The role of thin films in wetting

Abstract

The role of thin films in wetting is reviewed. Three modes of spontaneous spreading are discussed : incomplete spreading, complete spreading and mixed-mode spreading. A thin film can be either molecular or colloidal in thickness. Molecularly adsorbed films are mainly associated with incomplete spreading. Colloidal films usually extend from the bulk of the liquid in dynamic situations of complete spreading. Their existence at equilibriuim with the bulk depends on the orientation in the gravitational field. The spreading of mixtures involves complex phenomenology, much of which is yet unaccounted for by theory. The differences in surface tensions, volatilities and tendencies for adsorption among the components determine the quantitative as well as qualitative features of the spreading