Glass transition and molecular dynamics in poly(dimethylsiloxane)/silica nanocomposites

The molecular dynamics of a series of poly(dimethylsiloxane) networks filled with silica nanoparticles synthesized in situ was investigated using thermally stimulated depolarization currents, broadband dielectric relaxation spectroscopy and differential scanning calorimetry. The techniques used cover together a broad frequency range (10⁻³-10⁹ Hz), thus allowing to gain a more complete understanding of the effects of the nanoparticles on the chain dynamics. In addition to the α relaxation associated with the glass transition of the polymer matrix, we observe in dielectric measurements a slower α relaxation which is assigned to polymer chains close to the polymer/filler interface whose mobility is restricted due to interactions with the filler surface. The thickness of the interfacial layer is estimated to be about 2.1-2.4 nm. Differential scanning calorimetry shows a change in the shape of the glass transition step, as well as a decrease in both the degree of crystallinity and the crystallization rate by the addition of silica.     

Reinforcement of natural rubber: use of in situ generated silicas and nanofibres of sepiolite

Natural rubber composites containing silica particles generated in situ by the sol-gel process are investigated. The sol-gel processing is conducted before and after the cross-linking reaction. A good dispersion of the inorganic particles is obtained when the sol-gel reaction takes place after curing. In each case, the level of reinforcement is assessed from the mechanical and orientational behaviors. The reinforcement provided by in situ silica is compared with that obtained with anisotropic particles such as nanofibers of sepiolite.     

Reinforcement of natural rubber

In this article, we report on recent investigations on filled natural rubber. These investigations include a mechanical characterization as well as a molecular analysis based on measurements of chain orientation. It is demonstrated that at intermediate strains, the increase in the moduli can be explained by the inclusion of rigid particles in the soft matrix and from molecular interactions between the rubber and the filler. These interactions can be evaluated by equilibrium swelling and by orientational measurements. With regard to the unfilled formulation, carbon black– and silanized‐filled natural rubber exhibit increases in the cross‐linking density ascribed to filler‐polymer links, whereas a large decrease in the orientational level, evidenced by birefringence and by infrared dichroism, is observed when silica is added without any coupling agent. Finally, two specific effects—the Payne and Mullins effects, both related to energy dissipation phenomena—are discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2301–2316, 2002     

Effect of strain on the properties of a styrene–butadiene rubber filled with multiwall carbon nanotubes

Multiwall carbon nanotubes were dispersed in a styrene–butadiene copolymer. The effect of nanotube concentration on the tensile characteristics of the composites was examined. Electrical properties carried out under uniaxial extension show an increase in resistivity upon gradual stretching. A second stretch performed after total release of the stress was shown to lead to a flat response in resistivity. Atomic force microscopy was used to examine orientational effects and changes in filler structure occurring upon application of an uniaxial deformation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Evo-devo of Child Growth: The Role of Weaning in the Transition from Infancy to Childhood

Homo sapiens are unique in having a life history phase of childhood, which follows infancy, as defined by breastfeeding. This review uses evolutionary life history theory in understanding child growth in a broad evolutionary perspective, using the data and theory of evolutionary predictive adaptive growth-related strategies for transition from infancy to childhood. We have previously shown that a delayed infancy–childhood transition has a lifelong impact on stature. Feeding practices during infancy are fundamental elements of nutrition as they program for future growth and body composition. A relationship between the duration of breastfeeding and the nature of weaning has been suggested as a possible cause for later obesity and growth patterns. This review highlights the role that breast milk feeding and variations in the weaning age have on transition to childhood, growth, and body composition.     

Styrene–butadiene copolymers: mechanical,swelling and orientational properties

The results of equilibrium stress–strain and swelling experiments are reported for styrene–butadiene copolymers of varying crosslink density and varying butadiene microstructure. The orientation of polymer chains is investigated under uniaxial elongation by birefringence and infrared dichroism spectroscopies which probe orientation on a segmental scale. © 2000 Society of Chemical Industry     

扩展青霉侵染对苹果果实膜磷脂代谢的影响

目的:研究扩展青霉侵染对苹果果实膜透性及膜磷脂代谢的影响.方法:以'元帅'苹果为试材,测定扩展青霉损伤接种果实病健交界处组织的细胞膜透率、膜磷脂代谢关键酶活力以及相关底物和产物含量的变化.结果:扩展青霉侵染早期(2 d前)果实病斑直径无明显变化,侵染后期(2 d后)果实病斑直径和细胞膜透率明显增大.侵染期间,果实的磷脂...