Thickening process of polyethylene single crystals at an early stage of annealing

The thickening process of polyethylene single crystals was simulated with computer by the Monte Carlo method. According to the experimental results in the previous report, the time dependence of the long period changed greatly with annealing temperature; at lower temperatures the long period increased gradually, while at high temperatures the long period rapidly increased at a very early stage of annealing and then increased gradually after passing through a plateau. Through computer simulation, it was shown that such a great change in the time dependence of the long period with annealing temperature can be explained by combining two mechanisms: (A) sliding diffusion of molecular segments along the chain axis and (B) local melt-recrystallization (namely, local melting followed by recystallization).     

SELF-ASSEMBLING AMPHIPHILIC POLYELECTROLYTES AND THEIR NANOSTRUCTURES

The self-assembling behavior of random copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS)and hydrophobic comonomers possessing dodecyl groups linked by various spacer bonds was discussed with a focus on theeffect of the spacer. The characterization of association behavior of such polymers in water using quasielastic light scattering,capillary electrophoresis, NMR relaxation, various fluorescence, and viscoelastic methods was described. These copolymersform a variety of self-assembled nanostructures depending on the type of the spacer. Random copolymers of AMPS and N-dodecylmethacrylamide show a strong preference for intrapolymer self-association even in concentrated aqueous solutionsforming single-macromolecular self-assemblies (unimolecular micelles). In contrast, random copolymers of AMPS anddodecyl methacrylate are prone to undergo interpolymer associations yielding multipolymer micelles. In random copolymersof AMPS and a methacrylate substituted a nonionic surfactant (HO(CH_2CH_2O)_(25)C_(12)H_(25)) (C_(12)E_(25)), dodecyl groups are muchless restricted by the polymer backbone because they are linked via a long, flexible hydrophilic spacer. Thus, the polymer-bound C_(12)E_(25) surfactant moieties form micelles similar to those formed by discrete surfactants, but they are bridged bypolymer chains forming a network structure.     

The numerical simulation of the mechanical failure behavior of shear thickening fluid/fiber composites: A review

This study reveals the finite element modeling of mechanical failure behavior of shear thickening fluid (STF)/fiber composites under impact. Numerical analysis and finite element modeling of the rheological properties of non-Newtonian fluid, STF are introduced. This review summarizes the model coupling methods in finite element modeling and the mechanical failure behavior prediction models of STF/fiber composites under impact. Further, the influencing factors on the accuracy of mechanical failure simulation models are analyzed. Factors such as the friction between fibers, shear rate, filler particles in the fibers, hysteresis effect and the boundary conditions should be considered in simulating the shear thickening effect of the composites.     

基于棒状介孔SiO_2剪切增稠流体的流变行为

以三嵌段共聚物聚氧乙烯-聚氧丙烯-聚氧乙烯(PEO-PPO-PEO,P123)为模板剂,采用溶胶-凝胶法合成了介孔SiO_2-P123复合物,经煅烧除去P123得到不同长径比的棒状介孔SiO_2粒子,将其分散于聚乙二醇(PEG)中制成剪切增稠流体(STF),利用旋转流变仪对STF的流变性能进行了表征。结果表明:在稳态条件下,STF的剪切增稠效应随介孔SiO_2质量分数的增加而增强,随介孔SiO_2粒子长径比的增加而减弱;在动态条件下,STF的剪切增稠效应随介孔SiO_2质量分数的增加而减弱,随介孔SiO_2粒子长径比的增加而增强。     

气相白炭黑/低分子量聚乙二醇悬浮体系的分子弛豫与流变行为

采用亲水气相二氧化硅(FS)、非缠结聚乙二醇(PEG,重均分子量400)制备悬浮体系,考察FS体积分数(φ)对PEG本体相α-松弛、结晶行为及悬浮体系流变行为的影响.结果表明,FS可延缓PEG本体相α-松弛,提高玻璃化转变温度,并显著增加浮体系黏度,降低本体PEG相结晶与熔融焓.低填充时,FS起成核作用;高填充时,FS延迟PEG分子扩散,并降低结晶温度.FS对PEG结晶的不同作用发生在悬浮体系溶胶-凝胶转变附近,此时悬浮液非线性动态流变行为呈现显著的硬化软化特性,线性动态流变行为呈现最为显著的频率依赖性.通过建立线性动态流变行为叠加曲线,揭示了FS对PEG分子链扩散行为的显著推迟作用.     

Viscoelastic behaviour of butyl acrylate/styrene/2-hydroxyethyl methacrylate/acrylic acid latices thickened with associative thickeners

The rheological behaviour of butyl acrylate/styrene/acrylic acid latices thickened with a hydrophobically modified ethoxylated polyurethane (HEUR) or hydrophobically modified alkali-soluble polyacrylate emulsion (HASE) was investigated. While the pseudoplastic character of frequency dependence of complex viscosity was similar for both thickeners, viscoelastic behaviour, expressed as the ratio of loss and storage moduli, significantly differed, indicating that the HEUR molecules, unlike swollen HASE particles, create a viscoelastic space structure. The increase in hydrophilicity of the particle surface, achieved by incorporation of 2-hydroxyethyl methacrylate (HEMA) monomer into the latex copolymer reduced the viscoelasticity of latices thickened with HEUR, but not of those thickened with HASE. This confirms that adsorption of hydrophobic end-groups on particle surface is important for thickening of latices with HEUR and that a physical network of latex particles interconnected by the thickener macromolecules is formed. To cite this article: O. Quadrat et al., C. R. Chimie 6 (2003).     

Thickening effect of dispersions of ethyl acrylate-methacrylic acid copolymer prepared by different polymerization routes

Thickening of latices (particle diameters 105, 157 and 221 nm) by model dispersions of ethyl acrylate-methacrylic acid copolymer (15 wt.% of the acid) prepared by both non-seeded and seeded semicontinuous emulsion copolymerizations was investigated. Using viscometry and dynamic and steady shear measurements, we found that the thickening effect of the dispersions strongly depends on their particle structure and the intensity of interactions between the components in the system. In weakly interacting systems (lower latex concentrations, large latex particles) the thickening effect of the dispersions is controlled by effective volume fraction of swollen particles. This leads to a higher viscosity of systems thickened by more swollen (less crosslinked) particles obtained by the non-seeded process. On the other hand, in strongly interacting systems (high latex concentrations, small latex particles) lower deformability of more crosslinked particles prepared by the seeded process causes a higher flow resistance of the systems thickened by this dispersion.     

On Free Boundary Problem for the Non-Newtonian Shear Thickening Fluids

The aim of this paper is to explore the free boundary problem for the NonNewtonian shear thickening fluids. These fluids not only have vacuum, but also have strong nonlinear properties. In this paper, a class of approximate solutions is first constructed, and some uniform estimates are obtained for these approximate solutions. Finally, the existence of free boundary problem solutions is proved by these uniform estimates.     

氧化石墨烯对聚乙烯醇/硼酸水凝胶流变性能的影响

研究了氧化石墨烯(GO)对聚乙烯醇(PVA)/硼酸(borate)水凝胶线性及非线性流变性能的影响。 通过扫描电子显微镜、硼谱核磁共振波谱以及流变研究了水凝胶的流变性能。 结果表明,GO质量浓度在稀溶液区时,GO片层与PVA链间通过硼酸根离子形成了具有弹性活性的缔合点,有效地提高了水凝胶的平台模量、松弛时间和零切粘度;当GO进一步增加到亚浓溶液区,部分的交联剂被GO的团聚体捕获并处于非弹性活性的缔合状态,处于有效缔合状态的交联剂变少,导致平台模量、松弛时间和零切粘度降低。 稳态剪切测试下,样品在剪切增稠区的粘度增加随着GO添加量的增加明显加强,这与剪切场下取向的氧化石墨烯片层参与网络结构的重排有关。     

Synthesis and characterization of cubic cobalt oxide nanocomposite fluids

Narrow size distribution cubic Co₃O₄ nanoparticles were synthesized and rheological properties of suspensions of the cubes in oligomeric polyethylene glycol (PEG) were explored over a range of particle volume fractions and rotational shear flow conditions. At low and high particle volume fractions, the relative viscosity of the suspensions is described by a Krieger–Dougherty formula with an intrinsic viscosity consistent with expectations for suspensions of ideal cuboids. At intermediate to high particle loadings, the suspensions manifest complex rheological behavior, including shear thinning and shear-thickening features. These observations are discussed in terms of the charge carried by the cubes and the shear rate/volume fraction dependency of the transition from shear thinning to shear thickening.