[论文解读] Shear thickening, frictionless and frictional rheologies

Romain Mari, Ryohei Seto+2 more|arXiv (Cornell University)|Mar 26, 2014

Force Microscopy Techniques and Applications被引用 4

一句话总结

本文表明，稠密悬浮液中的剪切变稠主要源于剪切速率增加时摩擦接触作用的增强，使系统在接近阻塞转变时从无摩擦流变过渡到有摩擦流变。通过在模拟中同时考虑摩擦与润滑作用，作者重现了不连续剪切变稠现象，表明摩擦降低了阻塞堆积分数并驱动黏度发散，从而将剪切变稠重新定义为一种几何接触介导的现象，而非流体动力学现象。

ABSTRACT

Particles suspended in a Newtonian fluid raise the viscosity and also generally give rise to a shear-rate dependent rheology. In particular, pronounced shear thickening may be observed at large solid volume fractions. In a recent article (R. Seto, R. Mari, J. F. Morris, and M. M. Denn., Phys. Rev. Lett., 111:218301, 2013) we have considered the minimum set of components to reproduce the experimentally observed shear thickening behavior, including Discontinuous Shear Thickening (DST). We have found frictional contact forces to be essential, and were able to reproduce the experimental behavior by a simulation including this physical ingredient along with viscous lubrication. In the present article, we thoroughly investigate the effect of friction and express it in the framework of the jamming transition. The viscosity divergence at the jamming transition has been a well known phenomenon in suspension rheology, as reflected in many empirical laws for the viscosity. Friction can affect this divergence, and in particular the jamming packing fraction is reduced if particles are frictional. Within the physical description proposed here, shear thickening is a direct consequence of this effect: as the shear rate increases, friction is increasingly incorporated as more contacts form, leading to a transition from a mostly frictionless to a mostly frictional rheology. This result is significant because it shifts the emphasis from lubrication hydrodynamics and detailed microscopic interactions to geometry and steric constraints close to the jamming transition.

研究动机与目标

• 理解稠密悬浮液中不连续剪切变稠（DST）的物理起源，超越流体动力学效应。
• 研究摩擦如何改变颗粒悬浮液中的阻塞转变与黏度发散行为。
• 确定摩擦接触是否对重现实验观测到的剪切变稠行为至关重要。
• 将剪切变稠重新定义为接近阻塞时几何约束与接触网络演化的结果。

提出的方法

• 在牛顿流体中，通过模拟颗粒间同时包含粘性润滑力与摩擦接触力的系统。
• 采用最小物理框架建模颗粒相互作用，包含接触处的法向力与切向力。
• 分析接触网络演化及摩擦贡献随剪切速率的变化。
• 将阻塞堆积分数与摩擦的存在相关联，表明摩擦可降低阻塞临界体积分数。
• 利用阻塞转变框架解释剪切变稠的 onset 与幅度。
• 通过追踪不同剪切速率下摩擦接触的比例，量化从无摩擦到有摩擦流变的转变。

实验结果

研究问题

• RQ1 摩擦如何影响稠密悬浮液中的阻塞转变？
• RQ2 摩擦接触在不连续剪切变稠出现过程中起什么作用？
• RQ3 是否可以不依赖详细的流体动力学润滑力来解释剪切变稠？
• RQ4 接触网络随剪切速率的演化如何影响宏观流变行为？
• RQ5 与无摩擦系统相比，摩擦在多大程度上降低了阻塞堆积分数？

主要发现

• 摩擦降低了阻塞堆积分数，表明摩擦颗粒在比无摩擦颗粒更低的体积分数下即发生阻塞。
• 剪切变稠是剪切速率升高时摩擦接触增加的直接结果，标志着系统从无摩擦流变向有摩擦流变的转变。
• 摩擦显著影响阻塞点附近的黏度发散行为，改变了该点附近的标度特性。
• 同时包含润滑与摩擦的模拟成功重现了实验中的剪切变稠行为，证实了摩擦力的必要性。
• 从无摩擦到有摩擦流变的转变由几何约束与接触网络形成驱动，而非流体动力学相互作用。
• 本研究将剪切变稠重新定义为一种基于阻塞物理的立体接触介导现象，而非流体动力学现象。