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Materials, Volume 4, Issue 2 (February 2011) – 7 articles , Pages 339-456

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Open AccessArticle
Iron Oxide Silica Derived from Sol-Gel Synthesis
Materials 2011, 4(2), 448-456; https://doi.org/10.3390/ma4020448 - 17 Feb 2011
Cited by 26 | Viewed by 7262
Abstract
In this work we investigate the effect of iron oxide embedded in silica matrices as a function of Fe/Si molar ratio and sol pH. To achieve homogeneous dispersion of iron oxide particles, iron nitrate nonahydrate was dissolved in hydrogen peroxide and was mixed [...] Read more.
In this work we investigate the effect of iron oxide embedded in silica matrices as a function of Fe/Si molar ratio and sol pH. To achieve homogeneous dispersion of iron oxide particles, iron nitrate nonahydrate was dissolved in hydrogen peroxide and was mixed with tetraethyl orthosilicate and ethanol in a sol-gel synthesis method. Increasing the calcination temperature led to a reduction in surface area, although the average pore radius remained almost constant at about 10 Å, independent of the Fe/Si molar ratio or sol pH. Hence, the densification of the matrix was accompanied by similar reduction in pore volume. However, calcination at 700 °C resulted in samples with similar surface area though the iron oxide content increased from 5% to 50% Fe/Si molar ratio. As metal oxide particles have lower surface area than polymeric silica structures, these results strongly suggest that the iron oxides opposed the silica structure collapse. The effect of sol pH was found to be less significant than the Fe/Si molar ratio in the formation of molecular sieve structures derived from iron oxide silica. Full article
(This article belongs to the Special Issue Sol-Gel Technique)
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Open AccessReview
A Review of Domain Modelling and Domain Imaging Techniques in Ferroelectric Crystals
Materials 2011, 4(2), 417-447; https://doi.org/10.3390/ma4020417 - 16 Feb 2011
Cited by 48 | Viewed by 7104
Abstract
The present paper reviews models of domain structure in ferroelectric crystals, thin films and bulk materials. Common crystal structures in ferroelectric materials are described and the theory of compatible domain patterns is introduced. Applications to multi-rank laminates are presented. Alternative models employing phase-field [...] Read more.
The present paper reviews models of domain structure in ferroelectric crystals, thin films and bulk materials. Common crystal structures in ferroelectric materials are described and the theory of compatible domain patterns is introduced. Applications to multi-rank laminates are presented. Alternative models employing phase-field and related techniques are reviewed. The paper then presents methods of observing ferroelectric domain structure, including optical, polarized light, scanning electron microscopy, X-ray and neutron diffraction, atomic force microscopy and piezo-force microscopy. Use of more than one technique for unambiguous identification of the domain structure is also described. Full article
(This article belongs to the Special Issue Advances in Ferroelectric & Piezoelectric Materials)
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Open AccessArticle
Electro-Optic Effects in Colloidal Dispersion of Metal Nano-Rods in Dielectric Fluid
Materials 2011, 4(2), 390-416; https://doi.org/10.3390/ma4020390 - 14 Feb 2011
Cited by 19 | Viewed by 6491
Abstract
In modern transformation optics, one explores metamaterials with properties that vary from point to point in space and time, suitable for application in devices such as an “optical invisibility cloak” and an “optical black hole”. We propose an approach to construct spatially varying [...] Read more.
In modern transformation optics, one explores metamaterials with properties that vary from point to point in space and time, suitable for application in devices such as an “optical invisibility cloak” and an “optical black hole”. We propose an approach to construct spatially varying and switchable metamaterials that are based on colloidal dispersions of metal nano-rods (NRs) in dielectric fluids, in which dielectrophoretic forces, originating in the electric field gradients, create spatially varying configurations of aligned NRs. The electric field controls orientation and concentration of NRs and thus modulates the optical properties of the medium. Using gold (Au) NRs dispersed in toluene, we demonstrate electrically induced change in refractive index on the order of 0.1. Full article
(This article belongs to the Special Issue Next Wave of Metamaterials)
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Open AccessArticle
Different Molecular Weight Chitosan-Based Membranes for Tissue Regeneration
Materials 2011, 4(2), 380-389; https://doi.org/10.3390/ma4020380 - 10 Feb 2011
Cited by 9 | Viewed by 5898
Abstract
Natural polymers, such as chitosan, obtained from chitin, are been widely studied for use in the tissue regeneration field. This study established a protocol to attain membranes made from this biopolymer, consisting of high or low molecular weight chitosan. The biocompatibility of these [...] Read more.
Natural polymers, such as chitosan, obtained from chitin, are been widely studied for use in the tissue regeneration field. This study established a protocol to attain membranes made from this biopolymer, consisting of high or low molecular weight chitosan. The biocompatibility of these membranes was histologically evaluated, comparing them to collagen membrane surgically implanted in rat subcutaneous tissue. Fifteen Holtzmann rats were divided in three experimental groups: High and Low Molecular Weight Chitosan membranes (HMWC and LMWC) and Collagen membranes (C—control group); each of them with three experimental periods: 7, 15 and 30 days. As a result, after the seven days evaluation, the membranes were present and associated with a variable degree of inflammation, and after the 15 and 30 days evaluations, the membranes were absent in all groups. It is concluded that the chitosan-based membranes were successfully attained and presented comparable resorption times to collagen membranes. Full article
(This article belongs to the Special Issue Chitins)
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Open AccessArticle
Coalescence and Collisions of Gold Nanoparticles
Materials 2011, 4(2), 368-379; https://doi.org/10.3390/ma4020368 - 28 Jan 2011
Cited by 10 | Viewed by 7624
Abstract
We study the assembling of small gold clusters subject to collisions and close contact coalescence by using molecular dynamics simulations to simulate events that occur typically in the sputtering process of synthesis. Our results support the notion that the kinetics of coalescence processes [...] Read more.
We study the assembling of small gold clusters subject to collisions and close contact coalescence by using molecular dynamics simulations to simulate events that occur typically in the sputtering process of synthesis. Our results support the notion that the kinetics of coalescence processes strongly determine the geometry and structure of the final particle. While impact velocities, relative orientations, and the initial shape of the interacting particles are unlikely to strictly determine the structural details of the newly formed particle, we found that high initial temperatures and/or impact velocities increase the probability of appearance of icosahedral-like structures, Wulff polyhedra are likely to be formed as a product of the interactions between nanospheres, while the appearance of fcc particles of approximately cuboctahedral shape is mainly due to the interaction between icosahedra. Full article
(This article belongs to the Special Issue Metal Nanoparticles)
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Open AccessArticle
In vitro Biocompatibility of New Silver(I) Coordination Compound Coated-Surfaces for Dental Implant Applications
Materials 2011, 4(2), 355-367; https://doi.org/10.3390/ma4020355 - 28 Jan 2011
Cited by 26 | Viewed by 5447
Abstract
Biofilm formation on implant materials causes a common problem: resistance to aggressive pharmacological agents as well as host defenses. Therefore, to reduce bacterial adhesion to implant surfaces we propose to use silver(I) coordination networks as it is known that silver is the most [...] Read more.
Biofilm formation on implant materials causes a common problem: resistance to aggressive pharmacological agents as well as host defenses. Therefore, to reduce bacterial adhesion to implant surfaces we propose to use silver(I) coordination networks as it is known that silver is the most powerful antimicrobial inorganic agent. As a model surface, self-assembled monolayers (SAMs) on gold Au(111) was used to permit permanent attachment of our silver(I) coordination networks. The surface coatings showed typical nano-structured surfaces with a good biocompatibility for soft-tissue integration with fibroblast cells. Full article
(This article belongs to the Special Issue Dental Biomaterials)
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Open AccessArticle
A New Highly Bioactive Composite for Scaffold Applications: A Feasibility Study
Materials 2011, 4(2), 339-354; https://doi.org/10.3390/ma4020339 - 28 Jan 2011
Cited by 31 | Viewed by 6461
Abstract
Hydroxyapatite (HA) has been widely investigated as scaffolding material for bone tissue engineering, mainly for its excellent biocompatibility. Presently, there is an increasing interest in the composites of hydroxyapatite with bioactive glasses, with the aim to obtain systems with improved bioactivity or mechanical [...] Read more.
Hydroxyapatite (HA) has been widely investigated as scaffolding material for bone tissue engineering, mainly for its excellent biocompatibility. Presently, there is an increasing interest in the composites of hydroxyapatite with bioactive glasses, with the aim to obtain systems with improved bioactivity or mechanical properties. Moreover, modifying the ratio between bioactive glass and hydroxyapatite results in the possibility of controlling the reaction rate of the composite scaffold in the human body. However, high temperature treatments are usually required in order to sinter HA-based composites, causing the bioactive glass to crystallize into a glass-ceramic, with possible negative effects on its bioactivity. In the present research work, a glass composition belonging to the Na2O-CaO-P2O5-SiO2 system, with a reduced tendency to crystallize, is applied to realize HA-based composites. The novel samples can be sintered at a relative low temperature (750 °C) compared to the widely studied HA/45S5 Bioglass® composites. This fact greatly helps to preserve the amorphous nature of the glass, with excellent effects in terms of bioactivity, according to in vitro tests. As a first application, the obtained composites are also tested to realize highly porous scaffolds by means of the standard burning out method. Full article
(This article belongs to the Special Issue Tissue Engineering Scaffolds)
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