Light Scattering in a Critical Binary Mixture under a Flow

在这项工作中，我们研究了由二元混合物中的相分离和宏观流动中存在的剪切之间的耦合引起的剪切诱导效应。此外，为了得到剪切系统中随时间变化的相关函数的相关信息，我们测量了具有剪切的布朗粒子稀溶液的动态光散射。我们在这里总结了我们的主要结果：(1)使用相衬光学显微镜技术观察到，临界混合物在剪切作用下的相分离导致固定畴结构的形成，有时称为串相，其中以平行于流动的长管形式存在高度各向异性的浓度畴。当剪切关闭时，长管状柱状相被分解成小的球形畴。(2)我们测量了一种临界混合物的有效黏度，该混合物含有相分离浓度，在两个同心圆柱体之间的间隙由Couette流施加剪切。由此得到的有效粘度几乎与Onuki最近预测的流变方程一致，该方程是由双连续条件推导出来的，即当出现的两相具有不同的粘度时，剪切应力应在界面处平衡。(3)研究了聚苯乙烯胶乳剪切溶液的时间相关函数，该函数依赖于散射几何形状，特别是与流动方向相关的散射波矢量分量。影响时间相关函数的因素包括剪切速率、观测到的散射体积以及散射角相对于溶液中速度和剪切的方向。尽管存在这些问题，但对于给定的散射几何形状，可能有方法测量二元混合物在流动下的临界起伏。本文的结果将为从临界点普适性的角度理解流体混合物中的剪切过程提供一把钥匙。少

In this work we have investigated shear-induced effects arising from a coupling between the phase separation in a binary mixture and shear in presence of a macroscopic flow. Besides, for the purpose to get informations associated with the time-dependent correlation function in a sheared system we have measured dynamic light scattering for a dilute solution of Brownian particles with shear. We summarize here our main results :(1) It has been observed using a technique of phase-contrast optical microscopy that the phase separation of a critical mixture under shear results in the formation of a stationary domain structure, sometimes referred to a string phase, in which the highly anisotropic concentration-domains in the form of long tubes oriented parallel to the flow are present. The long tube-like string phase were broken up to small spherical domains when the shear was turned off.(2) We have measured the effective viscosity in a critical mixture involving phase-separating concentration … More -domains, which are imposed to shearing by a Couette flow in a gap between two concentric cylinders. The effective viscosity thus obtained are almost compatible with the rheological equation predicted very recently by Onuki, derived from the biccontinuous condition that the shear stresses should balance at the interface when the emerging two phases have different viscosities.(3) The time-dependent correlation function has been investigated for a sheared solution of a polystirene latex, which depends on the scattering geometry, especially the scattered wave vector component associated with the direction of the flow. The factors affecting the time-dependent correlation function include the rate of shear, the scattering volume observed, and the orientation of the scattering angle with respect to the velocity and shear in the solution. Despite these problems there may be ways to measure the critical fluctuations of a binary mixture under the flow for a given scattering geometry.The present results would provide a key to understanding the shearing process in a fluid mixture in terms of critical-point universality. Less