Mo' Mobilities, No Problems: An Excess Entropy Scaling Relation for Diffusivity of an Active Fluid

Active matter systems feature discrete particles that convert energy into motion. Such systems are intrinsically out of equilibrium, and exhibit a wide array of unusual transport phenomena, with many potential engineering applications. In this work, we demonstrate that excess-entropy scaling (a principle that has been shown to describe transport properties for a wide range of inactive fluids) can be adapted to also describe diffusivity in a simple model for active fluids. In support of this claim, we perform extensive molecular-dynamics (MD) simulations of an active fluid, in which we vary the total fraction of active particles and the active particles’ degree of activity. Our MD simulation results are consistent with a Rosenfeld-type scaling between active matter diffusion and excess entropy. This scaling relationship constitutes a novel connection between structure and transport in active matter, and is a promising step forward for predictive and generalizable models of other transport phenomena in active systems. We close by briefly describing the features of a system (whether inactive or active) that render its transport properties amenable to excess-entropy-type approaches.