Thin-layer template-free polycrystalline mordenite membranes on cylindrical mullite supports

Continuous nanoporous mordenite membranes were reproducibly fabricated on tubular microporous mullite supports. The ceramic supports were prepared during calcination of kaolin clay, followed by a leaching post-treatment. A template-free seeded hydrothermal synthesis in a brass autoclave was used to prepare the zeolite membranes. The membranes and the powder crystals collected from the bottom of the autoclave were characterized with XRD, SEM and EDAX. PV properties of the membranes were assessed using dehydration of different ethanol–water mixtures. XRD patterns showed that mordenite was the only zeolitic material present in the membrane. SEM examination of the membrane revealed that thickness of the mordenite crystals filling the voids as a dense thin-layer among the mullite support was 5–10 μm. The continuous top-layer of the membrane was formed by many large and oriented crystals. EDAX analysis showed a Si to Al ratio of 6 for the mordenite powder. The polycrystalline membranes were found to be selective for dehydration of different ethanol/water mixtures. It was concluded that selective adsorption of water on the zeolite pores, small intercrystalline defects and a pinhole-free structure of the membrane layer leaded to high water selectivity of the mordenite membranes studied.     

Stability of nanoparticles during semibatch emulsion polymerization of butyl methacrylate,in the presence of methacrylic acid via RSM

The size and stability of latex particles in the semibatch emulsion polymerization of butyl methacrylate (BMA), in the presence of 0–10% methacrylic acid (MAA), were investigated. Response surface methodology (RSM), as a design of experiment, was used to obtain a more systematic understanding of the role of emulsifier and MAA in the stability of the particles. The amount of coagulum can be greatly reduced by increasing the concentration of sodium lauryl sulfate (SLS) in the monomer emulsion feed (MEF) and initial reactor charge (IRC). On the other hand, increasing the concentration of SLS in the IRC can result in a decrease of the particles size. According to the experimental data, the yield of reaction can be improved with incorporation of MAA into the emulsion polymers. The size and morphology of particles were obtained by scanning electron microscopy (SEM). FTIR and titration were used to determine the percentage of MAA in the copolymer. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Barium carbonate nanostructures: Biosynthesis and their biomedical applications

In recent years, nanostructures and nanoarchitectures have attracted much attention in the development of biomedicine and nanomedicine. The plant-mediated synthesis of barium carbonate nanoparticles (BACN) has been performed using barium chloride and aqueous extract of natural sweetener (Stevia). In this study, the biosynthesis of BACN has been selected due to the useful medicinal potentials and suitable obtained biocompatibility of produced nanoparticles as well as its simplicity, lesser production steps, and cost-effectiveness. Barium carbonate nanostructures were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscope. The toxicity of BACN on U87 brain cancer cells was evaluated based on MTT assay. According to the results, the prepared nanostructures can be employed for biomedical applications, especially cancer therapy.     

Fabrication and electrical characterization of electrospun polyacrylonitrile‐derived carbon nanofibers

Carbon nanofibers were produced from a polyacrylonitrile/N,N‐dimethylformamide precursor solution by an electrospinning process and later pyrolysis at temperatures ranging from 500 to 1100°C in an N₂ atmosphere for about 1 h. The morphological structure of the nanofibers was studied with scanning electron microscopy. Scanning electron microscopy images of carbonized polyacrylonitrile nanofibers without a gold coating showed that the carbonized polyacrylonitrile nanofibers possessed electrical properties. The thermal behavior of the nanofibers was studied with thermogravimetric analysis. An indirect four‐point‐probe method was used for the measurement of the conductivity of nanofiber mats. The conductivity increased sharply with the pyrolysis temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Prediction of nanofiber diameter and optimization of electrospinning process via response surface methodology

Response surface methodology (RSM) was used to obtain a more systematic understanding of the electrospinning conditions of polyamide 6 solutions. This method was used to establish a quantitative basis for the relationships between the electrospinning parameters such as applied electric field, the polymer concentrations, the rate of injection and nozzle-collector distance with the diameter of the produced nanofibers, and to predict the optimum conditions for electrospinning to produce nanofibers with controlled size. A response function was empirically determined by central composite design (CCD) using fiber diameter as an observed response and the electrospinning parameters as variables. The relationship between the response and the variables is visualized by a response surface or contour plots. The study of the graphical representations of contour plots, prediction formulas and prediction profiler can predict the operating conditions necessary to generate nanofibers with the desired diameters.     

静电纺聚丙烯腈基碳纳米纤维的制备及电学表征

利用聚丙烯腈(PAN)及三甲基甲酰胺(DMF)制备静电纺纺丝液:纺制出的纤雏在N2保护下,于500～1500°C范围内进行高温分解,持续约1h后便得到碳纳米纤维.利用SEM分析了纤维的形态结构,未经喷金的碳化PAN纳米纤维的SEM照片表明制备的碳纤维具有导电性能.利用热重分析法(TGA)分析了纤维的热性能.利用间接的四探针方法测量了纳米纤维毡的导电性能,发现导电性会随着高温分解温度的增加而急剧增加.     

Encapsulation of magnetic nanoparticles with polystyrene via emulsifier-free miniemulsion polymerization

Magnetite nanoparticles (Fe₃O₄), with an average size of about 10 nm, were encapsulated with polystyrene using a new method based on emulsifier-free miniemulsion polymerization in the presence of 2, 2′ azobis (2-amidinopropane) dihydrochloride (V-50) as a cationic ionizable water-soluble initiator and hexadecane as a hydrophobe. Transmission electron microscopy (TEM) proved the presence of magnetite in polymer particles which appeared to be monodisperse in size, approximately 100-300 nm in diameter, through TEM and scanning electron microscopy (SEM). Thermogravimetric analysis (TGA) measurement was used to determine the percentage of magnetite in the products. The results of emulsifier-free miniemulsion polymerization were compared with those of conventional emulsifier-free emulsion polymerization using (V-50) as the initiator in both cases.     

Output‐capacitorless segmented low‐dropout voltage regulator with controlled pass transistors

This article presents a low quiescent current output‐capacitorless quasi‐digital complementary metal‐oxide‐semiconductor (CMOS) low‐dropout (LDO) voltage regulator with controlled pass transistors according to load demands. The pass transistor of the LDO is segmented into two smaller sizes based on a proposed segmentation criterion, which considers the maximum output voltage transient variations due to the load transient to different load current steps to find the suitable current boundary for segmentation. This criterion shows that low load conditions will cause more output variations and settling time if the pass transistor is used in its maximum size. Furthermore, this situation is the worst case for stability requirements of the LDO. Therefore, using one smaller transistor for low load currents and another one larger for higher currents, a proper trade‐off between output variations, complexity, and power dissipation is achieved. The proposed LDO regulator has been designed and post‐simulated in HSPICE in a 0.18 µm CMOS process to supply a stable load current between 0 and 100 mA with a 40 pF on‐chip output capacitor, while consuming 4.8 μA quiescent current. The dropout voltage of the LDO is set to 200 mV for 1.8 V input voltage. The results reveal an improvement of approximately 53% and 25% on the output voltage variations and settling time, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

Retracted: Fast and efficient electrospinning of chitosan‐Poly(ethylene oxide) nanofibers as potential wound dressing agents for tissue engineering

The following article from the Journal of Applied Polymer Science, “Fast and Efficient Electrospinning of Chitosan‐Poly(ethylene oxide) Nanofibers as Potential Wound Dressing Agents for Tissue Engineering” by Minoo Sadri, Ali Maleki, Farima Agend, and Hassan Hosseini, published online on 28 July 2011 in Wiley Online Library ( http://onlinelibrary.wiley.com/doi/10.1002/app.34520/full ), has been retracted by agreement between the journal's Editor in Chief, Stefano Tonzani, and the publisher, Wiley Periodicals, Inc. The retraction has been agreed due to significant overlap with respect to another article, “Electrospun Chitosan‐Based Nanofibers and Their Cellular Compatibility,” by Narayan Bhattarai, Dennis Edmondson, Omid Veiseh, Frederick A. Matsen, and Miqin Zhang, published online on 5 May 2005 in Biomaterials ( 2005 , 26, 6176).