Multiphase Coexistence and Non-linear Rheology of Colloidal. Dispersions as Observed in a Model Capillary Viscosimeter
Multiphase Coexistence and Non-linear Rheology of Colloidal. Dispersions as Observed in a Model Capillary Viscosimeter
复制标题
胶体的多相共存和非线性流变学。
DOI：
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发表时间：
1996
期刊：
影响因子：
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通讯作者：
M. Würth
中科院分区：
文献类型：
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作者：
T. Palberg;M. Würth
通过粘度计和流变仪研究胶体物质的流动特性是理解生物学、医学和材料工业处理中许多重要的传输过程的有价值的工具。细胞质、血液、胶束溶液或原油乳状液的流动只是一些明显的例子。胶体体系最有趣的性质之一是它们在剪切下变稀或变稠的能力。为了证实这种非牛顿流动行为，设计了不同的粘度和流变实验，毛细管粘度计是经典仪器之一。非线性流变学的基本物理机制是剪切诱导的长程位置和取向有序的形成和破坏。由于只有在极少数情况下，才能从粘度计内部获得全面的结构和速度信息，因此通常假设样品是均匀的。然而，有迹象表明，从最近的实验胶体模型系统的非均匀相和流动行为的几何形状依赖的演变，特别是对于较密集的系统的强相互作用的粒子。在这里，我们目前的调查进行了一个很好的特点，通过屏蔽静电势相互作用的球形颗粒悬浮液。本文详细研究了光学型毛细管粘度计中的局部结构和剪切速率。作为总通量的函数，在粘度计内观察到几种不同的流动情景，最引人注目的特征是在稳定流动条件下同时存在多达四个同心排列的相。
Investigations of the flow properties of colloidal substances by viscometry and rheometry are a valuable tool in understanding many transport processes of importance in biology, medicine and industrial treatment of materials. The streaming of cytoplasm, blood, micellar solutions or crude oil emulsions are but some obvious examples. One of the most intriguing properties of colloidal systems is their ability of thinning or thickening under shear. To characterise this non-Newtonian flow behaviour different visco- and rheometric experiments have been devised, the capillary viscometer being one of the classical instruments. The underlying physical mechanisms of non-linear rheometry are the shear-induced formation and destruction of long range positional and orientational order. Since only in rare cases comprehensive structure and velocity information is accessible from inside a viscosimeter, generally, homogeneous samples are assumed. However, there are indications of a geometry dependent evolution of inhomogeneous phase and flow behaviour from recent experiments on colloidal model systems, in particular for denser systems of strongly interacting particles. We here present investigations performed on a well characterised suspension of spherical particles interacting via a screened electrostatic potential. We give a detailed study of the local structures and shear rates in an optical model capillary viscosimeter. As a function of the overall flux several different flow scenarios are observed within the viscosimeter and the most striking feature is the simultaneous existence of up to four concentrically arranged phases under conditions of stationary flow.