标题： 胶体流体动力学相互作用在粘弹性流体中 显示英文标题

标题： Colloidal hydrodynamic interactions in viscoelastic fluids

摘要： 悬浮胶体粒子的运动在周围介质中产生流体扰动，这些扰动产生了粒子间的相互作用。 尽管在粘性牛顿介质中已经对胶体水动力相互作用（HIs）进行了广泛研究，但对粘弹性流体中的HIs缺乏全面的理解。 我们开发了一个框架，通过捕获胶体并诱导平移-旋转水动力耦合，以高时空精度量化粘弹性流体中的HIs。 以蠕虫状胶束（WLMs）溶液为例，我们发现HIs具有很强的时间依赖性，并依赖于粘弹性流体中产生的结构记忆，这与粘性牛顿流体中的“瞬时”HIs形成对比。 我们在瞬态启动过程中直接测量了静止探测器与驱动粒子之间的时间依赖性HIs，该过程发生在WLM松弛时间尺度上。 在驱动粒子突然停止后，我们观察到一种有趣的方向相反的流动反转，持续时间约为WLM松弛时间的十倍。 我们通过分析微流体力学理论、连续体模型的直接数值解以及基于粒子的Stokesian动力学模拟来验证我们的观察结果。 我们发现，WLMs从非线性应变中的结构恢复可以产生各向异性和不均匀的应力，从而在胶体之间产生流动反转和水动力吸引。 测量到的不均匀性表明，当胶体的尺寸与聚合物组分及其缠绕长度的尺度相当时，标准连续体模型在本构关系方面会出现失效。 显示英文摘要

摘要： The motion of suspended colloidal particles generates fluid disturbances in the surrounding medium that create interparticle interactions. While such colloidal hydrodynamic interactions (HIs) have been extensively studied in viscous Newtonian media, comprehensive understanding of HIs in viscoelastic fluids is lacking. We develop a framework to quantify HIs in viscoelastic fluids with high spatiotemporal precision by trapping colloids and inducing translation-rotation hydrodynamic coupling. Using solutions of wormlike micelles (WLMs) as a case study, we discover that HIs are strongly time-dependent and depend on the structural memory generated in the viscoelastic fluid, in contrast to "instantaneous" HIs in viscous Newtonian fluids. We directly measure time-dependent HIs between a stationary probe and a driven particle during transient start-up, developing on the WLM relaxation timescale. Following the sudden cessation of the driven particle, we observe an intriguing flow reversal in the opposing direction, lasting for a time about ten times larger than the WLM relaxation time. We corroborate our observations with analytical microhydrodynamic theory, direct numerical solutions of a continuum model, and particle-based Stokesian dynamics simulations. We find that the structural recovery of the WLMs from a nonlinear strain can generate anisotropic and heterogeneous stresses that produce flow reversals and hydrodynamic attraction among colloids. Measured heterogeneities indicate a breakdown of standard continuum models for constitutive relations when the size of colloids is comparable to the length scales of the polymeric constituents and their entanglement lengths.