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Materials, Volume 2, Issue 4 (December 2009), Pages 1417-2525

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Research

Jump to: Review, Other

Open AccessArticle Hydroxyapatite/MCM-41 and SBA-15 Nano-Composites: Preparation, Characterization and Applications
Materials 2009, 2(4), 1508-1519; doi:10.3390/ma2041508
Received: 29 July 2009 / Revised: 28 September 2009 / Accepted: 29 September 2009 / Published: 30 September 2009
Cited by 12 | PDF Full-text (995 KB) | HTML Full-text | XML Full-text
Abstract
Composites of hydroxyapatite (HaP) and highly ordered large pore mesoporous silica molecular sieves such as, Al-SBA-15 and Al-MCM-41 (denoted as SBA-15 and MCM-41. respectively) were developed, characterized by XRD, BET, FTIR, HRTEM and NMR-MAS, and applied to fluoride retention from contaminated water. The
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Composites of hydroxyapatite (HaP) and highly ordered large pore mesoporous silica molecular sieves such as, Al-SBA-15 and Al-MCM-41 (denoted as SBA-15 and MCM-41. respectively) were developed, characterized by XRD, BET, FTIR, HRTEM and NMR-MAS, and applied to fluoride retention from contaminated water. The proposed procedure by a new route to prepare the HaP/SBA-15 and HaP/MCM-41, composites generates materials with aluminum only in tetrahedral coordination, according to the 27Al NMR-MAS results. Free OH- groups of HaP nanocrystals, within the hosts, allowed high capacity fluoride retention. The activity of fluoride retention using HaP/MCM-41 or HaP/SBA-15 was 1-2 orders of magnitude greater, respectively, than with pure HaP. Full article
(This article belongs to the Special Issue Composite Materials)
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Open AccessArticle A Polarizer-Free Electro-Optical Switch Using Dye-Doped Liquid Crystal Gels
Materials 2009, 2(4), 1662-1673; doi:10.3390/ma2041662
Received: 3 September 2009 / Revised: 4 October 2009 / Accepted: 23 October 2009 / Published: 26 October 2009
Cited by 11 | PDF Full-text (1933 KB) | HTML Full-text | XML Full-text
Abstract
We demonstrate a polarizer-free electro-optical switch using dye-doped liquid crystal (LC) gels. The mechanism of dye-doped LC gels mainly involves the combination of polymer scattering and dye absorption. However, the domain size of polymer networks, dye concentration, LC concentration, and fabrication process can
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We demonstrate a polarizer-free electro-optical switch using dye-doped liquid crystal (LC) gels. The mechanism of dye-doped LC gels mainly involves the combination of polymer scattering and dye absorption. However, the domain size of polymer networks, dye concentration, LC concentration, and fabrication process can all affect the phase separation process and thus result in dye-doped LC gels with different electro-optical performance. We have studied experimentally the factors which can affect the dye-doped LC gels. The potential applications for dye-doped LC gels are flexible displays and electrically tunable light shutters. Full article
(This article belongs to the Special Issue Liquid Crystals)
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Open AccessArticle Present State of the Art of Composite Fabric Forming: Geometrical and Mechanical Approaches
Materials 2009, 2(4), 1835-1857; doi:10.3390/ma2041835
Received: 21 October 2009 / Revised: 5 November 2009 / Accepted: 12 November 2009 / Published: 17 November 2009
Cited by 7 | PDF Full-text (1760 KB) | HTML Full-text | XML Full-text
Abstract
Continuous fibre reinforced composites are now firmly established engineering materials for the manufacture of components in the automotive and aerospace industries. In this respect, composite fabrics provide flexibility in the design manufacture. The ability to define the ply shapes and material orientation has
[...] Read more.
Continuous fibre reinforced composites are now firmly established engineering materials for the manufacture of components in the automotive and aerospace industries. In this respect, composite fabrics provide flexibility in the design manufacture. The ability to define the ply shapes and material orientation has allowed engineers to optimize the composite properties of the parts. The formulation of new numerical models for the simulation of the composite forming processes must allow for reduction in the delay in manufacturing and an optimization of costs in an integrated design approach. We propose two approaches to simulate the deformation of woven fabrics: geometrical and mechanical approaches. Full article
(This article belongs to the Special Issue Composite Materials)
Open AccessArticle The Effect of Evolving Damage on the Finite Strain Response of Inelastic and Viscoelastic Composites
Materials 2009, 2(4), 1858-1894; doi:10.3390/ma2041858
Received: 14 October 2009 / Revised: 15 November 2009 / Accepted: 17 November 2009 / Published: 18 November 2009
Cited by 3 | PDF Full-text (402 KB) | HTML Full-text | XML Full-text
Abstract
A finite strain micromechanical model is generalized in order to incorporate the effect of evolving damage in the metallic and polymeric phases of unidirectional compostes. As a result, it is possible to predict the response of composites with ductile and brittle phases undergoing
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A finite strain micromechanical model is generalized in order to incorporate the effect of evolving damage in the metallic and polymeric phases of unidirectional compostes. As a result, it is possible to predict the response of composites with ductile and brittle phases undergoing large coupled inelastic-damage and viscoelastic-damage deformations, respectively. For inelastic composites, both finite strain elastoplastic (time-independent) and viscoplastic (time-dependent) behaviors are considered. The ductile phase exhibits initially a hyperelastic behavior which is followed by an inelastic one, and its analysis is based on the multiplicative split of its deformation gradient into elastic and inelastic parts. The embedded damage mechanisms and their evolutions are based on Gurson’s (which is suitable for the modeling of porous materials) and Lemaitre’s finite strain models. Similarly, the polymeric phase exhibits large viscoelastic deformations in which the damage evolves according to a suitable evolution law that depends on the amount of accumulated deformation. Evolving damage in hyperelastic materials can be analyzed as a special case by neglecting the viscous effects. The micromechanical analysis is based on the homogenization technique for periodic multiphase materials, which establishes the strong form of the Lagrangian equilibrium equations. These equations are implemented together with the interfacial and periodic boundary conditions, in conjunction with the current tangent tensor of the phase. As a result, the instantaneous strain concentration tensor that relates the local deformation gradient of the phase to the externally applied deformation gradient is established. This provides also the instantaneous effective stiffness tangent tensor of the composite as well as its current response. Results are given that exhibit the effect of damage on the initial yield surfaces, response and possible failure of the composite. Full article
(This article belongs to the Special Issue Composite Materials)
Open AccessArticle Tissue Response to Subcutaneously Implanted Recombinant Spider Silk: An in Vivo Study
Materials 2009, 2(4), 1908-1922; doi:10.3390/ma2041908
Received: 4 November 2009 / Revised: 17 November 2009 / Accepted: 19 November 2009 / Published: 20 November 2009
Cited by 29 | PDF Full-text (381 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Spider silk is an interesting biomaterial for medical applications. Recently, a method for production of recombinant spider silk protein (4RepCT) that forms macroscopic fibres in physiological solution was developed. Herein, 4RepCT and MersilkTM (control) fibres were implanted subcutaneously in rats for seven
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Spider silk is an interesting biomaterial for medical applications. Recently, a method for production of recombinant spider silk protein (4RepCT) that forms macroscopic fibres in physiological solution was developed. Herein, 4RepCT and MersilkTM (control) fibres were implanted subcutaneously in rats for seven days, without any negative systemic or local reactions. The tissue response, characterised by infiltration of macrophages and multinucleated cells, was similar with both fibres, while only the 4RepCT-fibres supported ingrowth of fibroblasts and newly formed capillaries. This in vivo study indicates that 4RepCT-fibres are well tolerated and could be used for medical applications, e.g., tissue engineering. Full article
(This article belongs to the Special Issue Advances in Biomaterials)
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Open AccessArticle Porous Ba Ferrite Prepared from Wood Template
Materials 2009, 2(4), 1923-1928; doi:10.3390/ma2041923
Received: 5 November 2009 / Revised: 16 November 2009 / Accepted: 19 November 2009 / Published: 20 November 2009
Cited by 4 | PDF Full-text (512 KB) | HTML Full-text | XML Full-text
Abstract
Ba ferrite materials with porous microstructures were prepared from a natural cedar wood template in order to investigate new electromagnetic shielding materials. The wood templates were infiltrated with barium nitrate and iron nitrate solutions (molar ratio = 1:12) and dried to form ferrite
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Ba ferrite materials with porous microstructures were prepared from a natural cedar wood template in order to investigate new electromagnetic shielding materials. The wood templates were infiltrated with barium nitrate and iron nitrate solutions (molar ratio = 1:12) and dried to form ferrite gel, then, they were sintered in air at a temperature between 800 °C and 1400 °C. The 1-dimensional porous structures were retained after sintering and the pore size was approximately 10–20 μm. These ferrites show large coercive force and anisotropy field. The largest coercive force was obtained for the specimen sintered at 800 °C. Full article
(This article belongs to the Special Issue Porous Materials)
Open AccessArticle Structure-Composition-Property Relationships in Polymeric Amorphous Calcium Phosphate-Based Dental Composites
Materials 2009, 2(4), 1929-1954; doi:10.3390/ma2041929
Received: 30 October 2009 / Revised: 19 November 2009 / Accepted: 23 November 2009 / Published: 24 November 2009
Cited by 10 | PDF Full-text (2157 KB) | HTML Full-text | XML Full-text
Abstract
Our studies of amorphous calcium phosphate (ACP)-based materials over the last decade have yielded bioactive polymeric composites capable of protecting teeth from demineralization or even regenerating lost tooth mineral. The anti-cariogenic/remineralizing potential of these ACP composites originates from their propensity, when exposed to
[...] Read more.
Our studies of amorphous calcium phosphate (ACP)-based materials over the last decade have yielded bioactive polymeric composites capable of protecting teeth from demineralization or even regenerating lost tooth mineral. The anti-cariogenic/remineralizing potential of these ACP composites originates from their propensity, when exposed to the oral environment, to release in a sustained manner sufficient levels of mineral-forming calcium and phosphate ions to promote formation of stable apatitic tooth mineral. However, the less than optimal ACP filler/resin matrix cohesion, excessive polymerization shrinkage and water sorption of these experimental materials can adversely affect their physicochemical and mechanical properties, and, ultimately, limit their lifespan. This study demonstrates the effects of chemical structure and composition of the methacrylate monomers used to form the matrix phase of composites on degree of vinyl conversion (DVC) and water sorption of both copolymers and composites and the release of mineral ions from the composites. Modification of ACP surface via introducing cations and/or polymers ab initio during filler synthesis failed to yield mechanically improved composites. However, moderate improvement in composite’s mechanical stability without compromising its remineralization potential was achieved by silanization and/or milling of ACP filler. Using ethoxylated bisphenol A dimethacrylate or urethane dimethacrylate as base monomers and adding moderate amounts of hydrophilic 2-hydroxyethyl methacrylate or its isomer ethyl-α-hydroxymethacrylate appears to be a promising route to maximize the remineralizing ability of the filler while maintaining high DVC. Exploration of the structure/composition/property relationships of ACP fillers and polymer matrices is complex but essential for achieving a better understanding of the fundamental mechanisms that govern dissolution/re-precipitation of bioactive ACP fillers, and, ultimately, the suitability of the composites for clinical evaluation. Full article
(This article belongs to the Special Issue Advances in Biomaterials)
Open AccessArticle Inorganic Polymer Matrix Composite Strength Related to Interface Condition
Materials 2009, 2(4), 2216-2227; doi:10.3390/ma2042216
Received: 31 October 2009 / Revised: 29 November 2009 / Accepted: 3 December 2009 / Published: 7 December 2009
Cited by 9 | PDF Full-text (874 KB) | HTML Full-text | XML Full-text
Abstract
Resin transfer molding of an inorganic polymer binder was successfully demonstrated in the preparation of ceramic fiber reinforced engine exhaust valves. Unfortunately, in the preliminary processing trials, the resulting composite valves were too brittle for in-engine evaluation. To address this limited toughness, the
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Resin transfer molding of an inorganic polymer binder was successfully demonstrated in the preparation of ceramic fiber reinforced engine exhaust valves. Unfortunately, in the preliminary processing trials, the resulting composite valves were too brittle for in-engine evaluation. To address this limited toughness, the effectiveness of a modified fiber-matrix interface is investigated through the use of carbon as a model material fiber coating. After sequential heat treatments composites molded from uncoated and carbon coated fibers are compared using room temperature 3-point bend testing. Carbon coated Nextel fiber reinforced geopolymer composites demonstrated a 50% improvement in strength, versus that of the uncoated fiber reinforced composites, after the 250 °C postcure. Full article
(This article belongs to the Special Issue Composite Materials)
Open AccessArticle Interactions between CO and Poly(p-phenylene vinylene) as Induced by Ion-Exchanged Zeolites
Materials 2009, 2(4), 2259-2275; doi:10.3390/ma2042259
Received: 28 September 2009 / Revised: 29 November 2009 / Accepted: 3 December 2009 / Published: 8 December 2009
Cited by 6 | PDF Full-text (792 KB) | HTML Full-text | XML Full-text
Abstract
The effects of zeolite type, ion-exchanged level, and ion type on the electrical conductivity responses of poly(p-phenylene vinylene) (PPV), doped poly(p-phenylene vinylene) (dPPV) and zeolite composites under CO exposures were investigated. The electrical sensitivity of dPPV/Cu+-ZSM5(Si/Al =
[...] Read more.
The effects of zeolite type, ion-exchanged level, and ion type on the electrical conductivity responses of poly(p-phenylene vinylene) (PPV), doped poly(p-phenylene vinylene) (dPPV) and zeolite composites under CO exposures were investigated. The electrical sensitivity of dPPV/Cu+-ZSM5(Si/Al = 23) system shows a negative sensitivity value of −0.154, while the Na+ system gives a positive sensitivity of 1.48. Based on FTIR and TPD data, the positive response of PPV/Na+-ZSM5 stems from the CO molecules acting as a secondary dopant. On the other hand, the negative response of PPV/Cu+-ZSM5 originates from the fact that CO molecules are selectively adsorbed on Cu+ sites rather than C+ sites of doped PPV. Full article
Open AccessArticle Hydroisomerization of n-Butane over Platinum-Promoted Cesium Hydrogen Salt of 12-Tungstophosphoric Acid
Materials 2009, 2(4), 2319-2336; doi:10.3390/ma2042319
Received: 13 November 2009 / Revised: 4 December 2009 / Accepted: 14 December 2009 / Published: 14 December 2009
Cited by 8 | PDF Full-text (466 KB) | HTML Full-text | XML Full-text
Abstract
The hydroisomerization of n-butane was carried out in a fixed-bed gas-flow reactor over Pt-promoted Cs2.5H0.5PW12O40 (denoted as Cs2.5). Two kinds of catalysts, a direct impregnation of Pt on Cs2.5 (denoted as Pt/Cs2.5), as well as a
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The hydroisomerization of n-butane was carried out in a fixed-bed gas-flow reactor over Pt-promoted Cs2.5H0.5PW12O40 (denoted as Cs2.5). Two kinds of catalysts, a direct impregnation of Pt on Cs2.5 (denoted as Pt/Cs2.5), as well as a mechanical mixture of Pt/Al2O3 and Cs2.5 (denoted as Pt/Al2O3+Cs2.5), were used for the hydroisomerization. Pt/Al2O3+Cs2.5 showed a higher stationary activity than Pt/Cs2.5 because the Pt particles supported on Al2O3 were much smaller than those supported on Cs2.5. The initial activity decreased with increasing H2 pressure over Pt/Al2O3+Cs2.5. This indicates that the hydroisomerization of n-butane over Pt/Al2O3+Cs2.5 proceeded through a bifunctional mechanism, in which n-butane was hydrogenated/dehydrogenated on Pt sites and was isomerized on acid sites of Cs2.5. For the hydroisomerization of n-butane over Pt/Al2O3+Cs2.5 the hydrogenation/dehydrogenation on Pt sites is a limiting step at a low Pt loading and the isomerization on solid acid sites is a limiting step at a high Pt loading. During the reaction, hydrogen molecules were dissociated to active hydrogen atoms on Pt sites, and then the formed active hydrogen atoms moved to the solid acid sites of Cs2.5 (spillover effect) to eliminate the carbonaceous deposits and suppress the catalyst deactivation. Because Cs2.5 has suitably strong and uniformly-distributed solid acid sites, Pt/Al2O3+Cs2.5 showed a higher stationary activity than Pt/Al2O3+H-ZSM-5 and Pt/Al2O3+SO4/ZrO2 for the hydroisomerization of n-butane at a low H2 pressure. Full article
(This article belongs to the Special Issue Polyoxometalate Compounds)
Open AccessArticle Highly Loaded Fe-MCM-41 Materials: Synthesis and Reducibility Studies
Materials 2009, 2(4), 2337-2359; doi:10.3390/ma2042337
Received: 4 November 2009 / Revised: 30 November 2009 / Accepted: 14 December 2009 / Published: 15 December 2009
Cited by 3 | PDF Full-text (1389 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Fe-MCM-41 materials were prepared by different methods. The Fe was both incorporated into the structure and formed crystallites attached to the silica. High Fe content MCM-41 (~16 wt%) with retention of mesoporosity and long-range order was achieved by a range of new synthetic
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Fe-MCM-41 materials were prepared by different methods. The Fe was both incorporated into the structure and formed crystallites attached to the silica. High Fe content MCM-41 (~16 wt%) with retention of mesoporosity and long-range order was achieved by a range of new synthetic methodologies: (i) by delaying the addition of Fe3+(aq) to the stirred synthesis gel by 2 h, (ii) by addition of Fe3+ precursor as a freshlyprecipitated aqueous slurry, (iii) by exploiting a secondary synthesis with Si-MCM-41 as SiO2 source. For comparative purposes the MCM-41 was also prepared by incipient wetness impregnation (IWI). Although all these synthesis methods preserved mesoporosity and long-range order of the SiO2 matrix, the hydrothermally-fabricated Fe materials prepared via the secondary synthesis route has the most useful properties for exploitation as a catalyst, in terms of hydrothermal stability of the resulting support. Temperatureprogrammed reduction (TPR) studies revealed a three-peak reduction pattern for this material instead of the commonly observed two-peak reduction pattern. The three peaks showed variable intensity that related to the presence of two components: crystalline Fe2O3 and Fe embedded in the SiO2 matrix (on the basis of ESR studies). The role of secondary synthesis of Si-MCM-41 on the iron reducibility was also demonstrated in IWI of sec-Si-MCM-41. Full article
(This article belongs to the Special Issue Porous Materials)
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Open AccessArticle A Self-Propagating Foaming Process of Porous Al-Ni Intermetallics Assisted by Combustion Reactions
Materials 2009, 2(4), 2360-2368; doi:10.3390/ma2042360
Received: 29 October 2009 / Revised: 3 December 2009 / Accepted: 14 December 2009 / Published: 15 December 2009
Cited by 1 | PDF Full-text (822 KB) | HTML Full-text | XML Full-text
Abstract
The self-propagating foaming process of porous Al-Ni intermetallics was investigated. Aluminum and nickel powders were blended, and titanium and boron carbide powders were added as reactive exothermic agents. The blended powder was extruded to make a rod-shape precursor. Only one end of the
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The self-propagating foaming process of porous Al-Ni intermetallics was investigated. Aluminum and nickel powders were blended, and titanium and boron carbide powders were added as reactive exothermic agents. The blended powder was extruded to make a rod-shape precursor. Only one end of the rod precursor was heated to ignite the reaction. The reaction propagated spontaneously throughout the precursor. Pore formation took place at the same time as the reaction occurred. Adding the exothermic agent was effective to increase the porosity. Preheating the precursor before the ignition was also very effective to produce porous Al-Ni intermetallics with high porosity. Full article
(This article belongs to the Special Issue Porous Materials)
Open AccessArticle Preparation and Hydrogen Absorption/Desorption of Nanoporous Palladium Thin Films
Materials 2009, 2(4), 2496-2509; doi:10.3390/ma2042496
Received: 29 October 2009 / Revised: 18 December 2009 / Accepted: 21 December 2009 / Published: 23 December 2009
Cited by 7 | PDF Full-text (1576 KB) | HTML Full-text | XML Full-text
Abstract
Nanoporous Pd (np-Pd) was prepared by co-sputtering Pd-Ni alloy films onto Si substrates, followed by chemical dealloying with sulfuric acid. X-ray diffractometry and chemical analysis were used to track the extent of dealloying. The np-Pd structure was changed from particle-like to sponge-like by
[...] Read more.
Nanoporous Pd (np-Pd) was prepared by co-sputtering Pd-Ni alloy films onto Si substrates, followed by chemical dealloying with sulfuric acid. X-ray diffractometry and chemical analysis were used to track the extent of dealloying. The np-Pd structure was changed from particle-like to sponge-like by diluting the sulfuric acid etchant. Using suitable precursor alloy composition and dealloying conditions, np-Pd films were prepared with uniform and open sponge-like structures, with interconnected ligaments and no cracks, yielding a large amount of surface area for reactions with hydrogen. Np-Pd films exhibited shorter response time for hydrogen absorption/desorption than dense Pd films, showing promise for hydrogen sensing. Full article
(This article belongs to the Special Issue Porous Materials)
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Review

Jump to: Research, Other

Open AccessReview Dielectric and Elastic Characterization of Nonlinear Heterogeneous Materials
Materials 2009, 2(4), 1417-1479; doi:10.3390/ma2041417
Received: 28 July 2009 / Revised: 5 September 2009 / Accepted: 29 September 2009 / Published: 30 September 2009
Cited by 4 | PDF Full-text (1736 KB) | HTML Full-text | XML Full-text
Abstract
This review paper deals with the dielectric and elastic characterization of composite materials constituted by dispersions of nonlinear inclusions embedded in a linear matrix. The dielectric theory deals with pseudo-oriented particles shaped as ellipsoids of revolution: it means that we are dealing with
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This review paper deals with the dielectric and elastic characterization of composite materials constituted by dispersions of nonlinear inclusions embedded in a linear matrix. The dielectric theory deals with pseudo-oriented particles shaped as ellipsoids of revolution: it means that we are dealing with mixtures of inclusions of arbitrary aspect ratio and arbitrary non-random orientational distributions. The analysis ranges from parallel spheroidal inclusions to completely random oriented inclusions. Each ellipsoidal inclusion is made of an isotropic dielectric material described by means of the so-called Kerr nonlinear relation. On the other hand, the nonlinear elastic characterization takes into consideration a dispersion of nonlinear (spherical or cylindrical) inhomogeneities. Both phases are considered isotropic (actually it means polycrystalline or amorphous solids). Under the simplifying hypotheses of small deformation for the material body and of small volume fraction of the embedded phase, we describe a theory for obtaining the linear and nonlinear elastic properties (bulk and shear moduli and Landau coefficients) of the overall material. Full article
(This article belongs to the Special Issue Composite Materials)
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Open AccessReview Biocompatibility of Different Nerve Tubes
Materials 2009, 2(4), 1480-1507; doi:10.3390/ma2041480
Received: 27 August 2009 / Revised: 24 September 2009 / Accepted: 25 September 2009 / Published: 30 September 2009
Cited by 22 | PDF Full-text (2567 KB) | HTML Full-text | XML Full-text
Abstract
Bridging nerve gaps with suitable grafts is a major clinical problem. The autologous nerve graft is considered to be the gold standard, providing the best functional results; however, donor site morbidity is still a major disadvantage. Various attempts have been made to overcome
[...] Read more.
Bridging nerve gaps with suitable grafts is a major clinical problem. The autologous nerve graft is considered to be the gold standard, providing the best functional results; however, donor site morbidity is still a major disadvantage. Various attempts have been made to overcome the problems of autologous nerve grafts with artificial nerve tubes, which are “ready-to-use” in almost every situation. A wide range of materials have been used in animal models but only few have been applied to date clinically, where biocompatibility is an inevitable prerequisite. This review gives an idea about artificial nerve tubes with special focus on their biocompatibility in animals and humans. Full article
(This article belongs to the Special Issue Biocompatibility of Materials)
Open AccessReview Characterization and Biocompatibility of Biopolyester Nanofibers
Materials 2009, 2(4), 1520-1546; doi:10.3390/ma2041520
Received: 7 August 2009 / Revised: 17 August 2009 / Accepted: 21 September 2009 / Published: 9 October 2009
Cited by 5 | PDF Full-text (10569 KB) | HTML Full-text | XML Full-text
Abstract
Biodegradable nanofibers are expected to be promising scaffold materials for biomedical engineering, however, biomedical applications require control of the degradation behavior and tissue response of nanofiber scaffolds in vivo. For this purpose, electrospun nanofibers of poly(hydroxyalkanoate)s (PHAs) and poly(lactide)s (PLAs) were subjected
[...] Read more.
Biodegradable nanofibers are expected to be promising scaffold materials for biomedical engineering, however, biomedical applications require control of the degradation behavior and tissue response of nanofiber scaffolds in vivo. For this purpose, electrospun nanofibers of poly(hydroxyalkanoate)s (PHAs) and poly(lactide)s (PLAs) were subjected to degradation tests in vitro and in vivo. In this review, characterization and biocompatibility of nanofibers derived from PHAs and PLAs are described. In particular, the effects of the crystalline structure of poly[(R)-3-hydroxybutyrate], stereocomplex structure of PLA, and monomer composition of PHA on the degradation behaviors are described in detail. These studies show the potential of biodegradable polyester nanofibers as scaffold material, for which suitable degradation rate and regulated interaction with surrounding tissues are required. Full article
(This article belongs to the Special Issue Biocompatibility of Materials)
Open AccessReview When Blood Is Touched
Materials 2009, 2(4), 1547-1557; doi:10.3390/ma2041547
Received: 7 September 2009 / Accepted: 16 October 2009 / Published: 16 October 2009
Cited by 5 | PDF Full-text (2500 KB) | HTML Full-text | XML Full-text
Abstract
The development of blood-compatible materials is reviewed. It grew from originally simplistic views of physical requirements such as surface charge and wettability, to endothelial cells seeded onto a biodegradable cast, and tissue engineering. In vitro findings grew from the discovery of one specific
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The development of blood-compatible materials is reviewed. It grew from originally simplistic views of physical requirements such as surface charge and wettability, to endothelial cells seeded onto a biodegradable cast, and tissue engineering. In vitro findings grew from the discovery of one specific protein being adsorbed, to that of sequential protein adsorption with complex implications of platelet and white cell adhesion. The main challenge is still the production of small blood vessels (capillaries). Full article
(This article belongs to the Special Issue Advances in Biomaterials)
Open AccessReview Organotin Polyethers as Biomaterials
Materials 2009, 2(4), 1558-1598; doi:10.3390/ma2041558
Received: 22 September 2009 / Revised: 13 October 2009 / Accepted: 19 October 2009 / Published: 21 October 2009
Cited by 23 | PDF Full-text (345 KB) | HTML Full-text | XML Full-text
Abstract
Organotin polyethers are easily synthesized employing interfacial polymerization systems involving the reaction of hydroxyl-containing Lewis bases and organotin halides. A wide variety of organotin-containing polymeric products have been synthesized including those derived from natural and synthetic polymers such as lignin, xylan, cellulose, dextran,
[...] Read more.
Organotin polyethers are easily synthesized employing interfacial polymerization systems involving the reaction of hydroxyl-containing Lewis bases and organotin halides. A wide variety of organotin-containing polymeric products have been synthesized including those derived from natural and synthetic polymers such as lignin, xylan, cellulose, dextran, and poly(vinyl alcohol). Others have been synthesized employing known drug diols such as dicumarol, DES, and dienestrol and a wide variety of synthetic diols. Included in these materials are the first water soluble organotin polymers. The organotin polyethers exhibit a wide range of biological activities. Some selectively inhibit a number of unwanted bacteria, including Staph. MRSA, and unwanted yeasts such as Candida albicans. Some also inhibit a variety of viruses including those responsible for herpes infections and smallpox. Others show good inhibition of a wide variety of cancer cell lines including cell lines associated with ovarian, colon, lung, prostrate, pancreatic and breast cancer. The synthesis, structural characterization, and biological characterization of these materials is described in this review. Full article
(This article belongs to the Special Issue Organometallic Compounds)
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Open AccessReview Progress to a Gallium-Arsenide Deep-Center Laser
Materials 2009, 2(4), 1599-1635; doi:10.3390/ma2041599
Received: 14 September 2009 / Revised: 9 October 2009 / Accepted: 20 October 2009 / Published: 22 October 2009
Cited by 6 | PDF Full-text (3781 KB) | HTML Full-text | XML Full-text | Correction | Supplementary Files
Abstract
Although photoluminescence from gallium-arsenide (GaAs) deep-centers was first observed in the 1960s, semiconductor lasers have always utilized conduction-to-valence-band transitions. Here we review recent materials studies leading to the first GaAs deep-center laser. First, we summarize well-known properties: nature of deep-center complexes, Franck-Condon effect,
[...] Read more.
Although photoluminescence from gallium-arsenide (GaAs) deep-centers was first observed in the 1960s, semiconductor lasers have always utilized conduction-to-valence-band transitions. Here we review recent materials studies leading to the first GaAs deep-center laser. First, we summarize well-known properties: nature of deep-center complexes, Franck-Condon effect, hotoluminescence. Second, we describe our recent work: insensitivity of photoluminescence with heating, striking differences between electroluminescence and photoluminescence, correlation between transitions to deep-states and absence of bandgap-emission. Room-temperature stimulated-emission from GaAs deep-centers was observed at low electrical injection, and could be tuned from the bandgap to half-the-bandgap (900–1,600 nm) by changing the electrical injection. The first GaAs deep-center laser was demonstrated with electrical injection, and exhibited a threshold of less than 27 mA/cm2 in continuous-wave mode at room temperature at the important 1.54 μm fiber-optic wavelength. This small injection for laser action was explained by fast depopulation of the lower state of the optical transition (fast capture of free holes onto deep-centers), which maintains the population inversion. The evidence for laser action included: superlinear L-I curve, quasi-Fermi level separations satisfying Bernard-Duraffourg’s criterion, optical gains larger than known significant losses, clamping of the optical-emission from lossy modes unable to reach laser action, pinning of the population distribution during laser action. Full article
(This article belongs to the Special Issue Luminescent Materials)
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Open AccessReview Development of Highly Soluble Anthraquinone Dichroic Dyes and Their Application to Three-Layer Guest-Host Liquid Crystal Displays
Materials 2009, 2(4), 1636-1661; doi:10.3390/ma2041636
Received: 31 August 2009 / Revised: 9 October 2009 / Accepted: 21 October 2009 / Published: 23 October 2009
Cited by 25 | PDF Full-text (531 KB) | HTML Full-text | XML Full-text | Correction | Supplementary Files
Abstract
The relationships between molecular structures and properties of anthraquinone dichroic dyes were studied and dyes with large solubilities and dichroic ratios were developed. The yellow anthraquinone dye behaves as a quencher of the coumarin dye, and the mixture has a large absorption coefficient
[...] Read more.
The relationships between molecular structures and properties of anthraquinone dichroic dyes were studied and dyes with large solubilities and dichroic ratios were developed. The yellow anthraquinone dye behaves as a quencher of the coumarin dye, and the mixture has a large absorption coefficient without fluorescence. These technologies can enlarge the color reproduction area of three-layer guest-host liquid crystal displays (GHLCDs) 1.6-fold. The performances of the prototype reflective three-layer GH-LCDs are as follows: the white state luminous reflectance is 43% and the contrast is 5.3, indicating that they are promising candidates for portable information systems with full-color images. Full article
(This article belongs to the Special Issue Liquid Crystals)
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Open AccessReview Anisotropic Porous Biodegradable Scaffolds for Musculoskeletal Tissue Engineering
Materials 2009, 2(4), 1674-1696; doi:10.3390/ma2041674
Received: 4 September 2009 / Revised: 30 September 2009 / Accepted: 10 October 2009 / Published: 29 October 2009
Cited by 20 | PDF Full-text (650 KB) | HTML Full-text | XML Full-text
Abstract
It has been generally accepted that tissue engineered constructs should closely resemble the in-vivo mechanical and structural properties of the tissues they are intended to replace. However, most scaffolds produced so far were isotropic porous scaffolds with non-characterized mechanical properties, different from those
[...] Read more.
It has been generally accepted that tissue engineered constructs should closely resemble the in-vivo mechanical and structural properties of the tissues they are intended to replace. However, most scaffolds produced so far were isotropic porous scaffolds with non-characterized mechanical properties, different from those of the native healthy tissue. Tissues that are formed into these scaffolds are initially formed in the isotropic porous structure and since most tissues have significant anisotropic extracellular matrix components and concomitant mechanical properties, the formed tissues have no structural and functional relationships with the native tissues. The complete regeneration of tissues requires a second differentiation step after resorption of the isotropic scaffold. It is doubtful if the required plasticity for this remains present in already final differentiated tissue. It would be much more efficacious if the newly formed tissues in the scaffold could differentiate directly into the anisotropic organization of the native tissues. Therefore, anisotropic scaffolds that enable such a direct differentiation might be extremely helpful to realize this goal. Up to now, anisotropic scaffolds have been fabricated using modified conventional techniques, solid free-form fabrication techniques, and a few alternative methods. In this review we present the current status and discuss the procedures that are currently being used for anisotropic scaffold fabrication. Full article
(This article belongs to the Special Issue Biocompatibility of Materials)
Open AccessReview Polymer Composite and Nanocomposite Dielectric Materials for Pulse Power Energy Storage
Materials 2009, 2(4), 1697-1733; doi:10.3390/ma2041697
Received: 12 September 2009 / Revised: 22 October 2009 / Accepted: 23 October 2009 / Published: 29 October 2009
Cited by 223 | PDF Full-text (1531 KB) | HTML Full-text | XML Full-text
Abstract
This review summarizes the current state of polymer composites used as dielectric materials for energy storage. The particular focus is on materials: polymers serving as the matrix, inorganic fillers used to increase the effective dielectric constant, and various recent investigations of functionalization of
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This review summarizes the current state of polymer composites used as dielectric materials for energy storage. The particular focus is on materials: polymers serving as the matrix, inorganic fillers used to increase the effective dielectric constant, and various recent investigations of functionalization of metal oxide fillers to improve compatibility with polymers. We review the recent literature focused on the dielectric characterization of composites, specifically the measurement of dielectric permittivity and breakdown field strength. Special attention is given to the analysis of the energy density of polymer composite materials and how the functionalization of the inorganic filler affects the energy density of polymer composite dielectric materials. Full article
(This article belongs to the Special Issue Energy Technology for the 21st Century - Materials and Devices)
Open AccessReview Liquid Crystalline Behavior and Related Properties of Colloidal Systems of Inorganic Oxide Nanosheets
Materials 2009, 2(4), 1734-1761; doi:10.3390/ma2041734
Received: 29 August 2009 / Revised: 16 October 2009 / Accepted: 27 October 2009 / Published: 29 October 2009
Cited by 25 | PDF Full-text (773 KB) | HTML Full-text | XML Full-text
Abstract
Inorganic layered crystals exemplified by clay minerals can be exfoliated in solvents to form colloidal dispersions of extremely thin inorganic layers that are called nanosheets. The obtained “nanosheet colloids” form lyotropic liquid crystals because of the highly anisotropic shape of the nanosheets. This
[...] Read more.
Inorganic layered crystals exemplified by clay minerals can be exfoliated in solvents to form colloidal dispersions of extremely thin inorganic layers that are called nanosheets. The obtained “nanosheet colloids” form lyotropic liquid crystals because of the highly anisotropic shape of the nanosheets. This system is a rare example of liquid crystals consisting of inorganic crystalline mesogens. Nanosheet colloids of photocatalytically active semiconducting oxides can exhibit unusual photoresponses that are not observed for organic liquid crystals. This review summarizes experimental work on the phase behavior of the nanosheet colloids as well as photochemical reactions observed in the clay and semiconducting nanosheets system. Full article
(This article belongs to the Special Issue Liquid Crystals)
Open AccessReview Long-Term Recordings of Multiple, Single-Neurons for Clinical Applications: The Emerging Role of the Bioactive Microelectrode
Materials 2009, 2(4), 1762-1794; doi:10.3390/ma2041762
Received: 30 September 2009 / Revised: 21 October 2009 / Accepted: 23 October 2009 / Published: 5 November 2009
Cited by 8 | PDF Full-text (1525 KB) | HTML Full-text | XML Full-text
Abstract
In 1999 we reported an important demonstration of a working brain-machine interface (BMI), in which recordings from multiple, single neurons in sensorimotor cortical areas of rats were used to directly control a robotic arm to retrieve a water reward. Subsequent studies in monkeys,
[...] Read more.
In 1999 we reported an important demonstration of a working brain-machine interface (BMI), in which recordings from multiple, single neurons in sensorimotor cortical areas of rats were used to directly control a robotic arm to retrieve a water reward. Subsequent studies in monkeys, using a similar approach, demonstrated that primates can use a BMI device to control a cursor on a computer screen and a robotic arm. Recent studies in humans with spinal cord injuries have shown that recordings from multiple, single neurons can be used by the patient to control the cursor on a computer screen. The promise is that one day it will be possible to use these control signals from neurons to reactivate the patient’s own limbs. However, the ability to record from large populations of single neurons for long periods of time has been hampered because either the electrode itself fails or the immunological response in the tissue surrounding the microelectrode produces a glial scar, preventing single-neuron recording. While we have largely solved the problem of mechanical or electrical failure of the electrode itself, much less is known about the long term immunological response to implantation of a microelectrode, its effect on neuronal recordings and, of greatest importance, how it can be reduced to allow long term single neuron recording. This article reviews materials approaches to resolving the glial scar to improve the longevity of recordings. The work to date suggests that approaches utilizing bioactive interventions that attempt to alter the glial response and attract neurons to the recording site are likely to be the most successful. Importantly, measures of the glial scar alone are not sufficient to assess the effect of interventions. It is imperative that recordings of single neurons accompany any study of glial activation because, at this time, we do not know the precise relationship between glial activation and loss of neuronal recordings. Moreover, new approaches to immobilize bioactive molecules on microelectrode surfaces while maintaining their functionality may open new avenues for very long term single neuron recording. Finally, it is important to have quantitative measures of glial upregulation and neuronal activity in order to assess the relationship between the two. These types of studies will help rationalize the study of interventions to improve the longevity of recordings from microelectrodes. Full article
(This article belongs to the Special Issue Biocompatibility of Materials)
Open AccessReview Combined Thermodynamic-Kinetic Analysis of the Interfacial Reactions between Ni Metallization and Various Lead-Free Solders
Materials 2009, 2(4), 1796-1834; doi:10.3390/ma2041796
Received: 19 October 2009 / Revised: 6 November 2009 / Accepted: 11 November 2009 / Published: 11 November 2009
Cited by 11 | PDF Full-text (5237 KB) | HTML Full-text | XML Full-text
Abstract
In this paper we will demonstrate how a thermodynamic-kinetic method can be utilized to rationalize a wide range of interfacial phenomena between Sn-based lead-free solders and Ni metallizations. First, the effect of P on the interfacial reactions, and thus on the reliability, between
[...] Read more.
In this paper we will demonstrate how a thermodynamic-kinetic method can be utilized to rationalize a wide range of interfacial phenomena between Sn-based lead-free solders and Ni metallizations. First, the effect of P on the interfacial reactions, and thus on the reliability, between Sn-based solders and electroless Ni/immersion Au (ENIG) metallizations, will be discussed. Next, the effect of small amounts of Cu in Sn-based solders on the intermetallic compound (IMC), which forms first on top of Ni metallization, will be covered. With the help of thermodynamic arguments a so called critical Cu concentration for the formation of (Cu,Ni)6Sn5 can be determined as a function of temperature. Then the important phenomenon of redeposition of (Au,Ni)Sn4 layer on top of Ni3Sn4 IMC will be discussed in detail. The reasons leading to this behaviour will be rationalized with the help of thermodynamic information and an explanation of why this phenomenon does not occur when an appropriate amount of Cu is present in the soldering system will be given. Finally, interfacial reaction issues related to low temperature Sn-Zn and Sn-Bi based solders and Ni metallization will be discussed. Full article
(This article belongs to the Special Issue Advances in Materials Science)
Open AccessReview The Use of Ceramics as Bone Substitutes in Revision Hip Arthroplasty
Materials 2009, 2(4), 1895-1907; doi:10.3390/ma2041895
Received: 19 October 2009 / Revised: 16 November 2009 / Accepted: 18 November 2009 / Published: 19 November 2009
Cited by 3 | PDF Full-text (207 KB) | HTML Full-text | XML Full-text
Abstract
The number of grafting procedures, including those performed in primary and revision hip arthroplasty, continues to rise around the world. Demand for musculoskeletal donor tissue now outstrips supply. There is no single bone substitute that is ideal for all circumstances. Bone substitutes act
[...] Read more.
The number of grafting procedures, including those performed in primary and revision hip arthroplasty, continues to rise around the world. Demand for musculoskeletal donor tissue now outstrips supply. There is no single bone substitute that is ideal for all circumstances. Bone substitutes act as a scaffold and are usually osteoconductive. They are rarely osteoinductive; if they are, a molecular bond is formed between the graft and host bone, improving fixation and longevity. Bone graft substitutes are very rarely osteogenic. There is a growing body of clinical evidence supporting the use of bone graft substitutes in vivo for complex hip arthroplasty. Full article
(This article belongs to the Special Issue Ceramics for Healthcare)
Open AccessReview Carbon Nanotube-Reinforced Thermotropic Liquid Crystal Polymer Nanocomposites
Materials 2009, 2(4), 1955-1974; doi:10.3390/ma2041955
Received: 5 October 2009 / Revised: 4 November 2009 / Accepted: 5 November 2009 / Published: 26 November 2009
Cited by 15 | PDF Full-text (717 KB) | HTML Full-text | XML Full-text
Abstract
This paper focuses on the fabrication via simple melt blending of thermotropic liquid crystal polyester (TLCP) nanocomposites reinforced with a very small quantity of modified carbon nanotube (CNT) and the unique effects of the modified CNT on the physical properties of the nanocomposites.
[...] Read more.
This paper focuses on the fabrication via simple melt blending of thermotropic liquid crystal polyester (TLCP) nanocomposites reinforced with a very small quantity of modified carbon nanotube (CNT) and the unique effects of the modified CNT on the physical properties of the nanocomposites. The thermal, mechanical, and rheological properties of modified CNT-reinforced TLCP nanocomposites are highly dependent on the uniform dispersion of CNT and the interactions between the CNT and TLCP, which can be enhanced by chemical modification of the CNT, providing a design guide of CNTreinforced TLCP nanocomposites with great potential for industrial uses. Full article
(This article belongs to the Special Issue Liquid Crystals)
Open AccessReview Nanodimensional and Nanocrystalline Apatites and Other Calcium Orthophosphates in Biomedical Engineering, Biology and Medicine
Materials 2009, 2(4), 1975-2045; doi:10.3390/ma2041975
Received: 27 October 2009 / Revised: 24 November 2009 / Accepted: 27 November 2009 / Published: 27 November 2009
Cited by 99 | PDF Full-text (1253 KB) | HTML Full-text | XML Full-text
Abstract
Recent developments in biomineralization have already demonstrated that nanosized particles play an important role in the formation of hard tissues of animals. Namely, the basic inorganic building blocks of bones and teeth of mammals are nanodimensional and nanocrystalline calcium orthophosphates (in the form
[...] Read more.
Recent developments in biomineralization have already demonstrated that nanosized particles play an important role in the formation of hard tissues of animals. Namely, the basic inorganic building blocks of bones and teeth of mammals are nanodimensional and nanocrystalline calcium orthophosphates (in the form of apatites) of a biological origin. In mammals, tens to hundreds nanocrystals of a biological apatite were found to be combined into self-assembled structures under the control of various bioorganic matrixes. In addition, the structures of both dental enamel and bones could be mimicked by an oriented aggregation of nanosized calcium orthophosphates, determined by the biomolecules. The application and prospective use of nanodimensional and nanocrystalline calcium orthophosphates for a clinical repair of damaged bones and teeth are also known. For example, a greater viability and a better proliferation of various types of cells were detected on smaller crystals of calcium orthophosphates. Thus, the nanodimensional and nanocrystalline forms of calcium orthophosphates have a great potential to revolutionize the field of hard tissue engineering starting from bone repair and augmentation to the controlled drug delivery devices. This paper reviews current state of knowledge and recent developments of this subject starting from the synthesis and characterization to biomedical and clinical applications. More to the point, this review provides possible directions of future research and development. Full article
(This article belongs to the Special Issue Advances in Biomaterials)
Open AccessReview Fracture Toughness of Polypropylene-Based Particulate Composites
Materials 2009, 2(4), 2046-2094; doi:10.3390/ma2042046
Received: 27 October 2009 / Revised: 24 November 2009 / Accepted: 27 November 2009 / Published: 30 November 2009
Cited by 19 | PDF Full-text (1561 KB) | HTML Full-text | XML Full-text
Abstract
The fracture behaviour of polymers is strongly affected by the addition of rigid particles. Several features of the particles have a decisive influence on the values of the fracture toughness: shape and size, chemical nature, surface nature, concentration by volume, and orientation. Among
[...] Read more.
The fracture behaviour of polymers is strongly affected by the addition of rigid particles. Several features of the particles have a decisive influence on the values of the fracture toughness: shape and size, chemical nature, surface nature, concentration by volume, and orientation. Among those of thermoplastic matrix, polypropylene (PP) composites are the most industrially employed for many different application fields. Here, a review on the fracture behaviour of PP-based particulate composites is carried out, considering the basic topics and experimental techniques of Fracture Mechanics, the mechanisms of deformation and fracture, and values of fracture toughness for different PP composites prepared with different particle scale size, either micrometric or nanometric. Full article
(This article belongs to the Special Issue Composite Materials)
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Open AccessReview Insight into the Broad Field of Polymer Nanocomposites: From Carbon Nanotubes to Clay Nanoplatelets, via Metal Nanoparticles
Materials 2009, 2(4), 2095-2153; doi:10.3390/ma2042095
Received: 28 October 2009 / Revised: 24 November 2009 / Accepted: 26 November 2009 / Published: 30 November 2009
Cited by 23 | PDF Full-text (1941 KB) | HTML Full-text | XML Full-text
Abstract
Highly ordered polymer nanocomposites are complex materials that display a rich morphological behavior owing to variations in composition, structure, and properties on a nanometer length scale. Metal-polymer nanocomposite materials are becoming more popular for applications requiring low cost, high metal surface areas. Catalytic
[...] Read more.
Highly ordered polymer nanocomposites are complex materials that display a rich morphological behavior owing to variations in composition, structure, and properties on a nanometer length scale. Metal-polymer nanocomposite materials are becoming more popular for applications requiring low cost, high metal surface areas. Catalytic systems seem to be the most prevalent application for a wide range of metals used in polymer nanocomposites, particularly for metals like Pt, Ni, Co, and Au, with known catalytic activities. On the other hand, among the most frequently utilized techniques to prepare polymer/CNT and/or polymer/clay nanocomposites are approaches like melt mixing, solution casting, electrospinning and solid-state shear pulverization. Additionally, some of the current and potential applications of polymer/CNT and/or polymer/clay nanocomposites include photovoltaic devices, optical switches, electromagnetic interference (EMI) shielding, aerospace and automotive materials, packaging, adhesives and coatings. This extensive review covers a broad range of articles, typically from high impact-factor journals, on most of the polymer-nanocomposites known to date: polymer/carbon nanotubes, polymer/metal nanospheres, and polymer/clay nanoplatelets composites. The various types of nanocomposites are described form the preparation stages to performance and applications. Comparisons of the various types of nanocomposites are conducted and conclusions are formulated. Full article
(This article belongs to the Special Issue Nanocomposites of Polymers and Inorganic Particles)
Open AccessReview Intercalated Nanocomposites Based on High-Temperature Superconducting Ceramics and Their Properties
Materials 2009, 2(4), 2154-2187; doi:10.3390/ma2042154
Received: 15 October 2009 / Revised: 18 November 2009 / Accepted: 30 November 2009 / Published: 2 December 2009
Cited by 3 | PDF Full-text (894 KB) | HTML Full-text | XML Full-text
Abstract
High temperature superconducting (SC) nanocomposites based on SC ceramics and various polymeric binders were prepared. Regardless of the size of the ceramics’ grains, the increase of their amount leads to an increase of resistance to rupture and modulus and a decrease in limiting
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High temperature superconducting (SC) nanocomposites based on SC ceramics and various polymeric binders were prepared. Regardless of the size of the ceramics’ grains, the increase of their amount leads to an increase of resistance to rupture and modulus and a decrease in limiting deformation, whereas an increase in the average ceramic grain size worsens resistance properties. The SC, thermo-chemical, mechanical and dynamic-mechanical properties of the samples were investigated. Superconducting properties of the polymer ceramic nanocomposites are explained by intercalation of macromolecule fragments into the interstitial layer of the ceramics’ grains. This phenomenon leads to a change in the morphological structure of the superconducting nanocomposites. Full article
(This article belongs to the Special Issue Composite Materials)
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Open AccessReview Nanoporous Gold: Fabrication, Characterization, and Applications
Materials 2009, 2(4), 2188-2215; doi:10.3390/ma2042188
Received: 27 October 2009 / Revised: 29 November 2009 / Accepted: 2 December 2009 / Published: 3 December 2009
Cited by 78 | PDF Full-text (2295 KB) | HTML Full-text | XML Full-text
Abstract
Nanoporous gold (np-Au) has intriguing material properties that offer potential benefits for many applications due to its high specific surface area, well-characterized thiol-gold surface chemistry, high electrical conductivity, and reduced stiffness. The research on np-Au has taken place on various fronts, including advanced
[...] Read more.
Nanoporous gold (np-Au) has intriguing material properties that offer potential benefits for many applications due to its high specific surface area, well-characterized thiol-gold surface chemistry, high electrical conductivity, and reduced stiffness. The research on np-Au has taken place on various fronts, including advanced microfabrication and characterization techniques to probe unusual nanoscale properties and applications spanning from fuel cells to electrochemical sensors. Here, we provide a review of the recent advances in np-Au research, with special emphasis on microfabrication and characterization techniques. We conclude the paper with a brief outline of challenges to overcome in the study of nanoporous metals. Full article
(This article belongs to the Special Issue Porous Materials)
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Open AccessReview Nanostructured Photocatalysts and Their Applications in the Photocatalytic Transformation of Lignocellulosic Biomass: An Overview
Materials 2009, 2(4), 2228-2258; doi:10.3390/ma2042228
Received: 7 November 2009 / Revised: 27 November 2009 / Accepted: 2 December 2009 / Published: 7 December 2009
Cited by 70 | PDF Full-text (783 KB) | HTML Full-text | XML Full-text
Abstract
Heterogeneous photocatalysis offer many possibilities for finding appropiate environmentally friendly solutions for many of the the problems affecting our society (i.e., energy issues). Researchers are still looking for novel routes to prepare solid photocatalysts able to transform solar into chemical energy
[...] Read more.
Heterogeneous photocatalysis offer many possibilities for finding appropiate environmentally friendly solutions for many of the the problems affecting our society (i.e., energy issues). Researchers are still looking for novel routes to prepare solid photocatalysts able to transform solar into chemical energy more efficiently. In many developing countries, biomass is a major energy source, but currently such countries lack of the technology to sustainably obtain chemicals and/or fuels from it. The Roadmap for Biomass Technologies, authored by 26 leading experts from academia, industry, and government agencies, has predicted a gradual shift back to a carbohydrate-based economy. Biomass and biofuels appear to hold the key to satisfy the basic needs of our societies for the sustainable production of liquid fuels and high value-added chemicals without compromising the scenario of future generations. In this review, we aim to discuss various design routes for nanostructured photocatalytic solid materials in view of their applications in the selective transformation of lignocellulosic biomass to high value-added chemicals. Full article
(This article belongs to the Special Issue Molecular Biomimetics and Materials Design)
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Open AccessReview Silk Fibroin Based Porous Materials
Materials 2009, 2(4), 2276-2295; doi:10.3390/ma2042276
Received: 28 October 2009 / Revised: 1 December 2009 / Accepted: 7 December 2009 / Published: 9 December 2009
Cited by 33 | PDF Full-text (229 KB) | HTML Full-text | XML Full-text
Abstract
Silk from the Bombyx mori silkworm is a protein-based fiber. Bombyx mori silk fibroin (SF) is one of the most important candidates for biomedical porous material based on its superior machinability, biocompatibility, biodegradation, bioresorbability, and so on. In this paper, we have reviewed
[...] Read more.
Silk from the Bombyx mori silkworm is a protein-based fiber. Bombyx mori silk fibroin (SF) is one of the most important candidates for biomedical porous material based on its superior machinability, biocompatibility, biodegradation, bioresorbability, and so on. In this paper, we have reviewed the key features of SF. Moreover we have focused on the morphous, technical processing, and biocompatibility of SF porous materials, followed by the application research. Finally, we provide a perspective the potential and problems of SF porous materials. Full article
(This article belongs to the Special Issue Porous Materials)
Open AccessReview Predicting New Materials for Hydrogen Storage Application
Materials 2009, 2(4), 2296-2318; doi:10.3390/ma2042296
Received: 2 December 2009 / Accepted: 11 December 2009 / Published: 14 December 2009
Cited by 3 | PDF Full-text (8126 KB) | HTML Full-text | XML Full-text
Abstract
Knowledge about the ground-state crystal structure is a prerequisite for the rational understanding of solid-state properties of new materials. To act as an efficient energy carrier, hydrogen should be absorbed and desorbed in materials easily and in high quantities. Owing to the complexity
[...] Read more.
Knowledge about the ground-state crystal structure is a prerequisite for the rational understanding of solid-state properties of new materials. To act as an efficient energy carrier, hydrogen should be absorbed and desorbed in materials easily and in high quantities. Owing to the complexity in structural arrangements and difficulties involved in establishing hydrogen positions by x-ray diffraction methods, the structural information of hydrides are very limited compared to other classes of materials (like oxides, intermetallics, etc.). This can be overcome by conducting computational simulations combined with selected experimental study which can save environment, money, and man power. The predicting capability of first-principles density functional theory (DFT) is already well recognized and in many cases structural and thermodynamic properties of single/multi component system are predicted. This review will focus on possible new classes of materials those have high hydrogen content, demonstrate the ability of DFT to predict crystal structure, and search for potential meta-stable phases. Stabilization of such meta-stable phases is also discussed. Full article
(This article belongs to the Special Issue Energy Technology for the 21st Century - Materials and Devices)
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Open AccessReview Fabrication and Properties of Carbon Fibers
Materials 2009, 2(4), 2369-2403; doi:10.3390/ma2042369
Received: 30 October 2009 / Revised: 8 December 2009 / Accepted: 14 December 2009 / Published: 16 December 2009
Cited by 138 | PDF Full-text (405 KB) | HTML Full-text | XML Full-text
Abstract
This paper reviews the research and development activities conducted over the past few decades on carbon fibers. The two most important precursors in the carbon fiber industry are polyacrylonitrile (PAN) and mesophase pitch (MP). The structure and composition of the precursor affect the
[...] Read more.
This paper reviews the research and development activities conducted over the past few decades on carbon fibers. The two most important precursors in the carbon fiber industry are polyacrylonitrile (PAN) and mesophase pitch (MP). The structure and composition of the precursor affect the properties of the resultant carbon fibers significantly. Although the essential processes for carbon fiber production are similar, different precursors require different processing conditions in order to achieve improved performance. The research efforts on process optimization are discussed in this review. The review also attempts to cover the research on other precursor materials developed mainly for the purpose of cost reduction. Full article
(This article belongs to the Special Issue Composite Materials)
Open AccessReview Surface Chemistry in Nanoscale Materials
Materials 2009, 2(4), 2404-2428; doi:10.3390/ma2042404
Received: 31 October 2009 / Revised: 5 December 2009 / Accepted: 14 December 2009 / Published: 16 December 2009
Cited by 18 | PDF Full-text (1274 KB) | HTML Full-text | XML Full-text
Abstract
Although surfaces or, more precisely, the surface atomic and electronic structure, determine the way materials interact with their environment, the influence of surface chemistry on the bulk of the material is generally considered to be small. However, in the case of high surface
[...] Read more.
Although surfaces or, more precisely, the surface atomic and electronic structure, determine the way materials interact with their environment, the influence of surface chemistry on the bulk of the material is generally considered to be small. However, in the case of high surface area materials such as nanoporous solids, surface properties can start to dominate the overall material behavior. This allows one to create new materials with physical and chemical properties that are no longer determined by the bulk material, but by their nanoscale architectures. Here, we discuss several examples, ranging from nanoporous gold to surface engineered carbon aerogels that demonstrate the tuneability of nanoporous solids for sustainable energy applications. Full article
(This article belongs to the Special Issue Porous Materials)
Open AccessReview Macroporous Monolithic Polymers: Preparation and Applications
Materials 2009, 2(4), 2429-2466; doi:10.3390/ma2042429
Received: 9 November 2009 / Revised: 8 December 2009 / Accepted: 14 December 2009 / Published: 18 December 2009
Cited by 21 | PDF Full-text (635 KB) | HTML Full-text | XML Full-text
Abstract
In the last years, macroporous monolithic materials have been introduced as a new and useful generation of polymers used in different fields. These polymers may be prepared in a simple way from a homogenous mixture into a mold and contain large interconnected pores
[...] Read more.
In the last years, macroporous monolithic materials have been introduced as a new and useful generation of polymers used in different fields. These polymers may be prepared in a simple way from a homogenous mixture into a mold and contain large interconnected pores or channels allowing for high flow rates at moderate pressures. Due to their porous characteristics, they could be used in different processes, such as stationary phases for different types of chromatography, high-throughput bioreactors and in microfluidic chip applications. This review reports the contributions of several groups working in the preparation of different macroporous monoliths and their modification by immobilization of specific ligands on the products for specific purposes. Full article
(This article belongs to the Special Issue Porous Materials)
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Open AccessReview Thermal Conductivity of Diamond Composites
Materials 2009, 2(4), 2467-2495; doi:10.3390/ma2042467
Received: 1 November 2009 / Revised: 16 December 2009 / Accepted: 17 December 2009 / Published: 21 December 2009
Cited by 58 | PDF Full-text (1608 KB) | HTML Full-text | XML Full-text
Abstract
A major problem challenging specialists in present-day materials sciences is the development of compact, cheap to fabricate heat sinks for electronic devices, primarily for computer processors, semiconductor lasers, high-power microchips, and electronics components. The materials currently used for heat sinks of such devices
[...] Read more.
A major problem challenging specialists in present-day materials sciences is the development of compact, cheap to fabricate heat sinks for electronic devices, primarily for computer processors, semiconductor lasers, high-power microchips, and electronics components. The materials currently used for heat sinks of such devices are aluminum and copper, with thermal conductivities of about 250 W/(m·K) and 400 W/(m·K), respectively. Significantly, the thermal expansion coefficient of metals differs markedly from those of the materials employed in semiconductor electronics (mostly silicon); one should add here the low electrical resistivity metals possess. By contrast, natural single-crystal diamond is known to feature the highest thermal conductivity of all the bulk materials studied thus far, as high as 2,200 W/(m·K). Needless to say, it cannot be applied in heat removal technology because of high cost. Recently, SiC- and AlN-based ceramics have started enjoying wide use as heat sink materials; the thermal conductivity of such composites, however, is inferior to that of metals by nearly a factor two. This prompts a challenging scientific problem to develop diamond-based composites with thermal characteristics superior to those of aluminum and copper, adjustable thermal expansion coefficient, low electrical conductivity and a moderate cost, below that of the natural single-crystal diamond. The present review addresses this problem and appraises the results reached by now in studying the possibility of developing composites in diamond-containing systems with a view of obtaining materials with a high thermal conductivity. Full article
(This article belongs to the Special Issue Composite Materials)
Open AccessReview A Novel Fabrication Method for Functionally Graded Materials under Centrifugal Force: The Centrifugal Mixed-Powder Method
Materials 2009, 2(4), 2510-2525; doi:10.3390/ma2042510
Received: 10 November 2009 / Revised: 14 December 2009 / Accepted: 18 December 2009 / Published: 23 December 2009
Cited by 30 | PDF Full-text (4636 KB) | HTML Full-text | XML Full-text
Abstract
One of the fabrication methods for functionally graded materials (FGMs) is a centrifugal solid-particle method, which is an application of the centrifugal casting technique. However, it is the difficult to fabricate FGMs containing nano-particles by the centrifugal solid-particle method. Recently, we proposed a
[...] Read more.
One of the fabrication methods for functionally graded materials (FGMs) is a centrifugal solid-particle method, which is an application of the centrifugal casting technique. However, it is the difficult to fabricate FGMs containing nano-particles by the centrifugal solid-particle method. Recently, we proposed a novel fabrication method, which we have named the centrifugal mixed-powder method, by which we can obtain FGMs containing nano-particles. Using this processing method, Cu-based FGMs containing SiC particles and Al-based FGMs containing TiO2 nano-particles on their surfaces have been fabricated. In this article, the microstructure and mechanical property of Cu/SiC and Al/TiO2 FGMs, fabricated by the centrifugal mixed-powder method are reviewed. Full article
(This article belongs to the Special Issue Composite Materials)

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Open AccessCorrection Correction: Pan, J.L. Progress to a Gallium-Arsenide Deep-Center Laser. Materials 2009, 2, 1599-1635
Materials 2009, 2(4), 1795; doi:10.3390/ma2041795
Received: 4 November 2009 / Published: 5 November 2009
PDF Full-text (178 KB) | HTML Full-text | XML Full-text
Abstract The author acknowledges that her former graduate students, J. E. McManis and M. Gupta, collected the data in the recent review [1], as indicated by the references therein. [...] Full article

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