ABSTRACT
For any multi-phase system of practical and fundamental significance, i.e. with distinct interfaces, wetting is a common phenomenon that frequently needs to be considered. For example, when an inert liquid is placed on the surface of a rigid solid, it spreads spontaneously or partially to form a film or a lens. The extent of spreading is, in general, controlled by the competition between the interfacial energies in the system. For the solid-liquid-vapor (or other immiscible liquid) system with a finite affinity between phases, the system at equilibrium (in thermodynamic terms) can be described by Young’s equation (1), or its modification
where ysv, Ksl, and yLV are the solid-vapor, solid-liquid, and liquid-vapor interfacial tensions, respectively, for phases that are saturated with each other; ysLv is the line tension (the excess of energy associated with the three-phase contact line); Ө is the contact angle as measured from the tangent to the liquid-vapor interface and the plane of the solid surface at the point of contact between three phases (solid, liquid, and vapor); ĸgs is the geodesic curvature of the three-phase contact line; a is the angle between the solid surface and the plane containing the wetting perimeter; and r is the radius of curvature of the three-phase contact line U L,S = \ / r for a drop on a flat solid surface, where r is the drop base radius). The line tension component of equation (2) becomes important when the radius of curvature for the three-phase contact line is small, a few micrometers or less [2, 3],
Although the line tension contribution to three-phase systems was recognized many years ago, it is just during the last several years that this parameter has re ceived greater attention from researchers working with solid-liquid-fluid systems. The analysis of the line tension phenomenon ends up with the old and unresolved problem in surface chemistry: what are the properties and significance of the mi croscopic region in the vicinity of the contact line, and what are the consequences of the specificity of this region on the dynamics and thermodynamics of the wetting phenomena?
