Nonequilibrium Thermodynamics of Multi-Component Interfaces

Interfacial thermodynamics has important implications for determining boundary conditions of crucial biological and industrial processes. We have developed a theory of local equilibrium for multi-phase multi-component interfaces that builds upon the "sharp" interface first introduced by Gibbs, allowing for a description of nonequilibrium interfacial transport. By requiring that the thermodynamics is insensitive to the precise location of the dividing surface, we identify conditions for local equilibrium and then use extensive, high-precision nonequilibrium molecular dynamics (NEMD) simulations to test these conditions, establishing the validity of the local equilibrium hypothesis at interfaces. In particular, we demonstrate that equilibrium equations of state for select observables can be used to determine interfacial temperature and chemical potential(s) which are consistent with nonequilibrium generalizations of the Clapeyron and Gibbs adsorption equations. These results hold even far from equilibrium in the presence of heat and/or mass fluxes, thereby providing a thermodynamic foundation and computational tools for studying a wide variety of interfacial transport phenomena.