Shear Thinning of Noncolloidal Suspensions.
Shear Thinning of Noncolloidal Suspensions.
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DOI：
10.1103/physrevlett.117.108001
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发表时间：
2016
影响因子：
8.6
通讯作者：
A. Vázquez-Quesada;R. Tanner;M. Ellero
中科院分区：
文献类型：
--
作者：
A. Vázquez-Quesada;R. Tanner;M. Ellero
剪切稀化-随着剪切速率的增加悬浮液粘度的降低-被认为是胶体体系中熵力相对贡献的降低。剪切稀化现象也经常在高体积分数的非胶体体系的实验中被报道。然而，它的起源是一个开放的理论问题和行为是很难再现的数值模拟中，剪切增稠，而不是典型的观察。在这封信中，我们提出了一个非牛顿模型的颗粒间润滑力来解释非胶体悬浮液中的剪切稀化。我们发现，隐藏的剪切稀化效应的悬浮介质，发生在剪切速率的数量级大于实验研究的范围，导致显着的剪切稀化的整体悬浮液在小得多的剪切速率。在高颗粒体积分数下，位于颗粒之间的狭窄间隙中的流体所经历的局部剪切速率远大于整个悬浮液的平均剪切速率。这允许悬浮介质探测其高剪切非牛顿状态，并且这意味着必须在宽范围的剪切速率上考虑基质流体流变性。
Shear thinning-a reduction in suspension viscosity with increasing shear rates-is understood to arise in colloidal systems from a decrease in the relative contribution of entropic forces. The shear-thinning phenomenon has also been often reported in experiments with noncolloidal systems at high volume fractions. However its origin is an open theoretical question and the behavior is difficult to reproduce in numerical simulations where shear thickening is typically observed instead. In this letter we propose a non-Newtonian model of interparticle lubrication forces to explain shear thinning in noncolloidal suspensions. We show that hidden shear-thinning effects of the suspending medium, which occur at shear rates orders of magnitude larger than the range investigated experimentally, lead to significant shear thinning of the overall suspension at much smaller shear rates. At high particle volume fractions the local shear rates experienced by the fluid situated in the narrow gaps between particles are much larger than the averaged shear rate of the whole suspension. This allows the suspending medium to probe its high-shear non-Newtonian regime and it means that the matrix fluid rheology must be considered over a wide range of shear rates.