Chemomechanical motility modes of partially wetting liquid droplets

Voss, Florian; Thiele, Uwe

Abstract

We consider a simple thermodynamically consistent model that captures the self- organized chemomechanical coupling resulting from the interplay between autocatalyti- cally reacting surfactants, the Marangoni effect, and wetting dynamics. An ambient bath of surfactant acts as a chemostat and provides the system with chemical fuel, thereby driving it away from thermodynamic equilibrium. We find that a positive feedback loop between the local reactions and the Marangoni effect induces surface tension gradients that allow for self-propelled droplets. Besides simple directional motion, we find crawling and shuttling droplets as well as droplets performing random walks, thus exploring the entire substrate. We study the occurring chemomechanical motility modes and show how the observed dynamic states emerge from local and global bifurcations. Due to the underlying generic thermodynamic structure, we expect that our results are relevant not only to directly related biomimetic droplet systems but also to structurally similar systems like chemically active phase-separating mixtures.