极性分子型电流变液导电机理研究

极性分子型电流变液是一种新型的电流变材料.其介电颗粒上吸附极性分子,极性分子在颗粒间强局域电场作用下发生取向是产生巨电流变效应的关键.通过对Ca—Ti—O(CTO)体系极性分子型电流变液电流密度的测量发现,其导电行为遵从Poole-Frenkel效应的规律,这是极性分子型电流变液的重要特征之一.而500 ℃处理过的CTO粉体不含极性分子,所配制的电流变液无巨电流变效应,其电流密度随外电场强度近似地呈线性关系,显示出传统电流变液特性.     

纳米TiO2颗粒对电流变悬浮液中硅油的挥发增强效应

物理化学性能稳定的二甲基硅油常作为电流变液分散相, 当与纳米量级的介电颗粒混合组成电流变悬浮液时, 在非密闭环境下极易挥发, 时间足够长时, 可完全挥发. 本文通过实验研究了纳米二氧化钛颗粒对二氧化钛和硅油组成的悬浮液中硅油挥发增强现象, 分析表明, 纳米颗粒在电流变悬浮液的硅油气-液界面上形成纳米尺度的凸型曲面, 使液面上蒸气压大大提高, 导致挥发增强. 本文还对颗粒浓度, 环境温度和硅油黏度等对硅油挥发增强效应的影响进行了系统的研究和分析.     

Anisotropic universe models in Brans–Dicke theory

This paper is devoted to study Bianchi type I cosmological model in Brans–Dicke theory with self-interacting potential by using perfect, anisotropic and magnetized anisotropic fluids. We assume that the expansion scalar is proportional to the shear scalar and also take a power law ansatz for the scalar field. The physical behavior of the resulting models are discussed through different parameters. We conclude that contrary to the universe model, the anisotropic fluid approaches isotropy at later times in all cases, which is consistent with observational data.     

Shear as a source of inhomogeneity in general relativistic stellar models

We investigate the class of spherically symmetric, anisotropic (principal stresses unequal) fluids admitting the existence of a vector field, assumed to be orthogonal to the four velocity of the fluid, and with respect to which the Lie derivative of the metric tensor is proportional to the shear tensor. The physical variables, as well as the evolution equation of the bounday surface, are found for different models.     

Shear-excited sound in magnetic fluid

Perceptible sound is shown to be excited in ferrofluids by the shear motion of a rigid plate, if the fluid is exposed to a magnetic field oblique both to the plate and to the direction of propagation. This is in contrast to other fluids, including anisotropic ones such as nematic liquids.     

微扩张管道内幂律流体非定常电渗流动

研究了电渗驱动下幂律流体在有限长微扩张管道内非稳态流动特性.基于Ostwald-de Wael幂律模型,采用高精度紧致差分离散二维Poisson-Nernst-Planck方程及修正的Cauchy动量方程,数值模拟了初始及稳态时刻微扩张管道内幂律流体电渗流流场分布情况,研究了管道截面改变对幂律流体无量纲剪切应变率及无量纲表观黏度的影响,以及无量纲表观黏度对拟塑性流体与胀流型流体流速分布的影响.数值模拟结果显示,当扩张角和无量纲电动宽度一定时,电场驱动下的幂律流体在近壁区域速度响应都很快;初始时刻,近壁处表观黏度的变化受到剪切应变率变化的影响,从而影响了三种幂律流体速度峰值的分布,出现拟塑性流体流速在扩张段上游及扩张段近壁处速度峰值均为幂律流体中最大、而在扩张段下游三种幂律流体速度峰值相近的现象;稳态时刻,幂律流体速度剖面呈现塞型分布,且满足连续性条件下,幂律流体流速随扩张管半径增大而减小,牛顿流体流动规律与宏观尺度下流动规律相同;初始时刻,在相同电动宽度、不同壁面电势作用下,幂律流体在扩张管近壁处剪切应变率分布的差异导致表观黏度分布的差异,并最终导致拟塑性流体与胀流型流体流速分布的差异.     

On the stability of the shear–free condition

The evolution equation for the shear is reobtained for a spherically symmetric anisotropic, viscous dissipative fluid distribution, which allows us to investigate conditions for the stability of the shear–free condition. The specific case of geodesic fluids is considered in detail, showing that the shear–free condition, in this particular case, may be unstable, the departure from the shear–free condition being controlled by the expansion scalar and a single scalar function defined in terms of the anisotropy of the pressure, the shear viscosity and the Weyl tensor or, alternatively, in terms of the anisotropy of the pressure, the dissipative variables and the energy density inhomogeneity.     

受限导致硬椭球液体的取向有序

Monte Carlo模拟研究了两平行硬墙受限下各向异相的硬椭球液体形成的有序结构. 墙壁对椭球粒子的过量吸附和椭球的长短径之比有关;对于高密度的椭球液体,它在一个临界的长短径之比 a/b=2.9处达到最大值,表明在墙表面附近发生了取向有序. 墙表面附近的密度分布和取向序参量进一步证实这结论. 相同密度条件下体相中的取向序参量计算表明体相结构均为各向同性,这是由于体系的密度依然低于各向同性相向相列向转变的临界密度. 该受限椭球液体中墙表面的取向有序是由墙面的几何受限所导致的.     

General symmetries of a string fluid space-time

It is shown that a string fluid is the simplest anisotropic fluid with vanishing heat flux. Furthermore it has the property that the Ricci tensor is obtained from the energy momentum tensor, and vice versa, if one interchanges the fluid variables. We use previous works on the collineations of anisotropic fluids, which include the string fluid as a particular case, to compute the kinematic and the dynamic effects of certain collineations of a string fluid. It is found that the possible spacetimes, which can carry a string fluid, are severely restricted and the possible string fluids in spacetimes, which can admit them are more or less fixed. We recover previous results on the effect of symmetries in string fluid spacetimes and get many new ones, for example the matter inheritance collineations. The study and the results are presented in a systematic manner, which allows the comprehension and the comparison of the restrictions imposed by each collineation. Finally one can use the same method of work for a systematic study of similar problems.     

极性分子型电流变液

电流变液在电场作用下软硬连续可调的奇特性质具有广泛和重要的应用价值。传统电流变液是基于颗粒极化产生的相互作用,根据介电理论预测,其剪切屈服强度的上限约为10kPa。电流变液被发明50年来,阻碍其应用的主要原因是剪切强度低。近年来发明的"极性分子型电流变液"是一类新型电流变液,其屈服强度比传统电流变液大一个数量级以上,且与电场强度呈线性关系,这一点和传统电流变液中的平方关系也明显不同。文章作者提出了极性分子在颗粒间强局域电场中的取向并与极化电荷作用的模型,成功地解释了观察到的实验现象。根据这一原理,有可能制备出屈服强度高达MPa的电流变液。     

Heat capacities of the dipolar Yukawa model polar fluid

The Stockmayer fluid is often used to describe a polar fluid. The dipolar Yukawa (DY) fluid is also a useful model for such fluids and is convenient for theoretical applications. Here we use the mean spherical approximation (MSA) and perturbation theory (PT) to study the heat capacities of the DY fluid model of a polar fluid and compare these results with Monte Carlo simulations for this model polar fluid. We find that the DY fluid shows the same features as the Stockmayer fluid does; demonstrating the utility of the DY fluid and further finding that the MSA and PT approaches give reasonably accurate results for the heat capacity.     

Simulations of complex fluids by mixed lattice Boltzmann—finite difference methods

We present the numerical results of simulations of complex fluids under shear flow. We employ a mixed approach which combines the lattice Boltzmann method for solving the Navier–Stokes equation and a finite difference scheme for the convection–diffusion equation. The evolution in time of shear banding phenomenon is studied. This is allowed by the presented numerical model which takes into account the evolution of local structures and their effect on fluid flow.     

Onset of shear thickening in a simple fluid

We report on nonequilibrium molecular-dynamics simulations of the shear-thickening transition in a simple fluid under shear. We relate the shear-thickening transition to the onset of instabilities in the flow profile and to that of dramatic variations in normal stress differences. The dependence of the critical shear rate, which indicates the onset of shear thickening, on density and temperature is rationalized by introducing a ratio between two characteristic times, quantifying the short-time mobility of a particle and the deformation imposed by the applied shear rate, respectively. The shear-thickening transition is shown to occur at a constant value for this ratio for all state points studied. From a structural point of view, this transition is accompanied by the formation of clusters as recently observed in experiments on complex fluids.Received: 26 July 2004, Published online: 21 September 2004PACS: 83.60.Rs Shear rate-dependent structure (shear thinning and shear thickening) - 47.50. + d Non-Newtonian fluid flows - 83.10.Mj Molecular dynamics, Brownian dynamics     

Gravitational collapse of dissipative fluid as a source of gravitational waves

Gravitational collapse of cylindrical anisotropic fluid has been considered in analogy with the work of Misner and Sharp. Using Darmois matching conditions, the interior cylindrical dissipative fluid (in the form of shear viscosity and heat flux) is matched to an exterior vacuum Einstein–Rosen space–time. It is found that on the bounding 3-surface the radial pressure of the anisotropic perfect fluid is linearly related to the shear viscosity and the heat flux of the dissipative fluid on the boundary. This non-zero radial pressure on the bounding surface may be considered as the source of gravitational waves outside the collapsing matter distribution.     

An equation of state contribution for dipolar and quadrupolar square-well fluids

A dipolar–quadrupolar contribution to the residual Helmholtz energy for a polar square well (a square well plus either a point dipole or a point quadrupole) fluid is developed based on the Padé approximation. Taking the square well system as reference, the contribution is formulated using an expansion for radial distribution function of the reference system. In addition to square well potential parameters the contribution depends only on dipole and quadrupole moments. This term is added as perturbation to a generalized equation of state for square well fluids. The results are then compared with the available simulation data in the literature. With the new equation obtained, it was possible to predict liquid–vapour equilibrium properties and critical properties of polar square well fluids more accurately than with available perturbation theories for multipolar square well systems. Application of the equation of state to a real dipolar (water) and a real quadrupolar (carbon dioxide) fluid indicated that the polar contribution greatly improved the predictions of saturation properties. Accurate prediction of critical properties for polar square well fluids remains as a challenge. This work can be useful in the development of better equations of state.     

Dynamics of locally rotationally symmetric Bianchi type VIII cosmologies with anisotropic matter

This paper is a study of the effects of anisotropic matter sources on the qualitative evolution of spatially homogenous cosmologies of Bianchi type VIII. The analysis is based on a dynamical system approach and makes use of an anisotropic matter family developed by Calogero and Heinzle which generalises perfect fluids and provides a measure of deviation from isotropy. Thereby the role of perfect fluid solutions is put into a broader context. The results of this paper concern the past and future asymptotic dynamics of locally rotationally symmetric solutions of type VIII with anisotropic matter. It is shown that solutions whose matter source is sufficiently close to being isotropic exhibit the same qualitative dynamics as perfect fluid solutions. However a high degree of anisotropy of the matter model can cause dynamics to differ significantly from the vacuum and perfect fluid case.     

Nonlinear refractive index and light scattering due to fluctuations of molecular multipole electric fields

Statistical fluctuations of multipolar electric molecular fields, leading to variations of isotropic and anisotropic light scattering, are moreover shown to give rise to a temperature-dependent nonlinear refractive index of dense fluids. Some selected models of dipolar and quadrupolar molecules, linearly and nonlinearly polarizable and correlated in binary as well as ternary assemblages, are discussed. The formulae derived for the isotropic and anisotropic scattering constants are applicable to one-and many-component fluids, consisting of atoms and polar molecules, and provide the basis for a deeper interpretation of the latest experimental results.     

Correlation functions for simple fluids in a finite system under nonequilibrium constraints

The Landau-Lifschitz fluctuating hydrodynamics formalism is applied to study the statistical properties of simple fluids in a finite system under nonequilibrium constraints. The boundary conditions are explicitly taken into account so that the results can be compared with particle simulations. Two scenarios are investigated: a fluid subjected to a constant shear and a fluid subjected to a constant temperature gradient. By considering a fluid with vanishing thermal expansivity, exact results are obtained for the static and dynamic correlation functions.     

Long-range boundary effects in simple fluids

We discuss long-range boundary effects in simple two- or three-dimensional fluids. These boundary effects are due to the existence of long-range correlations in nonequilibrium fluids and can be computed either by means of kinetic theory or phenomenological mode-coupling theories. In particular, we use kinetic theory to compute the stress tensor and heat flux vector for a fluid in a nonequilibrium steady state in a finite geometry and show that both the effective shear viscosity and effective heat conductivity have contributions due to the walls of the container that influence the behavior of the system far into the fluid. We also show that the mechanocaloric effect is present in the bulk of a three-dimensional fluid and that there are normal stresses in a fluid whenever the temperature gradient is nonzero.Work performed under National Science Foundation grant No. CHE 77-16308.     

The effect of shear flow on the Helfrich interaction in lyotropic lamellar systems

The European Physical Journal E - We study the effect of shear flow on the entropic Helfrich interaction in lyotropic surfactant smectic fluids. Arguing that flow induces an effective anisotropic...