Impact of currents on non-equilibrium coexistence in chemically driven mixtures.

Virtually every biological function emerges through the organization of molecules in time and space. Consequently, a major challenge in statistical physics is to uncover the universal principles governing macromolecular self-organization within the crowded, non-equilibrium environment of the cell. Here, we investigate a class of models where molecules maintain a conserved total concentration but can switch "identities," thereby modulating their intermolecular interactions. By enforcing thermodynamic consistency via the local detailed balance condition, we derive the steady-state criteria determining coexisting concentrations in a binary mixture. In particular, local detailed balance together with state-dependent kinetics impose a difference in chemical potentials across the interface, and we obtain jump conditions that generalize Gibbs' equilibrium coexistence criteria of equal pressure and chemical potential to chemically driven steady states. Maintaining the chemical potential differences requires particle currents, which are confined to the interfacial region.