EFFECT OF INTERFACIAL CONCENTRATION GRADIENTS OF INSOLUBLE SURFACTANTS ON LOCAL FILM-THINNING

A mathematical model is formulated and solved numerically describing t he local thinning of liquid films between a solid/liquid interface and a fluid/liquid interface with a variable surface concentration of an insoluble surfactant. Reynolds lubrication approximation is used. The initial excess surfactant distribution is two-dimensional Gaussian. Th e film thins most rapidly at the center of the disturbance until a thi ckness is reached at which rupture may occur. Alternatively a minimum film thickness is reached after which the film recovers and eventually regains its original thickness. The time to reach the minimum thickne ss lengthens as the background concentration of surfactant approaches zero. (C) 1994 Academic Press, Inc.