Dynamic Processes in Soap Films

ABSTRACT Some relations between the two main types of thin liquid films, the water-in-air "soap " films and the invert oil-in-water "lipid " films, are out-lined, and several dynamic aspects of film behavior are illustrated and briefly reviewed with reference to more complete treatments. These dynamic processes are important in both types of films, but are easier to study in soap films. The topics include the difference between rigid and mobile films and their inter-conversion; the origin and measurement of film elasticity; the effect of rate of formation upon film thickness, and the evidence against the existence of thick rigid water layers at the surface; and the kinetics of drainage and the role played in it by viscous flow, marginal regeneration, and intermolecular forces. There may be considerable question in the reader's mind-as there is some in mine-about the place of a discussion about soap films in a symposium on biological interfaces. The place of "lipid " films is apparent, since they are widely considered as models for biological membranes. Soap films presumably come in as models for these models. Despite many differences between th