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Materials, Volume 6, Issue 7 (July 2013), Pages 2578-3034

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Open AccessArticle Influence of Fracture Width on Sealability in High-Strength and Ultra-Low-Permeability Concrete in Seawater
Materials 2013, 6(7), 2578-2594; doi:10.3390/ma6072578
Received: 27 March 2013 / Revised: 17 June 2013 / Accepted: 19 June 2013 / Published: 25 June 2013
Cited by 3 | PDF Full-text (1446 KB) | HTML Full-text | XML Full-text
Abstract
For cementitious composites and materials, the sealing of fractures can occur in water by the precipitation of calcium compounds. In this study, the sealing behavior in a macro-fractured high-strength and ultra-low-permeability concrete (HSULPC) specimen was investigated in simulated seawater using micro-focus X-ray computed
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For cementitious composites and materials, the sealing of fractures can occur in water by the precipitation of calcium compounds. In this study, the sealing behavior in a macro-fractured high-strength and ultra-low-permeability concrete (HSULPC) specimen was investigated in simulated seawater using micro-focus X-ray computed tomography (CT). In particular, the influence of fracture width (0.10 and 0.25 mm) on fracture sealing was investigated. Precipitation occurred mainly at the outermost parts of the fractured surface of the specimen for both fracture widths. While significant sealing was observed for the fracture width of 0.10 mm, sealing was not attained for the fracture width of 0.25 mm within the observation period (49 days). Examination of the sealed regions on the macro-fracture was performed using a three-dimensional image registration technique and applying image subtraction between the CT images of the HSULPC specimen before and after maintaining the specimen in simulated seawater. The temporal change of the sealing deposits for the fracture width of 0.10 mm was much larger than that for the fracture width of 0.25 mm. Therefore, it is concluded that the sealability of the fracture in the HSULPC is affected by the fracture width. Full article
(This article belongs to the Section Advanced Composites)
Open AccessArticle Localized Overheating Phenomena and Optimization of Spark-Plasma Sintering Tooling Design
Materials 2013, 6(7), 2612-2632; doi:10.3390/ma6072612
Received: 22 April 2013 / Revised: 9 June 2013 / Accepted: 17 June 2013 / Published: 25 June 2013
Cited by 17 | PDF Full-text (1017 KB) | HTML Full-text | XML Full-text
Abstract
The present paper shows the application of a three-dimensional coupled electrical, thermal, mechanical finite element macro-scale modeling framework of Spark Plasma Sintering (SPS) to an actual problem of SPS tooling overheating, encountered during SPS experimentation. The overheating phenomenon is analyzed by varying the
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The present paper shows the application of a three-dimensional coupled electrical, thermal, mechanical finite element macro-scale modeling framework of Spark Plasma Sintering (SPS) to an actual problem of SPS tooling overheating, encountered during SPS experimentation. The overheating phenomenon is analyzed by varying the geometry of the tooling that exhibits the problem, namely by modeling various tooling configurations involving sequences of disk-shape spacers with step-wise increasing radii. The analysis is conducted by means of finite element simulations, intended to obtain temperature spatial distributions in the graphite press-forms, including punches, dies, and spacers; to identify the temperature peaks and their respective timing, and to propose a more suitable SPS tooling configuration with the avoidance of the overheating as a final aim. Electric currents-based Joule heating, heat transfer, mechanical conditions, and densification are imbedded in the model, utilizing the finite-element software COMSOL™, which possesses a distinguishing ability of coupling multiple physics. Thereby the implementation of a finite element method applicable to a broad range of SPS procedures is carried out, together with the more specific optimization of the SPS tooling design when dealing with excessive heating phenomena. Full article
(This article belongs to the Special Issue Progress in Net-shaped PM (Powder Metallurgical) Parts)
Open AccessCommunication A Fundamental Limitation of Small Diameter Single-Walled Carbon Nanotube Synthesis—A Scaling Rule of the Carbon Nanotube Yield with Catalyst Volume
Materials 2013, 6(7), 2633-2641; doi:10.3390/ma6072633
Received: 29 May 2013 / Revised: 18 June 2013 / Accepted: 24 June 2013 / Published: 2 July 2013
Cited by 9 | PDF Full-text (283 KB) | HTML Full-text | XML Full-text
Abstract
Understanding the fundamental mechanisms and limiting processes of the growth of single-walled carbon nanotube (SWCNT) would serve as a guide to achieve further control on structural parameters of SWCNT. In this paper, we have studied the growth kinetics of a series of SWCNT
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Understanding the fundamental mechanisms and limiting processes of the growth of single-walled carbon nanotube (SWCNT) would serve as a guide to achieve further control on structural parameters of SWCNT. In this paper, we have studied the growth kinetics of a series of SWCNT forests continuously spanning a wide range of diameters (1.9–3.2 nm), and have revealed an additional fundamental growth limiting process where the mass of the individual SWCNT is determined by the individual catalyst volume. Calculation of the conversion rate of carbon atoms into CNTs per Fe atom is 2 × 102 atoms per second. This rate limiting process provides an important understanding where the larger diameter SWCNT would grow faster, and thus be more suited for mass production. Full article
Open AccessArticle Spinnability and Characteristics of Polyvinylidene Fluoride (PVDF)-based Bicomponent Fibers with a Carbon Nanotube (CNT) Modified Polypropylene Core for Piezoelectric Applications
Materials 2013, 6(7), 2642-2661; doi:10.3390/ma6072642
Received: 26 March 2013 / Revised: 5 June 2013 / Accepted: 14 June 2013 / Published: 3 July 2013
Cited by 16 | PDF Full-text (1536 KB) | HTML Full-text | XML Full-text
Abstract
This research explains the melt spinning of bicomponent fibers, consisting of a conductive polypropylene (PP) core and a piezoelectric sheath (polyvinylidene fluoride). Previously analyzed piezoelectric capabilities of polyvinylidene fluoride (PVDF) are to be exploited in sensor filaments. The PP compound contains a 10
[...] Read more.
This research explains the melt spinning of bicomponent fibers, consisting of a conductive polypropylene (PP) core and a piezoelectric sheath (polyvinylidene fluoride). Previously analyzed piezoelectric capabilities of polyvinylidene fluoride (PVDF) are to be exploited in sensor filaments. The PP compound contains a 10 wt % carbon nanotubes (CNTs) and 2 wt % sodium stearate (NaSt). The sodium stearate is added to lower the viscosity of the melt. The compound constitutes the fiber core that is conductive due to a percolation CNT network. The PVDF sheath’s piezoelectric effect is based on the formation of an all-trans conformation β phase, caused by draw-winding of the fibers. The core and sheath materials, as well as the bicomponent fibers, are characterized through different analytical methods. These include wide-angle X-ray diffraction (WAXD) to analyze crucial parameters for the development of a crystalline β phase. The distribution of CNTs in the polymer matrix, which affects the conductivity of the core, was investigated by transmission electron microscopy (TEM). Thermal characterization is carried out by conventional differential scanning calorimetry (DSC). Optical microscopy is used to determine the fibers’ diameter regularity (core and sheath). The materials’ viscosity is determined by rheometry. Eventually, an LCR tester is used to determine the core’s specific resistance. Full article
(This article belongs to the Special Issue Smart Polymers and Polymeric Structures)
Open AccessArticle Diffusion Study by IR Micro-Imaging of Molecular Uptake and Release on Mesoporous Zeolites of Structure Type CHA and LTA
Materials 2013, 6(7), 2662-2688; doi:10.3390/ma6072662
Received: 2 May 2013 / Revised: 12 June 2013 / Accepted: 17 June 2013 / Published: 4 July 2013
Cited by 16 | PDF Full-text (1216 KB) | HTML Full-text | XML Full-text
Abstract
The presence of mesopores in the interior of microporous particles may significantly improve their transport properties. Complementing previous macroscopic transient sorption experiments and pulsed field gradient NMR self-diffusion studies with such materials, the present study is dedicated to an in-depth study of molecular
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The presence of mesopores in the interior of microporous particles may significantly improve their transport properties. Complementing previous macroscopic transient sorption experiments and pulsed field gradient NMR self-diffusion studies with such materials, the present study is dedicated to an in-depth study of molecular uptake and release on the individual particles of mesoporous zeolitic specimens, notably with samples of the narrow-pore structure types, CHA and LTA. The investigations are focused on determining the time constants and functional dependences of uptake and release. They include a systematic variation of the architecture of the mesopores and of the guest molecules under study as well as a comparison of transient uptake with blocked and un-blocked mesopores. In addition to accelerating intracrystalline mass transfer, transport enhancement by mesopores is found to be, possibly, also caused by a reduction of transport resistances on the particle surfaces. Full article
(This article belongs to the Special Issue Diffusion in Micropores and Mesopores 2013)
Open AccessArticle Effect of Ni Core Structure on the Electrocatalytic Activity of Pt-Ni/C in Methanol Oxidation
Materials 2013, 6(7), 2689-2700; doi:10.3390/ma6072689
Received: 16 February 2013 / Revised: 7 April 2013 / Accepted: 16 April 2013 / Published: 8 July 2013
Cited by 9 | PDF Full-text (1056 KB) | HTML Full-text | XML Full-text
Abstract
Methanol oxidation catalysts comprising an outer Pt-shell with an inner Ni-core supported on carbon, (Pt-Ni/C), were prepared with either crystalline or amorphous Ni core structures. Structural comparisons of the two forms of catalyst were made using transmission electron microscopy (TEM), X-ray diffraction (XRD)
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Methanol oxidation catalysts comprising an outer Pt-shell with an inner Ni-core supported on carbon, (Pt-Ni/C), were prepared with either crystalline or amorphous Ni core structures. Structural comparisons of the two forms of catalyst were made using transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and methanol oxidation activity compared using CV and chronoamperometry (CA). While both the amorphous Ni core and crystalline Ni core structures were covered by similar Pt shell thickness and structure, the Pt-Ni(amorphous)/C catalyst had higher methanol oxidation activity. The amorphous Ni core thus offers improved Pt usage efficiency in direct methanol fuel cells. Full article
(This article belongs to the Special Issue Advances in Catalytic Materials)
Open AccessArticle Millimeter Wave Radiations Affect Membrane Hydration in Phosphatidylcholine Vesicles
Materials 2013, 6(7), 2701-2712; doi:10.3390/ma6072701
Received: 8 May 2013 / Revised: 20 June 2013 / Accepted: 2 July 2013 / Published: 9 July 2013
Cited by 2 | PDF Full-text (498 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A clear understanding of the response of biological systems to millimeter waves exposure is of increasing interest for the scientific community due to the recent convincing use of these radiations in the ultrafast wireless communications. Here we report a deuterium nuclear magnetic resonance
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A clear understanding of the response of biological systems to millimeter waves exposure is of increasing interest for the scientific community due to the recent convincing use of these radiations in the ultrafast wireless communications. Here we report a deuterium nuclear magnetic resonance spectroscopy (2H-NMR) investigation on the effects of millimeter waves in the 53–78 GHz range on phosphocholine bio-mimetic membranes. Millimeter waves significantly affect the polar interface of the membrane causing a decrease of the heavy water quadrupole splitting. This effect is as important as inducing the transition from the fluid to the gel phase when the membrane exposure occurs in the neighborhood of the transition point. On the molecular level, the above effect can be well explained by membrane dehydration induced by the radiation. Full article
(This article belongs to the Special Issue Biointerfaces and Materials)
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Open AccessArticle Cytotoxic Effects of Hydroxylated Fullerenes in Three Types of Liver Cells
Materials 2013, 6(7), 2713-2722; doi:10.3390/ma6072713
Received: 27 April 2013 / Revised: 17 June 2013 / Accepted: 2 July 2013 / Published: 9 July 2013
Cited by 6 | PDF Full-text (480 KB) | HTML Full-text | XML Full-text
Abstract
Fullerenes C60 have attracted considerable attention in the biomedical field due to their interesting properties. Although there has been a concern that C60 could be metabolized to hydroxylated fullerenes (C60(OH)x) in vivo, there is little information
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Fullerenes C60 have attracted considerable attention in the biomedical field due to their interesting properties. Although there has been a concern that C60 could be metabolized to hydroxylated fullerenes (C60(OH)x) in vivo, there is little information on the effect of hydroxylated C60 on liver cells. In the present study, we evaluated the cytotoxic effects of fullerene C60 and various hydroxylated C60 derivatives, C60(OH)2, C60(OH)6–12, C60(OH)12 and C60(OH)36, with three different types of liver cells, dRLh-84, HepG2 and primary cultured rat hepatocytes. C60, C60(OH)2 and C60(OH)36 exhibited little or no cytotoxicity in all of the cell types, while C60(OH)6–12 and C60(OH)12 induced cytotoxic effects in dRLh-84 cells, accompanied by the appearance of numerous vacuoles around the nucleus. Moreover, mitochondrial activity in liver cells was significantly inhibited by C60(OH)6–12 and C60(OH)12. These results indicate that the number of hydroxyl groups on C60(OH)x contribute to the difference of their cytotoxic potential and mitochondrial damage in liver cells. Full article
Open AccessArticle Fractional Factorial Design Study on the Performance of GAC-Enhanced Electrocoagulation Process Involved in Color Removal from Dye Solutions
Materials 2013, 6(7), 2723-2746; doi:10.3390/ma6072723
Received: 21 January 2013 / Revised: 8 April 2013 / Accepted: 10 May 2013 / Published: 10 July 2013
Cited by 29 | PDF Full-text (1206 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this study was to determine the effects of main factors and interactions on the color removal performance from dye solutions using the electrocoagulation process enhanced by adsorption on Granular Activated Carbon (GAC). In this study, a mathematical approach was conducted
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The aim of this study was to determine the effects of main factors and interactions on the color removal performance from dye solutions using the electrocoagulation process enhanced by adsorption on Granular Activated Carbon (GAC). In this study, a mathematical approach was conducted using a two-level fractional factorial design (FFD) for a given dye solution. Three textile dyes: Acid Blue 74, Basic Red 1, and Reactive Black 5 were used. Experimental factors used and their respective levels were: current density (2.73 or 27.32 A/m2), initial pH of aqueous dye solution (3 or 9), electrocoagulation time (20 or 180 min), GAC dose (0.1 or 0.5 g/L), support electrolyte (2 or 50 mM), initial dye concentration (0.05 or 0.25 g/L) and current type (Direct Current—DC or Alternative Pulsed Current—APC). GAC-enhanced electrocoagulation performance was analyzed statistically in terms of removal efficiency, electrical energy, and electrode material consumptions, using modeling polynomial equations. The statistical significance of GAC dose level on the performance of GAC enhanced electrocoagulation and the experimental conditions that favor the process operation of electrocoagulation in APC regime were determined. The local optimal experimental conditions were established using a multi-objective desirability function method. Full article
(This article belongs to the Special Issue Advances in Colorants)
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Open AccessArticle Synthesis of New RE3+ Doped Li1+xTa1−xTixO3 (RE: Eu, Sm, Er, Tm, and Dy) Phosphors with Various Emission Colors
Materials 2013, 6(7), 2768-2776; doi:10.3390/ma6072768
Received: 19 April 2013 / Revised: 5 May 2013 / Accepted: 8 June 2013 / Published: 11 July 2013
Cited by 2 | PDF Full-text (1122 KB) | HTML Full-text | XML Full-text
Abstract
New phosphors with various emission colors for RE3+ doped Li1+xTa1−xTixO3 (LTT) (RE: Eu, Sm, Er, Tm, and Dy) were synthesized by electric furnace at 1423 K for 15 h. The microstructure of the
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New phosphors with various emission colors for RE3+ doped Li1+xTa1−xTixO3 (LTT) (RE: Eu, Sm, Er, Tm, and Dy) were synthesized by electric furnace at 1423 K for 15 h. The microstructure of the host material and the photoluminescence (PL) property were determined and compared to those of RE3+ doped Li1+xNb1−xTixO3 (LNT). In the LTT phosphor, the highest PL intensity was achieved for the mixture composition Li1.11Ta0.89Ti0.11O3 with a LiTaO3 structure, although it has an M-phase superstructure. In the LTT host material, the effective activators were Eu3+ and Sm3+ ions, in contrast to the LNT host material. Here, we discuss the relationship between PL property and the host material’s structure. Full article
(This article belongs to the Special Issue Luminescent Materials 2013)
Open AccessArticle Amino Alcohol Oxidation with Gold Catalysts: The Effect of Amino Groups
Materials 2013, 6(7), 2777-2788; doi:10.3390/ma6072777
Received: 28 February 2013 / Revised: 22 May 2013 / Accepted: 14 June 2013 / Published: 12 July 2013
Cited by 1 | PDF Full-text (752 KB) | HTML Full-text | XML Full-text
Abstract
Gold catalysts have been prepared by sol immobilization using Tetrakis(hydroxymethyl) phosphonium chloride (THPC) as a protective and reducing agent or by deposition on different supports (Al2O3, TiO2, MgAl2O4, and MgO). The catalytic systems
[...] Read more.
Gold catalysts have been prepared by sol immobilization using Tetrakis(hydroxymethyl) phosphonium chloride (THPC) as a protective and reducing agent or by deposition on different supports (Al2O3, TiO2, MgAl2O4, and MgO). The catalytic systems have been tested in the liquid phase oxidation of aminoalcohols (serinol and ethanolamine) and the corresponding polyols (glycerol and ethylene glycol). This comparison allowed us to state that the presence of amino groups has a crucial effect on the catalytic performance, in particular decreasing the durability to the catalysts, but did not substantially vary the selectivity. A support effect has been as well established. Full article
(This article belongs to the Special Issue Advances in Catalytic Materials)
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Open AccessArticle Optical Constants of Crystallized TiO2 Coatings Prepared by Sol-Gel Process
Materials 2013, 6(7), 2819-2830; doi:10.3390/ma6072819
Received: 9 April 2013 / Revised: 9 June 2013 / Accepted: 9 July 2013 / Published: 12 July 2013
Cited by 28 | PDF Full-text (517 KB) | HTML Full-text | XML Full-text
Abstract
Titanium oxide coatings have been deposited by the sol-gel dip-coating method. Crystallization of titanium oxide coatings was then achieved through thermal annealing at temperatures above 400 °C. The structural properties and surface morphology of the crystallized coatings were studied by micro-Raman spectroscopy and
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Titanium oxide coatings have been deposited by the sol-gel dip-coating method. Crystallization of titanium oxide coatings was then achieved through thermal annealing at temperatures above 400 °C. The structural properties and surface morphology of the crystallized coatings were studied by micro-Raman spectroscopy and atomic force microscopy, respectively. Characterization technique, based on least-square fitting to the measured reflectance and transmittance spectra, is used to determine the refractive indices of the crystallized TiO2 coatings. The stability of the synthesized sol was also investigated by dynamic light scattering particle size analyzer. The influence of the thermal annealing on the optical properties was then discussed. The increase in refractive index with high temperature thermal annealing process was observed, obtaining refractive index values from 1.98 to 2.57 at He-Ne laser wavelength of 633 nm. The Raman spectroscopy and atomic force microscopy studies indicate that the index variation is due to the changes in crystalline phase, density, and morphology during thermal annealing. Full article
(This article belongs to the Special Issue Advances in Surface Coatings 2013)
Open AccessArticle Self-Healing of Microcracks in Engineered Cementitious Composites (ECC) Under a Natural Environment
Materials 2013, 6(7), 2831-2845; doi:10.3390/ma6072831
Received: 5 June 2013 / Revised: 2 July 2013 / Accepted: 8 July 2013 / Published: 15 July 2013
Cited by 13 | PDF Full-text (358 KB) | HTML Full-text | XML Full-text
Abstract
This paper builds on previous self-healing engineered cementitious composites (ECC) research by allowing ECC to heal outdoors, in the natural environment, under random and sometimes extreme environmental conditions. Development of an ECC material that can heal itself in the natural environment could lower
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This paper builds on previous self-healing engineered cementitious composites (ECC) research by allowing ECC to heal outdoors, in the natural environment, under random and sometimes extreme environmental conditions. Development of an ECC material that can heal itself in the natural environment could lower infrastructure maintenance costs and allow for more sustainable development in the future by increasing service life and decreasing the amount of resources and energy needed for repairs. Determining to what extent current ECC materials self-heal in the natural environment is the first step in the development of an ECC that can completely heal itself when exposed to everyday environmental conditions. This study monitored outdoor ECC specimens for one year using resonant frequency (RF) and mechanical reloading to determine the rate and extent of self-healing in the natural environment. It was found that the level of RF, stiffness, and first cracking strength recovery increased as the duration of natural environment exposure increased. For specimens that underwent multiple damage cycles, it was found that the level of recovery was highly dependent on the average temperature and amount of precipitation between each damage event. However, RF, stiffness, and first cracking strength recovery data for specimens that underwent multiple loading cycles suggest that self-healing functionality can be maintained under multiple damage events. Full article
(This article belongs to the Special Issue Self-healing Concrete)
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Open AccessArticle Synthesis and Enhanced Phosphate Recovery Property of Porous Calcium Silicate Hydrate Using Polyethyleneglycol as Pore-Generation Agent
Materials 2013, 6(7), 2846-2861; doi:10.3390/ma6072846
Received: 13 May 2013 / Revised: 1 July 2013 / Accepted: 8 July 2013 / Published: 15 July 2013
Cited by 5 | PDF Full-text (467 KB) | HTML Full-text | XML Full-text
Abstract
The primary objective of this paper was to synthesize a porous calcium silicate hydrate (CSH) with enhanced phosphate recovery property using polyethyleneglycol (PEG) as pore-generation agent. The formation mechanism of porous CSH was proposed. PEG molecules were inserted into the void region of
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The primary objective of this paper was to synthesize a porous calcium silicate hydrate (CSH) with enhanced phosphate recovery property using polyethyleneglycol (PEG) as pore-generation agent. The formation mechanism of porous CSH was proposed. PEG molecules were inserted into the void region of oxygen–silicon tetrahedron chains and the layers of CSH. A steric hindrance layer was generated to prevent the aggregation of solid particles. A porous structure was formed due to the residual space caused by the removal of PEG through incineration. This porous CSH exhibited highly enhanced solubility of Ca2+ and OH due to the decreased particle size, declined crystalline, and increased specific surface area (SBET) and pore volume. Supersaturation was increased in the wastewater with the enhanced solubility, which was beneficial to the formation of hydroxyapatite (HAP) crystallization. Thus, phosphate can be recovered from wastewater by producing HAP using porous CSH as crystal seed. In addition, the regenerated phosphate-containing products (HAP) can be reused to achieve sustainable utilization of phosphate. The present research could provide an effective approach for the synthesis of porous CSH and the enhancement of phosphate recovery properties for environmental applications. Full article
(This article belongs to the Section Porous Materials)
Open AccessArticle Role of Fluxes in Optimizing the Optical Properties of Sr0.95Si2O2N2:0.05Eu2+ Green-Emitting Phosphor
Materials 2013, 6(7), 2862-2872; doi:10.3390/ma6072862
Received: 10 April 2013 / Revised: 14 June 2013 / Accepted: 8 July 2013 / Published: 15 July 2013
Cited by 7 | PDF Full-text (1194 KB) | HTML Full-text | XML Full-text
Abstract
Chlorides of NH4Cl and SrCl2 and fluorides of AlF3 and SrF2 were added to raw materials acting as the flux for preparing the SrSi2O2N2:Eu2+ phosphor. The effects of the fluxes on
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Chlorides of NH4Cl and SrCl2 and fluorides of AlF3 and SrF2 were added to raw materials acting as the flux for preparing the SrSi2O2N2:Eu2+ phosphor. The effects of the fluxes on the phase formation, particle morphology, particle size, and photoluminescence properties were investigated. The results revealed that particle size, particle morphology and photoluminescence intensity were largely dominated by the type of the flux material and its adding amount. The chloride-based flux was found to favor the formation of the SrSi2O2N2:Eu2+ phase. Among the chloride-based fluxes, the sample added with the SrCl2 flux presented the narrow particle distribution and cleaner surface, with enhanced emission intensity and an increased external quantum efficiency by 68% and 22%, respectively, compared with those of the sample without any flux adding. Full article
(This article belongs to the Special Issue Luminescent Materials)
Open AccessArticle Polymeric Materials Reinforced with Multiwall Carbon Nanotubes: A Constitutive Material Model
Materials 2013, 6(7), 2873-2891; doi:10.3390/ma6072873
Received: 12 April 2013 / Revised: 3 June 2013 / Accepted: 24 June 2013 / Published: 16 July 2013
Cited by 3 | PDF Full-text (997 KB) | HTML Full-text | XML Full-text
Abstract
In this paper we have modified an existing material model introduced by Cantournet and co-workers to take into account softening and residual strain effects observed in polymeric materials reinforced with carbon nanotubes when subjected to loading and unloading cycles. In order to assess
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In this paper we have modified an existing material model introduced by Cantournet and co-workers to take into account softening and residual strain effects observed in polymeric materials reinforced with carbon nanotubes when subjected to loading and unloading cycles. In order to assess the accuracy of the modified material model, we have compared theoretical predictions with uniaxial extension experimental data obtained from reinforced polymeric material samples. It is shown that the proposed model follows experimental data well as its maximum errors attained are lower than 2.67%, 3.66%, 7.11% and 6.20% for brominated isobutylene and paramethylstyrene copolymer reinforced with multiwall carbon nanotubes (BIMSM-MWCNT), reinforced natural rubber (NR-MWCNT), polybutadiene-carbon black (PB-CB), and PC/ABS reinforced with single-wall carbon nanotubes (SWCNT), respectively. Full article
(This article belongs to the Special Issue Constitutive Behavior of Composite Materials)
Open AccessArticle Order-Induced Selectivity Increase of Cu60Pd40 in the Semi-Hydrogenation of Acetylene
Materials 2013, 6(7), 2958-2977; doi:10.3390/ma6072958
Received: 22 May 2013 / Revised: 26 June 2013 / Accepted: 13 July 2013 / Published: 16 July 2013
Cited by 11 | PDF Full-text (923 KB) | HTML Full-text | XML Full-text
Abstract
The two structural modifications of Cu60Pd40 were synthesized as bulk powders and tested as unsupported model catalysts in the semi-hydrogenation of acetylene. The partly ordered low-temperature modification (CsCl type of structure) showed an outstanding ethylene selectivity of >90% over 20
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The two structural modifications of Cu60Pd40 were synthesized as bulk powders and tested as unsupported model catalysts in the semi-hydrogenation of acetylene. The partly ordered low-temperature modification (CsCl type of structure) showed an outstanding ethylene selectivity of >90% over 20 h on stream while the disordered high-temperature modification (Cu type of structure) was 20% less selective, indicating an influence of the degree of order in the crystal structure on the catalytic properties. The results are supported by XRD and in situ XPS experiments. The latter suggest the existence of partly isolated Pd sites on the surface. In situ PGAA investigations proved the absence of metal hydride formation during reaction. Quantum chemical calculations of the electronic structure of both modifications using the CPA-FPLO framework revealed significant differences in their respective density of states, thus still leaving open the question of whether the degree of structural order or/and the electronic hybridization is the decisive factor for the observed difference in selectivity. Full article
Open AccessArticle In Vivo Osteogenic Differentiation of Human Embryoid Bodies in an Injectable in Situ-Forming Hydrogel
Materials 2013, 6(7), 2978-2988; doi:10.3390/ma6072978
Received: 14 June 2013 / Revised: 8 July 2013 / Accepted: 11 July 2013 / Published: 17 July 2013
Cited by 4 | PDF Full-text (805 KB) | HTML Full-text | XML Full-text
Abstract
In this study, we examined the in vivo osteogenic differentiation of human embryoid bodies (hEBs) by using an injectable in situ-forming hydrogel. A solution containing MPEG-b-(polycaprolactone-ran-polylactide) (MCL) and hEBs was easily prepared at room temperature. The MCL solution
[...] Read more.
In this study, we examined the in vivo osteogenic differentiation of human embryoid bodies (hEBs) by using an injectable in situ-forming hydrogel. A solution containing MPEG-b-(polycaprolactone-ran-polylactide) (MCL) and hEBs was easily prepared at room temperature. The MCL solution with hEBs and osteogenic factors was injected into nude mice and developed into in situ-forming hydrogels at the injection sites; these hydrogels maintained their shape even after 12 weeks in vivo, thereby indicating that the in situ-forming MCL hydrogel was a suitable scaffold for hEBs. The in vivo osteogenic differentiation was observed only in the in situ gel-forming MCL hydrogel in the presence of hEBs and osteogenic factors. In conclusion, this preliminary study suggests that hEBs and osteogenic factors embedded in an in situ-forming MCL hydrogel may provide numerous benefits as a noninvasive alternative for allogeneic tissue engineering applications. Full article
(This article belongs to the Section Biomaterials)
Open AccessArticle Preparation and Characterization of New Geopolymer-Epoxy Resin Hybrid Mortars
Materials 2013, 6(7), 2989-3006; doi:10.3390/ma6072989
Received: 21 June 2013 / Revised: 29 June 2013 / Accepted: 9 July 2013 / Published: 17 July 2013
Cited by 18 | PDF Full-text (1347 KB) | HTML Full-text | XML Full-text
Abstract
The preparation and characterization of metakaolin-based geopolymer mortars containing an organic epoxy resin are presented here for the first time. The specimens have been prepared by means of an innovative in situ co-reticulation process, in mild conditions, of commercial epoxy based organic resins
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The preparation and characterization of metakaolin-based geopolymer mortars containing an organic epoxy resin are presented here for the first time. The specimens have been prepared by means of an innovative in situ co-reticulation process, in mild conditions, of commercial epoxy based organic resins and geopolymeric slurry. In this way, geopolymer based hybrid mortars characterized by a different content of normalized sand (up to 66% in weight) and by a homogeneous dispersion of the organic resin have been obtained. Once hardened, these new materials show improved compressive strength and toughness in respect to both the neat geopolymer and the hybrid pastes since the organic polymer provides a more cohesive microstructure, with a reduced amount of microcracks. The microstructural characterization allows to point out the presence of an Interfacial Transition Zone similar to that observed in cement based mortars and concretes. A correlation between microstructural features and mechanical properties has been studied too. Full article
Open AccessArticle Charged Polymers Transport under Applied Electric Fields in Periodic Channels
Materials 2013, 6(7), 3007-3021; doi:10.3390/ma6073007
Received: 3 June 2013 / Revised: 10 July 2013 / Accepted: 11 July 2013 / Published: 19 July 2013
PDF Full-text (2454 KB) | HTML Full-text | XML Full-text
Abstract
By molecular dynamics simulations, we investigated the transport of charged polymers in applied electric fields in confining environments, which were straight cylinders of uniform or non-uniform diameter. In the simulations, the solvent was modeled explicitly and, also, the counterions and coions of added
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By molecular dynamics simulations, we investigated the transport of charged polymers in applied electric fields in confining environments, which were straight cylinders of uniform or non-uniform diameter. In the simulations, the solvent was modeled explicitly and, also, the counterions and coions of added salt. The electrophoretic velocities of charged chains in relation to electrolyte friction, hydrodynamic effects due to the solvent, and surface friction were calculated. We found that the velocities were higher if counterions were moved away from the polymeric domain, which led to a decrease in hydrodynamic friction. The topology of the surface played a key role in retarding the motion of the polyelectrolyte and, even more so, in the presence of transverse electric fields. The present study showed that a possible way of improving separation resolution is by controlling the motion of counterions or electrolyte friction effects. Full article
(This article belongs to the Special Issue Diffusion in Micropores and Mesopores 2013)
Open AccessArticle The Influence of Alkoxy Substitutions on the Properties of Diketopyrrolopyrrole-Phenyl Copolymers for Solar Cells
Materials 2013, 6(7), 3022-3034; doi:10.3390/ma6073022
Received: 20 May 2013 / Revised: 2 July 2013 / Accepted: 9 July 2013 / Published: 22 July 2013
Cited by 2 | PDF Full-text (873 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A previously reported diketopyrrolopyrrole (DPP)-phenyl copolymer is modified by adding methoxy or octyloxy side chains on the phenyl spacer. The influence of these alkoxy substitutions on the physical, opto-electronic properties, and photovoltaic performance were investigated. It was found that the altered physical properties
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A previously reported diketopyrrolopyrrole (DPP)-phenyl copolymer is modified by adding methoxy or octyloxy side chains on the phenyl spacer. The influence of these alkoxy substitutions on the physical, opto-electronic properties, and photovoltaic performance were investigated. It was found that the altered physical properties correlated with an increase in chain flexibility. Well-defined oligomers were synthesized to verify the observed structure-property relationship. Surprisingly, methoxy substitution on the benzene spacer resulted in higher melting and crystallization temperatures in the synthesized oligomers. This trend is not observed in the polymers, where the improved interactions are most likely counteracted by the larger conformational possibilities in the polymer chain upon alkoxy substitution. The best photovoltaic performance was obtained for the parent polymer: fullerene blends whereas the modifications on the other two polymers result in reduced open-circuit voltage and varying current densities under similar processing conditions. The current densities could be related to different polymer: fullerene blend morphologies. These results show that supposed small structural alterations such as methoxy substitution already significantly altered the physical properties of the parent polymer and also that oligomers and polymers respond divergent to structural alterations made on a parent structure. Full article
(This article belongs to the Section Materials for Energy Applications)

Review

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Open AccessReview A Review of Luminescent Anionic Nano System: d10 Metallocyanide Excimers and Exciplexes in Alkali Halide Hosts
Materials 2013, 6(7), 2595-2611; doi:10.3390/ma6072595
Received: 2 May 2013 / Revised: 8 June 2013 / Accepted: 18 June 2013 / Published: 25 June 2013
Cited by 3 | PDF Full-text (918 KB) | HTML Full-text | XML Full-text
Abstract
Dicyanoaurate, dicyanoargentate, and dicyanocuprate ions in solution and doped in different alkali halide hosts exhibit interesting photophysical and photochemical behavior, such as multiple emission bands, exciplex tuning, optical memory, and thermochromism. This is attributed to the formation of different sizes of nanoclusters in
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Dicyanoaurate, dicyanoargentate, and dicyanocuprate ions in solution and doped in different alkali halide hosts exhibit interesting photophysical and photochemical behavior, such as multiple emission bands, exciplex tuning, optical memory, and thermochromism. This is attributed to the formation of different sizes of nanoclusters in solution and in doped hosts. A series of spectroscopic methods (luminescence, UV-reflectance, IR, and Raman) as well as theoretical calculations have confirmed the existence of excimers and exciplexes. This leads to the tunability of these nano systems over a wide wavelength interval. The population of these nanoclusters varies with temperature and external laser irradiation, which explains the thermochromism and optical memory. DFT calculations indicate an MLCT transition for each nanocluster and the emission energy decreases with increasing cluster size. This is in agreement with the relatively long life-time for the emission peaks and the multiple emission peaks dependence upon cluster concentration. Full article
(This article belongs to the Special Issue Luminescent Materials 2013)
Open AccessReview The Influence of Processing and the Polymorphism of Lignocellulosic Fillers on the Structure and Properties of Composite Materials—A Review
Materials 2013, 6(7), 2747-2767; doi:10.3390/ma6072747
Received: 19 February 2013 / Revised: 12 April 2013 / Accepted: 6 June 2013 / Published: 11 July 2013
Cited by 12 | PDF Full-text (342 KB) | HTML Full-text | XML Full-text
Abstract
Cellulose is the most important and the most abundant plant natural polymer. It shows a number of interesting properties including those making it attractive as a filler of composite materials with a thermoplastic polymer matrix. Production of such composite materials, meeting the standards
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Cellulose is the most important and the most abundant plant natural polymer. It shows a number of interesting properties including those making it attractive as a filler of composite materials with a thermoplastic polymer matrix. Production of such composite materials, meeting the standards of green technology, has increased from 0.36 million tons in 2007 to 2.33 million tons in 2012. It is predicted that by 2020 their production will reach 3.45 million tons. Production of biocomposites with lignocellulosic components poses many problems that should be addressed. This paper is a review of the lignocellulosic materials currently used as polymer fillers. First, the many factors determining the macroscopic properties of such composites are described, with particular attention paid to the poor interphase adhesion between the polymer matrix and a lignocellulosic filler and to the effects of cellulose occurrence in polymorphic varieties. The phenomenon of cellulose polymorphism is very important from the point of view of controlling the nucleation abilities of the lignocellulosic filler and hence the mechanical properties of composites. Macroscopic properties of green composites depend also on the parameters of processing which determine the magnitude and range of shearing forces. The influence of shearing forces appearing upon processing the supermolecular structure of the polymer matrix is also discussed. An important problem from the viewpoint of ecology is the possibility of composite recycling which should be taken into account at the design stage. The methods for recycling of the composites made of thermoplastic polymers filled with renewable lignocellulosic materials are presented and discussed. This paper is a review prepared on the basis of currently available literature which describes the many aspects of the problems related to the possibility of using lignocellulosic components for production of composites with polymers. Full article
(This article belongs to the Special Issue Advances in Cellulosic Materials)
Open AccessReview Persistent Luminescence in Non-Eu2+-Doped Compounds: A Review
Materials 2013, 6(7), 2789-2818; doi:10.3390/ma6072789
Received: 20 May 2013 / Revised: 18 June 2013 / Accepted: 3 July 2013 / Published: 12 July 2013
Cited by 84 | PDF Full-text (647 KB) | HTML Full-text | XML Full-text
Abstract
During the past few decades, the research on persistent luminescent materials has focused mainly on Eu2+-doped compounds. However, the yearly number of publications on non-Eu2+-based materials has also increased steadily. By now, the number of known persistent phosphors has
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During the past few decades, the research on persistent luminescent materials has focused mainly on Eu2+-doped compounds. However, the yearly number of publications on non-Eu2+-based materials has also increased steadily. By now, the number of known persistent phosphors has increased to over 200, of which over 80% are not based on Eu2+, but rather, on intrinsic host defects, transition metals (manganese, chromium, copper, etc.) or trivalent rare earths (cerium, terbium, dysprosium, etc.). In this review, we present an overview of these non-Eu2+-based persistent luminescent materials and their afterglow properties. We also take a closer look at some remaining challenges, such as the excitability with visible light and the possibility of energy transfer between multiple luminescent centers. Finally, we summarize the necessary elements for a complete description of a persistent luminescent material, in order to allow a more objective comparison of these phosphors. Full article
(This article belongs to the Special Issue Luminescent Materials 2013)
Open AccessReview Self-Ordered Titanium Dioxide Nanotube Arrays: Anodic Synthesis and Their Photo/Electro-Catalytic Applications
Materials 2013, 6(7), 2892-2957; doi:10.3390/ma6072892
Received: 1 March 2013 / Revised: 2 May 2013 / Accepted: 5 June 2013 / Published: 16 July 2013
Cited by 31 | PDF Full-text (1873 KB) | HTML Full-text | XML Full-text
Abstract
Metal oxide nanotubes have become a widely investigated material, more specifically, self-organized titania nanotube arrays synthesized by electrochemical anodization. As a highly investigated material with a wide gamut of applications, the majority of published literature focuses on the solar-based applications of this material.
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Metal oxide nanotubes have become a widely investigated material, more specifically, self-organized titania nanotube arrays synthesized by electrochemical anodization. As a highly investigated material with a wide gamut of applications, the majority of published literature focuses on the solar-based applications of this material. The scope of this review summarizes some of the recent advances made using metal oxide nanotube arrays formed via anodization in solar-based applications. A general methodology for theoretical modeling of titania surfaces in solar applications is also presented. Full article
(This article belongs to the Special Issue Advances in Catalytic Materials)

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