Response of an equilibrium film to external disturbances

Abstract

An equilibrium film situated in air saturated with water vapour is subjected to a disturbance consisting of a rapid change of the temperature of the surrounding atmosphere. The resulting large change in film thickness is found to be due to exchange of water between film and atmosphere, and not to expansion or contraction of the film. Pseudo-equilibrium films of widely varying thickness can be formed by means of this process. For a film with a sufficiently large area, the thickness of an element far from the border is determined by the water vapour pressure equilibrium rather than by the disjoining pressure equilibrium. The thickness profile of a large, vertical film in a state of apparent rest is explained on the basis of the different time scales associated with the various equilibrium processes.