A MOLECULAR THEORY OF THE LAPLACE RELATION AND OF THE LOCAL FORCES INA CURVED INTERFACE

Equilibrium in a two-phase system, a liquid in equilibrium with its va por, for example, is characterized by the constancy throughout the sys tem of the temperature and the chemical potential and a relation betwe en the pressures of the phases, the Laplace relation of macroscopic th ermodynamics. We give a molecular expression for this latter relation in terms of a local pressure defined as the thermodynamic response to a local volume change and we show that this local pressure is the same as the local force distribution in an interface. The macroscopic char acteristics of the two-phase system, including the bulk pressures, the surface tension and the location of the surface of tension are all de termined by this local pressure function. As shown in a companion pape r this function can easily be determined by numerical simulation. (C) 1997 American Institute of Physics.