ABSTRACT
This chapter explains the factors determining the contact angle, the phenomenon of wetting hysteresis and some mass transfer processes depending directly on the value of the contact angle and its variations during the course of flow. Capillary rise and capillary imbibition will be considered as an example when the kinetics is influenced by contact angles, their dependence on flow rate and surfactant adsorption. Calculations of capillary rise and imbibition are based on the Poiseuille equation for viscous flow and the expression for the meniscus capillary pressure. Surfactants adsorb on the walls of the capillaries in the course of imbibition. At a high rate of imbibition, this causes a decrease to zero of the concentration of surfactant at the moving meniscus. The problem of impregnation of porous bodies with badly wetting or non-wetting liquids can be solved by addition of surfactants into the impregnating liquid, because they adsorb on the pore surface and make the contact angle less than 90°.
