A study on surfactant adsorption kinetics: Effect of bulk concentration onthe limiting adsorption rate constant

A limiting. adsorption rate constant beta(1) was defined as the value at wh ich the mixed diffusive-kinetic controlled surface tension profile is indis tinguishable from the diffusion-controlled one (Hsu et al. J. Chem. Eng. Jp n. 1996, 29, 634). The value of beta(1) depends on surfactant, bulk concent ration, the shape of fluid interface, and the process (adsorption or desorp tion). In this work, the dependence of beta(1) on surfactant and bulk conce ntration (C) was examined. First, the dependence of beta(1) vs C of eight w ell-known surfactants was investigated. In the second part, the effects of equilibrium constant (surfactant activity), molecular interaction, and maxi mum surface concentration were systematically studied. The difference of be ta(1) for a planar and a spherical interface with 0.1 cm radius of curvatur e was also examined. A universal relationship in terms of dimensionless var iables was obtained. Using this universal relationship, one needs only the model constants of adsorption isotherm of surfactant to evaluate the value of beta(1) at any concentration and to know the dependence of beta(1) as a function of surfactant concentration.