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Materials, Volume 4, Issue 5 (May 2011), Pages 825-951

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Research

Jump to: Review

Open AccessArticle Preparation, Characterization and Performance of Templated Silica Membranes in Non-Osmotic Desalination
Materials 2011, 4(5), 845-856; doi:10.3390/ma4040845
Received: 8 April 2011 / Revised: 18 April 2011 / Accepted: 28 April 2011 / Published: 2 May 2011
Cited by 10 | PDF Full-text (1043 KB) | HTML Full-text | XML Full-text
Abstract
In this work we investigate the potential of a polyethylene glycol-polypropylene glycol-polyethylene glycol, tri-block copolymer as a template for a hybrid carbon/silica membrane for use in the non-osmotic desalination of seawater. Silica samples were loaded with varying amounts of tri-block copolymer and calcined
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In this work we investigate the potential of a polyethylene glycol-polypropylene glycol-polyethylene glycol, tri-block copolymer as a template for a hybrid carbon/silica membrane for use in the non-osmotic desalination of seawater. Silica samples were loaded with varying amounts of tri-block copolymer and calcined in a vacuum to carbonize the template and trap it within the silica matrix. The resultant xerogels were analyzed with FTIR, Thermogravimetric analysis (TGA) and N2 sorption techniques, wherein it was determined that template loadings of 10 and 20% produced silica networks with enhanced pore volumes and appropriately sized pores for desalination. Membranes were created via two different routes and tested with feed concentrations of 3, 10 and 35 ppk of NaCl at room temperature employing a transmembrane pressure drop of 85% (in most cases >95%) and fluxes higher than 1.6 kg m−2 h−1. Furthermore, the carbonized templated membranes displayed equal or improved performance compared to similarly prepared non-templated silica membranes, with the best results of a flux of 3.7 kg m−2 h−1 with 98.5% salt rejection capacity, exceeding previous literature reports. In addition, the templated silica membranes exhibited superior hydrostability demonstrating their potential for long-term operation. Full article
(This article belongs to the Special Issue Porous Materials 2011)
Open AccessArticle Synthesis and Characterization of Multilayered Diamond Coatings for Biomedical Implants
Materials 2011, 4(5), 857-868; doi:10.3390/ma4050857
Received: 6 April 2011 / Revised: 25 April 2011 / Accepted: 5 May 2011 / Published: 9 May 2011
Cited by 20 | PDF Full-text (1028 KB) | HTML Full-text | XML Full-text
Abstract
With incredible hardness and excellent wear-resistance, nanocrystalline diamond (NCD) coatings are gaining interest in the biomedical community as articulating surfaces of structural implant devices. The focus of this study was to deposit multilayered diamond coatings of alternating NCD and microcrystalline diamond (MCD) layers
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With incredible hardness and excellent wear-resistance, nanocrystalline diamond (NCD) coatings are gaining interest in the biomedical community as articulating surfaces of structural implant devices. The focus of this study was to deposit multilayered diamond coatings of alternating NCD and microcrystalline diamond (MCD) layers on Ti-6Al-4V alloy surfaces using microwave plasma chemical vapor deposition (MPCVD) and validate the multilayer coating’s effect on toughness and adhesion. Multilayer samples were designed with varying NCD to MCD thickness ratios and layer numbers. The surface morphology and structural characteristics of the coatings were studied with X-ray diffraction (XRD), Raman spectroscopy, and atomic force microscopy (AFM). Coating adhesion was assessed by Rockwell indentation and progressive load scratch adhesion tests. Multilayered coatings shown to exhibit the greatest adhesion, comparable to single-layered NCD coatings, were the multilayer samples having the lowest average grain sizes and the highest titanium carbide to diamond ratios. Full article
Open AccessArticle Thermodynamic Origin of the Vitreous Transition
Materials 2011, 4(5), 869-892; doi:10.3390/ma4050869
Received: 22 March 2011 / Revised: 19 April 2011 / Accepted: 5 May 2011 / Published: 9 May 2011
Cited by 4 | PDF Full-text (547 KB) | HTML Full-text | XML Full-text
Abstract
The vitreous transition is characterized by a freezing of atomic degrees of freedom at a temperature Tg depending on the heating and cooling rates. A kinetic origin is generally attributed to this phenomenon instead of a thermodynamic one which we develop here.
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The vitreous transition is characterized by a freezing of atomic degrees of freedom at a temperature Tg depending on the heating and cooling rates. A kinetic origin is generally attributed to this phenomenon instead of a thermodynamic one which we develop here. Completed homogeneous nucleation laws reflecting the energy saving due to Fermi energy equalization of nascent crystals and their melt are used. They are applied to bulk metallic glasses and extended to inorganic glasses and polymers. A transition T*g among various Tg corresponds to a crystal homogeneous nucleation temperature, leading to a preliminary formation of a cluster distribution during the relaxation time preceding the long steady-state nucleation time of crystals in small samples. The thermally-activated energy barrier ΔG*2ls/kBT at T*g for homogeneous nucleation is nearly the same in all glass-forming melts and determined by similar values of viscosity and a thermally-activated diffusion barrier from melt to cluster. The glass transition T*g is a material constant and a linear function of the energy saving associated with charge transfers from nascent clusters to the melt. The vitreous transition and the melting temperatures alone are used to predict the free-volume disappearance temperature equal to the Vogel-Fulcher-Tammann temperature of fragile glass-forming melts, in agreement with many viscosity measurements. The reversible thermodynamic vitreous transition is determined by the disappearance temperature T*g of the fully-relaxed enthalpy Hr that is not time dependent; the observed specific heat jump at T*g is equal to the proportionality coefficient of Hr with (T*g − Ta) for T ≤ T*g as expected from the enthalpy excess stored by a quenched undercooled melt at the annealing temperature Ta and relaxed towards an equilibrium vitreous state. However, the heat flux measurements found in literature over the last 50 years only gave an out-of-equilibrium Tg since the enthalpy is continuous at T*g without visible heat jump. Full article
(This article belongs to the Special Issue Advances in Bulk Metallic Glasses)
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Open AccessArticle Role of Titanium Surface Topography and Surface Wettability on Focal Adhesion Kinase Mediated Signaling in Fibroblasts
Materials 2011, 4(5), 893-907; doi:10.3390/ma4050893
Received: 8 April 2011 / Revised: 22 April 2011 / Accepted: 5 May 2011 / Published: 9 May 2011
Cited by 10 | PDF Full-text (752 KB) | HTML Full-text | XML Full-text
Abstract
Changes of titanium surface roughness and surface free energy may influence protein absorption that increases cell differentiation through activation of focal adhesion kinase related pathways. However, the influence of titanium surface roughness and hydrophilicity on fibroblast behavior is not well understood. The aim
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Changes of titanium surface roughness and surface free energy may influence protein absorption that increases cell differentiation through activation of focal adhesion kinase related pathways. However, the influence of titanium surface roughness and hydrophilicity on fibroblast behavior is not well understood. The aim of this study was to investigate the influence of topography and hydrophilicity on fibroblast attachment, spreading, morphology, intracellular signaling, proliferation, and collagen I mRNA levels. Using a cellular FAK knockout (FAK−/−) model and wild-type (WT) controls, we also investigated the contribution of adhesion in fibroblasts cultured on smooth (PT), sand-blasted, large grit, acid-etched (SLA) and hydrophilic SLA topographies. Loss of FAK did not significantly affect fibroblast attachment to any surface, but SLA and hydrophilic SLA surface attenuated spreading of WT cells significantly more than FAK−/− fibroblasts. Both FAK−/− and WT cells formed numerous focal adhesions on PT surfaces, but significantly less on SLA and hydrophilic SLA surfaces. In WT cells, phosphorylation levels of FAK were lower on SLA and hydrophilic SLA in comparison with PT 24 h post seeding. Labeling of cells with antibodies to cortactin showed that FAK−/−cells contained significantly more cortactin-rich focal adhesion in comparison with WT cells on PT surfaces, but not on SLA or hydrophilic SLA. ERK 1/2 phosphorylation was highest in WT cells on all surfaces which correlated with collagen I expression levels. We conclude that fibroblasts are sensitive to changes in surface roughness and hydrophilicity, with adhesive interactions mediated through FAK, an important modulator of fibroblast response. Full article
(This article belongs to the Special Issue Advances in Biomaterials 2011)
Open AccessArticle Nanohardness and Residual Stress in TiN Coatings
Materials 2011, 4(5), 929-940; doi:10.3390/ma4050929
Received: 29 March 2011 / Revised: 27 April 2011 / Accepted: 13 May 2011 / Published: 17 May 2011
Cited by 7 | PDF Full-text (483 KB) | HTML Full-text | XML Full-text
Abstract
TiN films were prepared by the Cathodic arc evaporation deposition method under different negative substrate bias. AFM image analyses show that the growth mode of biased coatings changes from 3D island to lateral when the negative bias potential is increased. Nanohardness of the
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TiN films were prepared by the Cathodic arc evaporation deposition method under different negative substrate bias. AFM image analyses show that the growth mode of biased coatings changes from 3D island to lateral when the negative bias potential is increased. Nanohardness of the thin films was measured by nanoindentation, and residual stress was determined using Grazing incidence X ray diffraction. The maximum value of residual stress is reached at −100 V substrate bias coinciding with the biggest values of adhesion and nanohardness. Nanoindentation measurement proves that the force-depth curve shifts due to residual stress. The experimental results demonstrate that nanohardness is seriously affected by the residual stress. Full article
(This article belongs to the Special Issue Hard Materials: Advances in Synthesis and Understanding)
Open AccessArticle Layer Transfer from Chemically Etched 150 mm Porous Si Substrates
Materials 2011, 4(5), 941-951; doi:10.3390/ma4050941
Received: 20 April 2011 / Accepted: 19 May 2011 / Published: 23 May 2011
PDF Full-text (331 KB) | HTML Full-text | XML Full-text
Abstract
We demonstrate for the first time the successful layer transfer of an epitaxially grown monocrystalline Si film from a purely chemically etched porous Si substrate of 150 mm diameter to a glass carrier. The surface conditioning for all Si layer transfer processes based on
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We demonstrate for the first time the successful layer transfer of an epitaxially grown monocrystalline Si film from a purely chemically etched porous Si substrate of 150 mm diameter to a glass carrier. The surface conditioning for all Si layer transfer processes based on porous Si has been, up to now without exception, carried out by electrochemical etching. In contrast, our chemical stain etching process uses an aqueous HF-rich HF/HNO3 solution. The porosity increases with increasing doping concentration of the Si substrate wafer and with increasing porous layer thickness. In contrast to the electrochemically etched double layers, the porosity profile of the stain etched substrates is highest at the original wafer surface and lowest at the interface between the porous layer and the Si bulk. The epitaxy process is adapted to the high porosity at the surface with regard to the reorganization of the porous layer. Full article
(This article belongs to the Special Issue Porous Materials 2011)
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Review

Jump to: Research

Open AccessReview Electrochemically Formed Porous Silica
Materials 2011, 4(5), 825-844; doi:10.3390/ma4050825
Received: 7 March 2011 / Revised: 6 April 2011 / Accepted: 20 April 2011 / Published: 26 April 2011
Cited by 4 | PDF Full-text (1209 KB) | HTML Full-text | XML Full-text
Abstract
Controlled electrochemical formation of porous silica can be realized in dilute aqueous, neutral-pH, fluoride medium. Formation of a porous film is initiated by sweeping the potential applied to silicon to values higher than 20 V. Film formation, reaching a steady state, may be
[...] Read more.
Controlled electrochemical formation of porous silica can be realized in dilute aqueous, neutral-pH, fluoride medium. Formation of a porous film is initiated by sweeping the potential applied to silicon to values higher than 20 V. Film formation, reaching a steady state, may be pursued in a wide range of potentials, including lower potentials. The origin of a threshold potential for porous film initiation has been explained quantitatively. All of the films appear mesoporous. Films grown at high potentials exhibit a variety of macrostructures superimposed on the mesoporosity. These macrostructures result from selective dissolution of silica induced by local pH lowering due to oxygen evolution. Films grown at potentials lower than 15 V appear uniform on the micrometer scale. However, all of the films also exhibit a stratified structure on the scale of a few tens of nanometres. This periodic structure can be traced back to the oscillatory behavior observed during the electrochemical dissolution of silicon in fluoride medium. It suggests that periodic breaking of the growing film may be responsible for this morphology. Full article
(This article belongs to the Special Issue Porous Materials 2011)
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Open AccessReview Magnetic Nanoparticles Embedded in a Silicon Matrix
Materials 2011, 4(5), 908-928; doi:10.3390/ma4050908
Received: 13 April 2011 / Accepted: 12 May 2011 / Published: 17 May 2011
Cited by 19 | PDF Full-text (1113 KB) | HTML Full-text | XML Full-text
Abstract
This paper represents a short overview of nanocomposites consisting of magnetic nanoparticles incorporated into the pores of a porous silicon matrix by two different methods. On the one hand, nickel is electrochemically deposited whereas the nanoparticles are precipitated on the pore walls. The
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This paper represents a short overview of nanocomposites consisting of magnetic nanoparticles incorporated into the pores of a porous silicon matrix by two different methods. On the one hand, nickel is electrochemically deposited whereas the nanoparticles are precipitated on the pore walls. The size of these particles is between 2 and 6 nm. These particles cover the pore walls and form a tube-like arrangement. On the other hand, rather well monodispersed iron oxide nanoparticles, of 5 and 8 nm respectively, are infiltrated into the pores. From their size the particles would be superparamagnetic if isolated but due to magnetic interactions between them, ordering of magnetic moments occurs below a blocking temperature and thus the composite system displays a ferromagnetic behavior. This transition temperature of the nanocomposite can be varied by changing the filling factor of the particles within the pores. Thus samples with magnetic properties which are variable in a broad range can be achieved, which renders this composite system interesting not only for basic research but also for applications, especially because of the silicon base material which makes it possible for today’s process technology. Full article
(This article belongs to the Special Issue Porous Materials 2011)
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