Enhanced particle diffusion in fluctuating binary environments

Abstract

We investigate single-particle diffusion in a two-state Langevin model where the friction coefficient randomly switches between low-friction (liquid-like) and high-friction (glassy-like) states. The dynamics are governed by the ratio between the friction switching time $\ddot{I}„$ and the intrinsic velocity relaxation time $\ddot{I}{„}_0$. For fast switching ($\ddot{I}„/\ddot{I}{„}_0\lesssim 1$) the motion is homogeneous and Brownian, whereas for slow switching ($\ddot{I}„/\ddot{I}{„}_0\gg 1$) the particle exhibits intermittent dynamics and an enhanced diffusion coefficient. Analysis of the single-particle overlap function $Q(t)$ and the dynamic susceptibility $\ddot{I}{‡}_4(t)$ reveals decoupling of the diffusion coefficient from the average friction upon cooling, which coincides with increasing temporal dynamic heterogeneity. This minimal model provides a transparent framework for understanding single-particle transport in media with fluctuating local mobility, including supercooled liquids and phase-separated soft materials.