Universal Transport Dynamics of Complex Fluids

TL;DR

This paper introduces a unified transport equation that quantitatively explains the complex, non-Gaussian motion of particles in various fluids, accounting for disorder and environmental effects.

Contribution

A new, explicit model of complex fluid transport dynamics that unifies MSD, NGP, and displacement relaxation across different systems.

Findings

Quantitative explanation of MSD and NGP in complex fluids

Identification of environment-coupled diffusion kernel and correlation function as key factors

Introduction of intrinsic and extrinsic disorder concepts affecting transport

Abstract

Thermal motion in complex fluids is a complicated stochastic process but ubiquitously exhibits initial ballistic, intermediate sub-diffusive, and long-time non-Gaussian diffusive motion, unless interrupted. Despite its relevance to numerous dynamical processes of interest in modern science, a unified, quantitative understanding of thermal motion in complex fluids remains a long-standing problem. Here, we present a new transport equation and its solutions, which yield a unified quantitative explanation of the mean square displacement (MSD) and the non-Gaussian parameter (NGP) of various fluid systems. We find the environment-coupled diffusion kernel and its time correlation function are two essential quantities determining transport dynamics of complex fluids. From our analysis, we construct a general, explicit model of the complex fluid transport dynamics. This model quantitatively explains not only the MSD and NGP, but also the time-dependent relaxation of the displacement distribution for various systems. We introduce the concepts of intrinsic disorder and extrinsic disorder that have distinct effects on transport dynamics and different dependencies on temperature and density. This work presents a new paradigm for quantitative understanding of transport and transport-coupled processes in complex disordered media.