Wetting and Spreading

Chapter 17 addresses the associated phenomena of the wetting of solid surfaces by a liquid and the spreading of a liquid on a solid or liquid surface. Previously introduced in Chapter 6, the concepts of contact angle, its roots, and its implications in wetting and spreading processes are amplified. Included are discussions of contact angle measurement, hysteresis, the effects of surface roughness and heterogeneity, and the thermodynamics of wetting. The use of spreading coefficients and the classification of various wetting processes is included along with a number of potentially useful variations on standard thermodynamic relationships between surface tension and contact angle. The use of contact angle measurements as a tool for evaluating the nature of a solid surface is explained along with some of the implications of the kinetic aspects of wetting processes. Discussions are provided on the effects of surfactant structure, the solution environment, and the nature of the solid surface on expected and observed wetting processes.