Silver/polystyrene nanocomposites: Optical and thermal properties

Nanocomposites consisted of different quantities of silver (Ag) nanoparticles incorporated in a polystyrene (PS) matrix have been prepared by solution mixing method. Transmission electron microscopy was applied to determine the size distribution of the Ag nanoparticles, while the morphology of fractured surfaces of pure PS and Ag/PS nanocomposites was examined by scanning electron microscopy. Absorption spectra of nanocomposites were compared with theoretically calculated spectra based on the Maxwell‐Garnett effective medium theory. The influence of Ag content on thermal properties of Ag/PS nanocomposites was investigated by thermogravimetric analysis and differential scanning calorimetry. Thermal and thermo‐oxidative stability of the host polymer were improved by introduction of silver nanoparticles. The glass transition temperature of the prepared Ag/PS nanocomposites was lower in comparison with the neat PS and decreased with the increase of the Ag content due to the very weak interfacial interaction between Ag nanoparticles and polymer matrix. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Influence of the chemical structure of poly(urea-urethane-siloxane)s on their morphological, surface and thermal properties

Segmented poly(urethane-urea-siloxane)s (PUUS) were synthesized using 4,4′-methylenediphenyl diisocyanate (MDI) and ethylene diamine (ED) as the hard segment components and hydroxypropyl-terminated poly(dimethylsiloxane) (PDMS) as the soft segment component, where the hard segment content ranged from 38 to 65 wt%. Segmented PUUSs were prepared by a two-step polymerization procedure in tetrahydrofuran/N-methylpyrrolidone (THF/NMP) mixture with a large proportion of polar solvent. The structure, composition and hard segment length were determined by ¹³C NMR and two-dimensional correlation spectroscopy. Thermal, mechanical, small-angle X-ray scattering and hydrogen bonding analyses indicated the formation of the microphase-separated copolymers with high tensile strength. Globular superstructures observed in the copolymer films by scanning electron microscopy (SEM) and atomic force microscopy (AFM) were probably arisen from the microstructural organization of the MDI-ED segments, depending on their content and length. The PUUS copolymers showed high water resistance and became more hydrophobic with increasing weight fraction of PDMS.     

Investigation of P-odd correlations in the capture of thermal polarized neutrons involving emission of secondary charged particles (technical issues)

An installation for measuring parity violation in reactions with polarized neutrons involving the emission of secondary charged particles is described. The main part of the experimental setup is a multisection proportional chamber operated in the current mode. The ⁶Li(n,)³H and ¹⁰B(n,)⁷Li reactions are studied. The P-odd asymmetry was measured with an accuracy of δ 5 × 10⁻⁸.     

The role of social support networks in proxy Internet use from the intergenerational solidarity perspective

Digital inequalities research has documented a set of practices related to people’s Internet use that questions the binary division between Internet users and non-users. In particular, among older adults, a considerably large group of individuals has been identified as not using the Internet by themselves; rather, they ask members of their personal networks to do things online for them—they “use” the Internet by proxy. Since previous research shows that children and grandchildren are important sources of help when it comes to Internet use, the current paper indicates that the notion of intergenerational solidarity is a sound conceptual basis for understanding the relationship between social support networks and proxy Internet use among Internet non-users. Notably, the concept of functional solidarity as a dimension of intergenerational solidarity is advanced, as this relates to the frequency of the intergenerational exchange of resources and services encompassing various types of assistance and support offered between two generations. Empirically, this paper investigates how the two types of social support networks and their characteristics are associated with proxy Internet use. The results from multivariate analyses of survey data from a nation-wide representative sample show that when comparing emotional support and socializing networks, only the latter is associated with proxy Internet use: Internet non-users who have (grand-)children in their socializing support network are more likely to engage in proxy Internet use. The results also indicate that non-users who are younger, more educated, have children, and live in urban areas are more inclined to engage in proxy Internet use, regardless of the type of social support. The findings indicate the importance of empirical investigation related to different aspects of functional solidarity, as the effects on proxy Internet use depend on the type of social support.     

Micro- and nanostructures of iridescent wing scales in purple emperor butterflies (Lepidoptera: Apatura ilia and A. iris)

Apatura ilia (Denis and Schiffermüller, 1775) and A. iris (Linnaeus, 1758) are fascinating butterflies found in the Palaearctic ecozone (excepting the north of Africa). The wings of these insects are covered with a great number of two types of scales positioned like roof tiles. Type I scales are on the surface, while type II scales are situated below them. The structural color of the type I scales is recognized only on the dorsal side of both the fore and hind wings of the males of the aforementioned species. Both types of scales are responsible for pigment color of the wings, but iridescence is observed only in the type I scales. The brilliant structural color is due to a multilayer structure. The features of the scales, their dimensions and fine structure were obtained using scanning electron microscopy. Cross sections of the scales were then analyzed by transmission electron microscopy. The scales of the "normal" and clytie forms of A. ilia have a different nanostructure, but are of the same type. A similar type of structure, but with a different morphology, was also noticed in A. iris. The scales of the analyzed species resemble the scales of tropical Morpho butterflies.     

Experimental and theoretical insight into the electronic properties of 4-aryl-5-arylazo-3-cyano-6-hydroxy-2-pyridone dyes

In this paper, spectroscopic and quantum mechanical investigation of nine 4-aryl-5-arylazo-3-cyano-6-hydroxy-2-pyridone dyes was performed, and obtained density functional theory (DFT) results were compared with experimental data. The structural and spectroscopic properties of azo-2-pyridone dyes were studied by DFT using B3LYP, CAM-B3LYP, and M06-2X methods with a 6-311++G(d,p) basis set. Comparison of results reveals that the scaled theoretical vibrational frequencies of azo dyes are in good agreement with experimental data. The time-dependent DFT calculated and experimental ultraviolet-visible (UV-vis) absorption spectra are also in good agreement. The effect of electron-donating –OCH₃ and electron-withdrawing –NO₂ groups on the structural parameters, vibrational frequencies, UV-vis absorption, and natural bond orbital (NBO) atomic charges were thoroughly analysed. Vibrational, UV-vis, and NBO analyses confirm that investigated dyes exist in the hydrazo tautomeric form in the solid state and ethanol solution. These analyses signify the occurrence of intramolecular charge transfer in these azo-pyridone dyes.     

Gangliosides in membranes fromTorpedo electric organ

The electric organ membrane has been the subject of many studies, due principally to its rich content of nicotinic acetylcholine receptor (AChR). Knowing its lipid composition is clearly important. Although its major membrane lipids have been characterized, its ganglioside composition has not been as well-described. In this study, gangliosides were characterized in membranes prepared from two species of electric organ,Torpedo californica andT. nobiliana. The ganglioside content of total electric organ membranes and AChR-enriched membranes was similar in both species, accounting for from 0.9 to 1.5% of membrane lipid by weight. However, the AChR-enriched membranes contained significantly less ganglioside relative to AChR than did the total membrane preparations. Five major gangliosides were purified fromT. californica and identified as II³NeuNAc-GgOse₃ (GM2); II³(NeuNAc)₂-GgOse₃ (GD2), IV³NeuNAc, II³NeuNAc-GgOse₄ (GD1a), IV³NeuNAc, II³(NeuNAc)₂−GgOse₅ (GT1b), and IV³(NeuNAc)₂, II³(NeuNAc)₂−GgOse₄ (GQ1b). Together these five gangliosides accounted for over 90% of the total ganglioside present in the two membrane preparations from both species. The most abundant ganglioside by far was GM2, which accounted for about one-half of the ganglioside content, followed by GD2. Determination of the N-fatty acid composition was performed on gangliosides purified fromT. nobiliana. The lower-order gangliosides, GM2, GD2, and GD1a, contained substantial amounts of very long chain fatty acids (>20 carbons), including α-hydroxynervonic acid (15–21% of total). In contrast, unsubstituted, 14–18 carbon chains accounted for about 90% of the fatty acids on the two higher-order gangliosides, GT1b and GQ1b.     

Application of the monoliths in DeNOx catalysis

Air pollution abatement catalysis refers to catalytic technologies and processes for reducing emissions of environmentally unacceptable compounds. Major problems related to these catalytic clean-up technologies are mobile emission control, removal of nitrogen oxides (NO_x), sulphur compounds, volatile organic compounds (VOCs) and other pollutants generated by industry or by other stationary sources. Application of the monolith catalysts and/or reactors is a key solution to these problems. This overview describes basic features of the monolithic structures and discusses their development and application prospects focusing on DeNO_x catalysis. The status and ongoing modeling of the monolithic reactors are outlined. Particular emphasis is put on experimental validation and practical applications of the mathematical models of a monolithic reactor.     

Influence of Dopants on Nucleation and Growth of High-Quartz Solid Solution in Lithium Aluminosilicate Glass

The kinetic parameters of nucleation and crystal growth of high-quartz solid solution in multicomponent lithium aluminosilicate glasses doped with various transition-metalions were studied by nonisothermal DTA. The crystallization of glasses nucleated at different temperatures was carried out, and plots of the DTA peak versus the nucleation temperatures were used to determine the maximum nucleation rate temperature. Peak temperature data of nucleated samples at varying heating rates (5–20 K/min) were used to determine the activation energy for crystallization via the JMA equation. The temperature of maximum nucleation rate depends greatly on the doped transition- metal ions present. The activation energy for crystallization obtained for undoped glass or glasses doped with Fe₂O₃ is of the same order as that already published, and the Avrami exponent is consistent with predominantly three-dimensional crystal growth. The much higher activation energy values for glasses doped with CoO could be a consequence of two crystallization processes proceeding simultaneously.