General isotherm equation for adsorption of surfactants at solid/liquid interfaces. Part 2. Applications

Abstract

This work describes a number of results of surfactant adsorption (including non-ionic, cationic and anionic surfactants on various adsorbents) illustrating the applications of the general isotherm equation proposed in part 1. The results show that the calculated curves from the general isotherm equation can represent the experiment data very well. Based on the calculation of the thermodynamics of adsorption, it is evident that the principal contribution to the ΔG°hm of negative value is the large negative value is the large positive value of ΔS°hm, whereas ΔH°hm is positive. Therefore, similar to the micellization in bulk solution, the second step of surfactant adsorption (see part 1) is an entropy-driven process. For S-type and LS-type isotherms, two approaches and corresponding equations for calculation of h.m.c. have been proposed respectively, and the calculated h.m.c.s. by both approaches agree with the empirical value very well.