ABSTRACT
Intermolecular interactions in the three-phase contact line region, where a liquidvapor interface intersects a solid substrate, have been extensively studied because of their importance to many equilibrium and non-equilibrium phenomena such as contact angle, adsorption, spreading, evaporation, condensation, boiling, wetting and stability. Since the chemical potential is a function of both pressure and temperature, the Kelvin-Clapeyron (K-C) continuum model for the contact line re-
gion, which includes these effects on the local vapor pressure, gives an enhanced understanding of both equilibrium and non-equilibrium processes. Conceptually, the contact line region can be modeled as a meniscus in which the shape gives the interfacial pressure jump [1-17], with the equilibrium vapor pressure being a function of the film thickness and the radius of curvature [e.g., 1-4, 15, 17-20]. Experimentally, with completely wetting systems, the adsorbed film thickness, curvature, and the related disjoining pressure isotherm are of principal importance. With partially wetting systems, the observable apparent contact angle and curvature are of principal importance. Since the molecular exchange process at interfaces is very dynamic, kinetic theory connects the variation of the local vapor pressure to interfacial mass transfer [e.g., 4, 15, 19, 20]. These observations led to the development of the K-C model for the dynamic contact line region [4, 7, 15, 21-24], which is discussed herein. Although only simple examples are emphasized herein, the presented equations can also be solved numerically for additional detail. At the outset, the use of a simple, one-dimensional models is noted. For example, at the monolayer scale, a continuum model is used to describe the effects of the average film thickness and profile. However, we believe that the resulting theoretical insights, which are consistent with many observations, justify this approximate average approach used by many modelers.
