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Materials, Volume 7, Issue 3 (March 2014), Pages 1444-2394

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Editorial

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Open AccessEditorial Acknowledgement to Reviewers of Materials in 2013
Materials 2014, 7(3), 1444-1454; doi:10.3390/ma7031444
Received: 25 February 2014 / Accepted: 25 February 2014 / Published: 25 February 2014
PDF Full-text (162 KB) | HTML Full-text | XML Full-text
Abstract The editors of Materials would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2013 [...] Full article

Research

Jump to: Editorial, Review, Other

Open AccessArticle Influence of Magnetic Microparticles Isolation on Adenine Homonucleotides Structure
Materials 2014, 7(3), 1455-1472; doi:10.3390/ma7031455
Received: 17 November 2013 / Revised: 16 December 2013 / Accepted: 17 February 2014 / Published: 25 February 2014
Cited by 1 | PDF Full-text (758 KB) | HTML Full-text | XML Full-text
Abstract
The electroactivity of purine and pyrimidine bases is the most important property of nucleic acids that is very useful for determining oligonucleotides using square wave voltammetry. This study was focused on the electrochemical behavior of adenine-containing oligonucleotides before and after their isolation using
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The electroactivity of purine and pyrimidine bases is the most important property of nucleic acids that is very useful for determining oligonucleotides using square wave voltammetry. This study was focused on the electrochemical behavior of adenine-containing oligonucleotides before and after their isolation using paramagnetic particles. Two peaks were detected—peak A related to the reduction of adenine base and another peak B involved in the interactions between individual adenine strands and contributes to the formation of various spatial structures. The influence of the number of adenine bases in the strand in the isolation process using paramagnetic particles was investigated too. Full article
(This article belongs to the Section Biomaterials)
Open AccessArticle Flash Thermography to Evaluate Porosity in Carbon Fiber Reinforced Polymer (CFRPs)
Materials 2014, 7(3), 1483-1501; doi:10.3390/ma7031483
Received: 13 November 2013 / Revised: 14 February 2014 / Accepted: 19 February 2014 / Published: 26 February 2014
Cited by 3 | PDF Full-text (1175 KB) | HTML Full-text | XML Full-text
Abstract
It is a fact that the presence of porosity in composites has detrimental effects on their mechanical properties. Then, due to the high probability of void formation during manufacturing processes, it is necessary to have the availability of non-destructive evaluation techniques, which may
[...] Read more.
It is a fact that the presence of porosity in composites has detrimental effects on their mechanical properties. Then, due to the high probability of void formation during manufacturing processes, it is necessary to have the availability of non-destructive evaluation techniques, which may be able to discover the presence and the distribution of porosity in the final parts. In recent years, flash thermography has emerged as the most valuable method, but it is still not adequately enclosed in the industrial enterprise. The main reason of this is the lack of sufficient quantitative data for a full validation of such a technique. The intention of the present work is to supply an overview on the current state-of-the-art regarding the use of flash thermography to evaluate the porosity percentage in fiber reinforced composite materials and to present the latest results, which are gathered by the authors, on porous carbon fiber reinforced polymer laminates. To this end, several coupons of two different stacking sequences and including a different amount of porosity are fabricated and inspected with both non-destructive and destructive testing techniques. Data coming from non-destructive testing with either flash thermography or ultrasonics are plotted against the porosity percentage, which was previously estimated with the volumetric method. The new obtained results are a witness to the efficacy of flash thermography. Some key points that need further consideration are also highlighted. Full article
(This article belongs to the Special Issue Carbon Fibers) Print Edition available
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Open AccessArticle Dispersion of γ-Alumina Nano-Sized Spherical Particles in a Calamitic Liquid Crystal. Study and Optimization of the Confinement Effects
Materials 2014, 7(3), 1502-1519; doi:10.3390/ma7031502
Received: 16 January 2014 / Revised: 5 February 2014 / Accepted: 12 February 2014 / Published: 27 February 2014
Cited by 2 | PDF Full-text (879 KB) | HTML Full-text | XML Full-text
Abstract
We report an experimental study on confined systems formed by butyloxybenzylidene octylaniline liquid crystal (4O.8) + γ-alumina nanoparticles. The effects of the confinement in the thermal and dielectric properties of the liquid crystal under different densities of nanoparticles is analyzed by means of
[...] Read more.
We report an experimental study on confined systems formed by butyloxybenzylidene octylaniline liquid crystal (4O.8) + γ-alumina nanoparticles. The effects of the confinement in the thermal and dielectric properties of the liquid crystal under different densities of nanoparticles is analyzed by means of high resolution Modulated Differential Scanning Calorimetry (MDSC) and broadband dielectric spectroscopy. First, a drastic depression of the N-I and SmA-N transition temperatures is observed with confinement, the more concentration of nanoparticles the deeper this depression is, driving the nematic range closer to the room temperature. An interesting experimental law is found for both transition temperatures. Second, the change in shape of the heat capacity peaks is quantified by means of the full width half maximum (FWHM). Third, the confinement does not noticeably affect the molecular dynamics. Finally, the combination of nanoparticles and the external applied electric field tends to favor the alignment of the molecules in metallic cells. All these results indicate that the confinement of liquid crystals by means of γ-alumina nanoparticles could be optimum for liquid crystal-based electrooptic devices. Full article
(This article belongs to the Special Issue Liquid Crystals) Print Edition available
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Open AccessArticle Properties of Graphene/Shape Memory Thermoplastic Polyurethane Composites Actuating by Various Methods
Materials 2014, 7(3), 1520-1538; doi:10.3390/ma7031520
Received: 15 October 2013 / Revised: 10 January 2014 / Accepted: 11 February 2014 / Published: 27 February 2014
Cited by 16 | PDF Full-text (1312 KB) | HTML Full-text | XML Full-text
Abstract
Shape memory behavior of crystalline shape memory polyurethane (SPU) reinforced with graphene, which utilizes melting temperature as a shape recovery temperature, was examined with various external actuating stimuli such as direct heating, resistive heating, and infrared (IR) heating. Compatibility of graphene with crystalline
[...] Read more.
Shape memory behavior of crystalline shape memory polyurethane (SPU) reinforced with graphene, which utilizes melting temperature as a shape recovery temperature, was examined with various external actuating stimuli such as direct heating, resistive heating, and infrared (IR) heating. Compatibility of graphene with crystalline SPU was adjusted by altering the structure of the hard segment of the SPU, by changing the structure of the graphene, and by changing the preparation method of the graphene/SPU composite. The SPU made of aromatic 4,4′-diphenylmethane diisocyanate (MSPU) exhibited better compatibility with graphene, having an aromatic structure, compared to that made of the aliphatic hexamethylene diisocyanate. The finely dispersed graphene effectively reinforced MSPU, improved shape recovery of MSPU, and served effectively as a filler, triggering shape recovery by resistive or IR heating. Compatibility was enhanced when the graphene was modified with methanol. This improved shape recovery by direct heating, but worsened the conductivity of the composite, and consequently the efficiency of resistive heating for shape recovery also declined. Graphene modified with methanol was more effective than pristine graphene in terms of shape recovery by IR heating. Full article
(This article belongs to the Special Issue Shape Memory Materials)
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Open AccessArticle Erbium-Doped Amorphous Carbon-Based Thin Films: A Photonic Material Prepared by Low-Temperature RF-PEMOCVD
Materials 2014, 7(3), 1539-1554; doi:10.3390/ma7031539
Received: 26 November 2013 / Revised: 17 February 2014 / Accepted: 19 February 2014 / Published: 27 February 2014
Cited by 2 | PDF Full-text (792 KB) | HTML Full-text | XML Full-text
Abstract
The integration of photonic materials into CMOS processing involves the use of new materials. A simple one-step metal-organic radio frequency plasma enhanced chemical vapor deposition system (RF-PEMOCVD) was deployed to grow erbium-doped amorphous carbon thin films (a-C:(Er)) on Si substrates at low temperatures
[...] Read more.
The integration of photonic materials into CMOS processing involves the use of new materials. A simple one-step metal-organic radio frequency plasma enhanced chemical vapor deposition system (RF-PEMOCVD) was deployed to grow erbium-doped amorphous carbon thin films (a-C:(Er)) on Si substrates at low temperatures (<200 °C). A partially fluorinated metal-organic compound, tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5- octanedionate) Erbium(+III) or abbreviated Er(fod)3, was incorporated in situ into a-C based host. Six-fold enhancement of Er room-temperature photoluminescence at 1.54 µm was demonstrated by deuteration of the a-C host. Furthermore, the effect of RF power and substrate temperature on the photoluminescence of a-C:D(Er) films was investigated and analyzed in terms of the film structure. Photoluminescence signal increases with increasing RF power, which is the result of an increase in [O]/[Er] ratio and the respective erbium-oxygen coordination number. Moreover, photoluminescence intensity decreases with increasing substrate temperature, which is attributed to an increased desorption rate or a lower sticking coefficient of the fluorinated fragments during film growth and hence [Er] decreases. In addition, it is observed that Er concentration quenching begins at ~2.2 at% and continues to increase until 5.5 at% in the studied a-C:D(Er) matrix. This technique provides the capability of doping Er in a vertically uniform profile. Full article
Open AccessArticle Uptake of Eudragit Retard L (Eudragit® RL) Nanoparticles by Human THP-1 Cell Line and Its Effects on Hematology and Erythrocyte Damage in Rats
Materials 2014, 7(3), 1555-1572; doi:10.3390/ma7031555
Received: 18 October 2013 / Revised: 18 November 2013 / Accepted: 18 February 2014 / Published: 28 February 2014
Cited by 1 | PDF Full-text (583 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this study was to prepare Eudragit Retard L (Eudragit RL) nanoparticles (ENPs) and to determine their properties, their uptake by the human THP-1 cell line in vitro and their effect on the hematological parameters and erythrocyte damage in rats. ENPs
[...] Read more.
The aim of this study was to prepare Eudragit Retard L (Eudragit RL) nanoparticles (ENPs) and to determine their properties, their uptake by the human THP-1 cell line in vitro and their effect on the hematological parameters and erythrocyte damage in rats. ENPs showed an average size of 329.0 ± 18.5 nm, a positive zeta potential value of +57.5 ± 5.47 mV and nearly spherical shape with a smooth surface. THP-1 cell lines could phagocyte ENPs after 2 h of incubation. In the in vivo study, male Sprague-Dawley rats were exposed orally or intraperitoneally (IP) with a single dose of ENP (50 mg/kg body weight). Blood samples were collected after 4 h, 48 h, one week and three weeks for hematological and erythrocytes analysis. ENPs induced significant hematological disturbances in platelets, red blood cell (RBC) total and differential counts of white blood cells (WBCs) after 4 h, 48 h and one week. ENP increased met-Hb and Co-Hb derivatives and decreased met-Hb reductase activity. These parameters were comparable to the control after three weeks when administrated orally. It could be concluded that the route of administration has a major effect on the induction of hematological disturbances and should be considered when ENPs are applied for drug delivery systems. Full article
(This article belongs to the Special Issue Nanocomposites of Polymers and Inorganic Particles 2013)
Open AccessArticle Effect of Thermal History on Microstructures and Mechanical Properties of AZ31 Magnesium Alloy Prepared by Friction Stir Processing
Materials 2014, 7(3), 1573-1589; doi:10.3390/ma7031573
Received: 13 January 2014 / Revised: 6 February 2014 / Accepted: 19 February 2014 / Published: 28 February 2014
Cited by 6 | PDF Full-text (1575 KB) | HTML Full-text | XML Full-text
Abstract
Hot-rolled AZ31 (Mg-2.57Al-0.84Zn-0.32Mn, in mass percentage) magnesium alloy is subjected to friction stir processing in air (normal friction stir processing, NFSP) and under water (submerged friction stir processing, SFSP). Thermal history of the two FSP procedures is measured, and its effect on microstructures
[...] Read more.
Hot-rolled AZ31 (Mg-2.57Al-0.84Zn-0.32Mn, in mass percentage) magnesium alloy is subjected to friction stir processing in air (normal friction stir processing, NFSP) and under water (submerged friction stir processing, SFSP). Thermal history of the two FSP procedures is measured, and its effect on microstructures and mechanical properties of the experimental materials is investigated. Compared with NFSP, the peak temperature during SFSP is lower and the duration time at a high temperature is shorter due to the enhanced cooling effect of water. Consequently, SFSP results in further grain refinement, and the average grain size of the NFSP and SFSP specimens in the stir zone (SZ) are 2.9 μm and 1.3 μm, respectively. Transmission electron microscopy (TEM) examinations confirm that grain refinement is attributed to continuous dynamic recrystallization both for NFSP and SFSP. The average Vickers hardness in the SZ of the NFSP and SFSP AZ31 magnesium alloy are 76 HV and 87 HV. Furthermore, the ultimate tensile strength and the elongation of the SFSP specimen increase from 191 MPa and 31.3% in the NFSP specimen to 210 MPa and 50.5%, respectively. Both the NFSP and SFSP alloys fail through ductile fracture, but the dimples are much more obvious in the SFSP alloy. Full article
(This article belongs to the Special Issue Light Alloys and Their Applications)
Open AccessArticle Microstructure and Tensile Behavior of Laser Arc Hybrid Welded Dissimilar Al and Ti Alloys
Materials 2014, 7(3), 1590-1602; doi:10.3390/ma7031590
Received: 17 December 2013 / Revised: 16 January 2014 / Accepted: 21 January 2014 / Published: 28 February 2014
Cited by 7 | PDF Full-text (1004 KB) | HTML Full-text | XML Full-text
Abstract
Fiber laser-cold metal transfer arc hybrid welding was developed to welding-braze dissimilar Al and Ti alloys in butt configuration. Microstructure, interface properties, tensile behavior, and their relationships were investigated in detail. The results show the cross-weld tensile strength of the joints is up
[...] Read more.
Fiber laser-cold metal transfer arc hybrid welding was developed to welding-braze dissimilar Al and Ti alloys in butt configuration. Microstructure, interface properties, tensile behavior, and their relationships were investigated in detail. The results show the cross-weld tensile strength of the joints is up to 213 MPa, 95.5% of same Al weld. The optimal range of heat input for accepted joints was obtained as 83–98 J·mm−1. Within this range, the joint is stronger than 200 MPa and fractures in weld metal, or else, it becomes weaker and fractures at the intermetallic compounds (IMCs) layer. The IMCs layer of an accepted joint is usually thin and continuous, which is about 1μm-thick and only consists of TiAl2 due to fast solidification rate. However, the IMCs layer at the top corner of fusion zone/Ti substrate is easily thickened with increasing heat input. This thickened IMCs layer consists of a wide TiAl3 layer close to FZ and a thin TiAl2 layer close to Ti substrate. Furthermore, both bead shape formation and interface growth were discussed by laser-arc interaction and melt flow. Tensile behavior was summarized by interface properties. Full article
(This article belongs to the Special Issue Light Alloys and Their Applications)
Open AccessArticle Surface Finish and Residual Stresses Induced by Orthogonal Dry Machining of AA7075-T651
Materials 2014, 7(3), 1603-1624; doi:10.3390/ma7031603
Received: 19 December 2013 / Revised: 20 February 2014 / Accepted: 24 February 2014 / Published: 28 February 2014
Cited by 3 | PDF Full-text (4559 KB) | HTML Full-text | XML Full-text
Abstract
The surface finish was extensively studied in usual machining processes (turning, milling, and drilling). For these processes, the surface finish is strongly influenced by the cutting feed and the tool nose radius. However, a basic understanding of tool/surface finish interaction and residual stress
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The surface finish was extensively studied in usual machining processes (turning, milling, and drilling). For these processes, the surface finish is strongly influenced by the cutting feed and the tool nose radius. However, a basic understanding of tool/surface finish interaction and residual stress generation has been lacking. This paper aims to investigate the surface finish and residual stresses under the orthogonal cutting since it can provide this information by avoiding the effect of the tool nose radius. The orthogonal machining of AA7075-T651 alloy through a series of cutting experiments was performed under dry conditions. Surface finish was studied using height and amplitude distribution roughness parameters. SEM and EDS were used to analyze surface damage and built-up edge (BUE) formation. An analysis of the surface topography showed that the surface roughness was sensitive to changes in cutting parameters. It was found that the formation of BUE and the interaction between the tool edge and the iron-rich intermetallic particles play a determinant role in controlling the surface finish during dry orthogonal machining of the AA7075-T651 alloy. Hoop stress was predominantly compressive on the surface and tended to be tensile with increased cutting speed. The reverse occurred for the surface axial stress. The smaller the cutting feed, the greater is the effect of cutting speed on both axial and hoop stresses. By controlling the cutting speed and feed, it is possible to generate a benchmark residual stress state and good surface finish using dry machining. Full article
(This article belongs to the Special Issue Light Alloys and Their Applications)
Open AccessArticle Numerical Simulation and Optimization of Directional Solidification Process of Single Crystal Superalloy Casting
Materials 2014, 7(3), 1625-1639; doi:10.3390/ma7031625
Received: 17 December 2013 / Revised: 19 February 2014 / Accepted: 21 February 2014 / Published: 28 February 2014
Cited by 2 | PDF Full-text (825 KB) | HTML Full-text | XML Full-text
Abstract
The rapid development of numerical modeling techniques has led to more accurate results in modeling metal solidification processes. In this study, the cellular automaton-finite difference (CA-FD) method was used to simulate the directional solidification (DS) process of single crystal (SX) superalloy blade samples.
[...] Read more.
The rapid development of numerical modeling techniques has led to more accurate results in modeling metal solidification processes. In this study, the cellular automaton-finite difference (CA-FD) method was used to simulate the directional solidification (DS) process of single crystal (SX) superalloy blade samples. Experiments were carried out to validate the simulation results. Meanwhile, an intelligent model based on fuzzy control theory was built to optimize the complicate DS process. Several key parameters, such as mushy zone width and temperature difference at the cast-mold interface, were recognized as the input variables. The input variables were functioned with the multivariable fuzzy rule to get the output adjustment of withdrawal rate (v) (a key technological parameter). The multivariable fuzzy rule was built, based on the structure feature of casting, such as the relationship between section area, and the delay time of the temperature change response by changing v, and the professional experience of the operator as well. Then, the fuzzy controlling model coupled with CA-FD method could be used to optimize v in real-time during the manufacturing process. The optimized process was proven to be more flexible and adaptive for a steady and stray-grain free DS process. Full article
Open AccessArticle Mechanical Properties and Durability of CNT Cement Composites
Materials 2014, 7(3), 1640-1651; doi:10.3390/ma7031640
Received: 15 November 2013 / Revised: 20 February 2014 / Accepted: 24 February 2014 / Published: 28 February 2014
Cited by 10 | PDF Full-text (509 KB) | HTML Full-text | XML Full-text
Abstract
In the present paper, changes in mechanical properties of Portland cement-based mortars due to the addition of carbon nanotubes (CNT) and corrosion of embedded steel rebars in CNT cement pastes are reported. Bending strength, compression strength, porosity and density of mortars were determined
[...] Read more.
In the present paper, changes in mechanical properties of Portland cement-based mortars due to the addition of carbon nanotubes (CNT) and corrosion of embedded steel rebars in CNT cement pastes are reported. Bending strength, compression strength, porosity and density of mortars were determined and related to the CNT dosages. CNT cement paste specimens were exposed to carbonation and chloride attacks, and results on steel corrosion rate tests were related to CNT dosages. The increase in CNT content implies no significant variations of mechanical properties but higher steel corrosion intensities were observed. Full article
Open AccessArticle Topological Defects in Topological Insulators and Bound States at Topological Superconductor Vortices
Materials 2014, 7(3), 1652-1686; doi:10.3390/ma7031652
Received: 9 September 2013 / Revised: 10 February 2014 / Accepted: 11 February 2014 / Published: 4 March 2014
Cited by 4 | PDF Full-text (712 KB) | HTML Full-text | XML Full-text
Abstract
The scattering of Dirac electrons by topological defects could be one of the most relevant sources of resistance in graphene and at the boundary surfaces of a three-dimensional topological insulator (3D TI). In the long wavelength, continuous limit of the Dirac equation, the
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The scattering of Dirac electrons by topological defects could be one of the most relevant sources of resistance in graphene and at the boundary surfaces of a three-dimensional topological insulator (3D TI). In the long wavelength, continuous limit of the Dirac equation, the topological defect can be described as a distortion of the metric in curved space, which can be accounted for by a rotation of the Gamma matrices and by a spin connection inherited with the curvature. These features modify the scattering properties of the carriers. We discuss the self-energy of defect formation with this approach and the electron cross-section for intra-valley scattering at an edge dislocation in graphene, including corrections coming from the local stress. The cross-section contribution to the resistivity, ρ, is derived within the Boltzmann theory of transport. On the same lines, we discuss the scattering of a screw dislocation in a two-band 3D TI, like Bi1-xSbx, and we present the analytical simplified form of the wavefunction for gapless helical states bound at the defect. When a 3D TI is sandwiched between two even-parity superconductors, Dirac boundary states acquire superconductive correlations by proximity. In the presence of a magnetic vortex piercing the heterostructure, two Majorana states are localized at the two interfaces and bound to the vortex core. They have a half integer total angular momentum each, to match with the unitary orbital angular momentum of the vortex charge. Full article
(This article belongs to the Special Issue Spintronics)
Open AccessArticle Osteoblasts Interaction with PLGA Membranes Functionalized with Titanium Film Nanolayer by PECVD. In vitro Assessment of Surface Influence on Cell Adhesion during Initial Cell to Material Interaction
Materials 2014, 7(3), 1687-1708; doi:10.3390/ma7031687
Received: 29 October 2013 / Revised: 10 February 2014 / Accepted: 25 February 2014 / Published: 4 March 2014
Cited by 3 | PDF Full-text (6598 KB) | HTML Full-text | XML Full-text
Abstract
New biomaterials for Guided Bone Regeneration (GBR), both resorbable and non-resorbable, are being developed to stimulate bone tissue formation. Thus, the in vitro study of cell behavior towards material surface properties turns a prerequisite to assess both biocompatibility and bioactivity of any material
[...] Read more.
New biomaterials for Guided Bone Regeneration (GBR), both resorbable and non-resorbable, are being developed to stimulate bone tissue formation. Thus, the in vitro study of cell behavior towards material surface properties turns a prerequisite to assess both biocompatibility and bioactivity of any material intended to be used for clinical purposes. For this purpose, we have developed in vitro studies on normal human osteoblasts (HOB®) HOB® osteoblasts grown on a resorbable Poly (lactide-co-glycolide) (PLGA) membrane foil functionalized by a very thin film (around 15 nm) of TiO2 (i.e., TiO2/PLGA membranes), designed to be used as barrier membrane. To avoid any alteration of the membranes, the titanium films were deposited at room temperature in one step by plasma enhanced chemical vapour deposition. Characterization of the functionalized membranes proved that the thin titanium layer completely covers the PLGA foils that remains practically unmodified in their interior after the deposition process and stands the standard sterilization protocols. Both morphological changes and cytoskeletal reorganization, together with the focal adhesion development observed in HOB osteoblasts, significantly related to TiO2 treated PLGA in which the Ti deposition method described has revealed to be a valuable tool to increase bioactivity of PLGA membranes, by combining cell nanotopography cues with the incorporation of bioactive factors. Full article
(This article belongs to the Special Issue Titanium Materials for Biomedical Application 2013)
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Open AccessArticle Titania Nanotubes Grown on Carbon Fibers for Photocatalytic Decomposition of Gas-Phase Aromatic Pollutants
Materials 2014, 7(3), 1801-1813; doi:10.3390/ma7031801
Received: 27 November 2013 / Revised: 27 December 2013 / Accepted: 24 February 2014 / Published: 4 March 2014
Cited by 2 | PDF Full-text (999 KB) | HTML Full-text | XML Full-text
Abstract
This study aimed to prepare titania (TiO2) nanotube (TNT) arrays grown on un-activated carbon fibers (UCFs), with the application of different TiO2 loadings based on the coating-hydrothermal process, and to evaluate their photocatalytic activity for the degradation of sub-ppm levels
[...] Read more.
This study aimed to prepare titania (TiO2) nanotube (TNT) arrays grown on un-activated carbon fibers (UCFs), with the application of different TiO2 loadings based on the coating-hydrothermal process, and to evaluate their photocatalytic activity for the degradation of sub-ppm levels of aromatic pollutants (benzene, toluene, ethyl benzene, and o-xylene (BTEX)) using a plug-flow photocatalytic reactor. The characteristics of the prepared photocatalysts were determined by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), transmission electron microscopy (TEM), UV-visible absorption spectroscopy (UV-Vis) and X-ray diffraction (XRD) analyses. Spectral analysis showed that the prepared photocatalysts were closely associated with the characteristics of one-dimensional nanostructured TiO2 nanotubes for TNTUCFs and spherical shapes for TiO2-coated UCF (TUCF). The photocatalytic activities of BTEX obtained from TNTUCFs were higher than those obtained from a reference photocatalyst, TUCF). Specifically, the average degradation efficiencies of BTEX observed for TNTUCF-10 were 81%, 97%, 99%, and 99%, respectively, while those observed for TUCF were 14%, 42%, 52%, and 79%, respectively. Moreover, the photocatalytic activities obtained for TNTUCFs suggested that the degradation efficiencies of BTEX varied with changes in TiO2 loadings, allowing for the optimization of TiO2 loading. Another important finding was that input concentrations and air flow rates could be important parameters for the treatment of BTEX, which should be considered for the optimization of TNTUCFs application. Taken together, TNTUCFs can be applied to effectively degrade sub-ppm levels of gas-phase aromatic pollutants through the optimization of operational conditions. Full article
(This article belongs to the Special Issue Carbon Fibers) Print Edition available
Open AccessArticle Electrophoretic Deposition of Chitosan/h-BN and Chitosan/h-BN/TiO2 Composite Coatings on Stainless Steel (316L) Substrates
Materials 2014, 7(3), 1814-1829; doi:10.3390/ma7031814
Received: 27 November 2013 / Revised: 9 February 2014 / Accepted: 19 February 2014 / Published: 4 March 2014
Cited by 7 | PDF Full-text (516 KB) | HTML Full-text | XML Full-text
Abstract
This article presents the results of an experimental investigation designed to deposit chitosan/hexagonal boron nitride (h-BN) and chitosan/h-BN/titania (TiO2) composites on SS316L substrates using electrophoretic deposition (EPD) for potential antibacterial applications. The influence of EPD parameters (voltage and deposition time) and
[...] Read more.
This article presents the results of an experimental investigation designed to deposit chitosan/hexagonal boron nitride (h-BN) and chitosan/h-BN/titania (TiO2) composites on SS316L substrates using electrophoretic deposition (EPD) for potential antibacterial applications. The influence of EPD parameters (voltage and deposition time) and relative concentrations of chitosan, h-BN and TiO2 in suspension on deposition yield was studied. The composition and structure of deposited coatings were investigated by FTIR, XRD and SEM. It was observed that h-BN and TiO2 particles were dispersed in the chitosan matrix through simultaneous deposition. The adhesion between the electrophoretic coatings and the stainless steel substrates was tested by using tape test technique, and the results showed that the adhesion strength corresponded to 3B and 4B classes. Corrosion resistance was evaluated by electrochemical polarization curves, indicating enhanced corrosion resistance of the chitosan/h-BN/TiO2 and chitosan/h-BN coatings compared to the bare stainless steel substrate. In order to investigate the in-vitro inorganic bioactivity, coatings were immersed in simulated body fluid (SBF) for 28 days. FTIR and XRD results showed no formation of hydroxyapatite on the surface of chitosan/h-BN/TiO2 and chitosan/h-BN coatings, which are therefore non bioactive but potentially useful as antibacterial coatings. Full article
(This article belongs to the Special Issue Nanocomposites of Polymers and Inorganic Particles 2013)
Open AccessArticle A New Epoxy-Based Layered Silicate Nanocomposite Using a Hyperbranched Polymer: Study of the Curing Reaction and Nanostructure Development
Materials 2014, 7(3), 1830-1849; doi:10.3390/ma7031830
Received: 28 November 2013 / Revised: 14 February 2014 / Accepted: 17 February 2014 / Published: 4 March 2014
Cited by 9 | PDF Full-text (1932 KB) | HTML Full-text | XML Full-text
Abstract
Polymer layered silicate (PLS) nanocomposites have been prepared with diglycidyl ether of bisphenol-A (DGEBA) epoxy resin as the matrix and organically modified montmorillonite (MMT) as the clay nanofiller. Resin-clay mixtures with different clay contents (zero, two, five and 10 wt%) were cured, both
[...] Read more.
Polymer layered silicate (PLS) nanocomposites have been prepared with diglycidyl ether of bisphenol-A (DGEBA) epoxy resin as the matrix and organically modified montmorillonite (MMT) as the clay nanofiller. Resin-clay mixtures with different clay contents (zero, two, five and 10 wt%) were cured, both isothermally and non-isothermally, using a poly(ethyleneimine) hyperbranched polymer (HBP), the cure kinetics being monitored by differential scanning calorimetry (DSC). The nanostructure of the cured nanocomposites was characterized by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), and their mechanical properties were determined by dynamic mechanical analysis (DMA) and impact testing. The results are compared with an earlier study of the structure and properties of the same DGEBA-MMT system cured with a polyoxypropylene diamine, Jeffamine. There are very few examples of the use of HBP as a curing agent in epoxy PLS nanocomposites; here, it is found to enhance significantly the degree of exfoliation of these nanocomposites compared with those cured with Jeffamine, with a corresponding enhancement in the impact energy for nanocomposites with the low clay content of 2 wt%. These changes are attributed to the different cure kinetics with the HBP, in which the intra-gallery homopolymerization reaction is accelerated, such that it occurs before the bulk cross-linking reaction. Full article
(This article belongs to the Special Issue Nanocomposites of Polymers and Inorganic Particles 2013)
Open AccessArticle Simulation of Waveforms of a Ferrite Inductor with Saturation and Power Losses
Materials 2014, 7(3), 1850-1865; doi:10.3390/ma7031850
Received: 3 December 2013 / Revised: 14 February 2014 / Accepted: 24 February 2014 / Published: 4 March 2014
PDF Full-text (1312 KB) | HTML Full-text | XML Full-text
Abstract
We propose a model of an equivalent electrical circuit specifically designed for a ferrite inductor excited by a sinusoidal waveform. The purpose of this model is its use in a circuit simulator. We calculate the model parameters by means of Finite Elements in
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We propose a model of an equivalent electrical circuit specifically designed for a ferrite inductor excited by a sinusoidal waveform. The purpose of this model is its use in a circuit simulator. We calculate the model parameters by means of Finite Elements in 2D which leads to significant computational advantages over the 3D model. We carry out the validation for a toroidal ferrite inductor by comparing the experimental results and computed ones. We consider the saturation and power losses in the core. In addition, we have tested the model for the case of square waveform in order to generalize the results. We find excellent agreement between the experimental data and the results obtained by numerical calculations. Full article
Open AccessArticle Surface Characterization of Retrieved Metal-on-Metal Total Hip Implants from Patients with Adverse Reaction to Metal Debris
Materials 2014, 7(3), 1866-1879; doi:10.3390/ma7031866
Received: 29 December 2013 / Revised: 20 February 2014 / Accepted: 25 February 2014 / Published: 4 March 2014
Cited by 3 | PDF Full-text (1124 KB) | HTML Full-text | XML Full-text
Abstract
The use of metal-on-metal (MoM) total hip implants has decreased recently due to reports of high failure rates and adverse local tissue reaction (ALTR). It has been hypothesized that wear metal debris released from CoCr bearing surfaces may provoke delayed hypersensitivity reactions. The
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The use of metal-on-metal (MoM) total hip implants has decreased recently due to reports of high failure rates and adverse local tissue reaction (ALTR). It has been hypothesized that wear metal debris released from CoCr bearing surfaces may provoke delayed hypersensitivity reactions. The goal of this study is to evaluate the microscopic bearing surface characteristics of implants revised due to evidence of ALTR. The bearing surface of each head and cup was analyzed using multiple microscopy techniques for characterization of the surface features. The presence of severe mechanical scratching was a common characteristic found in all of the implants evaluated. Mechanical factors seemed to be the prevalent failure mode related to the appearance of ALTR with this particular set of retrieved implants. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle Sorptive Uptake Studies of an Aryl-Arsenical with Iron Oxide Composites on an Activated Carbon Support
Materials 2014, 7(3), 1880-1898; doi:10.3390/ma7031880
Received: 25 December 2013 / Revised: 30 January 2014 / Accepted: 25 February 2014 / Published: 5 March 2014
Cited by 10 | PDF Full-text (519 KB) | HTML Full-text | XML Full-text
Abstract
Sorption uptake kinetics and equilibrium studies for 4-hydroxy-3-nitrobenzene arsonic acid (roxarsone) was evaluated with synthetic magnetite (Mag-P), commercial magnetite (Mag-C), magnetite 10%, 19%, and 32% composite material (CM-10, -19, -32) that contains granular activated carbon (GAC), and synthetic goethite at pH 7.00 in
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Sorption uptake kinetics and equilibrium studies for 4-hydroxy-3-nitrobenzene arsonic acid (roxarsone) was evaluated with synthetic magnetite (Mag-P), commercial magnetite (Mag-C), magnetite 10%, 19%, and 32% composite material (CM-10, -19, -32) that contains granular activated carbon (GAC), and synthetic goethite at pH 7.00 in water at 21 °C for 24 h. GAC showed the highest sorptive removal of roxarsone and the relative uptake for each sorbent material with roxarsone are listed in descending order as follows: GAC (471 mg/g) > goethite (418 mg/g) > CM-10 (377 mg/g) CM-19 (254 mg/g) > CM-32 (227 mg/g) > Mag-P (132 mg/g) > Mag-C (29.5 mg/g). The As (V) moiety of roxarsone is adsorbed onto the surface of the iron oxide/oxyhydrate and is inferred as inner-sphere surface complexes; monodentate-mononuclear, bidentate-mononuclear, and bidentate-binuclear depending on the protolytic speciation of roxarsone. The phenyl ring of roxarsone provides the primary driving force for the sorptive interaction with the graphene surface of GAC and its composites. Thus, magnetite composites are proposed as multi-purpose adsorbents for the co-removal of inorganic and organic arsenicals due to the presence of graphenic and iron oxide active adsorption sites. Full article
(This article belongs to the Section Advanced Composites)
Open AccessArticle Nanocomposites Polarizing by Absorption: Dichroism in the Near-Infrared Region (NIR)
Materials 2014, 7(3), 1899-1911; doi:10.3390/ma7031899
Received: 15 January 2014 / Revised: 21 February 2014 / Accepted: 25 February 2014 / Published: 5 March 2014
Cited by 1 | PDF Full-text (538 KB) | HTML Full-text | XML Full-text
Abstract
We describe the preparation of nanocomposites which exhibit dichroism in the near infrared region (NIR). These materials consist of crosslinked poly(dimethylsiloxane) (PDMS) and gold nanoparticles, coated with 1-dodecanethiol or tert-tetradecanethiol. The alkanethiols improve dispersibility of the gold particles, and accordingly composites were
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We describe the preparation of nanocomposites which exhibit dichroism in the near infrared region (NIR). These materials consist of crosslinked poly(dimethylsiloxane) (PDMS) and gold nanoparticles, coated with 1-dodecanethiol or tert-tetradecanethiol. The alkanethiols improve dispersibility of the gold particles, and accordingly composites were manufactured by diffusion of the particles into swollen self-supporting PDMS elastomer films. After drying, the films were exposed to solvents for one minute, stretched in wet state, dried again and annealed. This procedure led to formation of oriented linear gold particle assemblies within stretched polymer. If the aspect ratio of the particle assemblies is high, the absorption of polarized light in the NIR region is expected to depend on the angle between the polarization plane and the orientation direction of the particle assemblies, and this was observed to be the case. Full article
(This article belongs to the Special Issue Nanocomposites of Polymers and Inorganic Particles 2013)
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Open AccessArticle Transformation-Induced Relaxation and Stress Recovery of TiNi Shape Memory Alloy
Materials 2014, 7(3), 1912-1926; doi:10.3390/ma7031912
Received: 4 December 2013 / Revised: 15 January 2014 / Accepted: 24 February 2014 / Published: 6 March 2014
Cited by 3 | PDF Full-text (1283 KB) | HTML Full-text | XML Full-text
Abstract
The transformation-induced stress relaxation and stress recovery of TiNi shape memory alloy (SMA) in stress-controlled subloop loading were investigated based on the local variation in temperature and transformation band on the surface of the tape in the tension test. The results obtained are
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The transformation-induced stress relaxation and stress recovery of TiNi shape memory alloy (SMA) in stress-controlled subloop loading were investigated based on the local variation in temperature and transformation band on the surface of the tape in the tension test. The results obtained are summarized as follows. (1) In the loading process, temperature increases due to the exothermic martensitic transformation (MT) until the holding strain and thereafter temperature decreases while holding the strain constant, resulting in stress relaxation due to the MT; (2) In the unloading process, temperature decreases due to the endothermic reverse transformation until the holding strain and thereafter temperature increases while holding the strain constant, resulting in stress recovery due to the reverse transformation; (3) Stress varies markedly in the initial stage followed by gradual change while holding the strain constant; (4) If the stress rate is high until the holding strain in the loading and unloading processes, both stress relaxation and stress recovery are large; (5) It is important to take into account this behavior in the design of SMA elements, since the force of SMA elements varies even if the atmospheric temperature is kept constant. Full article
(This article belongs to the Special Issue Shape Memory Materials)
Open AccessArticle In vitro and in vivo Biocompatibility of Alginate Dialdehyde/Gelatin Hydrogels with and without Nanoscaled Bioactive Glass for Bone Tissue Engineering Applications
Materials 2014, 7(3), 1957-1974; doi:10.3390/ma7031957
Received: 23 December 2013 / Revised: 9 February 2014 / Accepted: 26 February 2014 / Published: 6 March 2014
Cited by 12 | PDF Full-text (1507 KB) | HTML Full-text | XML Full-text
Abstract
In addition to good mechanical properties needed for three-dimensional tissue engineering, the combination of alginate dialdehyde, gelatin and nano-scaled bioactive glass (45S5) is supposed to combine excellent cellular adhesion, proliferation and differentiation properties, good biocompatibility and predictable degradation rates. The goal of this
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In addition to good mechanical properties needed for three-dimensional tissue engineering, the combination of alginate dialdehyde, gelatin and nano-scaled bioactive glass (45S5) is supposed to combine excellent cellular adhesion, proliferation and differentiation properties, good biocompatibility and predictable degradation rates. The goal of this study was to evaluate the in vitro and in vivo biocompatibility as a first step on the way to its use as a scaffold in bone tissue engineering. In vitro evaluation showed good cell adherence and proliferation of bone marrow derived mesenchymal stem cells seeded on covalently crosslinked alginate dialdehyde-gelatin (ADA-GEL) hydrogel films with and without 0.1% nano-Bioglass® (nBG). Lactate dehydrogenase (LDH)- and mitochondrial activity significantly increased in both ADA-GEL and ADA-GEL-nBG groups compared to alginate. However, addition of 0.1% nBG seemed to have slight cytotoxic effect compared to ADA-GEL. In vivo implantation did not produce a significant inflammatory reaction, and ongoing degradation could be seen after four weeks. Ongoing vascularization was detected after four weeks. The good biocompatibility encourages future studies using ADA-GEL and nBG for bone tissue engineering application. Full article
(This article belongs to the Special Issue Biocompatibility of Materials 2013)
Open AccessArticle All-Carbon Electrode Consisting of Carbon Nanotubes on Graphite Foil for Flexible Electrochemical Applications
Materials 2014, 7(3), 1975-1983; doi:10.3390/ma7031975
Received: 27 January 2014 / Revised: 28 February 2014 / Accepted: 3 March 2014 / Published: 7 March 2014
Cited by 1 | PDF Full-text (833 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We demonstrate the fabrication of an all-carbon electrode by plasma-enhanced chemical vapor deposition for use in flexible electrochemical applications. The electrode is composed of vertically aligned carbon nanotubes that are grown directly on a flexible graphite foil. Being all-carbon, the simple fabrication process
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We demonstrate the fabrication of an all-carbon electrode by plasma-enhanced chemical vapor deposition for use in flexible electrochemical applications. The electrode is composed of vertically aligned carbon nanotubes that are grown directly on a flexible graphite foil. Being all-carbon, the simple fabrication process and the excellent electrochemical characteristics present an approach through which high-performance, highly-stable and cost-effective electrochemical applications can be achieved. Full article
(This article belongs to the Section Biomaterials)
Open AccessArticle Synthesis and Characterization of Superconducting Ca1xNaxFFeAs
Materials 2014, 7(3), 1984-1994; doi:10.3390/ma7031984
Received: 14 January 2014 / Revised: 15 February 2014 / Accepted: 25 February 2014 / Published: 7 March 2014
Cited by 2 | PDF Full-text (1317 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A representative of the fluoride-containing iron pnictide high-temperature superconductors, namely CaFFeAs, was doped with sodium up to the composition Ca0.86Na0.14FFeAs for the first time. Single crystals with an edge length in the range of 0.1 – 2.0 mm were
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A representative of the fluoride-containing iron pnictide high-temperature superconductors, namely CaFFeAs, was doped with sodium up to the composition Ca0.86Na0.14FFeAs for the first time. Single crystals with an edge length in the range of 0.1 – 2.0 mm were obtained via solid-state and flux syntheses, respectively. The composition of the crystals was verified by means of single crystal X-ray diffractometry and energy dispersive X-ray spectroscopy (EDX). Measurements of the electrical resistivity, as well as the magnetization on a crystal of Ca0.89Na0.11FFeAs both show a transition to the superconducting state on cooling to 34.5 K. Investigations of the upper critical fields reveal an anisotropy ratio of about five. The lattice parameters and molar volumes increase with rising sodium content. This effect is clearly observable for the c-axis and the volume, whereas the increase of the a-axis is rather minor. Full article
(This article belongs to the Section Structure Analysis and Characterization)
Open AccessArticle Metallocene Based Polyolefin Nanocomposites
Materials 2014, 7(3), 1995-2013; doi:10.3390/ma7031995
Received: 25 November 2013 / Revised: 12 February 2014 / Accepted: 14 February 2014 / Published: 10 March 2014
Cited by 8 | PDF Full-text (1016 KB) | HTML Full-text | XML Full-text
Abstract
One of the most efficient and versatile ways to synthesize polyolefin nanocomposites is the in-situ polymerization of olefins in the presence of nano particles by metallocene catalysts. Metallocene/methylaluminoxane (MAO) catalysts are soluble in hydrocarbons and therefore they can be absorbed perfectly in solution
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One of the most efficient and versatile ways to synthesize polyolefin nanocomposites is the in-situ polymerization of olefins in the presence of nano particles by metallocene catalysts. Metallocene/methylaluminoxane (MAO) catalysts are soluble in hydrocarbons and therefore they can be absorbed perfectly in solution onto the surface of particles or fibers and after addition of ethene or propene they can then catalyze a polyolefin film on the surface. Metallocene/MAO and other single site catalysts allow the synthesis of polymers with a precisely defined microstructure, tacticity, and stereoregularity as well as new copolymers with superior properties such as film clarity, high tensile strength and lower content of extractables. The polymer properties can be enlarged by the incorporation of nanofillers. The resulting polyethylene or polypropylene nanocomposites give a tremendous boost to the physical and chemical properties such as dramatically improved stiffness, high gas barrier properties, significant flame retardancy, and high crystallization rates. Full article
(This article belongs to the Special Issue Nanocomposites of Polymers and Inorganic Particles 2013)
Open AccessArticle Formation of Nanocones on Highly Oriented Pyrolytic Graphite by Oxygen Plasma
Materials 2014, 7(3), 2014-2029; doi:10.3390/ma7032014
Received: 14 January 2014 / Revised: 28 February 2014 / Accepted: 3 March 2014 / Published: 11 March 2014
Cited by 5 | PDF Full-text (1254 KB) | HTML Full-text | XML Full-text
Abstract
Improvement in hemocompatibility of highly oriented pyrolytic graphite (HOPG) by formation of nanostructured surface by oxygen plasma treatment is reported. We have showed that by appropriate fine tuning of plasma and discharge parameters we are able to create nanostructured surface which is densely
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Improvement in hemocompatibility of highly oriented pyrolytic graphite (HOPG) by formation of nanostructured surface by oxygen plasma treatment is reported. We have showed that by appropriate fine tuning of plasma and discharge parameters we are able to create nanostructured surface which is densely covered with nanocones. The size of the nanocones strongly depended on treatment time. The optimal results in terms of material hemocompatibility were obtained after treatment with oxygen plasma for 15 s, when both the nanotopography and wettability were the most favorable, since marked reduction in adhesion and activation of platelets was observed on this surface. At prolonged treatment times, the rich surface topography was lost and thus also its antithrombogenic properties. Chemical composition of the surface was always more or less the same, regardless of its morphology and height of the nanocones. Namely, on all plasma treated samples, only a few atomic percent of oxygen was found, meaning that plasma caused mostly etching, leading to changes in the surface morphology. This indicates that the main preventing mechanism against platelets adhesion was the right surface morphology. Full article
(This article belongs to the Section Biomaterials)
Open AccessArticle Preparation and Chemical Properties of π-Conjugated Polymers Containing Indigo Unit in the Main Chain
Materials 2014, 7(3), 2030-2043; doi:10.3390/ma7032030
Received: 19 January 2014 / Revised: 21 February 2014 / Accepted: 26 February 2014 / Published: 11 March 2014
Cited by 4 | PDF Full-text (684 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
π-Conjugated polymers based on indigo unit were prepared. Dehalogenative polycondensation of N-hexyl-6,6'-dibromoindigo with a zerovalent nickel complex gave a homopolymer, P(HexI), in 77% yield. Copolymer of N-hexyl-indigo and pyridine, P(HexI-Py), was also prepared in 50% yield. P(HexI) showed good
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π-Conjugated polymers based on indigo unit were prepared. Dehalogenative polycondensation of N-hexyl-6,6'-dibromoindigo with a zerovalent nickel complex gave a homopolymer, P(HexI), in 77% yield. Copolymer of N-hexyl-indigo and pyridine, P(HexI-Py), was also prepared in 50% yield. P(HexI) showed good solubility in organic solvents, whereas P(HexI-Py) was only soluble in acids such as HCOOH. The weight-average molecular weights (Mw) of P(HexI) and P(HexI-Py) were determined to be 10,000 and 40,000, respectively, by a light scattering method. Pd-catalyzed polycondensation between 6,6'-dibromoindigo with N-BOC (BOC = t-butoxycarbonyl) substituents and a diboronic compound of 9,9-dioctylfluorene afforded the corresponding alternating copolymer, P(BOCI-Flu), as a deep red solid in 98% yield. P(BOCI-Flu) was soluble in N-methyl-2-pyrroridone and showed an Mw of 29,000 in GPC analysis. Treatment of P(BOCI-Flu) with CF3COOH smoothly led to a BOC-deprotection reaction to give an insoluble deep green polymer, P(I-Flu), in a quantitative yield. Diffuse reflectance spectra of powdery P(BOCI-Flu) and P(I-Flu) showed peaks at about 580 nm and 630 nm, respectively, which are thought to originate from the indigo unit. Full article
(This article belongs to the Special Issue Conjugated Polymers)
Open AccessArticle Low Concentration Fe-Doped Alumina Catalysts Using Sol-Gel and Impregnation Methods: The Synthesis, Characterization and Catalytic Performance during the Combustion of Trichloroethylene
Materials 2014, 7(3), 2062-2086; doi:10.3390/ma7032062
Received: 3 February 2014 / Revised: 26 February 2014 / Accepted: 4 March 2014 / Published: 12 March 2014
Cited by 5 | PDF Full-text (926 KB) | HTML Full-text | XML Full-text
Abstract
The role of iron in two modes of integration into alumina catalysts was studied at 0.39 wt% Fe and tested in trichloroethylene combustion. One modified alumina was synthesized using the sol-gel method with Fe added in situ during hydrolysis; another modification was performed
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The role of iron in two modes of integration into alumina catalysts was studied at 0.39 wt% Fe and tested in trichloroethylene combustion. One modified alumina was synthesized using the sol-gel method with Fe added in situ during hydrolysis; another modification was performed using calcined alumina, prepared using the sol-gel method and impregnated with Fe. Several characterization techniques were used to study the level of Fe modification in the γ-Al2O3 phase formed and to correlate the catalytic properties during trichloroethylene (TCE) combustion. The introduction of Fe in situ during the sol-gel process influenced the crystallite size, and three iron species were generated, namely, magnetite, maghemite and hematite. The impregnated Fe-alumina formed hematite and maghemite, which were highly dispersed on the γ-Al2O3 surface. The X-ray photoelectron spectra (XPS), FT-IR and Mössbauer spectroscopy analyses revealed how Fe interacted with the γ-Al2O3 lattice in both catalysts. The impregnated Fe-catalyst showed the best catalytic performance compared to the catalyst that was Fe-doped in situ by the sol-gel method; both had better catalytic activity than pure alumina. This difference in activity was correlated with the accessibility of the reactants to the hematite iron species on the surface. The chlorine poisoning for all three catalysts was less than 1.8%. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle A Technology Platform to Test the Efficacy of Purification of Alginate
Materials 2014, 7(3), 2087-2103; doi:10.3390/ma7032087
Received: 10 January 2014 / Revised: 12 February 2014 / Accepted: 5 March 2014 / Published: 12 March 2014
Cited by 8 | PDF Full-text (1015 KB) | HTML Full-text | XML Full-text
Abstract
Alginates are widely used in tissue engineering technologies, e.g., in cell encapsulation, in drug delivery and various immobilization procedures. The success rates of these studies are highly variable due to different degrees of tissue response. A cause for this variation in success is,
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Alginates are widely used in tissue engineering technologies, e.g., in cell encapsulation, in drug delivery and various immobilization procedures. The success rates of these studies are highly variable due to different degrees of tissue response. A cause for this variation in success is, among other factors, its content of inflammatory components. There is an urgent need for a technology to test the inflammatory capacity of alginates. Recently, it has been shown that pathogen-associated molecular patterns (PAMPs) in alginate are potent immunostimulatories. In this article, we present the design and evaluation of a technology platform to assess (i) the immunostimulatory capacity of alginate or its contaminants, (ii) where in the purification process PAMPs are removed, and (iii) which Toll-like receptors (TLRs) and ligands are involved. A THP1 cell-line expressing pattern recognition receptors (PRRs) and the co-signaling molecules CD14 and MD2 was used to assess immune activation of alginates during the different steps of purification of alginate. To determine if this activation was mediated by TLRs, a THP1-defMyD88 cell-line was applied. This cell-line possesses a non-functional MyD88 coupling protein, necessary for activating NF-κB via TLRs. To identify the specific TLRs being activated by the PAMPs, we use different human embryonic kidney (HEK) cell-line that expresses only one specific TLR. Finally, specific enzyme-linked immunosorbent assays (ELISAs) were applied to identify the specific PAMP. By applying this three-step procedure, we can screen alginate in a manner, which is both labor and cost efficient. The efficacy of the platform was evaluated with an alginate that did not pass our quality control. We demonstrate that this alginate was immunostimulatory, even after purification due to reintroduction of the TLR5 activating flagellin. In addition, we tested two commercially available purified alginates. Our experiments show that these commercial alginates contained peptidoglycan, lipoteichoic acid, flagellin, and even lipopolysaccharides (LPS). The platform presented here can be used to evaluate the efficacy of purification procedures in removing PAMPs from alginates in a cost-efficient manner. Full article
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Open AccessArticle Cartilage Tissue Engineering with Silk Fibroin Scaffolds Fabricated by Indirect Additive Manufacturing Technology
Materials 2014, 7(3), 2104-2119; doi:10.3390/ma7032104
Received: 30 September 2013 / Revised: 27 February 2014 / Accepted: 10 March 2014 / Published: 13 March 2014
Cited by 13 | PDF Full-text (673 KB) | HTML Full-text | XML Full-text
Abstract
Advanced tissue engineering (TE) technology based on additive manufacturing (AM) can fabricate scaffolds with a three-dimensional (3D) environment suitable for cartilage regeneration. Specifically, AM technology may allow the incorporation of complex architectural features. The present study involves the fabrication of 3D TE scaffolds
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Advanced tissue engineering (TE) technology based on additive manufacturing (AM) can fabricate scaffolds with a three-dimensional (3D) environment suitable for cartilage regeneration. Specifically, AM technology may allow the incorporation of complex architectural features. The present study involves the fabrication of 3D TE scaffolds by an indirect AM approach using silk fibroin (SF). From scanning electron microscopic observations, the presence of micro-pores and interconnected channels within the scaffold could be verified, resulting in a TE scaffold with both micro- and macro-structural features. The intrinsic properties, such as the chemical structure and thermal characteristics of SF, were preserved after the indirect AM manufacturing process. In vitro cell culture within the SF scaffold using porcine articular chondrocytes showed a steady increase in cell numbers up to Day 14. The specific production (per cell basis) of the cartilage-specific extracellular matrix component (collagen Type II) was enhanced with culture time up to 12 weeks, indicating the re-differentiation of chondrocytes within the scaffold. Subcutaneous implantation of the scaffold-chondrocyte constructs in nude mice also confirmed the formation of ectopic cartilage by histological examination and immunostaining. Full article
(This article belongs to the Section Biomaterials)
Open AccessArticle Selective Interaction of a Cationic Polyfluorene with Model Lipid Membranes: Anionic versus Zwitterionic Lipids
Materials 2014, 7(3), 2120-2140; doi:10.3390/ma7032120
Received: 2 January 2014 / Revised: 19 February 2014 / Accepted: 4 March 2014 / Published: 13 March 2014
Cited by 5 | PDF Full-text (1036 KB) | HTML Full-text | XML Full-text
Abstract
This paper explores the interaction mechanism between the conjugated polyelectrolyte {[9,9-bis(6'-N,N,N-trimethylammonium)hexyl]fluorene-phenylene}bromide (HTMA-PFP) and model lipid membranes. The study was carried out using different biophysical techniques, mainly fluorescence spectroscopy and microscopy. Results show that despite the preferential interaction of HTMA-PFP with anionic lipids, HTMA-PFP
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This paper explores the interaction mechanism between the conjugated polyelectrolyte {[9,9-bis(6'-N,N,N-trimethylammonium)hexyl]fluorene-phenylene}bromide (HTMA-PFP) and model lipid membranes. The study was carried out using different biophysical techniques, mainly fluorescence spectroscopy and microscopy. Results show that despite the preferential interaction of HTMA-PFP with anionic lipids, HTMA-PFP shows affinity for zwitterionic lipids; although the interaction mechanism is different as well as HTMA-PFP’s final membrane location. Whilst the polyelectrolyte is embedded within the lipid bilayer in the anionic membrane, it remains close to the surface, forming aggregates that are sensitive to the physical state of the lipid bilayer in the zwitterionic system. The different interaction mechanism is reflected in the polyelectrolyte fluorescence spectrum, since the maximum shifts to longer wavelengths in the zwitterionic system. The intrinsic fluorescence of HTMA-PFP was used to visualize the interaction between polymer and vesicles via fluorescence microscopy, thanks to its high quantum yield and photostability. This technique allows the selectivity of the polyelectrolyte and higher affinity for anionic membranes to be observed. The results confirmed the appropriateness of using HTMA-PFP as a membrane fluorescent marker and suggest that, given its different behaviour towards anionic and zwitterionic membranes, HTMA-PFP could be used for selective recognition and imaging of bacteria over mammalian cells. Full article
(This article belongs to the Special Issue Conjugated Polymers)
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Open AccessArticle Self-Healing Capability of Fiber-Reinforced Cementitious Composites for Recovery of Watertightness and Mechanical Properties
Materials 2014, 7(3), 2141-2154; doi:10.3390/ma7032141
Received: 30 November 2013 / Revised: 28 February 2014 / Accepted: 10 March 2014 / Published: 13 March 2014
Cited by 7 | PDF Full-text (1148 KB) | HTML Full-text | XML Full-text
Abstract
Various types of fiber reinforced cementitious composites (FRCCs) were experimentally studied to evaluate their self-healing capabilities regarding their watertightness and mechanical properties. Cracks were induced in the FRCC specimens during a tensile loading test, and the specimens were then immersed in static water
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Various types of fiber reinforced cementitious composites (FRCCs) were experimentally studied to evaluate their self-healing capabilities regarding their watertightness and mechanical properties. Cracks were induced in the FRCC specimens during a tensile loading test, and the specimens were then immersed in static water for self-healing. By water permeability and reloading tests, it was determined that the FRCCs containing synthetic fiber and cracks of width within a certain range (<0.1 mm) exhibited good self-healing capabilities regarding their watertightness. Particularly, the high polarity of the synthetic fiber (polyvinyl alcohol (PVA)) series and hybrid fiber reinforcing (polyethylene (PE) and steel code (SC)) series showed high recovery ratio. Moreover, these series also showed high potential of self-healing of mechanical properties. It was confirmed that recovery of mechanical property could be obtained only in case when crack width was sufficiently narrow, both the visible surface cracks and the very fine cracks around the bridging of the SC fibers. Recovery of the bond strength by filling of the very fine cracks around the bridging fibers enhanced the recovery of the mechanical property. Full article
(This article belongs to the Special Issue Self-healing Concrete)
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Open AccessArticle In Vitro Cytotoxicity of a Ti-35Nb-7Zr-5Ta Alloy Doped with Different Oxygen Contents
Materials 2014, 7(3), 2183-2193; doi:10.3390/ma7032183
Received: 31 October 2013 / Revised: 21 January 2014 / Accepted: 21 January 2014 / Published: 13 March 2014
PDF Full-text (744 KB) | HTML Full-text | XML Full-text
Abstract
Cp-Ti is the most common material used for dental implants, but its elastic modulus is around five times higher than that of bone. Recently, promising alloys that add Nb, Ta, Zr and Mo to Ti have been developed. The mechanical properties of these
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Cp-Ti is the most common material used for dental implants, but its elastic modulus is around five times higher than that of bone. Recently, promising alloys that add Nb, Ta, Zr and Mo to Ti have been developed. The mechanical properties of these alloys are directly related to its microstructure and the presence of interstitial elements, such as oxygen, carbon, nitrogen and hydrogen. In this study, the in vitro cytotoxicity of Ti-35Nb-7Zr-5Ta (TNZT) alloys was analyzed in the as-received condition and after being doped with several small quantities of oxygen on a cultured osteogenic cell. The cell’s morphology was also examined by scanning electron microscopy (SEM). The TNZT alloy presented no cytotoxic effects on osteoblastic cells in the studied conditions. Full article
(This article belongs to the Special Issue Titanium Materials for Biomedical Application 2013)
Open AccessArticle A Model for Creep and Creep Damage in the γ-Titanium Aluminide Ti-45Al-2Mn-2Nb
Materials 2014, 7(3), 2194-2209; doi:10.3390/ma7032194
Received: 6 January 2014 / Revised: 24 February 2014 / Accepted: 3 March 2014 / Published: 14 March 2014
Cited by 3 | PDF Full-text (1107 KB) | HTML Full-text | XML Full-text
Abstract
Gamma titanium aluminides (γ-TiAl) display significantly improved high temperature mechanical properties over conventional titanium alloys. Due to their low densities, these alloys are increasingly becoming strong candidates to replace nickel-base superalloys in future gas turbine aeroengine components. To determine the safe operating life
[...] Read more.
Gamma titanium aluminides (γ-TiAl) display significantly improved high temperature mechanical properties over conventional titanium alloys. Due to their low densities, these alloys are increasingly becoming strong candidates to replace nickel-base superalloys in future gas turbine aeroengine components. To determine the safe operating life of such components, a good understanding of their creep properties is essential. Of particular importance to gas turbine component design is the ability to accurately predict the rate of accumulation of creep strain to ensure that excessive deformation does not occur during the component’s service life and to quantify the effects of creep on fatigue life. The theta (θ) projection technique is an illustrative example of a creep curve method which has, in this paper, been utilised to accurately represent the creep behaviour of the γ-TiAl alloy Ti -45Al-2Mn-2Nb. Furthermore, a continuum damage approach based on the θ-projection method has also been used to represent tertiary creep damage and accurately predict creep rupture. Full article
Open AccessArticle Cathodic Polarization Coats Titanium Based Implant Materials with Enamel Matrix Derivate (EMD)
Materials 2014, 7(3), 2210-2228; doi:10.3390/ma7032210
Received: 29 January 2014 / Revised: 5 March 2014 / Accepted: 10 March 2014 / Published: 14 March 2014
Cited by 3 | PDF Full-text (912 KB) | HTML Full-text | XML Full-text
Abstract
The idea of a bioactive surface coating that enhances bone healing and bone growth is a strong focus of on-going research for bone implant materials. Enamel matrix derivate (EMD) is well documented to support bone regeneration and activates growth of mesenchymal tissues. Thus,
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The idea of a bioactive surface coating that enhances bone healing and bone growth is a strong focus of on-going research for bone implant materials. Enamel matrix derivate (EMD) is well documented to support bone regeneration and activates growth of mesenchymal tissues. Thus, it is a prime candidate for coating of existing implant surfaces. The aim of this study was to show that cathodic polarization can be used for coating commercially available implant surfaces with an immobilized but functional and bio-available surface layer of EMD. After coating, XPS revealed EMD-related bindings on the surface while SIMS showed incorporation of EMD into the surface. The hydride layer of the original surface could be activated for coating in an integrated one-step process that did not require any pre-treatment of the surface. SEM images showed nano-spheres and nano-rods on coated surfaces that were EMD-related. Moreover, the surface roughness remained unchanged after coating, as it was shown by optical profilometry. The mass peaks observed in the matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF MS) analysis confirmed the integrity of EMD after coating. Assessment of the bioavailability suggested that the modified surfaces were active for osteoblast like MC3M3-E1 cells in showing enhanced Coll-1 gene expression and ALP activity. Full article
(This article belongs to the Section Biomaterials)
Open AccessArticle Passive Temperature Stabilization of Silicon Photonic Devices Using Liquid Crystals
Materials 2014, 7(3), 2229-2241; doi:10.3390/ma7032229
Received: 7 February 2014 / Revised: 1 March 2014 / Accepted: 6 March 2014 / Published: 14 March 2014
Cited by 9 | PDF Full-text (779 KB) | HTML Full-text | XML Full-text
Abstract
In this work we explore the negative thermo-optic properties of liquid crystal claddings for passive temperature stabilization of silicon photonic integrated circuits. Photonic circuits are playing an increasing role in communications and computing, but they suffer from temperature dependent performance variation. Most existing
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In this work we explore the negative thermo-optic properties of liquid crystal claddings for passive temperature stabilization of silicon photonic integrated circuits. Photonic circuits are playing an increasing role in communications and computing, but they suffer from temperature dependent performance variation. Most existing techniques aimed at compensation of thermal effects rely on power hungry Joule heating. We show that integrating a liquid crystal cladding helps to minimize the effects of a temperature dependent drift. The advantage of liquid crystals lies in their high negative thermo-optic coefficients in addition to low absorption at the infrared wavelengths. Full article
(This article belongs to the Special Issue Liquid Crystals) Print Edition available
Open AccessArticle Interaction of Heavy Metal Ions with Carbon and Iron Based Particles
Materials 2014, 7(3), 2242-2256; doi:10.3390/ma7032242
Received: 24 November 2013 / Revised: 6 January 2014 / Accepted: 18 February 2014 / Published: 18 March 2014
Cited by 4 | PDF Full-text (501 KB) | HTML Full-text | XML Full-text
Abstract
Due to the rapid development of industry and associated production of toxic waste, especially heavy metals, there is a great interest in creating and upgrading new sorption materials to remove these pollutants from the environment. This study aims to determine the effectiveness of
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Due to the rapid development of industry and associated production of toxic waste, especially heavy metals, there is a great interest in creating and upgrading new sorption materials to remove these pollutants from the environment. This study aims to determine the effectiveness of different carbon forms (graphene, expanded carbon, multi-wall nanotubes) and paramagnetic particles (Fe2O3) for adsorption of cadmium(II), lead(II), and copper(II) on its surface, with different interaction time from 1 min to 24 h. The main attention is paid to the detection of these metals using differential pulse voltammetry. Based on the obtained results, graphene and Fe2O3 are found to be good candidates for removal of heavy metals from the environment. Full article
Open AccessArticle Investigation of the Process Conditions for Hydrogen Production by Steam Reforming of Glycerol over Ni/Al2O3 Catalyst Using Response Surface Methodology (RSM)
Materials 2014, 7(3), 2257-2272; doi:10.3390/ma7032257
Received: 5 December 2013 / Revised: 27 February 2014 / Accepted: 7 March 2014 / Published: 19 March 2014
Cited by 2 | PDF Full-text (406 KB) | HTML Full-text | XML Full-text
Abstract
In this work; a response surface methodology (RSM) was implemented to investigate the process variables in a hydrogen production system. The effects of five independent variables; namely the temperature (X1); the flow rate (X2); the catalyst weight (X3
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In this work; a response surface methodology (RSM) was implemented to investigate the process variables in a hydrogen production system. The effects of five independent variables; namely the temperature (X1); the flow rate (X2); the catalyst weight (X3); the catalyst loading (X4) and the glycerol-water molar ratio (X5) on the H2 yield (Y1) and the conversion of glycerol to gaseous products (Y2) were explored. Using multiple regression analysis; the experimental results of the H2 yield and the glycerol conversion to gases were fit to quadratic polynomial models. The proposed mathematical models have correlated the dependent factors well within the limits that were being examined. The best values of the process variables were a temperature of approximately 600 °C; a feed flow rate of 0.05 mL/min; a catalyst weight of 0.2 g; a catalyst loading of 20% and a glycerol-water molar ratio of approximately 12; where the H2 yield was predicted to be 57.6% and the conversion of glycerol was predicted to be 75%. To validate the proposed models; statistical analysis using a two-sample t-test was performed; and the results showed that the models could predict the responses satisfactorily within the limits of the variables that were studied. Full article
(This article belongs to the Section Materials for Energy Applications)
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Open AccessArticle Highly Dispersed Nickel-Containing Mesoporous Silica with Superior Stability in Carbon Dioxide Reforming of Methane: The Effect of Anchoring
Materials 2014, 7(3), 2340-2355; doi:10.3390/ma7032340
Received: 26 January 2014 / Revised: 12 March 2014 / Accepted: 12 March 2014 / Published: 19 March 2014
Cited by 10 | PDF Full-text (1362 KB) | HTML Full-text | XML Full-text
Abstract
A series of nickel-containing mesoporous silica samples (Ni-SiO2) with different nickel content (3.1%–13.2%) were synthesized by the evaporation-induced self-assembly method. Their catalytic activity was tested in carbon dioxide reforming of methane. The characterization results revealed that the catalysts, e.g., 6.7%Ni-SiO2
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A series of nickel-containing mesoporous silica samples (Ni-SiO2) with different nickel content (3.1%–13.2%) were synthesized by the evaporation-induced self-assembly method. Their catalytic activity was tested in carbon dioxide reforming of methane. The characterization results revealed that the catalysts, e.g., 6.7%Ni-SiO2, with highly dispersed small nickel particles, exhibited excellent catalytic activity and long-term stability. The metallic nickel particle size was significantly affected by the metal anchoring effect between metallic nickel particles and unreduced nickel ions in the silica matrix. A strong anchoring effect was suggested to account for the remaining of small Ni particle size and the improved catalytic performance. Full article
(This article belongs to the Special Issue Advances in Mesoporous Materials)
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Open AccessArticle Fabricating Nanoporous Silica Structure on D-Fibres through Room Temperature Self-Assembly
Materials 2014, 7(3), 2356-2369; doi:10.3390/ma7032356
Received: 19 February 2014 / Revised: 6 March 2014 / Accepted: 11 March 2014 / Published: 19 March 2014
Cited by 1 | PDF Full-text (722 KB) | HTML Full-text | XML Full-text
Abstract
The room temperature deposition of self-assembling silica nanoparticles onto D-shaped optical fibres (“D-fibre”), drawn from milled preforms fabricated by modified chemical vapour deposition (MCVD), is studied. Vertical dip-and-withdraw produces tapered layers, with one end thicker (surface coverage >0.85) than the other, whilst horizontal
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The room temperature deposition of self-assembling silica nanoparticles onto D-shaped optical fibres (“D-fibre”), drawn from milled preforms fabricated by modified chemical vapour deposition (MCVD), is studied. Vertical dip-and-withdraw produces tapered layers, with one end thicker (surface coverage >0.85) than the other, whilst horizontal dip-and-withdraw produces much more uniform layers over the core region. The propagation of induced fracturing over the core region during drying is overcome using a simple protrusion of the inner cladding. Thick coatings are discernible through thin film interference colouring, but thinner coatings require scanning electron microscopy (SEM) imaging. Here, we show that fluorescence imaging, using Rhodamine B, in this example, can provide some qualitative and speedy assessment of coverage. Full article
Open AccessArticle Electrical Characteristics of the Uniaxial-Strained nMOSFET with a Fluorinated HfO2/SiON Gate Stack
Materials 2014, 7(3), 2370-2381; doi:10.3390/ma7032370
Received: 3 January 2014 / Revised: 10 March 2014 / Accepted: 12 March 2014 / Published: 20 March 2014
Cited by 2 | PDF Full-text (398 KB) | HTML Full-text | XML Full-text
Abstract
The channel fluorine implantation (CFI) process was integrated with the Si3N4 contact etch stop layer (SiN CESL) uniaxial-strained n-channel metal-oxide-semiconductor field-effect transistor (nMOSFET) with the hafnium oxide/silicon oxynitride (HfO2/SiON) gate stack. The SiN CESL process clearly improves basic
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The channel fluorine implantation (CFI) process was integrated with the Si3N4 contact etch stop layer (SiN CESL) uniaxial-strained n-channel metal-oxide-semiconductor field-effect transistor (nMOSFET) with the hafnium oxide/silicon oxynitride (HfO2/SiON) gate stack. The SiN CESL process clearly improves basic electrical performance, due to induced uniaxial tensile strain within the channel. However, further integrating of the CFI process with the SiN CESL-strained nMOSFET exhibits nearly identical transconductance, subthreshold swing, drain current, gate leakage and breakdown voltage, which indicates that the strain effect is not affected by the fluorine incorporation. Moreover, hydrogen will diffuse toward the interface during the SiN deposition, then passivate dangling bonds to form weak Si-H bonds, which is detrimental for channel hot electron stress (CHES). Before hydrogen diffusion, fluorine can be used to terminate oxygen vacancies and dangling bonds, which can create stronger Hf-F and Si-F bonds to resist consequent stress. Accordingly, the reliability of constant voltage stress (CVS) and CHES for the SiN CESL uniaxial-strained nMOSFET can be further improved by the fluorinated HfO2/SiON using the CFI process. Nevertheless, the nMOSFET with either the SiN CESL or CFI process exhibits less charge detrapping, which means that a greater part of stress-induced charges would remain in the gate stack after nitrogen (SiN CESL) or fluorine (CFI) incorporation. Full article
(This article belongs to the Special Issue High-k Materials and Devices)
Open AccessArticle Tensile Properties and Fracture Behavior of Aluminum Alloy Foam Fabricated from Die Castings without Using Blowing Agent by Friction Stir Processing Route
Materials 2014, 7(3), 2382-2394; doi:10.3390/ma7032382
Received: 17 February 2014 / Revised: 11 March 2014 / Accepted: 13 March 2014 / Published: 21 March 2014
Cited by 3 | PDF Full-text (608 KB) | HTML Full-text | XML Full-text
Abstract
Al foam has been used in a wide range of applications owing to its light weight, high energy absorption and high sound insulation. One of the promising processes for fabricating Al foam involves the use of a foamable precursor. In this study, ADC12
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Al foam has been used in a wide range of applications owing to its light weight, high energy absorption and high sound insulation. One of the promising processes for fabricating Al foam involves the use of a foamable precursor. In this study, ADC12 Al foams with porosities of 67%–78% were fabricated from Al alloy die castings without using a blowing agent by the friction stir processing route. The pore structure and tensile properties of the ADC12 foams were investigated and compared with those of commercially available ALPORAS. From X-ray computed tomography (X-ray CT) observations of the pore structure of ADC12 foams, it was found that they have smaller pores with a narrower distribution than those in ALPORAS. Tensile tests on the ADC12 foams indicated that as their porosity increased, the tensile strength and tensile strain decreased, with strong relation between the porosity, tensile strength, and tensile strain. ADC12 foams exhibited brittle fracture, whereas ALPORAS exhibited ductile fracture, which is due to the nature of the Al alloy used as the base material of the foams. By image-based finite element (FE) analysis using X-ray CT images corresponding to the tensile tests on ADC12 foams, it was shown that the fracture path of ADC12 foams observed in tensile tests and the regions of high stress obtained from FE analysis correspond to each other. Therefore, it is considered that the fracture behavior of ADC12 foams in relation to their pore structure distribution can be investigated by image-based FE analysis. Full article
(This article belongs to the Special Issue Light Alloys and Their Applications)

Review

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Open AccessReview New Developments of Ti-Based Alloys for Biomedical Applications
Materials 2014, 7(3), 1709-1800; doi:10.3390/ma7031709
Received: 20 November 2013 / Revised: 24 December 2013 / Accepted: 24 January 2014 / Published: 4 March 2014
Cited by 61 | PDF Full-text (4511 KB) | HTML Full-text | XML Full-text
Abstract
Ti-based alloys are finding ever-increasing applications in biomaterials due to their excellent mechanical, physical and biological performance. Nowdays, low modulus β-type Ti-based alloys are still being developed. Meanwhile, porous Ti-based alloys are being developed as an alternative orthopedic implant material, as they can
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Ti-based alloys are finding ever-increasing applications in biomaterials due to their excellent mechanical, physical and biological performance. Nowdays, low modulus β-type Ti-based alloys are still being developed. Meanwhile, porous Ti-based alloys are being developed as an alternative orthopedic implant material, as they can provide good biological fixation through bone tissue ingrowth into the porous network. This paper focuses on recent developments of biomedical Ti-based alloys. It can be divided into four main sections. The first section focuses on the fundamental requirements titanium biomaterial should fulfill and its market and application prospects. This section is followed by discussing basic phases, alloying elements and mechanical properties of low modulus β-type Ti-based alloys. Thermal treatment, grain size, texture and properties in Ti-based alloys and their limitations are dicussed in the third section. Finally, the fourth section reviews the influence of microstructural configurations on mechanical properties of porous Ti-based alloys and all known methods for fabricating porous Ti-based alloys. This section also reviews prospects and challenges of porous Ti-based alloys, emphasizing their current status, future opportunities and obstacles for expanded applications. Overall, efforts have been made to reveal the latest scenario of bulk and porous Ti-based materials for biomedical applications. Full article
(This article belongs to the Special Issue Titanium Materials for Biomedical Application 2013)
Open AccessReview Advanced Ceramics from Preceramic Polymers Modified at the Nano-Scale: A Review
Materials 2014, 7(3), 1927-1956; doi:10.3390/ma7031927
Received: 13 December 2013 / Revised: 24 February 2014 / Accepted: 26 February 2014 / Published: 6 March 2014
Cited by 17 | PDF Full-text (1066 KB) | HTML Full-text | XML Full-text
Abstract
Preceramic polymers, i.e., polymers that are converted into ceramics upon heat treatment, have been successfully used for almost 40 years to give advanced ceramics, especially belonging to the ternary SiCO and SiCN systems or to the quaternary SiBCN system. One of their
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Preceramic polymers, i.e., polymers that are converted into ceramics upon heat treatment, have been successfully used for almost 40 years to give advanced ceramics, especially belonging to the ternary SiCO and SiCN systems or to the quaternary SiBCN system. One of their main advantages is the possibility of combining the shaping and synthesis of ceramics: components can be shaped at the precursor stage by conventional plastic-forming techniques, such as spinning, blowing, injection molding, warm pressing and resin transfer molding, and then converted into ceramics by treatments typically above 800 °C. The extension of the approach to a wider range of ceramic compositions and applications, both structural and thermo-structural (refractory components, thermal barrier coatings) or functional (bioactive ceramics, luminescent materials), mainly relies on modifications of the polymers at the nano-scale, i.e., on the introduction of nano-sized fillers and/or chemical additives, leading to nano-structured ceramic components upon thermal conversion. Fillers and additives may react with the main ceramic residue of the polymer, leading to ceramics of significant engineering interest (such as silicates and SiAlONs), or cause the formation of secondary phases, significantly affecting the functionalities of the polymer-derived matrix. Full article
(This article belongs to the Special Issue Nanocomposites of Polymers and Inorganic Particles 2013)
Open AccessReview Emerging Applications of Liquid Crystals Based on Nanotechnology
Materials 2014, 7(3), 2044-2061; doi:10.3390/ma7032044
Received: 27 January 2014 / Revised: 25 February 2014 / Accepted: 28 February 2014 / Published: 11 March 2014
Cited by 2 | PDF Full-text (912 KB) | HTML Full-text | XML Full-text
Abstract
Diverse functionalities of liquid crystals (LCs) offer enormous opportunities for their potential use in advanced mobile and smart displays, as well as novel non-display applications. Here, we present snapshots of the research carried out on emerging applications of LCs ranging from electronics to
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Diverse functionalities of liquid crystals (LCs) offer enormous opportunities for their potential use in advanced mobile and smart displays, as well as novel non-display applications. Here, we present snapshots of the research carried out on emerging applications of LCs ranging from electronics to holography and self-powered systems. In addition, we will show our recent results focused on the development of new LC applications, such as programmable transistors, a transparent and active-type two-dimensional optical array and self-powered display systems based on LCs, and will briefly discuss their novel concepts and basic operating principles. Our research will give insights not only into comprehensively understanding technical and scientific applications of LCs, but also developing new discoveries of other LC-based devices. Full article
(This article belongs to the Special Issue Liquid Crystals) Print Edition available
Open AccessReview A Review on Resistive Switching in High-k Dielectrics: A Nanoscale Point of View Using Conductive Atomic Force Microscope
Materials 2014, 7(3), 2155-2182; doi:10.3390/ma7032155
Received: 18 January 2014 / Revised: 13 February 2014 / Accepted: 14 February 2014 / Published: 13 March 2014
Cited by 38 | PDF Full-text (1957 KB) | HTML Full-text | XML Full-text
Abstract
Metal-Insulator-Metal (MIM) structures have raised as the most promising configuration for next generation information storage, leading to great performance and fabrication-friendly Resistive Random Access Memories (RRAM). In these cells, the memory concept is no more based on the charge storage, but on tuning
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Metal-Insulator-Metal (MIM) structures have raised as the most promising configuration for next generation information storage, leading to great performance and fabrication-friendly Resistive Random Access Memories (RRAM). In these cells, the memory concept is no more based on the charge storage, but on tuning the electrical resistance of the insulating layer by applying electrical stresses to reach a high resistive state (HRS or “0”) and a low resistive state (LRS or “1”), which makes the memory point. Some high-k dielectrics show this unusual property and in the last years high-k based RRAM have been extensively analyzed, especially at the device level. However, as resistance switching (in the most promising cells) is a local phenomenon that takes place in areas of ~100 nm2, the use of characterization tools with high lateral spatial resolution is necessary. In this paper the status of resistive switching in high-k materials is reviewed from a nanoscale point of view by means of conductive atomic force microscope analyses. Full article
(This article belongs to the Special Issue High-k Materials and Devices 2014)
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Open AccessReview Influence of Molecular Conformations and Microstructure on the Optoelectronic Properties of Conjugated Polymers
Materials 2014, 7(3), 2273-2300; doi:10.3390/ma7032273
Received: 13 January 2014 / Revised: 3 March 2014 / Accepted: 7 March 2014 / Published: 19 March 2014
Cited by 29 | PDF Full-text (998 KB) | HTML Full-text | XML Full-text
Abstract
It is increasingly obvious that the molecular conformations and the long-range arrangement that conjugated polymers can adopt under various experimental conditions in bulk, solutions or thin films, significantly impact their resulting optoelectronic properties. As a consequence, the functionalities and efficiencies of resulting organic
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It is increasingly obvious that the molecular conformations and the long-range arrangement that conjugated polymers can adopt under various experimental conditions in bulk, solutions or thin films, significantly impact their resulting optoelectronic properties. As a consequence, the functionalities and efficiencies of resulting organic devices, such as field-effect transistors, light-emitting diodes, or photovoltaic cells, also dramatically change due to the close structure/property relationship. A range of structure/optoelectronic properties relationships have been investigated over the last few years using various experimental and theoretical methods, and, further, interesting correlations are continuously revealed by the scientific community. In this review, we discuss the latest findings related to the structure/optoelectronic properties interrelationships that exist in organic devices fabricated with conjugated polymers in terms of charge mobility, absorption, photoluminescence, as well as photovoltaic properties. Full article
(This article belongs to the Special Issue Conjugated Polymers)
Open AccessReview Germanium Based Field-Effect Transistors: Challenges and Opportunities
Materials 2014, 7(3), 2301-2339; doi:10.3390/ma7032301
Received: 18 January 2014 / Revised: 6 March 2014 / Accepted: 7 March 2014 / Published: 19 March 2014
Cited by 23 | PDF Full-text (1482 KB) | HTML Full-text | XML Full-text
Abstract
The performance of strained silicon (Si) as the channel material for today’s metal-oxide-semiconductor field-effect transistors may be reaching a plateau. New channel materials with high carrier mobility are being investigated as alternatives and have the potential to unlock an era of ultra-low-power and
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The performance of strained silicon (Si) as the channel material for today’s metal-oxide-semiconductor field-effect transistors may be reaching a plateau. New channel materials with high carrier mobility are being investigated as alternatives and have the potential to unlock an era of ultra-low-power and high-speed microelectronic devices. Chief among these new materials is germanium (Ge). This work reviews the two major remaining challenges that Ge based devices must overcome if they are to replace Si as the channel material, namely, heterogeneous integration of Ge on Si substrates, and developing a suitable gate stack. Next, Ge is compared to compound III-V materials in terms of p-channel device performance to review how it became the first choice for PMOS devices. Different Ge device architectures, including surface channel and quantum well configurations, are reviewed. Finally, state-of-the-art Ge device results and future prospects are also discussed. Full article
(This article belongs to the Special Issue High-k Materials and Devices 2014)

Other

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Open AccessLetter The Effect of Cobalt-Sublattice Disorder on Spin Polarisation in Co2FexMn1−xSi Heusler Alloys
Materials 2014, 7(3), 1473-1482; doi:10.3390/ma7031473
Received: 2 December 2013 / Revised: 26 December 2013 / Accepted: 18 February 2014 / Published: 25 February 2014
Cited by 5 | PDF Full-text (505 KB) | HTML Full-text | XML Full-text
Abstract
In this work we present a theoretical study of the effect of disorder on spin polarisation at the Fermi level, and the disorder formation energies for Co2FexMn1−xSi (CFMS) alloys. The electronic calculations are based on density
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In this work we present a theoretical study of the effect of disorder on spin polarisation at the Fermi level, and the disorder formation energies for Co2FexMn1−xSi (CFMS) alloys. The electronic calculations are based on density functional theory with a Hubbard U term. Chemical disorders studied consist of swapping Co with Fe/Mn and Co with Si; in all cases we found these are detrimental for spin polarisation, i.e., the spin polarisation not only decreases in magnitude, but also can change sign depending on the particular disorder. Formation energy calculation shows that Co–Si disorder has higher energies of formation in CFMS compared to Co2MnSi and Co2FeSi, with maximum values occurring for x in the range 0.5–0.75. Cross-sectional structural studies of reference Co2MnSi, Co2Fe0.5Mn0.5Si, and Co2FeSi by Z-contrast scanning transmission electron microscopy are in qualitative agreement with total energy calculations of the disordered structures. Full article
(This article belongs to the Special Issue Spintronics)

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