Generalized thermodynamics of motility-induced phase separation: phase equilibria, Laplace pressure, and change of ensembles

Motility-induced phase separation leads to cohesive active matter in the absence of cohesive forces. We present, extend and illustrate a recent generalized thermodynamic formalism which accounts for its binodal curve. Using this formalism, we identify both a generalized surface tension, that controls finite-size corrections to coexisting densities, and generalized forces, that can be used to construct new thermodynamic ensembles. Our framework is based on a non-equilibrium generalization of the Cahn–Hilliard equation and we discuss its application to active particles interacting either via quorum-sensing interactions or directly through pairwise forces. (paper)