Effects of weak shear on hyperswollen lyotropic smectic liquid crystals

We have developed a Zimm-type viscometer specially designed for the simultaneous measurements of the structure factor and the viscosity of hyperswollen lyotropic liquid crystals under a very weak shear. We have investigated the shear effects on the layer undulation fluctuation in the lamellar structure and the transition from the anisotropic lamellar to the isotropic sponge phase. We have found a significant difference in the rheological properties between the lamellar and the sponge phase: The former exhibits non-Newtonian flow behavior, while the latter exhibits Newtonian behavior.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

PVDF热致相分离法成膜体系铸膜液流变性能研究

利用流变仪对聚偏氟乙烯(PVDF)/己内酰胺(CPL)热致相分离法(TIPS)成膜体系铸膜液的流变性能进行研究.考察了剪切频率、温度、PVDF质量分数对PVDF/CPL铸膜液体系的黏度、非牛顿性指数、黏流活化能、溶液黏弹性的影响,利用TIPS法制备PVDF膜,进一步探讨了铸膜液体系的流变性能对刮膜速率、制膜温度等成膜条件的指导作用.实验结果表明:PVDF/CPL铸膜液体系为非牛顿性流体,随着PVDF质量分数的升高,PVDF/CPL铸膜液体系的黏度增加,非牛顿性指数增加,黏流活化能升高,对应膜的结构越致密,水通量降低,截留率升高,膜的拉伸强度增强.PVDF质量分数低的铸膜液体系,制膜时对温度的灵敏度低,刮膜速率对膜的制备影响大,制膜过程需要对刮膜速率精确地控制;PVDF质量分数高的铸膜液体系,对温度的灵敏度高,可以在较宽的刮膜速度范围下制膜.     

Stability of He II phase separation - investigations with the active phase separator

External influences or internal disturbances may result in phase separation instabilities which could lead to operational failure of He II space cooling systems. Possible instabilities are defined and, using the active phase separator, suitable measures for prevention and control are discussed. Experimental results with a superleak arranged in parallel to the active phase separator indicate an additional possibility for adaptation of the latter to specific demands.     

混合稀释剂对热致相分离法制备等规聚丙烯微孔膜的影响

以邻苯二甲酸二丁酯(DBP)和大豆油混合物为稀释剂,利用热致相分离(ThermallyInduced Phase Separation,TIPS)法制备了等规聚丙烯(iPP)微孔膜.结果表明,稀释剂体系中DBP和大豆油的质量比对浊点温度影响较大,而对结晶温度影响较小;随着稀释剂体系中DBP含量的增加,在固定聚合物浓度及相同的冷却条件下,多孔膜由空间网状结构逐渐转变为腔胞状结构,表面孔径也有明显的增大趋势;稀释剂的加入降低了iPP球晶的生长速率,其组成对iPP球晶生长速率也有一定影响.     

On the effective viscosity of suspensions

This work discusses the classical problem of effective viscosity of a Newtonian fluid with rigid spherical particles. It argues that the simple non-interaction approximation when formulated correctly yields an effective viscosity ratio for the suspension in the form μ/μ₀ = (1 − 2.5?)⁻¹ that remains accurate at much higher volume fractions of particles ? than the usual first-order approximation μ/μ₀ = 1 + 2.5?.     

热致相分离法制备聚偏氟乙烯微孔膜的研究

热致相分离法是一种制备聚合物微孔材料的有效方法.介绍了聚合物初始浓度、稀释剂、降温速率、成核剂、萃取剂等因素对热致相分离法制备聚偏氟乙烯(PVDF)微孔材料的影响,并对热致相分离法制备聚偏氟乙烯(PVDF)微孔膜的最新研究进展进行了介绍.     

Multiple shear step approach to determine the rotational viscosity of asphalt emulsions and its correlation with water content of original and diluted emulsions

Viscosity determination of thixotropic emulsions with good repeatability has always been a major challenge. Currently, Saybolt Furol viscometer (SFV) is used to determine the viscosity of the emulsion, but the main drawback of the SFV is that it cannot simulate the behaviour of emulsion under different shear rate. Rotational viscometer (RV) can measure viscosity at different shear rates. Due to the thixotropic behaviour of the emulsions, getting repeatable results by following the hot binder specification is a problematic task. In this study, a new multiple shear step approach is used to determine the viscosity of the emulsified asphalt using RV. Three low viscous (SS-1, SS-1H and SS-1L) and two high viscous (CRS-2 and CRS-2P) emulsions were used in this study. Shear stress is gradually stepped up to different levels after certain time interval to determine the viscosity. In this manner, emulsion undergoes a known shear state and each reading is preceded by a certain repeatable shear history. It was observed that with the progression of time and simultaneous increase in shear rate, the viscosity results are much more stable and repeatable with less than 5% coefficient of variance. The final specifications proposed are 220–730 and 5–90 cP at 50 rpm and 30 °C for high and low viscous emulsions, respectively, which are based on 98% probability. Viscosity measured by this approach also showed strong correlation with water content (R² > 0.94). The correlation between viscosity and water content is even stronger after dilution. With different dilution water content, viscosity of CRS-2 and CRS-2P exhibited R² values of 0.97 and 0.98, respectively.     

Apparatus for Neutron Scattering Measurements on Sheared Fluids

We report on the construction of an apparatus to allow neutron scattering measurements on fluids undergoing shear. The apparatus has been used with the cold neutron small-angle-neutron-scattering (SANS) spectrometer at the NIST research reactor and will be made available to users as a permanent part of the NIST facility.     

Microstructures and liquid phase separation in multicomponent CoCrCuFeNi high entropy alloys

The microstructures of high entropy alloys of the system CoCrCuFe_xNi and CoCrCuFeNi_x (where x indicates the molar ratio, which, where not specified, is 1) have been investigated. Many Cu rich spheres were evident in the microstructure of CoCrCuFe_0.5Ni and CoCrCuFeNi_0.5 alloys, which indicates that liquid phase separation had occurred before solidification. During liquid phase separation, the original liquids separated into two liquids: Cu rich and Cu depleted. In contrast, in other alloys (x?=?1.0, 1.5 and 2.0), typical dendritic and interdendritic structures are obtained. Cu and/or Cr rich precipitates, with various morphologies, can be seen in the interdendritic region. Additionally, Cu rich nanoparticles and Cr rich bird shaped structures can be observed in the Cu rich spheres. Sluggish cooperative diffusion causes the element segregation and formation of nanoprecipitates in the microstructures. The calculated positive mixing enthalpies of CoCrCuFe_0.5Ni and CoCrCuFeNi_0.5 alloys are likely reasons for their liquid phase separation.     

Experimental investigation on storage stability and phase separation behaviour of polymer-modified bitumen

Storage stability and phase separation behaviour of four styrene-butadiene-styrene (SBS) polymer-modified bitumen (PMB) binders are investigated by conventional binder tests and fluorescence microscopy in this paper. Since no separation happened in the stable PMBs, research focus was placed on capturing and analysing the phase separation process in the unstable PMBs. A phase inversion phenomenon was observed in one unstable PMB during the phase separation, showing the possible viscoelastic effects. Furthermore, it is indicated that criteria only based on compositional parameters can give misleading predictions of PMB storage stability. New criteria still need to be defined. The potential approaches to PMB phase behaviour prediction are reviewed and exploratively discussed in the context of the four investigated PMBs. This leads to a further discussion on the possibility of having a thermodynamic approach to PMB phase behaviour prediction by looking into the free energy of PMB. The Flory–Huggins theory provides a way to do this, upon the consideration of PMB as a pseudo-binary blend and some made assumptions. Free energy curves have the strength of giving more information like the equilibrium phase composition. In addition, some more aspects should be also considered for PMB phase behaviour prediction towards an applicable criterion.     

热致相分离法制备聚偏氟乙烯膜的研究

基于热致相分离基本原理,通过熔融共混聚偏氟乙烯/CaCO3/邻苯二甲酸二丁酯三元体系,制备了聚偏氟乙烯膜.考察了稀释剂和CaCO3含量对膜微观结构及拉伸强度的影响,以及CaCO3含量对聚偏氟乙烯结晶温度、结晶度的影响.结果显示,稀释剂和CaCO3含量对膜微观结构和拉伸强度影响显著;而CaCO3含量虽然对共混体系结晶度影响不太明显,但是对其结晶温度有较为显著的影响.     

热致相分离法制备聚合物微孔膜的研究进展

热致相分离（TIPS）是制备聚合物微孔膜的重要方法,自发明以来一直是膜技术研究领域的热点。近年来,随着人们对其研究的深入,针对其原有的缺点进行了改进。主要体现在：（1）将TIPS与其它制膜方法（例如非溶剂致相分离法、拉伸法、超临界二氧化碳法）相结合,进行制备方法的改进;（2）通过使用亲水本体材料或添加两亲共聚物,在制膜同时实现膜的亲水改性;（3）材料由结晶聚合物拓展到无定型聚合物,扩大了TIPS制膜的选材范围。就以上方面,综述了当前TIPS制备聚合物微孔膜研究领域的新进展。     

The study of anisotropically shaped micelles subjected to shear flow by small-angle neutron scattering

The development of Couette shear-flow cells for use with small-angle neutron scattering (SANS) has provided the opportunity for the morphology of solutions of anisotropically shaped surfactant micelles to be probed in more detail and for the effects of shear on such structures to be explored. The effects of finite concentration (hindered rotation and interactions), flexibility, and shear-induced changes/structures are described for elongated micelles in their dilute phase (for a range of ionic, nonionic, and mixed ionic-nonionic micelles). Some recent measurements on nonionic and mixed ionic-nonionic micelles demonstrate that SANS can provide a vital insight into the rheological properties and morphology of micellar solutions over a wider region of their complex phase diagrams.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, USA.     

密差分相式液膜法提取L-苯丙氨酸

采用密差分相液膜分离技术，以P204为载体，H2SO4为反萃剂，以初始浓度15．28g/L的L－苯丙氨酸水溶液提取5次后，浓度降至1．92g/L，反萃相中L－苯丙氨酸浓度达54．35g/L，膜溶胀和破裂均较小，过程不需要制乳和破乳；对反萃剂也进行了后处理。     

Parallel bulk-heterojunction solar cell by electrostatically driven phase separation

Thermal co-evaporation of C(60) fullerene and two merocyanine dyes affords bulk heterojunction solar cells with improved short-circuit currents and power conversion efficiencies in comparison with the respective single donor cells. These results are rationalized by the formation of three distinct subphases driven by differences in molecular shape and electrostatic interactions.     

热致相分离法制备聚合物微孔膜的研究进展

分别从S-L相分离和L-L相分离两方面简述了热致相分离法制备聚合物微孔膜的成膜过程.从聚合物分子量、聚合物浓度、稀释剂与聚合物的相互作用、稀释剂的流动性及结晶、冷却速度及冷却方式、萃取剂的种类及萃取剂的抽提方式、成核剂几方面总结TIPS法制膜的研究进展,并从膜材料、膜结构以及制膜方法三方面阐述热致相分离法制膜的发展趋势.     

Nonequilibrium molecular dynamics calculation of the shear viscosity of carbon dioxide

Nonequilibrium molecular dynamics calculations of the shear viscosity of supercritical carbon dioxide along the 313 K isotherm are reported. Three different intermolecular potential models of increasing complexity are considered: a spherically symmetric Lennard-Jones potential, a two-site Lennard-Jones potential, and a three-site potential which includes a quadrupole-quadrupole moment. Results for the three potentials are compared with experimental data.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

热致相分离法聚偏氟乙烯膜的制备及应用

以课题组通过热致相分离法(TIPS)制备聚偏氟乙烯(PVDF)微孔膜及其产业化的相关工作为基础,从PVDF材料性能及其超微滤膜制备方法出发,全面回顾了课题组在TIPS法PVDF膜制备方面的研究历程,包括稀释剂和非溶剂的探索,纳米粒子、共聚物、两性离子等对PVDF膜的改性研究以及PVDF中空纤维膜组件的研制和规模化生产等等,最后还简要介绍了膜组件在不同工业领域的应用情况.     

两步法制备醋酸纤维素微滤膜的研究

以二醋酸纤维素酯为制膜材料，以DMF／丙酮为混合溶剂体系，采用两步法制备微滤膜，第一步在水蒸气气氛中吸湿并挥发溶剂而分相凝胶，第二步浸入水中固化制膜．研究了聚合物浓度、溶剂比例、添加剂含量、吸湿时间等因素对膜性能的影响，制备了孔径约0．5μm的微孔滤膜，其性能指标可基本达到商业膜的标准．