Fluctuation-induced forces in driven systems with a diffusivity anomaly.

Abstract

We show that Casimir-like forces in boundary-driven systems with a bulk diffusivity anomaly are enhanced by cooperative dynamical effects and can be made locally attractive or repulsive depending on the boundary densities. Theoretical predictions based on mean-field arguments and the explicit evaluation of the Casimir force in the fluctuating hydrodynamics framework are supported by Monte Carlo simulation of a two-dimensional (2D) exclusion process with selective kinetic constraints. Consistent with the entropic interpretation of the Casimir effect, we find that local repulsive forces do appear whenever finite-size transverse density fluctuations exceed their infinite-size value. Our results suggest that the bulk diffusivity anomaly is a crucial ingredient in the small-scale design of driven soft-matter systems with tunable fluctuation-induced forces.