DYNAMIC SURFACE-TENSION OF SOLUTIONS OF SURFACTANT MIXTURES .1. DIFFUSION-CONVECTIVE-CONTROLLED ADSORPTION

A quantitative theory of the dynamic surface tension for 2 multicomponent mixture of surfactants obeying the Langmuir adsorption isotherms with constant diffusion coefficients in the bulk and in the adsorbed layer is developed for diffusion-controlled and diffusion-convective-controlled adsorption models. The effect of the mutual diffusion in the adsorbed layer and the effect of the convective transfer are estimated in an analytical form for the short-time and long-time approximations. It is coneluded that the dynamic surface tension can be described by the diffusion-convective-controlled model. It is shown that the equation F(gamma(t)) = log[(gamma 0 - gamma(t))/(gamma(t) - gamma(e))] = n log(t/(rel)) is valid over a wide range of time for the multicomponent mixture of surfactants. Because the diffusion-controlled and diffusion-convective-controlled adsorption models are shown to be asymptotical, correlation n equals one-half. Simple formulae are derived to calculate the parameters n and t(rel) and the dynamic surface tension over a wide range of time for adsorption isotherms of multicomponent mixtures obeying the Langmuir adsorption isotherms. (C) 1994 Academic Press, Inc.