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Materials, Volume 7, Issue 7 (July 2014), Pages 4878-5426

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Research

Jump to: Review

Open AccessArticle Fabrication of an Optical Fiber Micro-Sphere with a Diameter of Several Tens of Micrometers
Materials 2014, 7(7), 4878-4895; doi:10.3390/ma7074878
Received: 30 April 2014 / Revised: 9 June 2014 / Accepted: 19 June 2014 / Published: 25 June 2014
Cited by 3 | PDF Full-text (989 KB) | HTML Full-text | XML Full-text
Abstract
A new method to fabricate an integrated optical fiber micro-sphere with a diameter within 100 µm, based on the optical fiber tapering technique and the Taguchi method is proposed. Using a 125 µm diameter single-mode (SM) optical fiber, an optical fiber taper with
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A new method to fabricate an integrated optical fiber micro-sphere with a diameter within 100 µm, based on the optical fiber tapering technique and the Taguchi method is proposed. Using a 125 µm diameter single-mode (SM) optical fiber, an optical fiber taper with a cone angle is formed with the tapering technique, and the fabrication optimization of a micro-sphere with a diameter of less than 100 µm is achieved using the Taguchi method. The optimum combination of process factors levels is obtained, and the signal-to-noise ratio (SNR) of three quality evaluation parameters and the significance of each process factors influencing them are selected as the two standards. Using the minimum zone method (MZM) to evaluate the quality of the fabricated optical fiber micro-sphere, a three-dimensional (3D) numerical fitting image of its surface profile and the true sphericity are subsequently realized. From the results, an optical fiber micro-sphere with a two-dimensional (2D) diameter less than 80 µm, 2D roundness error less than 0.70 µm, 2D offset distance between the micro-sphere center and the fiber stylus central line less than 0.65 µm, and true sphericity of about 0.5 µm, is fabricated. Full article
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Open AccessArticle Experimental Investigation of the Effect of the Driving Voltage of an Electroadhesion Actuator
Materials 2014, 7(7), 4963-4981; doi:10.3390/ma7074963
Received: 25 March 2014 / Revised: 14 June 2014 / Accepted: 18 June 2014 / Published: 25 June 2014
Cited by 4 | PDF Full-text (1668 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This paper investigates the effect of driving voltage on the attachment force of an electroadhesion actuator, as the existing literature on the saturation of the adhesive force at a higher electric field is incomplete. A new type of electroadhesion actuator using normally available
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This paper investigates the effect of driving voltage on the attachment force of an electroadhesion actuator, as the existing literature on the saturation of the adhesive force at a higher electric field is incomplete. A new type of electroadhesion actuator using normally available materials, such as aluminum foil, PVC tape and a silicone rubber sheet used for keyboard protection, has been developed with a simple layered structure that is capable of developing adhesive force consistently. The developed actuator is subjected to the experiment for the evaluation of various test surfaces; aluminum, brick, ceramic, concrete and glass. The driving high voltage is varied in steps to determine the characteristics of the output holding force. Results show a quadratic relation between F (adhesion force) and V (driving voltage) within the 2 kV range. After this range, the F-V responses consistently show a saturation trend at high electric fields. Next, the concept of the leakage current that can occur in the dielectric material and the corona discharge through air has been introduced. Results show that the voltage level, which corresponds to the beginning of the supply current, matches well with the beginning of the force saturation. With the confirmation of this hypothesis, a working model for electroadhesion actuation is proposed. Based on the experimental results, it is proposed that such a kind of actuator can be driven within a range of optimum high voltage to remain electrically efficient. This practice is recommended for the future design, development and characterization of electroadhesion actuators for robotic applications. Full article
Open AccessArticle Structural and Optical Properties of La1−xSrxTiO3+δ
Materials 2014, 7(7), 4982-4993; doi:10.3390/ma7074982
Received: 9 April 2014 / Revised: 28 May 2014 / Accepted: 18 June 2014 / Published: 25 June 2014
Cited by 4 | PDF Full-text (1167 KB) | HTML Full-text | XML Full-text
Abstract
La1−xSrxTiO3+δ has attracted much attention as an important perovskite oxide. However, there are rare reports on its optical properties, especially reflectivity. In this paper, its structural and optical properties were studied. The X-ray diffraction, X-ray photoelectron spectroscopy,
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La1−xSrxTiO3+δ has attracted much attention as an important perovskite oxide. However, there are rare reports on its optical properties, especially reflectivity. In this paper, its structural and optical properties were studied. The X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and spectrophotometer were used to characterize the sample. The results show that with increasing Sr concentration, the number of TiO6 octahedral layers in each “slab” increases and the crystal structure changes from layered to cubic structure. A proper Sr doping (x = 0.1) can increase the reflectivity, reaching 95% in the near infrared range, which is comparable with metal Al measured in the same condition. This indicates its potential applications as optical protective coatings or anti-radiation materials at high temperatures. Full article
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Open AccessArticle The Design and Analysis of a Novel Split-H-Shaped Metamaterial for Multi-Band Microwave Applications
Materials 2014, 7(7), 4994-5011; doi:10.3390/ma7074994
Received: 26 March 2014 / Revised: 7 May 2014 / Accepted: 20 June 2014 / Published: 2 July 2014
Cited by 11 | PDF Full-text (979 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents the design and analysis of a novel split-H-shaped metamaterial unit cell structure that is applicable in a multi-band frequency range and that exhibits negative permeability and permittivity in those frequency bands. In the basic design, the separate split-square resonators are
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This paper presents the design and analysis of a novel split-H-shaped metamaterial unit cell structure that is applicable in a multi-band frequency range and that exhibits negative permeability and permittivity in those frequency bands. In the basic design, the separate split-square resonators are joined by a metal link to form an H-shaped unit structure. Moreover, an analysis and a comparison of the 1 × 1 array and 2 × 2 array structures and the 1 × 1 and 2 × 2 unit cell configurations were performed. All of these configurations demonstrate multi-band operating frequencies (S-band, C-band, X-band and Ku-band) with double-negative characteristics. The equivalent circuit model and measured result for each unit cell are presented to validate the resonant behavior. The commercially available finite-difference time-domain (FDTD)-based simulation software, Computer Simulation Technology (CST) Microwave Studio, was used to obtain the reflection and transmission parameters of each unit cell. This is a novel and promising design in the electromagnetic paradigm for its simplicity, scalability, double-negative characteristics and multi-band operation. Full article
(This article belongs to the Section Materials for Energy Applications)
Open AccessArticle Indium Doped Zinc Oxide Thin Films Deposited by Ultrasonic Chemical Spray Technique, Starting from Zinc Acetylacetonate and Indium Chloride
Materials 2014, 7(7), 5038-5046; doi:10.3390/ma7075038
Received: 2 April 2014 / Revised: 8 May 2014 / Accepted: 14 May 2014 / Published: 4 July 2014
Cited by 9 | PDF Full-text (657 KB) | HTML Full-text | XML Full-text
Abstract
The physical characteristics of ultrasonically sprayed indium-doped zinc oxide (ZnO:In) thin films, with electrical resistivity as low as 3.42 × 10−3 Ω·cm and high optical transmittance, in the visible range, of 50%–70% is presented. Zinc acetylacetonate and indium chloride were used as
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The physical characteristics of ultrasonically sprayed indium-doped zinc oxide (ZnO:In) thin films, with electrical resistivity as low as 3.42 × 10−3 Ω·cm and high optical transmittance, in the visible range, of 50%–70% is presented. Zinc acetylacetonate and indium chloride were used as the organometallic zinc precursor and the doping source, respectively, achieving ZnO:In thin films with growth rate in the order of 100 nm/min. The effects of both indium concentration and the substrate temperature on the structural, morphological, optical, and electrical characteristics were measured. All the films were polycrystalline, fitting well with hexagonal wurtzite type ZnO. A switching in preferential growth, from (002) to (101) planes for indium doped samples were observed. The surface morphology of the films showed a change from hexagonal slices to triangle shaped grains as the indium concentration increases. Potential applications as transparent conductive electrodes based on the resulting low electrical resistance and high optical transparency of the studied samples are considered. Full article
(This article belongs to the Special Issue Opto-Electronic Materials)
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Open AccessArticle Property Criteria for Automotive Al-Mg-Si Sheet Alloys
Materials 2014, 7(7), 5047-5068; doi:10.3390/ma7075047
Received: 28 April 2014 / Revised: 13 June 2014 / Accepted: 24 June 2014 / Published: 4 July 2014
Cited by 4 | PDF Full-text (1806 KB) | HTML Full-text | XML Full-text
Abstract
In this study, property criteria for automotive Al-Mg-Si sheet alloys are outlined and investigated in the context of commercial alloys AA6016, AA6005A, AA6063 and AA6013. The parameters crucial to predicting forming behavior were determined by tensile tests, bending tests, cross-die tests, hole-expansion tests
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In this study, property criteria for automotive Al-Mg-Si sheet alloys are outlined and investigated in the context of commercial alloys AA6016, AA6005A, AA6063 and AA6013. The parameters crucial to predicting forming behavior were determined by tensile tests, bending tests, cross-die tests, hole-expansion tests and forming limit curve analysis in the pre-aged temper after various storage periods following sheet production. Roping tests were performed to evaluate surface quality, for the deployment of these alloys as an outer panel material. Strength in service was also tested after a simulated paint bake cycle of 20 min at 185 °C, and the corrosion behavior was analyzed. The study showed that forming behavior is strongly dependent on the type of alloy and that it is influenced by the storage period after sheet production. Alloy AA6016 achieves the highest surface quality, and pre-ageing of alloy AA6013 facilitates superior strength in service. Corrosion behavior is good in AA6005A, AA6063 and AA6016, and only AA6013 shows a strong susceptibility to intergranular corrosion. The results are discussed below with respect to the chemical composition, microstructure and texture of the Al-Mg-Si alloys studied, and decision-making criteria for appropriate automotive sheet alloys for specific applications are presented. Full article
(This article belongs to the Special Issue Light Alloys and Their Applications)
Open AccessArticle Validation of the Anhysteretic Magnetization Model for Soft Magnetic Materials with Perpendicular Anisotropy
Materials 2014, 7(7), 5109-5116; doi:10.3390/ma7075109
Received: 6 May 2014 / Revised: 25 June 2014 / Accepted: 3 July 2014 / Published: 14 July 2014
Cited by 8 | PDF Full-text (713 KB) | HTML Full-text | XML Full-text
Abstract
The paper presents results of validation of the anhysteretic magnetization model for a soft amorphous alloy with significant perpendicular anisotropy. The validation was carried out for the Jiles-Atherton model with Ramesh extension considering anisotropy. Due to the fact that it is difficult to
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The paper presents results of validation of the anhysteretic magnetization model for a soft amorphous alloy with significant perpendicular anisotropy. The validation was carried out for the Jiles-Atherton model with Ramesh extension considering anisotropy. Due to the fact that it is difficult to measure anhysteretic magnetization directly, the soft magnetic core with negligible hysteresis was used. The results of validation indicate that the Jiles-Atherton model with Ramesh extension should be corrected to allow accurate modeling of the anhysteretic magnetization. The corrected model may be applied for modeling the cores of current transformers operating in a wide range of measured currents. Full article
(This article belongs to the Section Structure Analysis and Characterization)
Open AccessArticle SAXS Studies of the Endoglucanase Cel12A from Gloeophyllum trabeum Show Its Monomeric Structure and Reveal the Influence of Temperature on the Structural Stability of the Enzyme
Materials 2014, 7(7), 5202-5211; doi:10.3390/ma7075202
Received: 25 April 2014 / Revised: 10 June 2014 / Accepted: 24 June 2014 / Published: 17 July 2014
PDF Full-text (1035 KB) | HTML Full-text | XML Full-text
Abstract
Endoglucanases are key enzymes applied to the conversion of biomass aiming for second generation biofuel production. In the present study we obtained the small angle X-ray scattering (SAXS) structure of the G. trabeum endo-1,4-β-glucanase Cel12A and investigated the influence of an important
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Endoglucanases are key enzymes applied to the conversion of biomass aiming for second generation biofuel production. In the present study we obtained the small angle X-ray scattering (SAXS) structure of the G. trabeum endo-1,4-β-glucanase Cel12A and investigated the influence of an important parameter, temperature, on both secondary and tertiary structure of the enzyme and its activity. The CD analysis for GtCel12A revealed that changes in the CD spectra starts at 55 °C and the Tm calculated from the experimental CD sigmoid curve using the Boltzmann function was 60.2 ± 0.6 °C. SAXS data showed that GtCel12A forms monomers in solution and has an elongated form with a maximum diameter of 60 ± 5 Å and a gyration radius of 19.4 ± 0.1 Å as calculated from the distance distribution function. Kratky analysis revealed that 60 °C is the critical temperature above which we observed clear indications of denaturation. Our results showed the influence of temperature on the stability and activity of enzymes and revealed novel structural features of GtCel12A. Full article
(This article belongs to the Special Issue Advances in Cellulosic Materials 2014)
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Open AccessArticle Microwave Irradiation Effect on the Dispersion and Thermal Stability of RGO Nanosheets within a Polystyrene Matrix
Materials 2014, 7(7), 5212-5224; doi:10.3390/ma7075212
Received: 19 April 2014 / Revised: 2 July 2014 / Accepted: 8 July 2014 / Published: 18 July 2014
Cited by 10 | PDF Full-text (1035 KB) | HTML Full-text | XML Full-text
Abstract
Polystyrene-reduced graphene oxide (PSTY/RGO) composites were prepared via the in situ bulk polymerization method using two different preparation techniques. The general approach is to use microwave irradiation (MWI) to enhance the exfoliation and the dispersion of RGO nanosheets within the PSTY matrix. In
[...] Read more.
Polystyrene-reduced graphene oxide (PSTY/RGO) composites were prepared via the in situ bulk polymerization method using two different preparation techniques. The general approach is to use microwave irradiation (MWI) to enhance the exfoliation and the dispersion of RGO nanosheets within the PSTY matrix. In the first approach, a mixture of GO and styrene monomers (STY) were polymerized using a bulk polymerization method facilitated by microwave irradiation (MWI) to obtain R-(GO-PSTY) composites. In the second approach, a mixture of RGO and STY monomers were polymerized using a bulk polymerization method to obtain RGO-(PSTY) composites. The two composites were characterized by FTIR, 1H-NMR, XRD, SEM, HRTEM, TGA and DSC. The results indicate that the composite obtained using the first approach, which involved MWI, had a better morphology and dispersion with enhanced thermal stability, compared with the composites prepared without MWI. Moreover, DSC results showed that the Tg value of the composites after loading the RGO significantly increased by 24.6 °C compared to the neat polystyrene. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessCommunication The Challenge of Producing Fiber-Based Organic Electronic Devices
Materials 2014, 7(7), 5254-5267; doi:10.3390/ma7075254
Received: 27 May 2014 / Revised: 11 June 2014 / Accepted: 15 July 2014 / Published: 18 July 2014
Cited by 1 | PDF Full-text (1468 KB) | HTML Full-text | XML Full-text
Abstract
The implementation of organic electronic devices on fibers is a challenging task, not yet investigated in detail. As was shown earlier, a direct transition from a flat device structure to a fiber substrate is in principle possible. However, a more detailed investigation of
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The implementation of organic electronic devices on fibers is a challenging task, not yet investigated in detail. As was shown earlier, a direct transition from a flat device structure to a fiber substrate is in principle possible. However, a more detailed investigation of the process reveals additional complexities than just the transition in geometry. It will be shown, that the layer formation of evaporated materials behaves differently due to the multi-angled incidence on the fibers surface. In order to achieve homogenous layers the evaporation process has to be adapted. Additionally, the fiber geometry itself facilitates damaging of its surface due to mechanical impact and leads to a high surface roughness, thereby often hindering commercial fibers to be used as substrates. In this article, a treatment of commercial polymer-coated glass fibers will be demonstrated that allows for the fabrication of rather flexible organic light-emitting diodes (OLEDs) with cylindrical emission characteristics. Since OLEDs rely the most on a smooth substrate, fibers undergoing the proposed treatment are applicable for other organic electronic devices such as transistors and solar cells. Finally, the technique also supports the future fabrication of organic electronics not only in smart textiles and woven electronics but also in bent surfaces, which opens a wide range of applications. Full article
(This article belongs to the Special Issue Opto-Electronic Materials)
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Open AccessArticle Synthesis and Phase Behavior of Poly(N-isopropylacrylamide)-b- Poly(L-Lysine Hydrochloride) and Poly(N-Isopropylacrylamide- co-Acrylamide)-b-Poly(L-Lysine Hydrochloride)
Materials 2014, 7(7), 5305-5326; doi:10.3390/ma7075305
Received: 7 May 2014 / Revised: 8 July 2014 / Accepted: 17 July 2014 / Published: 22 July 2014
Cited by 2 | PDF Full-text (1394 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The synthesis of poly(N-isopropylacrylamide)-b-poly(L-lysine) and poly(N- isopropylacrylamide-co-acrylamide)-b-poly(L-lysine) copolymers was accomplished by combining atom transfer radical polymerization (ATRP) and ring opening polymerization (ROP). For this purpose, a di-functional initiator with protected amino group was successfully synthetized. The ATRP of N
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The synthesis of poly(N-isopropylacrylamide)-b-poly(L-lysine) and poly(N- isopropylacrylamide-co-acrylamide)-b-poly(L-lysine) copolymers was accomplished by combining atom transfer radical polymerization (ATRP) and ring opening polymerization (ROP). For this purpose, a di-functional initiator with protected amino group was successfully synthetized. The ATRP of N-isopropylacrylamide yielded narrowly dispersed polymers with consistent high yields (~80%). Lower yields (~50%) were observed when narrowly dispersed random copolymers of N-isopropylacrylamide and acrylamide where synthesized. Amino-terminated poly(N-isopropylacrylamide) and poly(N-isopropylacrylamide- co-acrylamide) were successfully used as macroinitiators for ROP of N6-carbobenzoxy-L- lysine N-carboxyanhydride. The thermal behavior of the homopolymers and copolymers in aqueous solutions was studied by turbidimetry, dynamic light scattering (DLS) and proton nuclear magnetic resonance spectroscopy (1H-NMR). Full article
Open AccessArticle Liquid Crystalline Network Composites Reinforced by Silica Nanoparticles
Materials 2014, 7(7), 5356-5365; doi:10.3390/ma7075356
Received: 11 March 2014 / Revised: 4 June 2014 / Accepted: 6 June 2014 / Published: 22 July 2014
Cited by 1 | PDF Full-text (1031 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Liquid crystalline networks (LCNs) are a class of polymers, which are able to produce mechanical actuation in response to external stimuli. Recent creation of LCNs with exchangeable links (xLCNs) makes LCNs easy moldable. As the xLCNs need to be shaped at a high
[...] Read more.
Liquid crystalline networks (LCNs) are a class of polymers, which are able to produce mechanical actuation in response to external stimuli. Recent creation of LCNs with exchangeable links (xLCNs) makes LCNs easy moldable. As the xLCNs need to be shaped at a high temperature, it is important to enhance their thermal and mechanical properties. In this paper, a series of xLCNs/SiO2 composites containing 1%–7% SiO2 nanoparitcles (SNP) were prepared and their thermal and mechanical properties were examined. The results show that xLCNs/SNP composites have lower liquid crystalline-isotropic phase transition temperature and higher decomposition temperature than pure LCN. The tensile strength and the elongation at break of xLCNs at high temperatures were also enhanced due to the addition of SNPs. Full article
(This article belongs to the Special Issue Liquid Crystals) Print Edition available
Open AccessArticle A Perspective on the Prowaste Concept: Efficient Utilization of Plastic Waste through Product Design and Process Innovation
Materials 2014, 7(7), 5385-5402; doi:10.3390/ma7075385
Received: 12 May 2014 / Revised: 16 July 2014 / Accepted: 21 July 2014 / Published: 23 July 2014
PDF Full-text (1427 KB) | HTML Full-text | XML Full-text
Abstract
This work is aimed to present an innovative technology for the reinforcement of beams for urban furniture, produced by in-mold extrusion of plastics from solid urban waste. This material, which is usually referred to as “recycled plastic lumber”, is characterized by very poor
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This work is aimed to present an innovative technology for the reinforcement of beams for urban furniture, produced by in-mold extrusion of plastics from solid urban waste. This material, which is usually referred to as “recycled plastic lumber”, is characterized by very poor mechanical properties, which results in high deflections under flexural loads, particularly under creep conditions. The Prowaste project, founded by the EACI (European Agency for Competitiveness and Innovation) in the framework of the Eco-Innovation measure, was finalized to develop an innovative technology for selective reinforcement of recycled plastic lumber. Selective reinforcement was carried out by the addition of pultruded glass rods in specific positions with respect to the cross section of the beam, which allowed optimizing the reinforcing efficiency. The reinforcement of the plastic lumber beams with pultruded rods was tested at industrial scale plant, at Solteco SL (Alfaro, Spain). The beams obtained, characterized by low cost and weight, were commercialized by the Spanish company. The present paper presents the most relevant results of the Prowaste project. Initially, an evaluation of the different materials candidates for the reinforcement of recycled plastic lumber is presented. Plastic lumber beams produced in the industrial plant were characterized in terms of flexural properties. The results obtained are interpreted by means of beam theory, which allows for extrapolation of the characteristic features of beams produced by different reinforcing elements. Finally, a theoretical comparison with other approaches which can be used for the reinforcement of plastic lumber is presented, highlighting that, among others, the Prowaste concept maximizes the stiffening efficiency, allowing to significantly reduce the weight of the components. Full article
(This article belongs to the Special Issue Recycled Materials)

Review

Jump to: Research

Open AccessReview Plasma-Enabled Carbon Nanostructures for Early Diagnosis of Neurodegenerative Diseases
Materials 2014, 7(7), 4896-4929; doi:10.3390/ma7074896
Received: 27 March 2014 / Revised: 18 June 2014 / Accepted: 20 June 2014 / Published: 25 June 2014
Cited by 1 | PDF Full-text (1862 KB) | HTML Full-text | XML Full-text
Abstract
Carbon nanostructures (CNs) are amongst the most promising biorecognition nanomaterials due to their unprecedented optical, electrical and structural properties. As such, CNs may be harnessed to tackle the detrimental public health and socio-economic adversities associated with neurodegenerative diseases (NDs). In particular, CNs may
[...] Read more.
Carbon nanostructures (CNs) are amongst the most promising biorecognition nanomaterials due to their unprecedented optical, electrical and structural properties. As such, CNs may be harnessed to tackle the detrimental public health and socio-economic adversities associated with neurodegenerative diseases (NDs). In particular, CNs may be tailored for a specific determination of biomarkers indicative of NDs. However, the realization of such a biosensor represents a significant technological challenge in the uniform fabrication of CNs with outstanding qualities in order to facilitate a highly-sensitive detection of biomarkers suspended in complex biological environments. Notably, the versatility of plasma-based techniques for the synthesis and surface modification of CNs may be embraced to optimize the biorecognition performance and capabilities. This review surveys the recent advances in CN-based biosensors, and highlights the benefits of plasma-processing techniques to enable, enhance, and tailor the performance and optimize the fabrication of CNs, towards the construction of biosensors with unparalleled performance for the early diagnosis of NDs, via a plethora of energy-efficient, environmentally-benign, and inexpensive approaches. Full article
(This article belongs to the Special Issue Advanced Nanomaterials for Biosensors)
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Open AccessReview Welding and Joining of Titanium Aluminides
Materials 2014, 7(7), 4930-4962; doi:10.3390/ma7074930
Received: 10 March 2014 / Revised: 19 June 2014 / Accepted: 20 June 2014 / Published: 25 June 2014
Cited by 6 | PDF Full-text (2249 KB) | HTML Full-text | XML Full-text
Abstract
Welding and joining of titanium aluminides is the key to making them more attractive in industrial fields. The purpose of this review is to provide a comprehensive overview of recent progress in welding and joining of titanium aluminides, as well as to introduce
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Welding and joining of titanium aluminides is the key to making them more attractive in industrial fields. The purpose of this review is to provide a comprehensive overview of recent progress in welding and joining of titanium aluminides, as well as to introduce current research and application. The possible methods available for titanium aluminides involve brazing, diffusion bonding, fusion welding, friction welding and reactive joining. Of the numerous methods, solid-state diffusion bonding and vacuum brazing have been most heavily investigated for producing reliable joints. The current state of understanding and development of every welding and joining method for titanium aluminides is addressed respectively. The focus is on the fundamental understanding of microstructure characteristics and processing–microstructure–property relationships in the welding and joining of titanium aluminides to themselves and to other materials. Full article
(This article belongs to the Special Issue Light Alloys and Their Applications)
Open AccessReview Surface Coating of Oxide Powders: A New Synthesis Method to Process Biomedical Grade Nano-Composites
Materials 2014, 7(7), 5012-5037; doi:10.3390/ma7075012
Received: 16 April 2014 / Revised: 13 June 2014 / Accepted: 24 June 2014 / Published: 4 July 2014
Cited by 4 | PDF Full-text (1631 KB) | HTML Full-text | XML Full-text
Abstract
Composite and nanocomposite ceramics have achieved special interest in recent years when used for biomedical applications. They have demonstrated, in some cases, increased performance, reliability, and stability in vivo, with respect to pure monolithic ceramics. Current research aims at developing new compositions
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Composite and nanocomposite ceramics have achieved special interest in recent years when used for biomedical applications. They have demonstrated, in some cases, increased performance, reliability, and stability in vivo, with respect to pure monolithic ceramics. Current research aims at developing new compositions and architectures to further increase their properties. However, the ability to tailor the microstructure requires the careful control of all steps of manufacturing, from the synthesis of composite nanopowders, to their processing and sintering. This review aims at deepening understanding of the critical issues associated with the manufacturing of nanocomposite ceramics, focusing on the key role of the synthesis methods to develop homogeneous and tailored microstructures. In this frame, the authors have developed an innovative method, named “surface-coating process”, in which matrix oxide powders are coated with inorganic precursors of the second phase. The method is illustrated into two case studies; the former, on Zirconia Toughened Alumina (ZTA) materials for orthopedic applications, and the latter, on Zirconia-based composites for dental implants, discussing the advances and the potential of the method, which can become a valuable alternative to the current synthesis process already used at a clinical and industrial scale. Full article
(This article belongs to the Special Issue Ceramics for Healthcare 2013)
Open AccessReview The Influence of Ziegler-Natta and Metallocene Catalysts on Polyolefin Structure, Properties, and Processing Ability
Materials 2014, 7(7), 5069-5108; doi:10.3390/ma7075069
Received: 6 April 2014 / Revised: 16 June 2014 / Accepted: 25 June 2014 / Published: 9 July 2014
Cited by 14 | PDF Full-text (1686 KB) | HTML Full-text | XML Full-text
Abstract
50 years ago, Karl Ziegler and Giulio Natta were awarded the Nobel Prize for their discovery of the catalytic polymerization of ethylene and propylene using titanium compounds and aluminum-alkyls as co-catalysts. Polyolefins have grown to become one of the biggest of all produced
[...] Read more.
50 years ago, Karl Ziegler and Giulio Natta were awarded the Nobel Prize for their discovery of the catalytic polymerization of ethylene and propylene using titanium compounds and aluminum-alkyls as co-catalysts. Polyolefins have grown to become one of the biggest of all produced polymers. New metallocene/methylaluminoxane (MAO) catalysts open the possibility to synthesize polymers with highly defined microstructure, tacticity, and steroregularity, as well as long-chain branched, or blocky copolymers with excellent properties. This improvement in polymerization is possible due to the single active sites available on the metallocene catalysts in contrast to their traditional counterparts. Moreover, these catalysts, half titanocenes/MAO, zirconocenes, and other single site catalysts can control various important parameters, such as co-monomer distribution, molecular weight, molecular weight distribution, molecular architecture, stereo-specificity, degree of linearity, and branching of the polymer. However, in most cases research in this area has reduced academia as olefin polymerization has seen significant advancements in the industries. Therefore, this paper aims to further motivate interest in polyolefin research in academia by highlighting promising and open areas for the future. Full article
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Open AccessReview Review on Non-Volatile Memory with High-k Dielectrics: Flash for Generation Beyond 32 nm
Materials 2014, 7(7), 5117-5145; doi:10.3390/ma7075117
Received: 15 January 2014 / Revised: 2 July 2014 / Accepted: 3 July 2014 / Published: 15 July 2014
Cited by 19 | PDF Full-text (2011 KB) | HTML Full-text | XML Full-text
Abstract
Flash memory is the most widely used non-volatile memory device nowadays. In order to keep up with the demand for increased memory capacities, flash memory has been continuously scaled to smaller and smaller dimensions. The main benefits of down-scaling cell size and increasing
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Flash memory is the most widely used non-volatile memory device nowadays. In order to keep up with the demand for increased memory capacities, flash memory has been continuously scaled to smaller and smaller dimensions. The main benefits of down-scaling cell size and increasing integration are that they enable lower manufacturing cost as well as higher performance. Charge trapping memory is regarded as one of the most promising flash memory technologies as further down-scaling continues. In addition, more and more exploration is investigated with high-k dielectrics implemented in the charge trapping memory. The paper reviews the advanced research status concerning charge trapping memory with high-k dielectrics for the performance improvement. Application of high-k dielectric as charge trapping layer, blocking layer, and tunneling layer is comprehensively discussed accordingly. Full article
(This article belongs to the Special Issue High-k Materials and Devices 2014)
Open AccessReview Structural Rheology of the Smectic Phase
Materials 2014, 7(7), 5146-5168; doi:10.3390/ma7075146
Received: 1 April 2014 / Revised: 13 June 2014 / Accepted: 24 June 2014 / Published: 16 July 2014
Cited by 4 | PDF Full-text (6487 KB) | HTML Full-text | XML Full-text
Abstract
In this review article, we discuss the rheological properties of the thermotropic smectic liquid crystal 8CB with focal conic domains (FCDs) from the viewpoint of structural rheology. It is known that the unbinding of the dislocation loops in the smectic phase drives the
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In this review article, we discuss the rheological properties of the thermotropic smectic liquid crystal 8CB with focal conic domains (FCDs) from the viewpoint of structural rheology. It is known that the unbinding of the dislocation loops in the smectic phase drives the smectic-nematic transition. Here we discuss how the unbinding of the dislocation loops affects the evolution of the FCD size, linear and nonlinear rheological behaviors of the smectic phase. By studying the FCD formation from the perpendicularly oriented smectic layers, we also argue that dislocations play a key role in the structural development in layered systems. Furthermore, similarities in the rheological behavior between the FCDs in the smectic phase and the onion structures in the lyotropic lamellar phase suggest that these systems share a common physical origin for the elasticity. Full article
(This article belongs to the Special Issue Liquid Crystals) Print Edition available
Open AccessReview New Gold Nanostructures for Sensor Applications: A Review
Materials 2014, 7(7), 5169-5201; doi:10.3390/ma7075169
Received: 20 May 2014 / Revised: 23 June 2014 / Accepted: 7 July 2014 / Published: 17 July 2014
Cited by 19 | PDF Full-text (1953 KB) | HTML Full-text | XML Full-text
Abstract
Gold based structures such as nanoparticles (NPs) and nanowires (NWs) have widely been used as building blocks for sensing devices in chemistry and biochemistry fields because of their unusual optical, electrical and mechanical properties. This article gives a detailed review of the new
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Gold based structures such as nanoparticles (NPs) and nanowires (NWs) have widely been used as building blocks for sensing devices in chemistry and biochemistry fields because of their unusual optical, electrical and mechanical properties. This article gives a detailed review of the new properties and fabrication methods for gold nanostructures, especially gold nanowires (GNWs), and recent developments for their use in optical and electrochemical sensing tools, such as surface enhanced Raman spectroscopy (SERS). Full article
(This article belongs to the Special Issue Advanced Nanomaterials for Biosensors)
Open AccessReview Nanostructural Engineering of Nanoporous Anodic Alumina for Biosensing Applications
Materials 2014, 7(7), 5225-5253; doi:10.3390/ma7075225
Received: 16 April 2014 / Revised: 1 July 2014 / Accepted: 10 July 2014 / Published: 18 July 2014
Cited by 9 | PDF Full-text (1973 KB) | HTML Full-text | XML Full-text
Abstract
Modifying the diameter of the pores in nanoporous anodic alumina opens new possibilities in the application of this material. In this work, we review the different nanoengineering methods by classifying them into two kinds: in situ and ex situ. Ex situ methods
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Modifying the diameter of the pores in nanoporous anodic alumina opens new possibilities in the application of this material. In this work, we review the different nanoengineering methods by classifying them into two kinds: in situ and ex situ. Ex situ methods imply the interruption of the anodization process and the addition of intermediate steps, while in situ methods aim at realizing the in-depth pore modulation by continuous changes in the anodization conditions. Ex situ methods permit a greater versatility in the pore geometry, while in situ methods are simpler and adequate for repeated cycles. As an example of ex situ methods, we analyze the effect of changing drastically one of the anodization parameters (anodization voltage, electrolyte composition or concentration). We also introduce in situ methods to obtain distributed Bragg reflectors or rugate filters in nanoporous anodic alumina with cyclic anodization voltage or current. This nanopore engineering permits us to propose new applications in the field of biosensing: using the unique reflectance or photoluminescence properties of the material to obtain photonic barcodes, applying a gold-coated double-layer nanoporous alumina to design a self-referencing protein sensor or giving a proof-of-concept of the refractive index sensing capabilities of nanoporous rugate filters. Full article
(This article belongs to the Special Issue Advanced Nanomaterials for Biosensors)
Open AccessReview Effect of Secondary Phase Precipitation on the Corrosion Behavior of Duplex Stainless Steels
Materials 2014, 7(7), 5268-5304; doi:10.3390/ma7075268
Received: 17 April 2014 / Revised: 2 July 2014 / Accepted: 11 July 2014 / Published: 22 July 2014
Cited by 10 | PDF Full-text (10333 KB) | HTML Full-text | XML Full-text
Abstract
Duplex stainless steels (DSSs) with austenitic and ferritic phases have been increasingly used for many industrial applications due to their good mechanical properties and corrosion resistance in acidic, caustic and marine environments. However, DSSs are susceptible to intergranular, pitting and stress corrosion in
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Duplex stainless steels (DSSs) with austenitic and ferritic phases have been increasingly used for many industrial applications due to their good mechanical properties and corrosion resistance in acidic, caustic and marine environments. However, DSSs are susceptible to intergranular, pitting and stress corrosion in corrosive environments due to the formation of secondary phases. Such phases are induced in DSSs during the fabrication, improper heat treatment, welding process and prolonged exposure to high temperatures during their service lives. These include the precipitation of sigma and chi phases at 700–900 °C and spinodal decomposition of ferritic grains into Cr-rich and Cr-poor phases at 350–550 °C, respectively. This article gives the state-of the-art review on the microstructural evolution of secondary phase formation and their effects on the corrosion behavior of DSSs. Full article
(This article belongs to the Special Issue Corrosion of Materials)
Open AccessReview Blends and Nanocomposite Biomaterials for Articular Cartilage Tissue Engineering
Materials 2014, 7(7), 5327-5355; doi:10.3390/ma7075327
Received: 4 April 2014 / Revised: 10 July 2014 / Accepted: 14 July 2014 / Published: 22 July 2014
Cited by 6 | PDF Full-text (1125 KB) | HTML Full-text | XML Full-text
Abstract
This review provides a comprehensive assessment on polymer blends and nanocomposite systems for articular cartilage tissue engineering applications. Classification of various types of blends including natural/natural, synthetic/synthetic systems, their combination and nanocomposite biomaterials are studied. Additionally, an inclusive study on their characteristics, cell
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This review provides a comprehensive assessment on polymer blends and nanocomposite systems for articular cartilage tissue engineering applications. Classification of various types of blends including natural/natural, synthetic/synthetic systems, their combination and nanocomposite biomaterials are studied. Additionally, an inclusive study on their characteristics, cell responses ability to mimic tissue and regenerate damaged articular cartilage with respect to have functionality and composition needed for native tissue, are also provided. Full article
(This article belongs to the Section Biomaterials)
Open AccessReview Nanomaterials-Based Sensing Strategies for Electrochemical Detection of MicroRNAs
Materials 2014, 7(7), 5366-5384; doi:10.3390/ma7075366
Received: 23 May 2014 / Revised: 10 June 2014 / Accepted: 14 July 2014 / Published: 23 July 2014
Cited by 10 | PDF Full-text (1613 KB) | HTML Full-text | XML Full-text
Abstract
MicroRNAs (miRNAs) play important functions in post-transcriptional regulation of gene expression. They have been regarded as reliable molecular biomarkers for many diseases including cancer. However, the content of miRNAs in cells can be low down to a few molecules per cell. Thus, highly
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MicroRNAs (miRNAs) play important functions in post-transcriptional regulation of gene expression. They have been regarded as reliable molecular biomarkers for many diseases including cancer. However, the content of miRNAs in cells can be low down to a few molecules per cell. Thus, highly sensitive analytical methods for miRNAs detection are desired. Recently, electrochemical biosensors have held great promise as devices suitable for point-of-care diagnostics and multiplexed platforms for fast, simple and low-cost nucleic acid analysis. Signal amplification by nanomaterials is one of the most popular strategies for developing ultrasensitive assay methods. This review surveys the latest achievements in the use of nanomaterials to detect miRNAs with a focus on electrochemical techniques. Full article
(This article belongs to the Special Issue Advanced Nanomaterials for Biosensors)
Open AccessReview Effects of Interfaces on the Structure and Novel Physical Properties in Epitaxial Multiferroic BiFeO3 Ultrathin Films
Materials 2014, 7(7), 5403-5426; doi:10.3390/ma7075403
Received: 29 April 2014 / Revised: 29 June 2014 / Accepted: 4 July 2014 / Published: 23 July 2014
PDF Full-text (1995 KB) | HTML Full-text | XML Full-text
Abstract
In functional oxide films, different electrical/mechanical boundaries near film surfaces induce rich phase diagrams and exotic phenomena. In this paper, we review some key points which underpin structure, phase transition and related properties in BiFeO3 ultrathin films. Compared with the bulk counterparts,
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In functional oxide films, different electrical/mechanical boundaries near film surfaces induce rich phase diagrams and exotic phenomena. In this paper, we review some key points which underpin structure, phase transition and related properties in BiFeO3 ultrathin films. Compared with the bulk counterparts, we survey the recent results of epitaxial BiFeO3 ultrathin films to illustrate how the atomic structure and phase are markedly influenced by the interface between the film and the substrate, and to emphasize the roles of misfit strain and depolarization field on determining the domain patterns, phase transformation and associated physical properties of BiFeO3 ultrathin films, such as polarization, piezoelectricity, and magnetism. One of the obvious consequences of the misfit strain on BiFeO3 ultrathin films is the emergence of a sequence of phase transition from tetragonal to mixed tetragonal & rhombohedral, the rhombohedral, mixed rhombohedral & orthorhombic, and finally orthorhombic phases. Other striking features of this system are the stable domain patterns and the crossover of 71° and 109° domains with different electrical boundary conditions on the film surface, which can be controlled and manipulated through the depolarization field. The external field-sensitive enhancements of properties for BiFeO3 ultrathin films, including the polarization, magnetism and morphotropic phase boundary-relevant piezoelectric response, offer us deeper insights into the investigations of the emergent properties and phenomena of epitaxial ultrathin films under various mechanical/electrical constraints. Finally, we briefly summarize the recent progress and list open questions for future study on BiFeO3 ultrathin films. Full article
(This article belongs to the Special Issue Ultra Thin Ferroic Materials)
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