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Materials, Volume 7, Issue 11 (November 2014), Pages 7173-7614

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Open AccessArticle Morphological Characterization and Effective Thermal Conductivity of Dual-Scale Reticulated Porous Structures
Materials 2014, 7(11), 7173-7195; doi:10.3390/ma7117173
Received: 3 September 2014 / Revised: 13 October 2014 / Accepted: 15 October 2014 / Published: 28 October 2014
Cited by 13 | PDF Full-text (1710 KB) | HTML Full-text | XML Full-text
Abstract
Reticulated porous ceramic (RPC) made of ceria are promising structures used in solar thermochemical redox cycles for splitting CO2 and H2O. They feature dual-scale porosity with mm-size pores for effective radiative heat transfer during reduction and µm-size pores within its
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Reticulated porous ceramic (RPC) made of ceria are promising structures used in solar thermochemical redox cycles for splitting CO2 and H2O. They feature dual-scale porosity with mm-size pores for effective radiative heat transfer during reduction and µm-size pores within its struts for enhanced kinetics during oxidation. In this work, the detailed 3D digital representation of the complex dual-scale RPC is obtained using synchrotron submicrometer tomography and X-ray microtomography. Total and open porosity, pore size distribution, mean pore diameter, and specific surface area are extracted from the computer tomography (CT) scans. The 3D digital geometry is then applied in direct pore level simulations (DPLS) of Fourier’s law within the solid and the fluid phases for the accurate determination of the effective thermal conductivity at each porosity scale and combined, and for fluid-to-solid thermal conductivity from 10−5 to 1. Results are compared to predictions by analytical models for structures with a wide range of porosities 0.09–0.9 in both the strut’s µm-scale and bulk’s mm-scale. The morphological properties and effective thermal conductivity determined in this work serve as an input to volume-averaged models for the design and optimization of solar chemical reactors. Full article
(This article belongs to the Section Porous Materials)
Open AccessArticle Mechanism for Tuning the Hydrophobicity of Microfibrillated Cellulose Films by Controlled Thermal Release of Encapsulated Wax
Materials 2014, 7(11), 7196-7216; doi:10.3390/ma7117196
Received: 8 August 2014 / Revised: 8 October 2014 / Accepted: 12 October 2014 / Published: 28 October 2014
Cited by 6 | PDF Full-text (1334 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Although films of microfibrillated cellulose (MFC) have good oxygen barrier properties due to its fine network structure, properties strongly deteriorate after absorption of water. In this work, a new approach has been followed for actively tuning the water resistance of a MFC fiber
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Although films of microfibrillated cellulose (MFC) have good oxygen barrier properties due to its fine network structure, properties strongly deteriorate after absorption of water. In this work, a new approach has been followed for actively tuning the water resistance of a MFC fiber network by the inclusion of dispersed organic nanoparticles with encapsulated plant wax. The modified pulp suspensions have been casted into films and were subsequently cured at 40 to 220 °C. As such, static water contact angles can be specifically tuned from 120 to 150° by selection of the curing temperature in relation with the intrinsic transition temperatures of the modified pulp, as determined by thermal analysis. The appearance of encapsulated wax after curing was followed by a combination of morphological analysis, infrared spectroscopy and Raman mapping, showing balanced mechanisms of progressive release and migration of wax into the fiber network controlling the surface properties and water contact angles. Finally, the appearance of nanoparticles covered with a thin wax layer after complete thermal release provides highest hydrophobicity. Full article
(This article belongs to the Special Issue Advances in Cellulosic Materials 2014)
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Open AccessArticle Structural Aspects LiNbO3 Nanoparticles and Their Ferromagnetic Properties
Materials 2014, 7(11), 7217-7225; doi:10.3390/ma7117217
Received: 1 May 2014 / Revised: 12 June 2014 / Accepted: 26 June 2014 / Published: 28 October 2014
Cited by 5 | PDF Full-text (759 KB) | HTML Full-text | XML Full-text
Abstract
We present a solid-state synthesis of ferromagnetic lithium niobate nanoparticles (LiNbO3) and their corresponding structural aspects. In order to investigate the effect of heat treatments, two batches of samples with a heat-treated (HT) and non-heat-treated (nHT) reduction at 650 °C in
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We present a solid-state synthesis of ferromagnetic lithium niobate nanoparticles (LiNbO3) and their corresponding structural aspects. In order to investigate the effect of heat treatments, two batches of samples with a heat-treated (HT) and non-heat-treated (nHT) reduction at 650 °C in 5% of hydrogen/argon were considered to investigate the multiferroic properties and their corresponding structural aspects; using magnetometry and scanning transmission electron microscopy (STEM). Results indicate the existence of ferromagnetic domains with a magnetic moment per unit cell of 5.24 × 10−3 μB; caused mainly due to voids and defects on the nanoparticle surface, as confirmed by STEM measurements. Full article
(This article belongs to the Special Issue Ultra Thin Ferroic Materials)
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Open AccessArticle Organic Field-Effect Transistors Based on a Liquid-Crystalline Polymeric Semiconductor using SU-8 Gate Dielectrics onFlexible Substrates
Materials 2014, 7(11), 7226-7242; doi:10.3390/ma7117226
Received: 11 August 2014 / Revised: 2 October 2014 / Accepted: 15 October 2014 / Published: 29 October 2014
Cited by 5 | PDF Full-text (1393 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In this work, the insulating properties of poly(4-vinylphenol) (PVP) and SU-8 (MicroChem, Westborough, MA, USA) dielectrics are analyzed and compared with each other. We further investigate the performance behavior of organic field-effect transistors based on a semiconducting liquid-crystal polymer (LCP) using both dielectric
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In this work, the insulating properties of poly(4-vinylphenol) (PVP) and SU-8 (MicroChem, Westborough, MA, USA) dielectrics are analyzed and compared with each other. We further investigate the performance behavior of organic field-effect transistors based on a semiconducting liquid-crystal polymer (LCP) using both dielectric materials and evaluate the results regarding the processability. Due to the lower process temperature needed for the SU-8 deposition, the realization of organic transistors on flexible substrates is demonstrated showing comparable charge carrier mobilities to devices using PVP on glass. In addition, a µ-dispensing procedure of the LCP on SU-8 is presented, improving the switching behavior of the organic transistors, and the promising stability data of the SU-8/LCP stack are verified after storing the structures for 60 days in ambient air showing negligible irreversible degradation of the organic semiconductor. Full article
(This article belongs to the Special Issue Organic Transistor)
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Open AccessArticle Tunable Band Gap and Conductivity Type of ZnSe/Si Core-Shell Nanowire Heterostructures
Materials 2014, 7(11), 7276-7288; doi:10.3390/ma7117276
Received: 20 August 2014 / Revised: 18 September 2014 / Accepted: 23 October 2014 / Published: 31 October 2014
Cited by 1 | PDF Full-text (1253 KB) | HTML Full-text | XML Full-text
Abstract
The electronic properties of zincblende ZnSe/Si core-shell nanowires (NWs) with a diameter of 1.1–2.8 nm are calculated by means of the first principle calculation. Band gaps of both ZnSe-core/Si-shell and Si-core/ZnSe-shell NWs are much smaller than those of pure ZnSe or Si NWs.
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The electronic properties of zincblende ZnSe/Si core-shell nanowires (NWs) with a diameter of 1.1–2.8 nm are calculated by means of the first principle calculation. Band gaps of both ZnSe-core/Si-shell and Si-core/ZnSe-shell NWs are much smaller than those of pure ZnSe or Si NWs. Band alignment analysis reveals that the small band gaps of ZnSe/Si core-shell NWs are caused by the interface state. Fixing the ZnSe core size and enlarging the Si shell would turn the NWs from intrinsic to p-type, then to metallic. However, Fixing the Si core and enlarging the ZnSe shell would not change the band gap significantly. The partial charge distribution diagram shows that the conduction band maximum (CBM) is confined in Si, while the valence band maximum (VBM) is mainly distributed around the interface. Our findings also show that the band gap and conductivity type of ZnSe/Si core-shell NWs can be tuned by the concentration and diameter of the core-shell material, respectively. Full article
(This article belongs to the Special Issue Inorganic Core-Shell Structures)
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Open AccessArticle The Upconversion Luminescence of Er3+/Yb3+/Nd3+ Triply-Doped β-NaYF4 Nanocrystals under 808-nm Excitation
Materials 2014, 7(11), 7289-7303; doi:10.3390/ma7117289
Received: 14 June 2014 / Revised: 10 October 2014 / Accepted: 30 October 2014 / Published: 4 November 2014
Cited by 12 | PDF Full-text (1437 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, Nd3+–Yb3+–Er3+-doped β-NaYF4 nanocrystals with different Nd3+ concentrations are synthesized, and the luminescence properties of the upconversion nanoparticles (UCNPs) have been studied under 808-nm excitation for sensitive biological applications. The upconversion luminescence spectra
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In this paper, Nd3+–Yb3+–Er3+-doped β-NaYF4 nanocrystals with different Nd3+ concentrations are synthesized, and the luminescence properties of the upconversion nanoparticles (UCNPs) have been studied under 808-nm excitation for sensitive biological applications. The upconversion luminescence spectra of NaYF4 nanoparticles with different dopants under 808-nm excitation proves that the Nd3+ ion can absorb the photons effectively, and the Yb3+ ion can play the role of an energy-transfer bridging ion between the Nd3+ ion and Er3+ ion. To investigate the effect of the Nd3+ ion, the decay curves of the 4S3/24I15/2 transition at 540 nm are measured and analyzed. The NaYF4: 20% Yb3+, 2% Er3+, 0.5% Nd3+ nanocrystals have the highest emission intensity among all samples under 808-nm excitation. The UC (upconversion) mechanism under 808-nm excitation is discussed in terms of the experimental results. Full article
(This article belongs to the Section Structure Analysis and Characterization)
Open AccessArticle Electrical Properties of CZO Films Prepared by Ultrasonic Spray Pyrolysis
Materials 2014, 7(11), 7304-7313; doi:10.3390/ma7117304
Received: 18 August 2014 / Revised: 18 September 2014 / Accepted: 24 October 2014 / Published: 5 November 2014
Cited by 7 | PDF Full-text (1116 KB) | HTML Full-text | XML Full-text
Abstract
CuZnO (CZO) films have attracted increasing amounts of attention due to their promising potential applications in semiconductor devices. ZnO shows n-type conductivity, and attempts have been made to dope several elements in ZnO to improve the electrical properties. This study investigated the electrical
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CuZnO (CZO) films have attracted increasing amounts of attention due to their promising potential applications in semiconductor devices. ZnO shows n-type conductivity, and attempts have been made to dope several elements in ZnO to improve the electrical properties. This study investigated the electrical property transitions of CZO films and determined the copper concentration at which the conductivity of CZO films will change from n-type to p-type. In this study, CZO films were fabricated by ultrasonic spray pyrolysis with copper acetate, zinc acetate, and ammonium acetate precursor solution. The concentrations of Cu ions in the CZO films were controlled by the concentration ratios of copper acetate to zinc acetate in the precursor solutions. In addition, these samples were analyzed by Hall effect measurements, X-ray diffraction, transmittance measurements, and photoluminescence measurements. The results show that the conductivity of the CZO film changes from n-type to p-type when the copper ion concentration in the film is 5%. Full article
(This article belongs to the Special Issue Selected Papers from the 1st International e-Conference on Materials)
Open AccessArticle Experimental Test of Heat Treatment Effect on Physical Properties of Red Oak (Quercus falcate Michx.) and Southern Pine (Pinus taeda L.)
Materials 2014, 7(11), 7314-7323; doi:10.3390/ma7117314
Received: 8 September 2014 / Revised: 15 October 2014 / Accepted: 22 October 2014 / Published: 5 November 2014
Cited by 4 | PDF Full-text (871 KB) | HTML Full-text | XML Full-text
Abstract
The objective of this work was to evaluate the effect of heat treatment and compression on the swelling and surface roughness of Southern red oak (Quercus falcate Michx.) and Southern pine (Pinus taeda L.). Specimens were exposed to temperature levels of
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The objective of this work was to evaluate the effect of heat treatment and compression on the swelling and surface roughness of Southern red oak (Quercus falcate Michx.) and Southern pine (Pinus taeda L.). Specimens were exposed to temperature levels of 110 °C or 200 °C for 8 h before they were compressed using 2.5 MPa pressure for 5 min. Swelling values of the control and heat-treated samples in three grain orientations were evaluated by soaking them in water for 48 h. A stylus method was employed to determine the surface characteristics of the samples. Three main roughness parameters, namely mean arithmetic deviation of profile (Ra), mean peak-to-valley height (Rz), and maximum roughness (Rmax) were used to evaluate the effect of heat treatment on surface characteristics of the samples. Oak and pine specimens had 39.8% and 28.7% lower tangential swelling values, respectively, than those of control samples as a result of exposure to a temperature of 200 °C. Heat treatment did not make any significant difference on surface quality. Micrographs taken from cross sections of the specimens revealed that there was some cell distortion and modification due to heat treatment as well as compression. Combination of heat treatment and compression can be considered an alternative method to improve certain physical properties of these two species. Full article
Open AccessArticle Development of Self-Healing Coatings Based on Linseed Oil as Autonomous Repairing Agent for Corrosion Resistance
Materials 2014, 7(11), 7324-7338; doi:10.3390/ma7117324
Received: 22 June 2014 / Revised: 27 October 2014 / Accepted: 3 November 2014 / Published: 11 November 2014
Cited by 7 | PDF Full-text (2122 KB) | HTML Full-text | XML Full-text
Abstract
In recent years corrosion-resistant self-healing coatings have witnessed strong growth and their successful laboratory design and synthesis categorises them in the family of smart/multi-functional materials. Among various approaches for achieving self-healing, microcapsule embedment through the material matrix is the main one for self-healing
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In recent years corrosion-resistant self-healing coatings have witnessed strong growth and their successful laboratory design and synthesis categorises them in the family of smart/multi-functional materials. Among various approaches for achieving self-healing, microcapsule embedment through the material matrix is the main one for self-healing ability in coatings. The present work focuses on optimizing the process parameters for developing microcapsules by in-situ polymerization of linseed oil as core and urea-formaldehyde as shell material. Characteristics of these microcapsules with respect to change in processing parameters such as stirring rate and reaction time were studied by using optical microscopy (OM), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The effectiveness of these microcapsules in coatings was characterized by studying their adhesion, performance, and mechanical properties. Full article
(This article belongs to the Special Issue Corrosion of Materials)
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Open AccessArticle Conduction Mechanisms in Resistance Switching Memory Devices Using Transparent Boron Doped Zinc Oxide Films
Materials 2014, 7(11), 7339-7348; doi:10.3390/ma7117339
Received: 21 August 2014 / Revised: 23 October 2014 / Accepted: 7 November 2014 / Published: 12 November 2014
Cited by 12 | PDF Full-text (545 KB) | HTML Full-text | XML Full-text
Abstract
In this work, metal/oxide/metal capacitors were fabricated and investigated using transparent boron doped zinc oxide (ZnO:B) films for resistance switching memory applications. The optical band gap of ZnO:B films was determined to be about 3.26 eV and the average value of transmittance of
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In this work, metal/oxide/metal capacitors were fabricated and investigated using transparent boron doped zinc oxide (ZnO:B) films for resistance switching memory applications. The optical band gap of ZnO:B films was determined to be about 3.26 eV and the average value of transmittance of ZnO:B films was about 91% in the visible light region. Experimental results indicated that the resistance switching in the W/ZnO:B/W structure is nonpolar. The resistance ratio of high resistance state (HRS) to low resistance state (LRS) is about of the order of 105 at room temperature. According to the temperature dependence of current-voltage characteristics, the conduction mechanism in ZnO:B films is dominated by hopping conduction and Ohmic conduction in HRS and LRS, respectively. Therefore, trap spacing (1.2 nm) and trap energy levels in ZnO:B films could be obtained. Full article
(This article belongs to the Special Issue Selected Papers from ICETI2014)
Open AccessArticle Photo-Electrochemical Treatment of Reactive Dyes in Wastewater and Reuse of the Effluent: Method Optimization
Materials 2014, 7(11), 7349-7365; doi:10.3390/ma7117349
Received: 1 July 2014 / Revised: 21 October 2014 / Accepted: 4 November 2014 / Published: 14 November 2014
Cited by 5 | PDF Full-text (822 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In this work, the efficiency of a photo-electrochemical method to remove color in textile dyeing effluents is discussed. The decolorization of a synthetic effluent containing a bi-functional reactive dye was carried out by applying an electrochemical treatment at different intensities (2 A, 5
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In this work, the efficiency of a photo-electrochemical method to remove color in textile dyeing effluents is discussed. The decolorization of a synthetic effluent containing a bi-functional reactive dye was carried out by applying an electrochemical treatment at different intensities (2 A, 5 A and 10 A), followed by ultraviolet irradiation. The combination of both treatments was optimized. The final percentage of effluent decolorization, the reduction of halogenated organic volatile compound and the total organic carbon removal were the determinant factors in the selection of the best treatment conditions. The optimized method was applied to the treatment of nine simulated dyeing effluents prepared with different reactive dyes in order to compare the behavior of mono, bi, and tri-reactive dyes. Finally, the nine treated effluents were reused in new dyeing processes and the color differences (DECMC (2:1)) with respect to a reference were evaluated. The influence of the effluent organic matter removal on the color differences was also studied. The reuse of the treated effluents provides satisfactory dyeing results, and an important reduction in water consumption and salt discharge is achieved. Full article
(This article belongs to the Special Issue Advances in Colorants 2014)
Open AccessArticle Copper Electrodeposition on a Magnesium Alloy (AZ80) with a U-Shaped Surface
Materials 2014, 7(11), 7366-7378; doi:10.3390/ma7117366
Received: 14 May 2014 / Revised: 9 October 2014 / Accepted: 6 November 2014 / Published: 14 November 2014
Cited by 2 | PDF Full-text (581 KB) | HTML Full-text | XML Full-text
Abstract
Cu electrodeposition was performed on a cylindrical AZ80 substrate with a U-shaped surface. A uniform deposition of Cu was achieved on an AZ80 electrode via galvanostatic etching, followed by Cu electrodeposition in an eco-friendly alkaline Cu plating bath. Improper wetting and lower rotational
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Cu electrodeposition was performed on a cylindrical AZ80 substrate with a U-shaped surface. A uniform deposition of Cu was achieved on an AZ80 electrode via galvanostatic etching, followed by Cu electrodeposition in an eco-friendly alkaline Cu plating bath. Improper wetting and lower rotational speeds of the AZ80 electrode resulted in an uneven Cu deposition at the inner upper site of the U-shaped surface during the Cu electroplating process. This wetting effect could be deduced from the variation in the anodic potential during the galvanostatic etching. The corrosion resistance of the Cu-deposited AZ80 electrode can be considerably improved after Ni electroplating. Full article
(This article belongs to the Special Issue Light Alloys and Their Applications)
Open AccessArticle Ceo2 Based Catalysts for the Treatment of Propylene in Motorcycle’s Exhaust Gases
Materials 2014, 7(11), 7379-7397; doi:10.3390/ma7117379
Received: 18 September 2014 / Revised: 6 November 2014 / Accepted: 7 November 2014 / Published: 17 November 2014
Cited by 3 | PDF Full-text (919 KB) | HTML Full-text | XML Full-text
Abstract
In this work, the catalytic activities of several single metallic oxides were studied for the treatment of propylene, a component in motorcycles’ exhaust gases, under oxygen deficient conditions. Amongst them, CeO2 is one of the materials that exhibit the highest activity for
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In this work, the catalytic activities of several single metallic oxides were studied for the treatment of propylene, a component in motorcycles’ exhaust gases, under oxygen deficient conditions. Amongst them, CeO2 is one of the materials that exhibit the highest activity for the oxidation of C3H6. Therefore, several mixtures of CeO2 with other oxides (SnO2, ZrO2, Co3O4) were tested to investigate the changes in catalytic activity (both propylene conversion and CO2 selectivity). Ce0.9Zr0.1O2, Ce0.8Zr0.2O2 solid solutions and the mixtures of CeO2 and Co3O4 was shown to exhibit the highest propylene conversion and CO2 selectivity. They also exhibited good activities when tested under oxygen sufficient and excess conditions and with the presence of co-existing gases (CO, H2O). Full article
Open AccessCommunication Sustained Release of Hydrophilic l-ascorbic acid 2-phosphate Magnesium from Electrospun Polycaprolactone Scaffold—A Study across Blend, Coaxial, and Emulsion Electrospinning Techniques
Materials 2014, 7(11), 7398-7408; doi:10.3390/ma7117398
Received: 5 September 2014 / Revised: 28 October 2014 / Accepted: 6 November 2014 / Published: 17 November 2014
Cited by 3 | PDF Full-text (782 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The purpose of this study was to achieve a sustained release of hydrophilic l-ascorbic acid 2-phosphate magnesium (ASP) from electrospun polycaprolactone (PCL) scaffolds, so as to promote the osteogenic differentiation of stem cells for bone tissue engineering (TE). ASP was loaded and electrospun
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The purpose of this study was to achieve a sustained release of hydrophilic l-ascorbic acid 2-phosphate magnesium (ASP) from electrospun polycaprolactone (PCL) scaffolds, so as to promote the osteogenic differentiation of stem cells for bone tissue engineering (TE). ASP was loaded and electrospun together with PCL via three electrospinning techniques, i.e., coaxial, emulsion, and blend electrospinning. For blend electrospinning, binary solvent systems of dichloromethane–methanol (DCM–MeOH) and dichloromethane–dimethylformamide (DCM–DMF) were used to achieve the desired ASP release through the effect of solvent polarity and volatility. The scaffold prepared via a blend electrospinning technique with a binary solvent system of DCM–MeOH at a 7:3 ratio demonstrated a desirable, sustained ASP release profile for as long as two weeks, with minimal burst release. However, an undesirable burst release (~100%) was observed within the first 24 h for scaffolds prepared by coaxial electrospinning. Scaffolds prepared by emulsion electrospinning displayed poorer mechanical properties. Sustained releasing blend electrospun scaffold could be a good potential candidate as an ASP-eluting scaffold for bone tissue engineering. Full article
(This article belongs to the Special Issue Materials for Drug Delivery)
Open AccessArticle Vibration Modes at Terahertz and Infrared Frequencies of Ionic Liquids Consisting of an Imidazolium Cation and a Halogen Anion
Materials 2014, 7(11), 7409-7422; doi:10.3390/ma7117409
Received: 25 September 2014 / Revised: 7 November 2014 / Accepted: 7 November 2014 / Published: 17 November 2014
Cited by 6 | PDF Full-text (1458 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The terahertz and infrared frequency vibration modes of room-temperature ionic liquids with imidazolium cations and halogen anions were extensively investigated. There is an intermolecular vibrational mode between the imidazolium ring of an imidazolium cation, a halogen atomic anion with a large absorption coefficient
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The terahertz and infrared frequency vibration modes of room-temperature ionic liquids with imidazolium cations and halogen anions were extensively investigated. There is an intermolecular vibrational mode between the imidazolium ring of an imidazolium cation, a halogen atomic anion with a large absorption coefficient and a broad bandwidth in the low THz frequency region (13–130 cm−1), the intramolecular vibrational modes of the alkyl-chain part of an imidazolium cation with a relatively small absorption coefficient in the mid THz frequency region (130–500 cm−1), the intramolecular skeletal vibrational modes of an imidazolium ring affected by the interaction between the imidazolium ring, and a halogen anion with a relatively large absorption coefficient in a high THz frequency region (500–670 cm−1). Interesting spectroscopic features on the interaction between imidazolium cations and halogen anions was also obtained from spectroscopic studies at IR frequencies (550–3300 cm−1). As far as the frequency of the intermolecular vibrational mode is concerned, we found the significance of the reduced mass in determining the intermolecular vibration frequency. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle Engineering Properties and Correlation Analysis of Fiber Cementitious Materials
Materials 2014, 7(11), 7423-7435; doi:10.3390/ma7117423
Received: 1 September 2014 / Revised: 11 November 2014 / Accepted: 12 November 2014 / Published: 20 November 2014
Cited by 4 | PDF Full-text (499 KB) | HTML Full-text | XML Full-text
Abstract
This study focuses on the effect of the amount of silica fume addition and volume fraction of steel fiber on the engineering properties of cementitious materials. Test variables include dosage of silica fume (5% and 10%), water/cement ratio (0.35 and 0.55) and steel
[...] Read more.
This study focuses on the effect of the amount of silica fume addition and volume fraction of steel fiber on the engineering properties of cementitious materials. Test variables include dosage of silica fume (5% and 10%), water/cement ratio (0.35 and 0.55) and steel fiber dosage (0.5%, 1.0% and 2.0%). The experimental results included: compressive strength, direct tensile strength, splitting tensile strength, surface abrasion and drop-weight test, which were collected to carry out the analysis of variance to realize the relevancy and significance between material parameters and those mechanical properties. Test results illustrate that the splitting tensile strength, direct tensile strength, strain capacity and ability of crack-arresting increase with increasing steel fiber and silica fume dosages, as well as the optimum mixture of the fiber cementitious materials is 5% replacement silica fume and 2% fiber dosage. In addition, the Pearson correlation coefficient was conducted to evaluate the influence of the material variables and corresponds to the experiment result. Full article
(This article belongs to the Special Issue Selected Papers from ICETI2014)
Open AccessArticle Kinetic Study on the Formation of Bimetallic Core-Shell Nanoparticles via Microemulsions
Materials 2014, 7(11), 7513-7532; doi:10.3390/ma7117513
Received: 23 July 2014 / Revised: 17 October 2014 / Accepted: 12 November 2014 / Published: 21 November 2014
Cited by 4 | PDF Full-text (854 KB) | HTML Full-text | XML Full-text
Abstract
Computer calculations were carried out to determine the reaction rates and the mean structure of bimetallic nanoparticles prepared via a microemulsion route. The rates of reaction of each metal were calculated for a particular microemulsion composition (fixed intermicellar exchange rate) and varying reduction
[...] Read more.
Computer calculations were carried out to determine the reaction rates and the mean structure of bimetallic nanoparticles prepared via a microemulsion route. The rates of reaction of each metal were calculated for a particular microemulsion composition (fixed intermicellar exchange rate) and varying reduction rate ratios between both metal and metal salt concentration inside the micelles. Model predictions show that, even in the case of a very small difference in reduction potential of both metals, the formation of an external shell in a bimetallic nanoparticle is possible if a large reactant concentration is used. The modification of metal arrangement with concentration was analyzed from a mechanistic point of view, and proved to be due to the different impact of confinement on each metal: the reaction rate of the faster metal is only controlled by the intermicellar exchange rate but the slower metal is also affected by a cage-like effect. Full article
(This article belongs to the Special Issue Inorganic Core-Shell Structures)
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Open AccessArticle Assessment of Pozzolanic Activity Using Methods Based on the Measurement of Electrical Conductivity of Suspensions of Portland Cement and Pozzolan
Materials 2014, 7(11), 7533-7547; doi:10.3390/ma7117533
Received: 14 October 2014 / Revised: 8 November 2014 / Accepted: 17 November 2014 / Published: 21 November 2014
Cited by 1 | PDF Full-text (1006 KB) | HTML Full-text | XML Full-text
Abstract
The use of methods based on measuring electrical conductivity to assess pozzolanic activity has recently been used primarily in aqueous suspensions of pozzolan: calcium hydroxide. However, the use of similar methods in suspensions of cement with pozzolans has not been widely studied. This
[...] Read more.
The use of methods based on measuring electrical conductivity to assess pozzolanic activity has recently been used primarily in aqueous suspensions of pozzolan: calcium hydroxide. However, the use of similar methods in suspensions of cement with pozzolans has not been widely studied. This paper proposes a new method for rapid assessment of the pozzolanic activity of mineral admixtures in aqueous cement suspensions. In this study, the conditions for the application of the method were optimized, such as time, temperature, w/c ratio and dosage procedure. Finally, results are presented from the application of this method for characterizing the pozzolanic activity of the spent catalytic cracking catalyst. These results corroborate as previously reported, namely the high reactivity of this pozzolan obtained by other methods, such as thermogravimetry or evolution of the mechanical strength. In addition, the pozzolanic activity of the catalyst was compared with other pozzolans such as metakaolin and silica fume. Full article
Open AccessArticle 1,7-Bis-(N,N-dialkylamino)perylene Bisimides: Facile Synthesis and Characterization as Near-Infrared Fluorescent Dyes
Materials 2014, 7(11), 7548-7565; doi:10.3390/ma7117548
Received: 20 October 2014 / Revised: 10 November 2014 / Accepted: 13 November 2014 / Published: 24 November 2014
Cited by 2 | PDF Full-text (1443 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Three symmetric alkylamino-substituted perylene bisimides with different n-alkyl chain lengths (n = 6, 12, or 18), 1,7-bis-(N,N-dialkylamino)perylene bisimides (1a1c), were synthesized under mild condition and were characterized by 1H NMR, 13
[...] Read more.
Three symmetric alkylamino-substituted perylene bisimides with different n-alkyl chain lengths (n = 6, 12, or 18), 1,7-bis-(N,N-dialkylamino)perylene bisimides (1a1c), were synthesized under mild condition and were characterized by 1H NMR, 13C NMR and high resolution mass spectroscopy. Their optical and electrochemical properties were measured using UV-Vis and emission spectroscopic techniques as well as cyclic voltammetry (CV). These compounds show deep green color in both solution and solid state, and are highly soluble in dichloromethane and even in nonpolar solvents such as hexane. The shapes of the absorption spectra of 1a1c in the solution and solid state were found to be almost the same, indicating that the long alkyl chains could efficiently prevent intermolecular contact and aggregation. They show a unique charge transfer emission in the near-infrared region, of which the peak wavelengths exhibit strong solvatochromism. The dipole moments of the molecules have been estimated using the Lippert–Mataga equation, and upon excitation, they show larger dipole moment changes than that of 1,7-diaminoperylene bisimide (2). Moreover, all the dyes exhibit two irreversible one-electron oxidations and two quasi-reversible one-electron reductions in dichloromethane at modest potentials. Complementary density functional theory calculations performed on these chromophores are reported in order to rationalize their electronic structure and optical properties. Full article
(This article belongs to the Special Issue Luminescent Materials and Devices)
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Open AccessArticle Microfluidic Flows and Heat Transfer and Their Influence on Optical Modes in Microstructure Fibers
Materials 2014, 7(11), 7566-7582; doi:10.3390/ma7117566
Received: 8 July 2014 / Revised: 16 September 2014 / Accepted: 14 November 2014 / Published: 24 November 2014
Cited by 2 | PDF Full-text (1207 KB) | HTML Full-text | XML Full-text
Abstract
A finite element analysis (FEA) model has been constructed to predict the thermo-fluidic and optical properties of a microstructure optical fiber (MOF) accounting for changes in external temperature, input water velocity and optical fiber geometry. Modeling a water laminar flow within a water
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A finite element analysis (FEA) model has been constructed to predict the thermo-fluidic and optical properties of a microstructure optical fiber (MOF) accounting for changes in external temperature, input water velocity and optical fiber geometry. Modeling a water laminar flow within a water channel has shown that the steady-state temperature is dependent on the water channel radius while independent of the input velocity. There is a critical channel radius below which the steady-state temperature of the water channel is constant, while above, the temperature decreases. However, the distance required to reach steady state within the water channel is dependent on both the input velocity and the channel radius. The MOF has been found capable of supporting multiple modes. Despite the large thermo-optic coefficient of water, the bound modes’ response to temperature was dominated by the thermo-optic coefficient of glass. This is attributed to the majority of the light being confined within the glass, which increased with increasing external temperature due to a larger difference in the refractive index between the glass core and the water channel. Full article
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Review

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Open AccessReview PbSe-Based Colloidal Core/Shell Heterostructures for Optoelectronic Applications
Materials 2014, 7(11), 7243-7275; doi:10.3390/ma7117243
Received: 31 August 2014 / Revised: 25 September 2014 / Accepted: 24 October 2014 / Published: 30 October 2014
Cited by 20 | PDF Full-text (2069 KB) | HTML Full-text | XML Full-text
Abstract
Lead-based (IV–VI) colloidal quantum dots (QDs) are of widespread scientific and technological interest owing to their size-tunable band-gap energy in the near-infrared optical region. This article reviews the synthesis of PbSe-based heterostructures and their structural and optical investigations at various temperatures. The review
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Lead-based (IV–VI) colloidal quantum dots (QDs) are of widespread scientific and technological interest owing to their size-tunable band-gap energy in the near-infrared optical region. This article reviews the synthesis of PbSe-based heterostructures and their structural and optical investigations at various temperatures. The review focuses on the structures consisting of a PbSe core coated with a PbSexS1–x (0 ≤ x ≤ 1) or CdSe shell. The former-type shells were epitaxially grown on the PbSe core, while the latter-type shells were synthesized using partial cation-exchange. The influence of the QD composition and the ambient conditions, i.e., exposure to oxygen, on the QD optical properties, such as radiative lifetime, Stokes shift, and other temperature-dependent characteristics, was investigated. The study revealed unique properties of core/shell heterostructures of various compositions, which offer the opportunity of fine-tuning the QD electronic structure by changing their architecture. A theoretical model of the QD electronic band structure was developed and correlated with the results of the optical studies. The review also outlines the challenges related to potential applications of colloidal PbSe-based heterostructures. Full article
(This article belongs to the Special Issue Inorganic Core-Shell Structures)
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Open AccessReview Polymer-Derived Boron Nitride: A Review on the Chemistry, Shaping and Ceramic Conversion of Borazine Derivatives
Materials 2014, 7(11), 7436-7459; doi:10.3390/ma7117436
Received: 19 August 2014 / Revised: 16 September 2014 / Accepted: 11 November 2014 / Published: 21 November 2014
Cited by 19 | PDF Full-text (743 KB) | HTML Full-text | XML Full-text
Abstract
Boron nitride (BN) is a III-V compound which is the focus of important research since its discovery in the early 19th century. BN is electronic to carbon and thus, in the same way that carbon exists as graphite, BN exists in the hexagonal
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Boron nitride (BN) is a III-V compound which is the focus of important research since its discovery in the early 19th century. BN is electronic to carbon and thus, in the same way that carbon exists as graphite, BN exists in the hexagonal phase. The latter offers an unusual combination of properties that cannot be found in any other ceramics. However, these properties closely depend on the synthesis processes. This review states the recent developments in the preparation of BN through the chemistry, shaping and ceramic conversion of borazine derivatives. This concept denoted as Polymer-Derived Ceramics (PDCs) route allows tailoring the chemistry of precursors to elaborate complex BN shapes which cannot be obtained by conventional process. The effect of the chemistry of the molecular precursors, i.e., borazine and trichloroborazine, and their polymeric derivatives i.e., polyborazylene and poly[tri(methylamino)borazine], in which the specific functional groups and structural motifs determine the shaping potential by conventional liquid-phase process and plastic-forming techniques is discussed. Nanotubes, nano-fibers, coatings, monoliths and fiber-reinforced matrix composites are especially described. This leads to materials which are of significant engineering interest. Full article
(This article belongs to the Special Issue Compound Semiconductor Materials 2014)
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Open AccessReview Core-Shell Structured Electro- and Magneto-Responsive Materials: Fabrication and Characteristics
Materials 2014, 7(11), 7460-7471; doi:10.3390/ma7117460
Received: 2 September 2014 / Revised: 24 October 2014 / Accepted: 11 November 2014 / Published: 21 November 2014
Cited by 10 | PDF Full-text (1181 KB) | HTML Full-text | XML Full-text
Abstract
Core-shell structured electrorheological (ER) and magnetorheological (MR) particles have attracted increasing interest owing to their outstanding field-responsive properties, including morphology, chemical and dispersion stability, and rheological characteristics of shear stress and yield stress. This study covers recent progress in the preparation of core-shell
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Core-shell structured electrorheological (ER) and magnetorheological (MR) particles have attracted increasing interest owing to their outstanding field-responsive properties, including morphology, chemical and dispersion stability, and rheological characteristics of shear stress and yield stress. This study covers recent progress in the preparation of core-shell structured materials as well as their critical characteristics and advantages. Broad emphasises from the synthetic strategy of various core-shell particles to their feature behaviours in the magnetic and electric fields have been elaborated. Full article
(This article belongs to the Special Issue Inorganic Core-Shell Structures)
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Open AccessReview Layer-by-Layer Assembly of Biopolyelectrolytes onto Thermo/pH-Responsive Micro/Nano-Gels
Materials 2014, 7(11), 7472-7512; doi:10.3390/ma7117472
Received: 13 October 2014 / Revised: 1 November 2014 / Accepted: 14 November 2014 / Published: 21 November 2014
Cited by 9 | PDF Full-text (10039 KB) | HTML Full-text | XML Full-text
Abstract
This review deals with the layer-by-layer (LbL) assembly of polyelectrolyte multilayers of biopolymers, polypeptides (i.e., poly-l-lysine/poly-l-glutamic acid) and polysaccharides (i.e., chitosan/dextran sulphate/sodium alginate), onto thermo- and/or pH-responsive micro- and nano-gels such as those based on synthetic poly(N-isopropylacrylamide)
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This review deals with the layer-by-layer (LbL) assembly of polyelectrolyte multilayers of biopolymers, polypeptides (i.e., poly-l-lysine/poly-l-glutamic acid) and polysaccharides (i.e., chitosan/dextran sulphate/sodium alginate), onto thermo- and/or pH-responsive micro- and nano-gels such as those based on synthetic poly(N-isopropylacrylamide) (PNIPAM) and poly(acrylic acid) (PAA) or biodegradable hyaluronic acid (HA) and dextran-hydroxyethyl methacrylate (DEX-HEMA). The synthesis of the ensembles and their characterization by way of various techniques is described. The morphology, hydrodynamic size, surface charge density, bilayer thickness, stability over time and mechanical properties of the systems are discussed. Further, the mechanisms of interaction between biopolymers and gels are analysed. Results demonstrate that the structure and properties of biocompatible multilayer films can be finely tuned by confinement onto stimuli-responsive gels, which thus provides new perspectives for biomedical applications, particularly in the controlled release of biomolecules, bio-sensors, gene delivery, tissue engineering and storage. Full article
(This article belongs to the Special Issue Gel-Based Particles for Biological and Environmental Applications)

Other

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Open AccessCorrection Correction: Hood, M.A., et al. Synthetic Strategies in the Preparation of Polymer/Inorganic Hybrid Nanoparticles. Materials 2014, 7, 4057–4087
Materials 2014, 7(11), 7583-7614; doi:10.3390/ma7117583
Received: 7 August 2014 / Accepted: 21 August 2014 / Published: 24 November 2014
PDF Full-text (1413 KB) | HTML Full-text | XML Full-text
Abstract
In [1], several sentences were repeated three times on pages 4062, 4063 and 4065. In addition, many references were incorrect. The errors were introduced by the editorial office during the editing process. We apologize for this mistake and any inconvenience this may have
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In [1], several sentences were repeated three times on pages 4062, 4063 and 4065. In addition, many references were incorrect. The errors were introduced by the editorial office during the editing process. We apologize for this mistake and any inconvenience this may have caused to authors and readers. The corrected manuscript is given below.[...] Full article

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