Abstract
We derive in a new way that the intensive properties of a fluid-fluid Gibbs interface are independent of the location of the dividing surface. When the system is out of global equilibrium, this finding is not trivial: In a one-component fluid, it can be used to obtain the interface temperature from the surface tension. In other words, the surface equation of state can serve as a thermometer for the liquid-vapor interface in a one-component fluid. In a multi-component fluid, one needs the surface tension and the relative adsorptions to obtain the interface temperature and chemical potentials. A consistent set of thermodynamic properties of multi-component surfaces are presented. They can be used to construct fluid-fluid boundary conditions during transport. These boundary conditions have a bearing on all thermodynamic modeling on transport related to phase transitions.
Highlights
To understand transport through, into, and along interfaces is of practical importance in physics, chemistry biology, and engineering [1,2,3,4,5,6,7,8]
The purpose of this subsection is to show that a set of geometry-dependent, excess densities in global equilibrium can be replaced by a set of absolute intensive variables, provided that we introduce a convenient reference chemical potential for the components
The overall conclusion is that a consistent thermodynamic description of a non-equilibrium interface can be found
Summary
Into, and along interfaces is of practical importance in physics, chemistry biology, and engineering [1,2,3,4,5,6,7,8]. Large efforts have been made to develop a rigorous and thermodynamically consistent description of surfaces at global equilibrium and away from this condition. The method of dynamic boundary conditions [10,11] was proposed in 1976 to deal with surfaces away from equilibrium. The method provides a description of interface transport phenomena that are compatible with the second law of thermodynamics. Current methods for interface transport often do not possess the symmetry required by this method (Onsager symmetry) [3]. In spite of the agreement with symmetry requirements and the second law, the dynamic boundary method has not yet gained common use. This article aims to mend this situation by presenting rigorous evidence for the validity and applicability of the basic assumptions of the theory of non-equilibrium thermodynamics for interfaces
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