Synthesis and characterization of PS-clay nanocomposite by emulsion polymerization

Summary Polystyrene-Na⁺-montmorillonite(PS-Na⁺-MMT) nanocomposites are prepared by a simple emulsion polymerization. The X-ray diffraction(XRD) and infrared spectroscopy (IR) analysis confirm that polystyrene(PS) macromolecules can be inserted between lamella layers and whose layer separation is consequently higher than in the polymer-free clay. The enhanced thermal properties of composites are measured by differential scanning calorimetry(DSC) and thermogravimetric analysis(TGA) thermogram and indicate that the glass transition and the decomposition onset temperature of obtained nanocomposites are found to be moved to the higher temperature region. The increased Young's modulus of the obtained nanocomposites is ascribed to the intercalation of PS in clay galleries as well as the fine dispersion of clay particles into the polymer matrix. Received: 23 February 1999/Revised version: 26 March 1999/Accepted: 1 April 1999     

Iron Accumulation and Changes in Cellular Organelles in WDR45 Mutant Fibroblasts

Iron overload in the brain, defined as excess stores of iron, is known to be associated with neurological disorders. In neurodegeneration accompanied by brain iron accumulation, we reported a specific point mutation, c.974-1G>A in WD Repeat Domain 45 (WDR45), showing iron accumulation in the brain, and autophagy defects in the fibroblasts. In this study, we investigated whether fibroblasts with mutated WDR45 accumulated iron, and other effects on cellular organelles. We first identified the main location of iron accumulation in the mutant fibroblasts and then investigated the effects of this accumulation on cellular organelles, including lipid droplets, mitochondria and lysosomes. Ultrastructure analysis using transmission electron microscopy (TEM) and confocal microscopy showed structural changes in the organelles. Increased numbers of lipid droplets, fragmented mitochondria and increased numbers of lysosomal vesicles with functional disorder due to WDR45 deficiency were observed. Based on correlative light and electron microscopy (CLEM) findings, most of the iron accumulation was noted in the lysosomal vesicles. These changes were associated with defects in autophagy and defective protein and organelle turnover. Gene expression profiling analysis also showed remarkable changes in lipid metabolism, mitochondrial function, and autophagy-related genes. These data suggested that functional and structural changes resulted in impaired lipid metabolism, mitochondrial disorder, and unbalanced autophagy fluxes, caused by iron overload.     

Copolymerization of styrene and ethylene with mononuclear and dinuclear half-titanocenes

With mononuclear half-titanocenes such as CpTiCl₃, IndTiCl₃, and Me₅CpTiCl₃, as well as the constrained geometry catalyst (CGC) and a new dinuclear hexamethyltrisiloxanediylbis(cyclopentadienyltitanium trichloride) (TSDT), the copolymerization of styrene and ethylene was examined. The thermal properties and structure of copolymerization products were investigated with differential scanning calorimetry and ¹³C-nuclear magnetic resonance. In addition, the raw polymer was separated into homopolymer and copolymer with an extraction method and cross fractionation chromatography. With the above analysis, it was concluded that the raw polymer obtained with CpTiCl₃ and IndTiCl₃ was a mixture of syndiotactic polystyrene and polyethylene homopolymers with 10–30 wt % copolymer, whereas that produced by Me₅CpTiCl₃ and TSDT was a homopolymer mixture with a negligible amount of copolymer. Only CGC produced the copolymer of styrene and ethylene perfectly. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2187–2198, 1998     

Comparison of characteristics of SAN–MMT nanocomposites prepared by emulsion and solution polymerization

Nonextractable styrene–acrylonitrile copolymer–montmollironite (SAN–MMT) nanocomposites were prepared by two different intercalation process: (1) a usual one‐step emulsion copolymerization in the presence of the Na⁺–MMT; and (2) a solution copolymerization with MMT modified by dimethyl dihydrogenated tallow ammonium. For comparative purposes, the copolymerization conditions (such as comonomer feed ratio and the polymerization temperature and times) were set up to be the same. The X‐ray diffraction pattern demonstrated that the net increase of basal spacing of the purified emulsion products (0.76 nm) far exceeded that of composite (0.39 nm) prepared by solution method. The average molecular masses recovered from the composite extracts revealed M_w = 53 × 10⁴ for emulsion products, while the composite made by solution yielded M_w = 4.8 × 10⁴ g/mol. Likewise, the hybrid from the emulsion polymerization exhibited higher stress at maximum load over the solution products. The dispersibility of MMT particles in the polymer matrix was investigated by using optical microscopy (OM) and scanning electron microscopy (SEM) for those unextracted samples. It was found that almost complete hybrids were obtained when the styrene (ST)–acrylonitryl (AN) comonomer was emulsion polymerized in the presence of Na⁺–MMT, yielding both better miscibility and intercalation capability. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2811–2819, 1999     

A Multiscale-Porous Anion Exchange Membrane for Convenient and Scalable Electrokinetic Concentration of Cationic Species

A device able to electrokinetically concentrate cationic samples has many potential medical and industrial applications, but until now has remained undeveloped due to the lack of a commercial anion-permselective material leading to a prohibitively complex fabrication procedure. Herein, a novel multiscale-porous anion exchange membrane (MP-AEM) that enables the convenient and scalable electrokinetic concentration of cationic species is proposed. A mechanically enhanced multiscale-porous structure with a solid framework is realized by adopting polyester resin as an additive to overcome the intrinsic limitations of the AEM material. The scalable MP-AEM-embedded electrokinetic concentrator is devised based on the peculiar properties of the MP-AEM that for allow both ion and fluid transport. With the MP-AEM, the concentrator is fabricated in a highly streamlined manner consisting only of a simple insertion and assembly. The concentration performance of the MP-AEM-embedded electrokinetic concentrator is demonstrated with a positively charged fluorescent dye and a fluorescein-labeled protein, and the results show enrichment factors of 250 and 500, respectively. The MP-AEM makes cationic electrokinetic concentration more accessible and scalable, thereby enabling further progress in a wide range of fields.     

Highly Improved Sb2S3 Sensitized‐Inorganic–Organic Heterojunction Solar Cells and Quantification of Traps by Deep‐Level Transient Spectroscopy

The light‐harvesting Sb₂S₃ surface on mesoporous‐TiO₂ in inorganic–organic heterojunction solar cells is sulfurized with thioacetamide (TA). The photovoltaic performances are compared before and after TA treatment, and the state of the Sb₂S₃ is investigated by X‐ray diffraction, X‐ray photoelectron spectroscopy, and deep‐level transient spectroscopy (DLTS). Although there are no differences in crystallinity and composition, the TA‐treated solar cells exhibit significantly enhanced performance compared to pristine Sb₂S₃‐sensitized solar cells. From DLTS analysis, the performance enhancement is mainly attributed to the extinction of trap sites, which are present at a density of (2–5) × 10¹⁴ cm^?3 in Sb₂S₃, by TA treatment. Through such a simple treatment, the cell records an overall power conversion efficiency (PCE) of 7.5% through a metal mask under simulated illumination (AM 1.5G, 100 mW cm^–2) with a very high open circuit voltage of 711.0 mV. This PCE is, thus far, the highest reported for fully solid‐state chalcogenide‐sensitized solar cells.     

Channel Magnifying Limited Feedback Technique for FDD Massive MIMO Systems

A limited feedback system, so-called, channel magnifying (CM) is proposed for a downlink (DL) frequency-division duplex (FDD) massive multiple-input multiple-output (MIMO) system. Although massive MIMO system has received significant research interest as a key technology for beyond 4G wireless communications systems, it has a number of issues that needs to be technically addressed. Among such issues is the difficulty of acquiring channel state information at transmitter for an FDD massive MIMO system which cannot exploit channel reciprocity as in a time-division duplex system. The proposed CM technique makes it possible to support a few user equipments in DL FDD massive MIMO system by finding a balance between spatial resources and channel quantization error (CQE). By choosing a subchannel with low CQE, CM can secure multiplexing gain at high SNR based on a fixed size codebook. Two types of subchannel indicator alignment (SIA) schemes are introduced for efficient interference nulling for the proposed CM technique. Specifically, we discuss how to maximize the sumrate of CM through genie added SIA and minimum CQE based SIA. Simulation results show that the sum rate of the proposed CM has a higher multiplexing gain than that of random vector quantization, especially when the number of transmit antennas is sufficiently large.