相互作用通过涌现流增强波动通道中的扩散
Interactions enhance dispersion in fluctuating channels via emergent flows
AI总结：
本研究通过引入排斥相互作用产生有效流场，发现粒子密度增加反而增强扩散，挑战了拥挤减少扩散的传统观点，并提出了普适机制及微扰理论。
摘要：
理解窄通道中的粒子运动对于指导从过滤到血管运输等众多应用中的进展至关重要。对于充满流体的通道，通道壁的热波动或主动波动可以减慢或增加示踪粒子的扩散。壁凸起中的熵捕获减慢了扩散，而由壁波动引起的流体动力学流动则增强了扩散。以往的研究主要集中在单个布朗示踪剂的情况，该示踪剂要么嵌入不可压缩流体中，要么在忽略流体存在的理想情况下。在这里，我们解决了当存在大量相互作用的布朗示踪剂时会发生什么的问题——这是应用中的常见情况。在忽略背景流体存在的情况下，引入示踪粒子之间的排斥相互作用会产生一个有效的流场。该流场增强了示踪剂的扩散，这一现象与在不可压缩背景流体中观察到的情况强烈相似。我们通过单个示踪剂的长时扩散系数，在数值上和解析上（通过平均场密度泛函分析）表征了这种扩散。我们发现了一个令人惊讶的效应：增加粒子密度会增强扩散系数，这挑战了拥挤效应往往会减少扩散的观点。在这里，粒子间的相互作用将粒子推向波动的通道壁附近。然后，波动壁与现在靠近的粒子之间的相互作用驱动了粒子混合。我们的机制具有足够的普适性，我们预计它将适用于各种系统。此外，我们推导的微扰理论量化了具有任意时空漂移的通用平流-扩散系统中的扩散。
英文摘要：
Understanding particle motion in narrow channels is essential to guide progress in numerous applications, from filtration to vascular transport. Thermal or active fluctuations of channel walls for fluid-filled channels can slow down or increase the dispersion of tracer particles. Entropic trapping in the wall bulges slows dispersion, and hydrodynamic flows induced by wall fluctuations enhance dispersion. Previous studies primarily concentrated on the case of a single Brownian tracer either embedded in an incompressible fluid or in the ideal case where the presence of fluid is ignored. Here we address the question of what happens when there is a large ensemble of interacting Brownian tracers -- a common situation in applications. Introducing repulsive interactions between the tracer particles, while ignoring the presence of a background fluid, leads to an effective flow field. This flow field enhances tracer dispersion, a phenomenon strongly reminiscent of that seen in incompressible background fluid. We characterise the dispersion by the long-time diffusion coefficient of a single tracer, numerically and analytically with a mean-field density functional analysis. We find a surprising effect where an increased particle density enhances the diffusion coefficient, challenging the notion that crowding effects tend to reduce diffusion. Here, inter-particle interactions push particles closer to the fluctuating channel walls. Then, interactions between the fluctuating wall and the now-nearby particles drive particle mixing. Our mechanism is sufficiently general that we expect it to apply to various systems. In addition, the perturbation theory we derive quantifies dispersion in generic advection-diffusion systems with arbitrary spatiotemporal drift.
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