ADSORPTION-KINETICS WITH SURFACE DILATATION .1. DESORPTION OF SLIGHTLY SOLUBLE MONOLAYERS AT CONSTANT SURFACE PRESSURE

A theory is presented for the desorption process of slightly soluble monolayers spread at an air/water interface. The surface pressure is kept constant, while the change in area with time is monitored. It is shown that a dilatation rate d ln Ω/dt (Ω being the area) induces a convection term in the diffusion equation. This diffusion equation is integrated, giving the area with time. The present theory is compared with published data resulting in a diffusion relaxation time as an adjustable parameter. The magnitude of this diffusion relaxation time is compared with data obtained from equilibrium surface tension measurements. © 1993 Academic Press, Inc.