber fraction approaches the critical value, the composites fatigue fracture. Full article

(This article belongs to the Section Advanced Composites)

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12 pages, 4707 KiB

Open AccessArticle

Site-Control of InAs/GaAs Quantum Dots with Indium-Assisted Deoxidation

by Sajid Hussain, Alessandro Pozzato, Massimo Tormen, Valentina Zannier and Giorgio Biasiol

Materials 2016, 9(3), 208; https://doi.org/10.3390/ma9030208 - 18 Mar 2016

Cited by 5 | Viewed by 5589

Abstract

Site-controlled epitaxial growth of InAs quantum dots on GaAs substrates patterned with periodic nanohole arrays relies on the deterministic nucleation of dots into the holes. In the ideal situation, each hole should be occupied exactly by one single dot, with no nucleation onto [...] Read more.

Site-controlled epitaxial growth of InAs quantum dots on GaAs substrates patterned with periodic nanohole arrays relies on the deterministic nucleation of dots into the holes. In the ideal situation, each hole should be occupied exactly by one single dot, with no nucleation onto planar areas. However, the single-dot occupancy per hole is often made difficult by the fact that lithographically-defined holes are generally much larger than the dots, thus providing several nucleation sites per hole. In addition, deposition of a thin GaAs buffer before the dots tends to further widen the holes in the [110] direction. We have explored a method of native surface oxide removal by using indium beams, which effectively prevents hole elongation along [110] and greatly helps single-dot occupancy per hole. Furthermore, as compared to Ga-assisted deoxidation, In-assisted deoxidation is efficient in completely removing surface contaminants, and any excess In can be easily re-desorbed thermally, thus leaving a clean, smooth GaAs surface. Low temperature photoluminescence showed that inhomogeneous broadening is substantially reduced for QDs grown on In-deoxidized patterns, with respect to planar self-assembled dots. Full article

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11 pages, 3057 KiB

Open AccessArticle

Perpendicular Magnetization Behavior of Low- Temperature Ordered FePt Films with Insertion of Ag Nanolayers

by Da-Hua Wei

Materials 2016, 9(3), 209; https://doi.org/10.3390/ma9030209 - 18 Mar 2016

Cited by 2 | Viewed by 5468

Abstract

FePt-Ag nanocomposite films with large perpendicular magnetic anisotropy have been fabricated by alternate-atomic-layer electron beam evaporation onto MgO(100) substrates at the low temperature of 300 °C. Their magnetization behavior and microstructure have been studied. The surface topography was observed and varied from continuous [...] Read more.

FePt-Ag nanocomposite films with large perpendicular magnetic anisotropy have been fabricated by alternate-atomic-layer electron beam evaporation onto MgO(100) substrates at the low temperature of 300 °C. Their magnetization behavior and microstructure have been studied. The surface topography was observed and varied from continuous to nanogranular microstructures with insertion of Ag nanolayers into Fe/Pt bilayer films. The measurement of angular-dependent coercivity showed a tendency of the domain-wall motion as a typical peak behavior shift toward more like a coherent Stoner-Wohlfarth rotation type with the insertion of Ag nanolayers into the FePt films. On the other hand, the inter-grain interaction was determined from a Kelly-Henkel plot. The FePt film without insertion of Ag nanolayers has a positive δM, indicating strong exchange coupling between neighboring grains, whereas the FePt film with insertion of Ag nanolayers has a negative δM, indicating that inter-grain exchange coupling is weaker, thus leading to the presence of dipole interaction in the FePt–Ag nanogranular films. The magnetic characteristic measurements confirmed that the perpendicular magnetization reversal behavior and related surface morphology of low-temperature-ordered FePt(001) nanogranular films can be systematically controlled by the insertion of Ag nanolayers into the FePt system for next generation magnetic storage medium applications. Full article

(This article belongs to the Section Advanced Composites)

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10 pages, 1574 KiB

Open AccessArticle

Effect of Curing Mode on Shear Bond Strength of Self-Adhesive Cement to Composite Blocks

by Jin-Young Kim, Ga-Young Cho, Byoung-Duck Roh and Yooseok Shin

Materials 2016, 9(3), 210; https://doi.org/10.3390/ma9030210 - 18 Mar 2016

Cited by 14 | Viewed by 6835

Abstract

To overcome the disadvantages of computer-aided design/computer-aided manufacturing (CAD/CAM) processed indirect restorations using glass-ceramics and other ceramics, resin nano ceramic, which has high strength and wear resistance with improved polish retention and optical properties, was introduced. The purpose of this study was to [...] Read more.

To overcome the disadvantages of computer-aided design/computer-aided manufacturing (CAD/CAM) processed indirect restorations using glass-ceramics and other ceramics, resin nano ceramic, which has high strength and wear resistance with improved polish retention and optical properties, was introduced. The purpose of this study was to evaluate the shear bond strength and fracture pattern of indirect CAD/CAM composite blocks cemented with two self-etch adhesive cements with different curing modes. Sand-blasted CAD/CAM composite blocks were cemented using conventional resin cement, Rely X Ultimate Clicker (RXC, 3M ESPE, St. Paul, MN, USA) with Single Bond Universal (SB, 3M ESPE, St. Paul, MN, USA) for the control group or two self-adhesive resin cements: Rely X U200 (RXU, 3M ESPE, St. Paul, MN, USA) and G-CEM Cerasmart (GC, GC corporation, Tokyo, Japan). RXU and GC groups included different curing modes (light-curing (L) and auto-curing (A)). Shear bond strength (SBS) analyses were performed on all the specimens. The RXC group revealed the highest SBS and the GC A group revealed the lowest SBS. According to Tukey’s post hoc test, the RXC group showed a significant difference compared to the GC A group (p < 0.05). For the curing mode, RXU A and RXU L did not show any significant difference between groups and GC A and GC L did not show any significant difference either. Most of the groups except RXC and RXU L revealed adhesive failure patterns predominantly. The RXC group showed a predominant cohesive failure pattern in their CAD/CAM composite, Lava^TM Ultimate (LU, 3M ESPE, St. Paul, MN, USA). Within the limitations of this study, no significant difference was found regarding curing modes but more mixed fracture patterns were showed when using the light-curing mode than when using the self-curing mode. Full article

(This article belongs to the Section Advanced Composites)

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12 pages, 2223 KiB

Open AccessArticle

Photoassisted Electrochemical Treatment of Azo and Phtalocyanine Reactive Dyes in the Presence of Surfactants

by Mireia Sala, Víctor López-Grimau and Carmen Gutiérrez-Bouzán

Materials 2016, 9(3), 211; https://doi.org/10.3390/ma9030211 - 18 Mar 2016

Cited by 13 | Viewed by 5157

Abstract

An electrochemical treatment (EC) was applied at different intensities to degrade the chromophoric groups of dyes C.I. Reactive Black 5 (RB5) and C.I. Reactive Blue 7 (Rb7) until uncolored species were obtained. Decolorization rate constants of the azo dye RB5 were higher than [...] Read more.

An electrochemical treatment (EC) was applied at different intensities to degrade the chromophoric groups of dyes C.I. Reactive Black 5 (RB5) and C.I. Reactive Blue 7 (Rb7) until uncolored species were obtained. Decolorization rate constants of the azo dye RB5 were higher than the phtalocyanine Rb7 ones. In addition, the EC treatment was more efficient at higher intensities, but these conditions significantly increased the generation of undesirable by-products such as chloroform. The combination of EC with UV irradiation (UVEC) drastically minimized the generation of chloroform. The photo-assisted electrochemical treatment was also able to achieve decolorization values of 99%. Finally, mixtures of dyes and surfactants were treated by EC and UVEC. In the presence of surfactants, the decolorization kinetic of dyes was slowed due to the competitive reactions of surfactants degradation. Both methods achieved total decolorization and in both cases, the generation of haloforms was negligible. Full article

(This article belongs to the Special Issue Functional Organic Dyes and Pigments)

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14 pages, 2064 KiB

Open AccessFeature PaperArticle

Polystyrene-co-Divinylbenzene PolyHIPE Monoliths in 1.0 mm Column Formats for Liquid Chromatography

by Sidratul Choudhury, Laurence Fitzhenry, Blánaid White and Damian Connolly

Materials 2016, 9(3), 212; https://doi.org/10.3390/ma9030212 - 18 Mar 2016

Cited by 14 | Viewed by 7021

Abstract

The reversed phase liquid chromatographic (RP-HPLC) separation of small molecules using a polystyrene-co-divinylbenzene (PS-co-DVB) polyHIPE stationary phases housed within 1.0 mm i.d. silcosteel columns is presented within this study. A 90% PS-co-DVB polyHIPE was covalently attached to [...] Read more.

The reversed phase liquid chromatographic (RP-HPLC) separation of small molecules using a polystyrene-co-divinylbenzene (PS-co-DVB) polyHIPE stationary phases housed within 1.0 mm i.d. silcosteel columns is presented within this study. A 90% PS-co-DVB polyHIPE was covalently attached to the walls of the column housing by prior wall modification with 3-(trimethoxysilyl) propyl methacrylate and could withstand operating backpressures in excess of 200 bar at a flow rate of 1.2 mL/min. Permeability studies revealed that the monolith swelled slightly in 100% acetonitrile relative to 100% water but could nevertheless be used to separate five alkylbenzenes using a flow rate of 40 µL/min (linear velocity: 0.57 mm/s). Remarkable column-to-column reproducibility is shown with retention factor variation between 2.6% and 6.1% for two separately prepared columns. Full article

(This article belongs to the Special Issue Porous Monolithic Materials for Applications in Separation Science)

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20 pages, 7631 KiB

Open AccessArticle

On the Behavior of Different PCMs in a Hot Water Storage Tank against Thermal Demands

by Jacobo Porteiro, José Luis Míguez, Bárbara Crespo, José De Lara and José María Pousada

Materials 2016, 9(3), 213; https://doi.org/10.3390/ma9030213 - 21 Mar 2016

Cited by 18 | Viewed by 6510

Abstract

Advantages, such as thermal storage improvement, are found when using PCMs (Phase Change Materials) in storage tanks. The inclusion of three different types of materials in a 60 l test tank is studied. Two test methodologies were developed, and four tests were performed [...] Read more.

Advantages, such as thermal storage improvement, are found when using PCMs (Phase Change Materials) in storage tanks. The inclusion of three different types of materials in a 60 l test tank is studied. Two test methodologies were developed, and four tests were performed following each methodology. A thermal analysis is performed to check the thermal properties of each PCM. The distributions of the water temperatures inside the test tanks are evaluated by installing four Pt-100 sensors at different heights. A temperature recovery is observed after exposing the test tank to an energy demand. An energetic analysis that takes into account the energy due to the water temperature, the energy due to the PCM and the thermal loss to the ambient environment is also presented. The percentage of each PCM that remains in the liquid state after the energy demand is obtained. Full article

(This article belongs to the Special Issue Development and Characterisation of Encapsulated PCM: Nano-, Micro-, and Macro-Encapsulation)

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Materials, Volume 9, Issue 3 (March 2016) – 95 articles

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