Evolution of microstructure and rheology during flow startup, and its connection to microscopic transport processes, is studied theoretically via active microrheology. At steady state, the balance between entropic, hydrodynamic, and other forces changes with flow strength, producing sustained microstructural asymmetry and non‐Newtonian rheology. However, the transition from equilibrium to steady flow is sometimes marked by overshoots in viscosity that suggests a temporally evolving competition between these rate processes. Here, we formulate and solve a Smoluchowski equation for the time‐dependent evolution of particle microstructure induced by the motion of a colloidal probe driven through a bath of colloidal spheres. The structure is then utilized to compute the time‐dependent microviscosity. Brownian diffusion always sets short‐time particle dynamics, which hinders maturation of the boundary layer. The disparity in Brownian and advective transport rates produces a reversal from flow thinning to flow thickening during startup, revealing that non‐Newtonian flow phenomenology is not instantaneously established. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3198–3214, 2018

中文翻译：

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流体动力学对胶体分散体粘度演变的影响：瞬态，非线性微观流变学

从理论上通过主动微观流变学研究了流动启动过程中微观结构和流变学的演变及其与微观传输过程的联系。在稳态下，熵，流体动力和其他力之间的平衡会随流动强度而变化，从而产生持续的微观结构不对称性和非牛顿流变学。但是，从平衡流向稳定流的过渡有时会以粘度过冲为特征，这表明这些速率过程之间存在着竞争。在这里，我们为通过胶体球浴驱动的胶体探针的运动引起的粒子微观结构的时间依赖性演化制定并求解了Smoluchowski方程。然后利用该结构来计算随时间变化的微粘度。布朗扩散总是设置短期的粒子动力学，这会阻碍边界层的成熟。在启动过程中，布朗和对流输运速率的差异导致了从稀流到浓流的逆转，这表明非牛顿流现象不是瞬间建立的。©2018美国化学工程师学会AIChE J，64：3198–3214，2018