2015-04-15
10:15 at HCI J 574

Nonequilibrium thermodynamics of an interface

Thierry Savin

Department of Engineering, Cambridge University

Interfacial thermodynamics has deep ramifications in understanding the boundary conditions of transport theories. Gibbs' pioneer treatment of phase coexistence describes an interface as a separate and autonomous 2D “dividing surface,” whose temperature is unequivocally the one adopted uniformly by the entire equilibrium system. However, in nonequilibrium processes such as evaporation/condensation or heterogeneous catalysis, large variations of temperature across the interface are observed and therefore invalidate Gibbs' approach to describing these most common situations. I will present a formulation of the local equilibrium for interfaces that extends the thermodynamics of the dividing surface to nonequilibrium. By identifying the position of the interface with a gauge degree of freedom, we exploit gauge-invariance requirements to consistently define the intensive variables for the interface. The model is verified under stringent conditions by employing high-precision nonequilibrium molecular dynamics simulations of a coexisting vapor-liquid Lennard-Jones fluid. We conclude that the interfacial temperature is determined using the surface tension as a “thermometer,” and can be significantly different from the temperatures of the adjacent phases. These findings lay new foundations for nonequilibrium interfacial thermodynamics.