Statistical Thermodynamics of the Fluid−Solid Interface

Abstract

Although the fluid−fluid interface has been fully described within the framework of classical statistical thermodynamics, a similarly complete treatment of the fluid−solid interface is lacking. Fluid−solid interfacial tension γf, which cannot be directly measured, is here defined operationally by a gedanken experiment (analogous to the classic experiment measuring fluid−fluid interfacial tension) in which the fluid is allowed to spread uniformly over the solid surface while the local intensive properties of the two phases are kept fixed. A general statistical-mechanical expression for γf is derived, which for the first time accounts for dynamic coupling between molecular motions in the solid and fluid phases. In the limit of decoupling (the molecules in the solid become fixed, the effective temperature of the solid approaches T = 0 K) this expression reduces to a previous formula for the interfacial tension based on a rigid solid (T = 0 K). A new contribution to the interfacial tension in the rigid-solid ...