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Materials, Volume 7, Issue 4 (April 2014), Pages 2395-3336

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Open AccessArticle Bioeutectic® Ceramics for Biomedical Application Obtained by Laser Floating Zone Method. In vivo Evaluation
Materials 2014, 7(4), 2395-2410; doi:10.3390/ma7042395
Received: 4 December 2013 / Revised: 20 February 2014 / Accepted: 10 March 2014 / Published: 25 March 2014
Cited by 4 | PDF Full-text (4354 KB) | HTML Full-text | XML Full-text
Abstract
In this study, the Bioeutectic® blocks were inserted into the critical size defects of eight rabbits, using both tibiae, and the physical and chemical nature of the remodeled interface between the Bioeutectic® implants and the surrounding bone were performed at [...] Read more.
In this study, the Bioeutectic® blocks were inserted into the critical size defects of eight rabbits, using both tibiae, and the physical and chemical nature of the remodeled interface between the Bioeutectic® implants and the surrounding bone were performed at four and 15 months. The results showed a new fully mineralized bone growing in direct contact with the implants. The ionic exchange, taking place at the implant interface with the body fluids was essential in the process of the implant integration through a dissolution-precipitation-transformation mechanism. The study found the interface biologically and chemically active over the 15 months implantation period. The osteoblastic cells migrated towards the interface and colonized the surface at the contact areas with the bone. The new developed apatite structure of porous morphology mimics natural bone. Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle Polypropylene Production Optimization in Fluidized Bed Catalytic Reactor (FBCR): Statistical Modeling and Pilot Scale Experimental Validation
Materials 2014, 7(4), 2440-2458; doi:10.3390/ma7042440
Received: 13 December 2013 / Revised: 12 March 2014 / Accepted: 13 March 2014 / Published: 27 March 2014
Cited by 8 | PDF Full-text (816 KB) | HTML Full-text | XML Full-text
Abstract
Propylene is one type of plastic that is widely used in our everyday life. This study focuses on the identification and justification of the optimum process parameters for polypropylene production in a novel pilot plant based fluidized bed reactor. This first-of-its-kind statistical [...] Read more.
Propylene is one type of plastic that is widely used in our everyday life. This study focuses on the identification and justification of the optimum process parameters for polypropylene production in a novel pilot plant based fluidized bed reactor. This first-of-its-kind statistical modeling with experimental validation for the process parameters of polypropylene production was conducted by applying ANNOVA (Analysis of variance) method to Response Surface Methodology (RSM). Three important process variables i.e., reaction temperature, system pressure and hydrogen percentage were considered as the important input factors for the polypropylene production in the analysis performed. In order to examine the effect of process parameters and their interactions, the ANOVA method was utilized among a range of other statistical diagnostic tools such as the correlation between actual and predicted values, the residuals and predicted response, outlier t plot, 3D response surface and contour analysis plots. The statistical analysis showed that the proposed quadratic model had a good fit with the experimental results. At optimum conditions with temperature of 75 °C, system pressure of 25 bar and hydrogen percentage of 2%, the highest polypropylene production obtained is 5.82% per pass. Hence it is concluded that the developed experimental design and proposed model can be successfully employed with over a 95% confidence level for optimum polypropylene production in a fluidized bed catalytic reactor (FBCR). Full article
(This article belongs to the Section Manufacturing Processes and Systems)
Open AccessArticle Preparation of Chitosan-Based Hemostatic Sponges by Supercritical Fluid Technology
Materials 2014, 7(4), 2459-2473; doi:10.3390/ma7042459
Received: 23 December 2013 / Revised: 7 March 2014 / Accepted: 20 March 2014 / Published: 27 March 2014
Cited by 1 | PDF Full-text (866 KB) | HTML Full-text | XML Full-text
Abstract
Using ammonium bicarbonate (AB) particles as a porogen, chitosan (CS)-based hemostatic porous sponges were prepared in supercritical carbon dioxide due to its low viscosity, small surface tension, and good compatibility with organic solvent. Fourier transform infrared spectroscopy (FTIR) spectra demonstrated that the [...] Read more.
Using ammonium bicarbonate (AB) particles as a porogen, chitosan (CS)-based hemostatic porous sponges were prepared in supercritical carbon dioxide due to its low viscosity, small surface tension, and good compatibility with organic solvent. Fourier transform infrared spectroscopy (FTIR) spectra demonstrated that the chemical compositions of CS and poly-(methyl vinyl ether-co-maleic anhydride) (PVM/MA) were not altered during the phase inversion process. The morphology and structure of the sponge after the supercritical fluid (SCF) process were observed by scanning electron microscopy (SEM). The resulting hemostatic sponges showed a relatively high porosity (about 80%) with a controllable pore size ranging from 0.1 to 200 µm. The concentration of PVM/MA had no significant influence on the porosity of the sponges. Comparative experiments on biological assessment and hemostatic effect between the resulting sponges and Avitene® were also carried out. With the incorporation of PVM/MA into the CS-based sponges, the water absorption rate of the sponges increased significantly, and the CS-PVM/MA sponges showed a similar water absorption rate (about 90%) to that of Avitene®. The results of the whole blood clotting experiment and animal experiment also demonstrated that the clotting ability of the CS-PVM/MA sponges was similar to that of Avitene®. All these results elementarily verified that the sponges prepared in this study were suitable for hemostasis and demonstrated the feasibility of using SCF-assisted phase inversion technology to produce hemostatic porous sponges. Full article
(This article belongs to the Section Biomaterials)
Open AccessArticle Performance-Based Specifications of Workability Characteristics of Prestressed, Precast Self-Consolidating Concrete—A North American Prospective
Materials 2014, 7(4), 2474-2489; doi:10.3390/ma7042474
Received: 9 January 2014 / Revised: 18 February 2014 / Accepted: 21 March 2014 / Published: 27 March 2014
Cited by 5 | PDF Full-text (457 KB) | HTML Full-text | XML Full-text
Abstract
Adequate selection of material constituents and test methods are necessary for workability specifications and performance of hardened concrete. An experimental program was performed to evaluate the suitability of various test methods for workability assessment and to propose performance specifications of prestressed concrete. [...] Read more.
Adequate selection of material constituents and test methods are necessary for workability specifications and performance of hardened concrete. An experimental program was performed to evaluate the suitability of various test methods for workability assessment and to propose performance specifications of prestressed concrete. In total, 33 self-consolidating concrete (SCC) mixtures made with various mixture proportioning parameters, including maximum size and type of aggregate, type and content of binder, and w/cm were evaluated. Correlations among various test results used in evaluating the workability responses are established. It is recommended that SCC should have slump flow values of 635–760 mm. To ensure proper filling capacity greater than 80%, such concrete should have a passing ability that corresponds to L-box blocking ratio (h2/h1) ≥ 0.5, J-Ring flow of 570–685 mm, slump flow minus J-Ring flow diameter ≤75 mm. Moreover, Stable SCC should develop a column segregation index lower than 5%, and rate of settlement at 30 min of 0.27%/h for SCC proportioned with 12.5 or 9.5 mm MSA. It is recommended that SCC should have a plastic viscosity of 100–225 Pa·s and 100–400 Pa·s for concrete made with crushed aggregate and gravel, respectively, to ensure proper workability. Full article
Open AccessArticle Field Effect Transistor Biosensor Using Antigen Binding Fragment for Detecting Tumor Marker in Human Serum
Materials 2014, 7(4), 2490-2500; doi:10.3390/ma7042490
Received: 3 February 2014 / Revised: 15 March 2014 / Accepted: 19 March 2014 / Published: 27 March 2014
Cited by 10 | PDF Full-text (536 KB) | HTML Full-text | XML Full-text
Abstract
Detection of tumor markers is important for cancer diagnosis. Field-effect transistors (FETs) are a promising method for the label-free detection of trace amounts of biomolecules. However, detection of electrically charged proteins using antibody-immobilized FETs is limited by ionic screening by the large [...] Read more.
Detection of tumor markers is important for cancer diagnosis. Field-effect transistors (FETs) are a promising method for the label-free detection of trace amounts of biomolecules. However, detection of electrically charged proteins using antibody-immobilized FETs is limited by ionic screening by the large probe molecules adsorbed to the transistor gate surface, reducing sensor responsiveness. Here, we investigated the effect of probe molecule size on the detection of a tumor marker, α-fetoprotein (AFP) using a FET biosensor. We demonstrated that the small receptor antigen binding fragment (Fab), immobilized on a sensing surface as small as 2–3 nm, offers a higher degree of sensitivity and a wider concentration range (100 pg/mL–1 μg/mL) for the FET detection of AFP in buffer solution, compared to the whole antibody. Therefore, the use of a small Fab probe molecule instead of a whole antibody is shown to be effective for improving the sensitivity of AFP detection in FET biosensors. Furthermore, we also demonstrated that a Fab-immobilized FET subjected to a blocking treatment, to avoid non-specific interactions, could sensitively and selectively detect AFP in human serum. Full article
(This article belongs to the Special Issue Advanced Nanomaterials for Biosensors)
Open AccessArticle Tunneling Conductivity and Piezoresistivity of Composites Containing Randomly Dispersed Conductive Nano-Platelets
Materials 2014, 7(4), 2501-2521; doi:10.3390/ma7042501
Received: 31 October 2013 / Revised: 2 December 2013 / Accepted: 18 March 2014 / Published: 28 March 2014
Cited by 7 | PDF Full-text (633 KB) | HTML Full-text | XML Full-text
Abstract
In this study, a three-dimensional continuum percolation model was developed based on a Monte Carlo simulation approach to investigate the percolation behavior of an electrically insulating matrix reinforced with conductive nano-platelet fillers. The conductivity behavior of composites rendered conductive by randomly dispersed [...] Read more.
In this study, a three-dimensional continuum percolation model was developed based on a Monte Carlo simulation approach to investigate the percolation behavior of an electrically insulating matrix reinforced with conductive nano-platelet fillers. The conductivity behavior of composites rendered conductive by randomly dispersed conductive platelets was modeled by developing a three-dimensional finite element resistor network. Parameters related to the percolation threshold and a power-low describing the conductivity behavior were determined. The piezoresistivity behavior of conductive composites was studied employing a reoriented resistor network emulating a conductive composite subjected to mechanical strain. The effects of the governing parameters, i.e., electron tunneling distance, conductive particle aspect ratio and size effects on conductivity behavior were examined. Full article
(This article belongs to the Special Issue Nanocomposites of Polymers and Inorganic Particles 2013)
Open AccessArticle Structural Properties of Zinc Oxide Nanorods Grown on Al-Doped Zinc Oxide Seed Layer and Their Applications in Dye-Sensitized Solar Cells
Materials 2014, 7(4), 2522-2533; doi:10.3390/ma7042522
Received: 25 January 2014 / Revised: 20 March 2014 / Accepted: 24 March 2014 / Published: 28 March 2014
Cited by 7 | PDF Full-text (1286 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We fabricated zinc oxide (ZnO) nanorods (NRs) with Al-doped ZnO (AZO) seed layers and dye-sensitized solar cells (DSSCs) employed the ZnO NRs between a TiO2 photoelectrode and a fluorine-doped SnO2 (FTO) electrode. The growth rate of the NRs was strongly [...] Read more.
We fabricated zinc oxide (ZnO) nanorods (NRs) with Al-doped ZnO (AZO) seed layers and dye-sensitized solar cells (DSSCs) employed the ZnO NRs between a TiO2 photoelectrode and a fluorine-doped SnO2 (FTO) electrode. The growth rate of the NRs was strongly dependent on the seed layer conditions, i.e., thickness, Al dopant and annealing temperature. Attaining a large particle size with a high crystallinity of the seed layer was vital to the well-aligned growth of the NRs. However, the growth was less related to the substrate material (glass and FTO coated glass). With optimized ZnO NRs, the DSSCs exhibited remarkably enhanced photovoltaic performance, because of the increase of dye absorption and fast carrier transfer, which, in turn, led to improved efficiency. The cell with the ZnO NRs grown on an AZO seed layer annealed at 350 °C showed a short-circuit current density (JSC) of 12.56 mA/cm2, an open-circuit voltage (VOC) of 0.70 V, a fill factor (FF) of 0.59 and a power conversion efficiency (PCE, η) of 5.20% under air mass 1.5 global (AM 1.5G) illumination of 100 mW/cm2. Full article
(This article belongs to the Special Issue New Energy Materials)
Open AccessArticle Effect of Native Oxide Film on Commercial Magnesium Alloys Substrates and Carbonate Conversion Coating Growth and Corrosion Resistance
Materials 2014, 7(4), 2534-2560; doi:10.3390/ma7042534
Received: 4 February 2014 / Revised: 19 March 2014 / Accepted: 21 March 2014 / Published: 28 March 2014
Cited by 4 | PDF Full-text (1352 KB) | HTML Full-text | XML Full-text
Abstract
Possible relations between the native oxide film formed spontaneously on the AZ31 and AZ61 magnesium alloy substrates with different surface finish, the chemistry of the outer surface of the conversion coatings that grows after their subsequent immersion on saturated aqueous NaHCO3 [...] Read more.
Possible relations between the native oxide film formed spontaneously on the AZ31 and AZ61 magnesium alloy substrates with different surface finish, the chemistry of the outer surface of the conversion coatings that grows after their subsequent immersion on saturated aqueous NaHCO3 solution treatment and the enhancement of corrosion resistance have been studied. The significant increase in the amount of aluminum and carbonate compounds on the surface of the conversion coating formed on the AZ61 substrate in polished condition seems to improve the corrosion resistance in low chloride ion concentration solutions. In contrast, the conversion coatings formed on the AZ31 substrates in polished condition has little effect on their protective properties compared to the respective as-received surface. Full article
(This article belongs to the Special Issue Light Alloys and Their Applications)
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Open AccessArticle Assessment of the Pozzolanic Activity of a Spent Catalyst by Conductivity Measurement of Aqueous Suspensions with Calcium Hydroxide
Materials 2014, 7(4), 2561-2576; doi:10.3390/ma7042561
Received: 18 February 2014 / Revised: 7 March 2014 / Accepted: 21 March 2014 / Published: 28 March 2014
Cited by 3 | PDF Full-text (1796 KB) | HTML Full-text | XML Full-text
Abstract
The pozzolanic activity of the spent catalyst produced by fluid catalytic cracking (FCC) has been studied by various methods in recent years. However, no quick and easy method has been reported for this activity based on the associated studies. In this work, [...] Read more.
The pozzolanic activity of the spent catalyst produced by fluid catalytic cracking (FCC) has been studied by various methods in recent years. However, no quick and easy method has been reported for this activity based on the associated studies. In this work, the pozzolanic activity of a spent catalyst was investigated by measuring its electrical conductivity in aqueous suspensions of pozzolan/calcium hydroxide. The behavior of the FCC catalyst residue was compared to that of reactive and inert materials of similar chemical compositions. Further, the influence of temperature on the suspension was studied, and also, a new method was proposed in which the pozzolan/calcium hydroxide ratio was varied (with the initial presence of solid Ca(OH)2 in the system). It was concluded that the method is effective, fast and simple for evaluating the high reactivity of the catalyst. Therefore, this method is an alternative for the evaluation of the reactivity of pozzolanic materials. Full article
(This article belongs to the Special Issue Construction Materials)
Open AccessArticle Liquid Crystal Lensacons, Logarithmic and Linear Axicons
Materials 2014, 7(4), 2593-2604; doi:10.3390/ma7042593
Received: 21 February 2014 / Revised: 12 March 2014 / Accepted: 24 March 2014 / Published: 28 March 2014
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Abstract
Until now, several attempts have been made to obtain axicons by using liquid crystals. Previous results had always a considerable deviation from the linear response and the resulting aperture is square. In addition, classical fabrications methods are expensive and only produce fixed [...] Read more.
Until now, several attempts have been made to obtain axicons by using liquid crystals. Previous results had always a considerable deviation from the linear response and the resulting aperture is square. In addition, classical fabrications methods are expensive and only produce fixed phase profiles. In this study, a novel structure to obtain tunable axicons with a perfect conical shape and a circular aperture is proposed and theoretically studied. The proposed optical device is based on nematic liquid crystal and phase shifted electrical signals. A simulation program consisted of Finite Elements Method to solve the voltage distribution combined with the Frank-Oseen equation to solve the molecular position of the nematic liquid crystal is employed. This device is totally reconfigurable by using low voltage signals. The focus depth and the position of this one can be controlled electrically. Full article
(This article belongs to the Special Issue Liquid Crystals) Print Edition available
Open AccessArticle Increased Adipogenic and Decreased Chondrogenic Differentiation of Adipose Derived Stem Cells on Nanowire Surfaces
Materials 2014, 7(4), 2605-2630; doi:10.3390/ma7042605
Received: 24 February 2014 / Revised: 18 March 2014 / Accepted: 20 March 2014 / Published: 28 March 2014
Cited by 4 | PDF Full-text (1857 KB) | HTML Full-text | XML Full-text
Abstract
Despite many advances in tissue engineering, there are still significant challenges associated with restructuring, repairing, or replacing damaged tissue in the body. Currently, a major obstacle has been trying to develop a scaffold for cartilage tissue engineering that provides the correct mechanical [...] Read more.
Despite many advances in tissue engineering, there are still significant challenges associated with restructuring, repairing, or replacing damaged tissue in the body. Currently, a major obstacle has been trying to develop a scaffold for cartilage tissue engineering that provides the correct mechanical properties to endure the loads associated with articular joints as well as promote cell-scaffold interactions to aid in extracellular matrix deposition. In addition, adipogenic tissue engineering is widely growing due to an increased need for more innovative reconstructive therapies following adipose tissue traumas and cosmetic surgeries. Recently, lipoaspirate tissue has been identified as a viable alternative source for mesenchymal stem cells because it contains a supportive stroma that can easily be isolated. Adipose derived stem cells (ADSCs) can differentiate into a variety of mesodermal lineages including the adipogenic and chondrogenic phenotypes. Biodegradable polymeric scaffolds have been shown to be a promising alternative and stem cells have been widely used to evaluate the compatibility, viability, and bioactivity of these materials. Polycaprolactone is a bioresorbable polymer, which has been widely used for biomedical and tissue engineering applications. The fundamental concept behind successful synthetic tissue-engineered scaffolds is to promote progenitor cell migration, adhesion, proliferation, and induce differentiation, extracellular matrix synthesis, and finally integration with host tissue. In this study, we investigated the adhesion, proliferation, and chondrogenic and adipogenic differentiation of ADSCs on nanowire surfaces. A solvent-free gravimetric template technique was used to fabricate polycaprolactone nanowires surfaces. The results indicated that during the growth period i.e., initial 7 days of culture, the nanowire surfaces (NW) supported adhesion and proliferation of the cells that had elongated morphologies. However, cell on surfaces without nanowires had non-elongated morphologies. Further, immunofluorescence imaging of marker proteins showed that the nanowires surfaces did not appear to support chondrogenic differentiation whereas supported adipogenic differentiation of ADSCs. Full article
(This article belongs to the Special Issue Biocompatibility of Materials 2013)
Open AccessArticle Isothermal Time-Temperature-Precipitation Diagram for an Aluminum Alloy 6005A by In Situ DSC Experiments
Materials 2014, 7(4), 2631-2649; doi:10.3390/ma7042631
Received: 13 December 2013 / Revised: 27 January 2014 / Accepted: 24 March 2014 / Published: 28 March 2014
Cited by 3 | PDF Full-text (1669 KB) | HTML Full-text | XML Full-text
Abstract
Time-temperature-precipitation (TTP) diagrams deliver important material data, such as temperature and time ranges critical for precipitation during the quenching step of the age hardening procedure. Although the quenching step is continuous, isothermal TTP diagrams are often applied. Together with a so-called Quench [...] Read more.
Time-temperature-precipitation (TTP) diagrams deliver important material data, such as temperature and time ranges critical for precipitation during the quenching step of the age hardening procedure. Although the quenching step is continuous, isothermal TTP diagrams are often applied. Together with a so-called Quench Factor Analysis, they can be used to describe very different cooling paths. Typically, these diagrams are constructed based on mechanical properties or microstructures after an interrupted quenching, i.e., ex situ analyses. In recent years, an in situ calorimetric method to record continuous cooling precipitation diagrams of aluminum alloys has been developed to the application level by our group. This method has now been transferred to isothermal experiments, in which the whole heat treatment cycle was performed in a differential scanning calorimeter. The Al-Mg-Si-wrought alloy 6005A was investigated. Solution annealing at 540 °C and overcritical quenching to several temperatures between 450 °C and 250 °C were followed by isothermal soaking. Based on the heat flow curves during isothermal soaking, TTP diagrams were determined. An appropriate evaluation method has been developed. It was found that three different precipitation reactions in characteristic temperature intervals exist. Some of the low temperature reactions are not accessible in continuous cooling experiments and require isothermal studies. Full article
(This article belongs to the Special Issue Light Alloys and Their Applications)
Open AccessArticle Immobilization of Methyltrioxorhenium on Mesoporous Aluminosilicate Materials
Materials 2014, 7(4), 2650-2668; doi:10.3390/ma7042650
Received: 23 January 2014 / Revised: 13 March 2014 / Accepted: 19 March 2014 / Published: 28 March 2014
Cited by 3 | PDF Full-text (477 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The presented report focuses on an in-depth detailed characterization of immobilized methyltrioxorhenium (MTO), giving catalysts with a wide spectra of utilization. The range of mesoporous materials with different SiO2/Al2O3 ratios, namely mesoporous alumina (MA), aluminosilicates type Siral [...] Read more.
The presented report focuses on an in-depth detailed characterization of immobilized methyltrioxorhenium (MTO), giving catalysts with a wide spectra of utilization. The range of mesoporous materials with different SiO2/Al2O3 ratios, namely mesoporous alumina (MA), aluminosilicates type Siral (with Al content 60%–90%) and MCM-41, were used as supports for immobilization of MTO. The tested support materials (aluminous/siliceous) exhibited high surface area, well-defined regular structure and narrow pore size distribution of mesopores, and therefore represent excellent supports for the active components. Some of the supports were modified by zinc chloride in order to obtain catalysts with higher activities for instance in metathesis reactions. The immobilization of MTO was optimized using these supports and it was successful using all supports. The success of the immobilization of MTO and the properties of the prepared heterogeneous catalysts were characterized using X-ray Fluorescence (XRF), atomic absorption spectroscopy (AAS), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), physical adsorption of N2, ultraviolet-visible spectroscopy (UV-Vis), infrared spectroscopy (FTIR), Fourier Transform Infrared Spectroscopy (FTIR) using pyridine as a probe molecule and X-ray photoelectron spectroscopy (XPS). Furthermore, the catalytic activity of the immobilized MTO on the tested supports was demonstrated on metathesis reactions of various substrates. Full article
(This article belongs to the Section Porous Materials)
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Open AccessArticle Investigation on the Enhanced Oxidation of Ferritic/Martensitic Steel P92 in Pure Steam
Materials 2014, 7(4), 2772-2783; doi:10.3390/ma7042772
Received: 17 December 2013 / Revised: 23 January 2014 / Accepted: 25 March 2014 / Published: 3 April 2014
Cited by 2 | PDF Full-text (1028 KB) | HTML Full-text | XML Full-text
Abstract
Oxidation of ferritic/martensitic steel P92 was investigated in pure oxygen and in pure steam at 600–800 °C by thermogravimetric analysis (TGA), optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results showed that the oxidation of P92 was significantly [...] Read more.
Oxidation of ferritic/martensitic steel P92 was investigated in pure oxygen and in pure steam at 600–800 °C by thermogravimetric analysis (TGA), optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results showed that the oxidation of P92 was significantly enhanced and multilayer scale with an outer iron oxides layer formed in pure steam. At 700 °C, the gas switch markedly influenced the scaling kinetics and scale microstructure. It was supposed that the higher affinity of iron to steam would be attributed to the enhanced oxidation of P92 in pure steam, and the much easier transport of hydroxyl would account for the significant difference induced by gas switch. Full article
(This article belongs to the Special Issue Corrosion of Materials)
Open AccessArticle Directional Scattering of Semiconductor Nanoparticles Embedded in a Liquid Crystal
Materials 2014, 7(4), 2784-2794; doi:10.3390/ma7042784
Received: 27 February 2014 / Revised: 28 March 2014 / Accepted: 28 March 2014 / Published: 3 April 2014
Cited by 1 | PDF Full-text (510 KB) | HTML Full-text | XML Full-text
Abstract
Light scattering by semiconductor nanoparticles has been shown to be more complex than was believed until now. Both electric and magnetic responses emerge in the visible range. In addition, directional effects on light scattering of these nanoparticles were recently obtained. In particular, [...] Read more.
Light scattering by semiconductor nanoparticles has been shown to be more complex than was believed until now. Both electric and magnetic responses emerge in the visible range. In addition, directional effects on light scattering of these nanoparticles were recently obtained. In particular, zero backward and minimum-forward scattering are observed. These phenomena are very interesting for several applications such as, for instance, optical switches or modulators. The strong dependence of these phenomena on the properties of both the particle and the surrounding medium can be used to tune them. The electrical control on the optical properties of liquid crystals could be used to control the directional effects of embedded semiconductor nanoparticles. In this work, we theoretically analyze the effects on the directional distribution of light scattering by these particles when the refractive index of a surrounded liquid crystal changes from the ordinary to the extraordinary configuration. Several semiconductor materials and liquid crystals are studied in order to optimize the contrast between the two states. Full article
(This article belongs to the Special Issue Liquid Crystals)
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Open AccessArticle Spin Relaxation in GaAs: Importance of Electron-Electron Interactions
Materials 2014, 7(4), 2795-2814; doi:10.3390/ma7042795
Received: 11 November 2013 / Revised: 14 March 2014 / Accepted: 26 March 2014 / Published: 9 April 2014
Cited by 2 | PDF Full-text (738 KB) | HTML Full-text | XML Full-text
Abstract
We study spin relaxation in n-type bulk GaAs, due to the Dyakonov–Perel mechanism, using ensemble Monte Carlo methods. Our results confirm that spin relaxation time increases with the electronic density in the regime of moderate electronic concentrations and high temperature. We show [...] Read more.
We study spin relaxation in n-type bulk GaAs, due to the Dyakonov–Perel mechanism, using ensemble Monte Carlo methods. Our results confirm that spin relaxation time increases with the electronic density in the regime of moderate electronic concentrations and high temperature. We show that the electron-electron scattering in the non-degenerate regime significantly slows down spin relaxation. This result supports predictions by Glazov and Ivchenko. Most importantly, our findings highlight the importance of many-body interactions for spin dynamics: we show that only by properly taking into account electron-electron interactions within the simulations, results for the spin relaxation time—with respect to both electron density and temperature—will reach good quantitative agreement with corresponding experimental data. Our calculations contain no fitting parameters. Full article
(This article belongs to the Special Issue Spintronics)
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Open AccessArticle Base Catalytic Approach: A Promising Technique for the Activation of Biochar for Equilibrium Sorption Studies of Copper, Cu(II) Ions in Single Solute System
Materials 2014, 7(4), 2815-2832; doi:10.3390/ma7042815
Received: 16 December 2013 / Revised: 26 February 2014 / Accepted: 28 February 2014 / Published: 9 April 2014
Cited by 9 | PDF Full-text (748 KB) | HTML Full-text | XML Full-text
Abstract
This study examines the feasibility of catalytically pretreated biochar derived from the dried exocarp or fruit peel of mangostene with Group I alkali metal hydroxide (KOH). The pretreated char was activated in the presence of carbon dioxide gas flow at high temperature [...] Read more.
This study examines the feasibility of catalytically pretreated biochar derived from the dried exocarp or fruit peel of mangostene with Group I alkali metal hydroxide (KOH). The pretreated char was activated in the presence of carbon dioxide gas flow at high temperature to upgrade its physiochemical properties for the removal of copper, Cu(II) cations in single solute system. The effect of three independent variables, including temperature, agitation time and concentration, on sorption performance were carried out. Reaction kinetics parameters were determined by using linear regression analysis of the pseudo first, pseudo second, Elovich and intra-particle diffusion models. The regression co-efficient, R2 values were best for the pseudo second order kinetic model for all the concentration ranges under investigation. This implied that Cu(II) cations were adsorbed mainly by chemical interactions with the surface active sites of the activated biochar. Langmuir, Freundlich and Temkin isotherm models were used to interpret the equilibrium data at different temperature. Thermodynamic studies revealed that the sorption process was spontaneous and endothermic. The surface area of the activated sample was 367.10 m2/g, whereas before base activation, it was only 1.22 m2/g. The results elucidated that the base pretreatment was efficient enough to yield porous carbon with an enlarged surface area, which can successfully eliminate Cu(II) cations from waste water. Full article
Open AccessArticle Hot Corrosion Behavior of Sputtered Nanocrystalline Coating with Yttrium Addition at 900 °C
Materials 2014, 7(4), 2882-2889; doi:10.3390/ma7042882
Received: 18 December 2013 / Revised: 4 March 2014 / Accepted: 1 April 2014 / Published: 9 April 2014
PDF Full-text (755 KB) | HTML Full-text | XML Full-text
Abstract
The high temperature corrosion behavior of sputtered nanocrystalline K38 coating with and without yttrium addition under mixed molten salt film in air was investigated. Accelerated corrosion occurred on the coating without yttrium (Y) addition locally after 60 h exposure at 900 °C, [...] Read more.
The high temperature corrosion behavior of sputtered nanocrystalline K38 coating with and without yttrium addition under mixed molten salt film in air was investigated. Accelerated corrosion occurred on the coating without yttrium (Y) addition locally after 60 h exposure at 900 °C, which resulted in negative weight gain in kinetics. A uniform and protective alumina scale formed on surface of the coating containing yttrium in comparison. Y enriched particle as corrosion product was observed on the top of alumina scale. The results indicated the beneficial influence of Y on the chemical stability of the protective scale in the presence of chloride. The mechanism was discussed. Full article
(This article belongs to the Special Issue Corrosion of Materials)
Open AccessArticle Interaction and UV-Stability of Various Organic Capping Agents on the Surface of Anatase Nanoparticles
Materials 2014, 7(4), 2890-2912; doi:10.3390/ma7042890
Received: 29 December 2013 / Revised: 20 March 2014 / Accepted: 25 March 2014 / Published: 10 April 2014
Cited by 8 | PDF Full-text (681 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Anatase nanoparticles synthesized by the sol-gel method were surface-functionalized with long alkyl chain coupling agents as compatibilizers for a nonpolar environment, containing different anchor groups for surface interaction namely phosphonate (dodecyl phosphonate), carboxylate (dodecanoic acid), sulfate (sodium dodecyl sulphate), and amine (dodecyl [...] Read more.
Anatase nanoparticles synthesized by the sol-gel method were surface-functionalized with long alkyl chain coupling agents as compatibilizers for a nonpolar environment, containing different anchor groups for surface interaction namely phosphonate (dodecyl phosphonate), carboxylate (dodecanoic acid), sulfate (sodium dodecyl sulphate), and amine (dodecyl amine). It was shown that the surface of the nanoparticles can be functionalized with the various surface groups applying similar reaction conditions. The kind of surface interaction was analyzed applying FTIR spectroscopy. The phosphonate and the carboxylate groups interact with the surface via quite strong covalent or coordinative interactions, respectively. The sulfate and amine based coupling agents on the other hand exhibit electrostatic interactions. UV stability studies of the surface bound groups revealed different degradation mechanisms for the various functionalities and moreover showed that phosphonates are the most stable among the investigated surface capping groups. Full article
(This article belongs to the Special Issue Advances in Functional Hybrid Materials)
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Open AccessCommunication Non-enzymatic Hydrogen Peroxide Sensors Based on Multi-wall Carbon Nanotube/Pt Nanoparticle Nanohybrids
Materials 2014, 7(4), 2945-2955; doi:10.3390/ma7042945
Received: 4 March 2014 / Revised: 25 March 2014 / Accepted: 25 March 2014 / Published: 10 April 2014
Cited by 17 | PDF Full-text (521 KB) | HTML Full-text | XML Full-text
Abstract
A novel strategy to fabricate a hydrogen peroxide (H2O2) sensor was developed by using platinum (Pt) electrodes modified with multi-wall carbon nanotube-platinum nanoparticle nanohybrids (MWCNTs/Pt nanohybrids). The process to synthesize MWCNTs/Pt nanohybrids was simple and effective. Pt nanoparticles [...] Read more.
A novel strategy to fabricate a hydrogen peroxide (H2O2) sensor was developed by using platinum (Pt) electrodes modified with multi-wall carbon nanotube-platinum nanoparticle nanohybrids (MWCNTs/Pt nanohybrids). The process to synthesize MWCNTs/Pt nanohybrids was simple and effective. Pt nanoparticles (Pt NPs) were generated in situ in a potassium chloroplatinate aqueous solution in the presence of multi-wall carbon nanotubes (MWCNTs), and readily attached to the MWCNTs convex surfaces without any additional reducing reagents or irradiation treatment. The MWCNT/Pt nanohybrids were characterized by transmission electron microscope (TEM), and the redox properties of MWCNTs/Pt nanohybrids-modified Pt electrode were studied by electrochemical measurements. The MWCNTs/Pt-modified electrodes exhibited a favorable catalytic ability in the reduction of H2O2. The modified electrodes can be used to detect H2O2 in the range of 0.01–2 mM with a lower detection limit of 0.3 μM at a signal-to-noise ratio of 3. The sensitivity of the electrode to H2O2 was calculated to be 205.80 μA mM−1 cm−2 at working potential of 0 mV. In addition, the electrodes exhibited an excellent reusability and long-term stability as well as negligible interference from ascorbic acid, uric acid, and acetaminophen. Full article
(This article belongs to the Section Advanced Composites)
Open AccessArticle Influence of Layer-by-Layer Polyelectrolyte Deposition and EDC/NHS Activated Heparin Immobilization onto Silk Fibroin Fabric
Materials 2014, 7(4), 2956-2977; doi:10.3390/ma7042956
Received: 2 February 2014 / Revised: 25 March 2014 / Accepted: 31 March 2014 / Published: 11 April 2014
Cited by 6 | PDF Full-text (2127 KB) | HTML Full-text | XML Full-text
Abstract
To enhance the hemocompatibility of silk fibroin fabric as biomedical material, polyelectrolytes architectures have been assembled through the layer-by-layer (LbL) technique on silk fibroin fabric (SFF). In particular, 1.5 and 2.5 bilayer of oppositely charged polyelectrolytes were assembled onto SFF using poly(allylamine [...] Read more.
To enhance the hemocompatibility of silk fibroin fabric as biomedical material, polyelectrolytes architectures have been assembled through the layer-by-layer (LbL) technique on silk fibroin fabric (SFF). In particular, 1.5 and 2.5 bilayer of oppositely charged polyelectrolytes were assembled onto SFF using poly(allylamine hydrochloride) (PAH) as polycationic polymer and poly(acrylic acid) (PAA) as polyanionic polymer with PAH topmost. Low molecular weight heparin (LMWH) activated with 1-ethyl-3-(dimethylaminopropyl) carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) was then immobilized on its surface. Alcian Blue staining, toluidine blue assay and X-ray photoelectron spectroscopy (XPS) confirmed the presence of heparin on modified SFF surfaces. The surface morphology of the modified silk fibroin fabric surfaces was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and obtained increased roughness. Negligible hemolytic effect and a higher concentration of free hemoglobin by a kinetic clotting time test ensured the improved biological performance of the modified fibroin fabric. Overall, the deposition of 2.5 bilayer was found effective in terms of biological and surface properties of the modified fibroin fabric compared to 1.5 bilayer self-assembly technique. Therefore, this novel approach to surface modification may demonstrate long term patency in future in vivo animal trials of small diameter silk fibroin vascular grafts. Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle A Procedure to Measure the in-Situ Hygrothermal Behavior of Earth Walls
Materials 2014, 7(4), 3002-3020; doi:10.3390/ma7043002
Received: 28 February 2014 / Revised: 28 March 2014 / Accepted: 3 April 2014 / Published: 11 April 2014
Cited by 5 | PDF Full-text (1677 KB) | HTML Full-text | XML Full-text
Abstract
Rammed earth is a sustainable material with low embodied energy. However, its development as a building material requires a better evaluation of its moisture-thermal buffering abilities and its mechanical behavior. Both of these properties are known to strongly depend on the amount [...] Read more.
Rammed earth is a sustainable material with low embodied energy. However, its development as a building material requires a better evaluation of its moisture-thermal buffering abilities and its mechanical behavior. Both of these properties are known to strongly depend on the amount of water contained in wall pores and its evolution. Thus the aim of this paper is to present a procedure to measure this key parameter in rammed earth or cob walls by using two types of probes operating on the Time Domain Reflectometry (TDR) principle. A calibration procedure for the probes requiring solely four parameters is described. This calibration procedure is then used to monitor the hygrothermal behavior of a rammed earth wall (1.5 m × 1 m × 0.5 m), instrumented by six probes during its manufacture, and submitted to insulated, natural convection and forced convection conditions. These measurements underline the robustness of the calibration procedure over a large range of water content, even if the wall is submitted to quite important temperature variations. They also emphasize the importance of gravity on water content heterogeneity when the saturation is high, as well as the role of liquid-to-vapor phase change on the thermal behavior. Full article
Open AccessArticle Preparation of Nanocomposite Plasmonic Films Made from Cellulose Nanocrystals or Mesoporous Silica Decorated with Unidirectionally Aligned Gold Nanorods
Materials 2014, 7(4), 3021-3033; doi:10.3390/ma7043021
Received: 1 March 2014 / Revised: 24 March 2014 / Accepted: 26 March 2014 / Published: 11 April 2014
Cited by 10 | PDF Full-text (791 KB) | HTML Full-text | XML Full-text
Abstract
Using liquid crystalline self-assembly of cellulose nanocrystals, we achieve long-range alignment of anisotropic metal nanoparticles in colloidal nanocrystal dispersions that are then used to deposit thin structured films with ordering features highly dependent on the deposition method. These hybrid films are comprised [...] Read more.
Using liquid crystalline self-assembly of cellulose nanocrystals, we achieve long-range alignment of anisotropic metal nanoparticles in colloidal nanocrystal dispersions that are then used to deposit thin structured films with ordering features highly dependent on the deposition method. These hybrid films are comprised of gold nanorods unidirectionally aligned in a matrix that can be made of ordered cellulose nanocrystals or silica nanostructures obtained by using cellulose-based nanostructures as a replica. The ensuing long-range alignment of gold nanorods in both cellulose-based and nanoporous silica films results in a polarization-sensitive surface plasmon resonance. The demonstrated device-scale bulk nanoparticle alignment may enable engineering of new material properties arising from combining the orientational ordering of host nanostructures and properties of the anisotropic plasmonic metal nanoparticles. Our approach may also allow for scalable fabrication of plasmonic polarizers and nanoporous silica structures with orientationally ordered anisotropic plasmonic nanoinclusions. Full article
(This article belongs to the Special Issue Liquid Crystals) Print Edition available
Open AccessArticle Physical Characterization of Natural Straw Fibers as Aggregates for Construction Materials Applications
Materials 2014, 7(4), 3034-3048; doi:10.3390/ma7043034
Received: 20 February 2014 / Revised: 29 March 2014 / Accepted: 1 April 2014 / Published: 11 April 2014
Cited by 4 | PDF Full-text (1683 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this paper is to find out new alternative materials that respond to sustainable development criteria. For this purpose, an original utilization of straw for the design of lightweight aggregate concretes is proposed. Four types of straw were used: three [...] Read more.
The aim of this paper is to find out new alternative materials that respond to sustainable development criteria. For this purpose, an original utilization of straw for the design of lightweight aggregate concretes is proposed. Four types of straw were used: three wheat straws and a barley straw. In the present study, the morphology and the porosity of the different straw aggregates was studied by SEM in order to understand their effects on the capillary structure and the hygroscopic behavior. The physical properties such as sorption-desorption isotherms, water absorption coefficient, pH, electrical conductivity and thermo-gravimetric analysis were also studied. As a result, it has been found that this new vegetable material has a very low bulk density, a high water absorption capacity and an excellent hydric regulator. The introduction of the straw in the water tends to make the environment more basic; this observation can slow carbonation of the binder matrix in the presence of the straw. Full article
(This article belongs to the Section Structure Analysis and Characterization)
Open AccessArticle Physical Characterization of Cementitious Materials on Casting and Placing Process
Materials 2014, 7(4), 3049-3064; doi:10.3390/ma7043049
Received: 25 February 2014 / Revised: 7 April 2014 / Accepted: 10 April 2014 / Published: 15 April 2014
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Abstract
Coagulation of cement particles is an inevitable phenomenon of fresh cement-based materials undergoing solidification. Coagulation can be classified into two types, reversible flocculation and irreversible coagulation, wherein microstructural change affects the rheological properties, including shear thinning and thixotropy, and the hydration process. [...] Read more.
Coagulation of cement particles is an inevitable phenomenon of fresh cement-based materials undergoing solidification. Coagulation can be classified into two types, reversible flocculation and irreversible coagulation, wherein microstructural change affects the rheological properties, including shear thinning and thixotropy, and the hydration process. This paper attempts to measure the mechanical property and the coagulation of cement particles according to the mix proportions of cement paste. Experimental setups were proposed for two different types of coagulations using a laser backscattering instrument. Volume fraction and size distribution of coagulated particles were obtained, and their variations were discussed. From the obtained results the microstructural buildup of freshly mixed cement pastes can be divided into three categories: permanent coagulation and strong and weak flocculation. Full article
(This article belongs to the Special Issue Construction Materials)
Open AccessArticle Numerical Study of Variation of Mechanical Properties of a Binary Aluminum Alloy with Respect to Its Grain Shapes
Materials 2014, 7(4), 3065-3083; doi:10.3390/ma7043065
Received: 28 February 2014 / Revised: 2 April 2014 / Accepted: 4 April 2014 / Published: 15 April 2014
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Abstract
To study the variation of the mechanical behavior of binary aluminum copper alloys with respect to their microstructure, a numerical simulation of their granular structure was carried out. The microstructures are created by a repeated inclusion of some predefined basic grain shapes [...] Read more.
To study the variation of the mechanical behavior of binary aluminum copper alloys with respect to their microstructure, a numerical simulation of their granular structure was carried out. The microstructures are created by a repeated inclusion of some predefined basic grain shapes into a representative volume element until reaching a given volume percentage of the α-phase. Depending on the grain orientations, the coalescence of the grains can be performed. Different granular microstructures are created by using different basic grain shapes. Selecting a suitable set of basic grain shapes, the modeled microstructure exhibits a realistic aluminum alloy microstructure which can be adapted to a particular cooling condition. Our granular models are automatically converted to a finite element model. The effect of grain shapes and sizes on the variation of elastic modulus and plasticity of such a heterogeneous domain was investigated. Our results show that for a given α-phase fraction having different grain shapes and sizes, the elastic moduli and yield stresses are almost the same but the ultimate stress and elongation are more affected. Besides, we realized that the distribution of the θ phases inside the α phases is more important than the grain shape itself. Full article
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Open AccessArticle R-HPDC Process with Forced Convection Mixing Device for Automotive Part of A380 Aluminum Alloy
Materials 2014, 7(4), 3084-3105; doi:10.3390/ma7043084
Received: 24 March 2014 / Revised: 4 April 2014 / Accepted: 4 April 2014 / Published: 15 April 2014
Cited by 3 | PDF Full-text (1891 KB) | HTML Full-text | XML Full-text
Abstract
The continuing quest for cost-effective and complex shaped aluminum castings with fewer defects for applications in the automotive industries has aroused the interest in rheological high pressure die casting (R-HPDC). A new machine, forced convection mixing (FCM) device, based on the mechanical [...] Read more.
The continuing quest for cost-effective and complex shaped aluminum castings with fewer defects for applications in the automotive industries has aroused the interest in rheological high pressure die casting (R-HPDC). A new machine, forced convection mixing (FCM) device, based on the mechanical stirring and convection mixing theory for the preparation of semisolid slurry in convenience and functionality was proposed to produce the automotive shock absorber part by R-HPDC process. The effect of barrel temperature and rotational speed of the device on the grain size and morphology of semi-solid slurry were extensively studied. In addition, flow behavior and temperature field of the melt in the FCM process was investigated combining computational fluid dynamics simulation. The results indicate that the microstructure and pore defects at different locations of R-HPDC casting have been greatly improved. The vigorous fluid convection in FCM process has changed the temperature field and composition distribution of conventional solidification. Appropriately increasing the rotational speed can lead to a uniform temperature filed sooner. The lower barrel temperature leads to a larger uniform degree of supercooling of the melt that benefits the promotion of nucleation rate. Both of them contribute to the decrease of the grain size and the roundness of grain morphology. Full article
(This article belongs to the Special Issue Light Alloys and Their Applications)
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Open AccessArticle Evaluation and Observation of Autogenous Healing Ability of Bond Cracks along Rebar
Materials 2014, 7(4), 3136-3146; doi:10.3390/ma7043136
Received: 10 January 2014 / Revised: 22 March 2014 / Accepted: 11 April 2014 / Published: 17 April 2014
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Abstract
Micro cracks occurring in concrete around tensile rebar is well known latent damage phenomenon. These micro cracks develop, and can be detected after reaching the surface of the concrete. Detection of these cracks before they are fully formed is preferable, but observing [...] Read more.
Micro cracks occurring in concrete around tensile rebar is well known latent damage phenomenon. These micro cracks develop, and can be detected after reaching the surface of the concrete. Detection of these cracks before they are fully formed is preferable, but observing the whole crack structure is difficult. Another problem is repairing micro cracks under the concrete surface. The autogenous ability of bond cracks along rebar was evaluated using the air permeability test. Air permeability coefficients were measured before and after tensile loading, and experimental air permeability coefficients became larger near cracks along rebar as a result of tensile loading. Recuring for 28 days after tensile loading made the air permeability coefficients smaller, but this restriction only occurred during water recuring. Observation of crack patterns helped the understanding of change in the air permeability coefficients. Several small cracks along rebar were observed after tensile loading, and most cracks along rebar were not found after water recuring. On the other hand, the crack pattern did not change after air recuring. These results indicate that bond cracks along rebar can be closed by autogenous healing, and cause the air permeability coefficients. Full article
(This article belongs to the Special Issue Self-healing Concrete)
Open AccessArticle Characterization of High-k Nanolayers by Grazing Incidence X-ray Spectrometry
Materials 2014, 7(4), 3147-3159; doi:10.3390/ma7043147
Received: 21 January 2014 / Revised: 27 March 2014 / Accepted: 8 April 2014 / Published: 17 April 2014
Cited by 9 | PDF Full-text (697 KB) | HTML Full-text | XML Full-text
Abstract
The accurate characterization of nanolayered systems is an essential topic for today’s developments in many fields of material research. Thin high-k layers and gate stacks are technologically required for the design of current and future electronic devices and can be deposited, e.g., [...] Read more.
The accurate characterization of nanolayered systems is an essential topic for today’s developments in many fields of material research. Thin high-k layers and gate stacks are technologically required for the design of current and future electronic devices and can be deposited, e.g., by Atomic Layer Deposition (ALD). However, the metrological challenges to characterize such systems demand further development of analytical techniques. Reference-free Grazing Incidence X-ray Fluorescence (GIXRF) based on synchrotron radiation can significantly contribute to the characterization of such nanolayered systems. GIXRF takes advantage of the incident angle dependence of XRF, in particular below the substrate’s critical angle where changes in the X-ray Standing Wave field (XSW) intensity influence the angular intensity profile. The reliable modeling of the XSW in conjunction with the radiometrically calibrated instrumentation at the PTB allows for reference-free, fundamental parameter-based quantitative analysis. This approach is very well suited for the characterization of nanoscaled materials, especially when no reference samples with sufficient quality are available. The capabilities of this method are demonstrated by means of two systems for transistor gate stacks, i.e., Al2O3 high-k layers grown on Si or Si/SiO2 and Sc2O3 layers on InGaAs/InP substrates. Full article
(This article belongs to the Special Issue High-k Materials and Devices 2014)
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Open AccessArticle Quantitative X-ray Elemental Imaging in Plant Materials at the Subcellular Level with a Transmission Electron Microscope: Applications and Limitations
Materials 2014, 7(4), 3160-3175; doi:10.3390/ma7043160
Received: 5 February 2014 / Revised: 10 March 2014 / Accepted: 11 April 2014 / Published: 21 April 2014
Cited by 2 | PDF Full-text (1415 KB) | HTML Full-text | XML Full-text
Abstract
Energy-dispersive X-ray microanalysis (EDX) is a technique for determining the distribution of elements in various materials. Here, we report a protocol for high-spatial-resolution X-ray elemental imaging and quantification in plant tissues at subcellular levels with a scanning transmission electron microscope (STEM). Calibration [...] Read more.
Energy-dispersive X-ray microanalysis (EDX) is a technique for determining the distribution of elements in various materials. Here, we report a protocol for high-spatial-resolution X-ray elemental imaging and quantification in plant tissues at subcellular levels with a scanning transmission electron microscope (STEM). Calibration standards were established by producing agar blocks loaded with increasing KCl or NaCl concentrations. TEM-EDX images showed that the salts were evenly distributed in the agar matrix, but tended to aggregate at high concentrations. The mean intensities of K+, Cl, and Na+ derived from elemental images were linearly correlated to the concentrations of these elements in the agar, over the entire concentration range tested (R > 0.916). We applied this method to plant root tissues. X-ray images were acquired at an actual resolution of 50 nm ´ 50 nm to 100 nm ´ 100 nm. We found that cell walls exhibited higher elemental concentrations than vacuoles. Plants exposed to salt stress showed dramatic accumulation of Na+ and Cl in the transport tissues, and reached levels similar to those applied in the external solution (300 mM). The advantage of TEM-EDX mapping was the high-spatial-resolution achieved for imaging elemental distributions in a particular area with simultaneous quantitative analyses of multiple target elements. Full article
(This article belongs to the Section Biomaterials)
Open AccessArticle Corrosion Behavior of Steel Reinforcement in Concrete with Recycled Aggregates, Fly Ash and Spent Cracking Catalyst
Materials 2014, 7(4), 3176-3197; doi:10.3390/ma7043176
Received: 5 March 2014 / Revised: 19 March 2014 / Accepted: 11 April 2014 / Published: 21 April 2014
Cited by 4 | PDF Full-text (588 KB) | HTML Full-text | XML Full-text
Abstract
The main strategy to reduce the environmental impact of the concrete industry is to reuse the waste materials. This research has considered the combination of cement replacement by industrial by-products, and natural coarse aggregate substitution by recycled aggregate. The aim is to [...] Read more.
The main strategy to reduce the environmental impact of the concrete industry is to reuse the waste materials. This research has considered the combination of cement replacement by industrial by-products, and natural coarse aggregate substitution by recycled aggregate. The aim is to evaluate the behavior of concretes with a reduced impact on the environment by replacing a 50% of cement by industrial by-products (15% of spent fluid catalytic cracking catalyst and 35% of fly ash) and a 100% of natural coarse aggregate by recycled aggregate. The concretes prepared according to these considerations have been tested in terms of mechanical strengths and the protection offered against steel reinforcement corrosion under carbonation attack and chloride-contaminated environments. The proposed concrete combinations reduced the mechanical performance of concretes in terms of elastic modulus, compressive strength, and flexural strength. In addition, an increase in open porosity due to the presence of recycled aggregate was observed, which is coherent with the changes observed in mechanical tests. Regarding corrosion tests, no significant differences were observed in the case of the resistance of these types of concretes under a natural chloride attack. In the case of carbonation attack, although all concretes did not stand the highly aggressive conditions, those concretes with cement replacement behaved worse than Portland cement concretes. Full article
(This article belongs to the Section Advanced Composites)
Open AccessArticle Aggregates of Chemically Functionalized Multiwalled Carbon Nanotubes as Viscosity Reducers
Materials 2014, 7(4), 3251-3261; doi:10.3390/ma7043251
Received: 11 February 2014 / Revised: 28 March 2014 / Accepted: 1 April 2014 / Published: 22 April 2014
Cited by 2 | PDF Full-text (1308 KB) | HTML Full-text | XML Full-text
Abstract
Confinement and surface effects provided by nanoparticles have been shown to produce changes in polymer molecules affecting their macroscopic viscosity. Nanoparticles may induce rearrangements in polymer conformation with an increase in free volume significantly lowering the viscosity. This phenomenon is generally attributed [...] Read more.
Confinement and surface effects provided by nanoparticles have been shown to produce changes in polymer molecules affecting their macroscopic viscosity. Nanoparticles may induce rearrangements in polymer conformation with an increase in free volume significantly lowering the viscosity. This phenomenon is generally attributed to the selective adsorption of the polymer high molar mass fraction onto nanoparticles surface when the polymer radius of gyration is comparable to the nanoparticles characteristic dimensions. Carbon nanotubes seem to be the ideal candidate to induce viscosity reduction of polymer due to both their high surface-to-volume ratio and their nanometric sizes, comparable to the gyration radius of polymer chains. However, the amount of nanotube in a polymer system is limited by the percolation threshold as, above this limit, the formation of a nanotubes network hinders the viscosity reduction effect. Based on these findings, we have used multiwalled carbon nanotubes MWCNT “aggregates” as viscosity reducers. Our results reveal both that the use of nanotube clusters reduce significantly the viscosity of the final system and strongly increase the nanotube limiting concentration for viscosity hindering. By using hydroxyl and carboxyl functionalized nanotubes, this effect has been rather maximized likely due to the hydrogen bridged stabilization of nanotube aggregates. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle Anodic Fabrication of Ti-Ni-O Nanotube Arrays on Shape Memory Alloy
Materials 2014, 7(4), 3262-3273; doi:10.3390/ma7043262
Received: 27 January 2014 / Revised: 26 March 2014 / Accepted: 17 April 2014 / Published: 22 April 2014
Cited by 6 | PDF Full-text (2137 KB) | HTML Full-text | XML Full-text
Abstract
Surface modification with oxide nanostructures is one of the efficient ways to improve physical or biomedical properties of shape memory alloys. This work reports a fabrication of highly ordered Ti-Ni-O nanotube arrays on Ti-Ni alloy substrates through pulse anodization in glycerol-based electrolytes. [...] Read more.
Surface modification with oxide nanostructures is one of the efficient ways to improve physical or biomedical properties of shape memory alloys. This work reports a fabrication of highly ordered Ti-Ni-O nanotube arrays on Ti-Ni alloy substrates through pulse anodization in glycerol-based electrolytes. The effects of anodization parameters and the annealing process on the microstructures and surface morphology of Ti-Ni-O were studied using scanning electron microscope and Raman spectroscopy. The electrolyte type greatly affected the formation of nanotube arrays. A formation of anatase phase was found with the Ti-Ni-O nanotube arrays annealed at 450 °C. The oxide nanotubes could be crystallized to rutile phase after annealing treatment at 650 °C. The Ti-Ni-O nanotube arrays demonstrated an excellent thermal stability by keeping their nanotubular structures up to 650 °C. Full article
(This article belongs to the Special Issue Shape Memory Materials)
Open AccessArticle Limits of ZnO Electrodeposition in Mesoporous Tin Doped Indium Oxide Films in View of Application in Dye-Sensitized Solar Cells
Materials 2014, 7(4), 3291-3304; doi:10.3390/ma7043291
Received: 12 February 2014 / Revised: 24 March 2014 / Accepted: 14 April 2014 / Published: 23 April 2014
PDF Full-text (742 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Well-ordered 3D mesoporous indium tin oxide (ITO) films obtained by a templated sol-gel route are discussed as conductive porous current collectors. This paper explores the use of such films modified by electrochemical deposition of zinc oxide (ZnO) on the pore walls to [...] Read more.
Well-ordered 3D mesoporous indium tin oxide (ITO) films obtained by a templated sol-gel route are discussed as conductive porous current collectors. This paper explores the use of such films modified by electrochemical deposition of zinc oxide (ZnO) on the pore walls to improve the electron transport in dye-sensitized solar cells (DSSCs). Mesoporous ITO film were dip-coated with pore sizes of 20–25 nm and 40–45 nm employing novel poly(isobutylene)-b-poly(ethylene oxide) block copolymers as structure-directors. After electrochemical deposition of ZnO and sensitization with the indoline dye D149 the films were tested as photoanodes in DSSCs. Short ZnO deposition times led to strong back reaction of photogenerated electrons from non-covered ITO to the electrolyte. ITO films with larger pores enabled longer ZnO deposition times before pore blocking occurred, resulting in higher efficiencies, which could be further increased by using thicker ITO films consisting of five layers, but were still lower compared to nanoporous ZnO films electrodeposited on flat ITO. The major factors that currently limit the application are the still low thickness of the mesoporous ITO films, too small pore sizes and non-ideal geometries that do not allow obtaining full coverage of the ITO surface with ZnO before pore blocking occurs. Full article
(This article belongs to the Special Issue Advances in Functional Hybrid Materials)
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Open AccessArticle Distributional Fate of Elements during the Synthesis of Zeolites from South African Coal Fly Ash
Materials 2014, 7(4), 3305-3318; doi:10.3390/ma7043305
Received: 13 September 2013 / Revised: 14 March 2014 / Accepted: 31 March 2014 / Published: 23 April 2014
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Abstract
The synthesis of zeolites from South African coal fly ash has been deemed a viable solution to the growing economical strain caused by the disposal of ash in the country. Two synthesis routes have been studied thus far namely the 2-step method [...] Read more.
The synthesis of zeolites from South African coal fly ash has been deemed a viable solution to the growing economical strain caused by the disposal of ash in the country. Two synthesis routes have been studied thus far namely the 2-step method and the fusion assisted process. Fly ash contains several elements originating from coal which is incorporated in the ash during combustion. It is vital to determine the final destination of these elements in order to unveil optimization opportunities for scale-up purposes. The aim of this study was to perform a material balance study on both synthesis routes to determine the distributional fate of these elements during the synthesis of zeolites. Zeolites were first synthesized by means of the two synthesis routes. The composition of all raw materials and products were determined after which an overall and elemental balance were performed. Results indicated that in the 2-step method almost all elements were concentrated in the solid zeolite product while during the fusion assisted route the elements mostly report to the solid waste. Toxic elements such as Pb, Hg, Al, As and Nb were found in both the supernatant waste and washing water resulting from each synthesis route. It has also been seen that large quantities of Si and Al are wasted in the supernatant waste. It is highly recommended that the opportunity to recycle this liquid waste be investigated for scale-up purposes. Results also indicate that efficiency whereby Si and Al are extracted from fused ash is exceptionally poor and should be optimized. Full article
(This article belongs to the Special Issue Molecular Sieving and Materials)
Open AccessArticle Quantitative Study of Porosity and Pore Features in Moldavites by Means of X-ray Micro-CT
Materials 2014, 7(4), 3319-3336; doi:10.3390/ma7043319
Received: 1 December 2013 / Revised: 9 April 2014 / Accepted: 10 April 2014 / Published: 24 April 2014
Cited by 2 | PDF Full-text (729 KB) | HTML Full-text | XML Full-text
Abstract
X-ray micro-computer aided tomography (μ-CT), together with optical microscopy and imaging, have been applied to the study of six moldavite samples. These techniques enabled a complete characterization to be made of the textural features of both Muong Nong-type and common splashform moldavites. [...] Read more.
X-ray micro-computer aided tomography (μ-CT), together with optical microscopy and imaging, have been applied to the study of six moldavite samples. These techniques enabled a complete characterization to be made of the textural features of both Muong Nong-type and common splashform moldavites. A detailed study of the size and distribution of pores or bubbles confirmed the marked variability in pore size among the samples, as well as within each sample, and indicated in the Muong Nong-type moldavites the presence of at least two deformation stages which occurred before and after pore formation. Full article
(This article belongs to the Section Porous Materials)

Review

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Open AccessReview Polythiophenes Comprising Conjugated Pendants for Polymer Solar Cells: A Review
Materials 2014, 7(4), 2411-2439; doi:10.3390/ma7042411
Received: 8 January 2014 / Revised: 7 March 2014 / Accepted: 14 March 2014 / Published: 27 March 2014
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Abstract
Polythiophene (PT) is one of the widely used donor materials for solution-processable polymer solar cells (PSCs). Much progress in PT-based PSCs can be attributed to the design of novel PTs exhibiting intense and broad visible absorption with high charge carrier mobility to [...] Read more.
Polythiophene (PT) is one of the widely used donor materials for solution-processable polymer solar cells (PSCs). Much progress in PT-based PSCs can be attributed to the design of novel PTs exhibiting intense and broad visible absorption with high charge carrier mobility to increase short-circuit current density (Jsc), along with low-lying highest occupied molecular orbital (HOMO) levels to achieve large open circuit voltage (Voc) values. A promising strategy to tailor the photophysical properties and energy levels via covalently attaching electron donor and acceptor pendants on PTs backbone has attracted much attention recently. The geometry, electron-donating capacity, and composition of conjugated pendants are supposed to be the crucial factors in adjusting the conformation, energy levels, and photovoltaic performance of PTs. This review will go over the most recent approaches that enable researchers to obtain in-depth information in the development of PTs comprising conjugated pendants for PSCs. Full article
(This article belongs to the Special Issue Conjugated Polymers)
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Open AccessReview Bismuth Telluride and Its Alloys as Materials for Thermoelectric Generation
Materials 2014, 7(4), 2577-2592; doi:10.3390/ma7042577
Received: 9 February 2014 / Revised: 21 March 2014 / Accepted: 24 March 2014 / Published: 28 March 2014
Cited by 46 | PDF Full-text (480 KB) | HTML Full-text | XML Full-text
Abstract
Bismuth telluride and its alloys are widely used as materials for thermoelectric refrigeration. They are also the best materials for use in thermoelectric generators when the temperature of the heat source is moderate. The dimensionless figure of merit, ZT, usually rises [...] Read more.
Bismuth telluride and its alloys are widely used as materials for thermoelectric refrigeration. They are also the best materials for use in thermoelectric generators when the temperature of the heat source is moderate. The dimensionless figure of merit, ZT, usually rises with temperature, as long as there is only one type of charge carrier. Eventually, though, minority carrier conduction becomes significant and ZT decreases above a certain temperature. There is also the possibility of chemical decomposition due to the vaporization of tellurium. Here we discuss the likely temperature dependence of the thermoelectric parameters and the means by which the composition may be optimized for applications above room temperature. The results of these theoretical predictions are compared with the observed properties of bismuth telluride-based thermoelements at elevated temperatures. Compositional changes are suggested for materials that are destined for generator modules. Full article
(This article belongs to the Special Issue New Energy Materials)
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Open AccessReview Lanthanum Gadolinium Oxide: A New Electronic Device Material for CMOS Logic and Memory Devices
Materials 2014, 7(4), 2669-2696; doi:10.3390/ma7042669
Received: 13 January 2014 / Revised: 19 March 2014 / Accepted: 25 March 2014 / Published: 31 March 2014
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Abstract
A comprehensive study on the ternary dielectric, LaGdO3, synthesized and qualified in our laboratory as a novel high-k dielectric material for logic and memory device applications in terms of its excellent features that include a high linear dielectric constant (k) [...] Read more.
A comprehensive study on the ternary dielectric, LaGdO3, synthesized and qualified in our laboratory as a novel high-k dielectric material for logic and memory device applications in terms of its excellent features that include a high linear dielectric constant (k) of ~22 and a large energy bandgap of ~5.6 eV, resulting in sufficient electron and hole band offsets of ~2.57 eV and ~1.91 eV, respectively, on silicon, good thermal stability with Si and lower gate leakage current densities within the International Technology Roadmap for Semiconductors (ITRS) specified limits at the sub-nanometer electrical functional thickness level, which are desirable for advanced complementary metal-oxide-semiconductor (CMOS), bipolar (Bi) and BiCMOS chips applications, is presented in this review article. Full article
(This article belongs to the Special Issue High-k Materials and Devices 2014)
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Open AccessReview Versatility of Evaporation-Induced Self-Assembly (EISA) Method for Preparation of Mesoporous TiO2 for Energy and Environmental Applications
Materials 2014, 7(4), 2697-2746; doi:10.3390/ma7042697
Received: 30 December 2013 / Revised: 25 February 2014 / Accepted: 24 March 2014 / Published: 31 March 2014
Cited by 14 | PDF Full-text (1792 KB) | HTML Full-text | XML Full-text
Abstract
Evaporation-Induced Self-Assembly (EISA) method for the preparation of mesoporous titanium dioxide materials is reviewed. The versatility of EISA method for the rapid and facile synthesis of TiO2 thin films and powders is highlighted. Non-ionic surfactants such as Pluronic P123, F127 and [...] Read more.
Evaporation-Induced Self-Assembly (EISA) method for the preparation of mesoporous titanium dioxide materials is reviewed. The versatility of EISA method for the rapid and facile synthesis of TiO2 thin films and powders is highlighted. Non-ionic surfactants such as Pluronic P123, F127 and cationic surfactants such as cetyltrimethylammonium bromide have been extensively employed for the preparation of mesoporous TiO2. In particular, EISA method allows for fabrication of highly uniform, robust, crack-free films with controllable thickness. Eleven characterization techniques for elucidating the structure of the EISA prepared mesoporous TiO2 are discussed in this paper. These many characterization methods provide a holistic picture of the structure of mesoporous TiO2. Mesoporous titanium dioxide materials have been employed in several applications that include Dye Sensitized Solar Cells (DSSCs), photocatalytic degradation of organics and splitting of water, and batteries. Full article
(This article belongs to the Special Issue Advances in Functional Hybrid Materials)
Open AccessReview Hybrid Organic/Inorganic Nanocomposites for Photovoltaic Cells
Materials 2014, 7(4), 2747-2771; doi:10.3390/ma7042747
Received: 28 November 2013 / Revised: 11 March 2014 / Accepted: 19 March 2014 / Published: 2 April 2014
Cited by 26 | PDF Full-text (856 KB) | HTML Full-text | XML Full-text
Abstract
Inorganic/organic hybrid solar cells have attracted a lot of interest due to their potential in combining the advantages of both components. To understand the key issues in association with photoinduced charge separation/transportation processes and to improve overall power conversion efficiency, various combinations [...] Read more.
Inorganic/organic hybrid solar cells have attracted a lot of interest due to their potential in combining the advantages of both components. To understand the key issues in association with photoinduced charge separation/transportation processes and to improve overall power conversion efficiency, various combinations with nanostructures of hybrid systems have been investigated. Here, we briefly review the structures of hybrid nanocomposites studied so far, and attempt to associate the power conversion efficiency with these nanostructures. Subsequently, we are then able to summarize the factors for optimizing the performance of inorganic/organic hybrid solar cells. Full article
(This article belongs to the Special Issue Nanocomposites of Polymers and Inorganic Particles 2013)
Open AccessReview Zinc Oxide—From Synthesis to Application: A Review
Materials 2014, 7(4), 2833-2881; doi:10.3390/ma7042833
Received: 17 December 2013 / Revised: 25 March 2014 / Accepted: 27 March 2014 / Published: 9 April 2014
Cited by 152 | PDF Full-text (1548 KB) | HTML Full-text | XML Full-text
Abstract
Zinc oxide can be called a multifunctional material thanks to its unique physical and chemical properties. The first part of this paper presents the most important methods of preparation of ZnO divided into metallurgical and chemical methods. The mechanochemical process, controlled precipitation, [...] Read more.
Zinc oxide can be called a multifunctional material thanks to its unique physical and chemical properties. The first part of this paper presents the most important methods of preparation of ZnO divided into metallurgical and chemical methods. The mechanochemical process, controlled precipitation, sol-gel method, solvothermal and hydrothermal method, method using emulsion and microemulsion enviroment and other methods of obtaining zinc oxide were classified as chemical methods. In the next part of this review, the modification methods of ZnO were characterized. The modification with organic (carboxylic acid, silanes) and inroganic (metal oxides) compounds, and polymer matrices were mainly described. Finally, we present possible applications in various branches of industry: rubber, pharmaceutical, cosmetics, textile, electronic and electrotechnology, photocatalysis were introduced. This review provides useful information for specialist dealings with zinc oxide. Full article
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Open AccessReview Emerging Applications for High K Materials in VLSI Technology
Materials 2014, 7(4), 2913-2944; doi:10.3390/ma7042913
Received: 27 January 2014 / Revised: 14 March 2014 / Accepted: 24 March 2014 / Published: 10 April 2014
Cited by 12 | PDF Full-text (1040 KB) | HTML Full-text | XML Full-text
Abstract
The current status of High K dielectrics in Very Large Scale Integrated circuit (VLSI) manufacturing for leading edge Dynamic Random Access Memory (DRAM) and Complementary Metal Oxide Semiconductor (CMOS) applications is summarized along with the deposition methods and general equipment types employed. [...] Read more.
The current status of High K dielectrics in Very Large Scale Integrated circuit (VLSI) manufacturing for leading edge Dynamic Random Access Memory (DRAM) and Complementary Metal Oxide Semiconductor (CMOS) applications is summarized along with the deposition methods and general equipment types employed. Emerging applications for High K dielectrics in future CMOS are described as well for implementations in 10 nm and beyond nodes. Additional emerging applications for High K dielectrics include Resistive RAM memories, Metal-Insulator-Metal (MIM) diodes, Ferroelectric logic and memory devices, and as mask layers for patterning. Atomic Layer Deposition (ALD) is a common and proven deposition method for all of the applications discussed for use in future VLSI manufacturing. Full article
(This article belongs to the Special Issue High-k Materials and Devices 2014)
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Open AccessReview Precursor Mediated Synthesis of Nanostructured Silicas: From Precursor-Surfactant Ion Pairs to Structured Materials
Materials 2014, 7(4), 2978-3001; doi:10.3390/ma7042978
Received: 13 February 2014 / Revised: 19 March 2014 / Accepted: 25 March 2014 / Published: 11 April 2014
Cited by 2 | PDF Full-text (1162 KB) | HTML Full-text | XML Full-text
Abstract
The synthesis of nanostructured anionic-surfactant-templated mesoporous silica (AMS) recently appeared as a new strategy for the formation of nanostructured silica based materials. This method is based on the use of anionic surfactants together with a co-structure-directing agent (CSDA), mostly a silylated ammonium [...] Read more.
The synthesis of nanostructured anionic-surfactant-templated mesoporous silica (AMS) recently appeared as a new strategy for the formation of nanostructured silica based materials. This method is based on the use of anionic surfactants together with a co-structure-directing agent (CSDA), mostly a silylated ammonium precursor. The presence of this CSDA is necessary in order to create ionic interactions between template and silica forming phases and to ensure sufficient affinity between the two phases. This synthetic strategy was for the first time applied in view of the synthesis of surface functionalized silica bearing ammonium groups and was then extended on the formation of materials functionalized with anionic carboxylate and bifunctional amine-carboxylate groups. In the field of silica hybrid materials, the “anionic templating” strategy has recently been applied for the synthesis of silica hybrid materials from cationic precursors. Starting from di- or oligosilylated imidazolium and ammonium precursors, only template directed hydrolysis-polycondensation reactions involving complementary anionic surfactants allowed accessing structured ionosilica hybrid materials. The mechanistic particularity of this approach resides in the formation of precursor-surfactant ion pairs in the hydrolysis-polycondensation mixture. This review gives a systematic overview over the various types of materials accessed from this cooperative ionic templating approach and highlights the high potential of this original strategy for the formation of nanostructured silica based materials which appears as a complementary strategy to conventional soft templating approaches. Full article
(This article belongs to the Special Issue Advances in Functional Hybrid Materials)
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Open AccessReview Gelatin-Based Materials in Ocular Tissue Engineering
Materials 2014, 7(4), 3106-3135; doi:10.3390/ma7043106
Received: 4 February 2014 / Revised: 17 March 2014 / Accepted: 24 March 2014 / Published: 17 April 2014
Cited by 18 | PDF Full-text (1157 KB) | HTML Full-text | XML Full-text
Abstract
Gelatin has been used for many years in pharmaceutical formulation, cell culture and tissue engineering on account of its excellent biocompatibility, ease of processing and availability at low cost. Over the last decade gelatin has been extensively evaluated for numerous ocular applications [...] Read more.
Gelatin has been used for many years in pharmaceutical formulation, cell culture and tissue engineering on account of its excellent biocompatibility, ease of processing and availability at low cost. Over the last decade gelatin has been extensively evaluated for numerous ocular applications serving as cell-sheet carriers, bio-adhesives and bio-artificial grafts. These different applications naturally have diverse physical, chemical and biological requirements and this has prompted research into the modification of gelatin and its derivatives. The crosslinking of gelatin alone or in combination with natural or synthetic biopolymers has produced a variety of scaffolds that could be suitable for ocular applications. This review focuses on methods to crosslink gelatin-based materials and how the resulting materials have been applied in ocular tissue engineering. Critical discussion of recent innovations in tissue engineering and regenerative medicine will highlight future opportunities for gelatin-based materials in ophthalmology. Full article
(This article belongs to the Special Issue Biocompatibility of Materials 2013)
Open AccessReview A Review on Breathing Behaviors of Metal-Organic-Frameworks (MOFs) for Gas Adsorption
Materials 2014, 7(4), 3198-3250; doi:10.3390/ma7043198
Received: 1 March 2014 / Revised: 31 March 2014 / Accepted: 11 April 2014 / Published: 21 April 2014
Cited by 28 | PDF Full-text (3237 KB) | HTML Full-text | XML Full-text
Abstract
Metal-organic frameworks (MOFs) are a new class of microporous materials that possess framework flexibility, large surface areas, “tailor-made” framework functionalities, and tunable pore sizes. These features empower MOFs superior performances and broader application spectra than those of zeolites and phosphine-based molecular sieves. [...] Read more.
Metal-organic frameworks (MOFs) are a new class of microporous materials that possess framework flexibility, large surface areas, “tailor-made” framework functionalities, and tunable pore sizes. These features empower MOFs superior performances and broader application spectra than those of zeolites and phosphine-based molecular sieves. In parallel with designing new structures and new chemistry of MOFs, the observation of unique breathing behaviors upon adsorption of gases or solvents stimulates their potential applications as host materials in gas storage for renewable energy. This has attracted intense research energy to understand the causes at the atomic level, using in situ X-ray diffraction, calorimetry, Fourier transform infrared spectroscopy, and molecular dynamics simulations. This article is developed in the following order: first to introduce the definition of MOFs and the observation of their framework flexibility. Second, synthesis routes of MOFs are summarized with the emphasis on the hydrothermal synthesis, owing to the environmental-benign and economically availability of water. Third, MOFs exhibiting breathing behaviors are summarized, followed by rationales from thermodynamic viewpoint. Subsequently, effects of various functionalities on breathing behaviors are appraised, including using post-synthetic modification routes. Finally, possible framework spatial requirements of MOFs for yielding breathing behaviors are highlighted as the design strategies for new syntheses. Full article
(This article belongs to the Section Porous Materials)
Open AccessReview Donor-Acceptor Block Copolymers: Synthesis and Solar Cell Applications
Materials 2014, 7(4), 3274-3290; doi:10.3390/ma7043274
Received: 4 March 2014 / Revised: 3 April 2014 / Accepted: 15 April 2014 / Published: 22 April 2014
Cited by 8 | PDF Full-text (1020 KB) | HTML Full-text | XML Full-text
Abstract
Fullerene derivatives have been widely used for conventional acceptor materials in organic photovoltaics (OPVs) because of their high electron mobility. However, there are also considerable drawbacks for use in OPVs, such as negligible light absorption in the visible-near-IR regions, less compatibility with [...] Read more.
Fullerene derivatives have been widely used for conventional acceptor materials in organic photovoltaics (OPVs) because of their high electron mobility. However, there are also considerable drawbacks for use in OPVs, such as negligible light absorption in the visible-near-IR regions, less compatibility with donor polymeric materials and high cost for synthesis and purification. Therefore, the investigation of non-fullerene acceptor materials that can potentially replace fullerene derivatives in OPVs is increasingly necessary, which gives rise to the possibility of fabricating all-polymer (polymer/polymer) solar cells that can deliver higher performance and that are potentially cheaper than fullerene-based OPVs. Recently, considerable attention has been paid to donor-acceptor (D-A) block copolymers, because of their promising applications as fullerene alternative materials in all-polymer solar cells. However, the synthesis of D-A block copolymers is still a challenge, and therefore, the establishment of an efficient synthetic method is now essential. This review highlights the recent advances in D-A block copolymers synthesis and their applications in all-polymer solar cells. Full article
(This article belongs to the Special Issue New Energy Materials)

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