Evidence for Activation−Diffusion Controlled Dynamic Surface Tension with a Nonionic Surfactant

Abstract

Dynamic surface tensions (DSTs) of aqueous solutions of a glucamide nonionic surfactant, di-(C6-Glu), below its critical micelle concentration, have been measured by a maximum bubble pressure method as a function of temperature, from 10 to 50 °C. Du Nouy tensiometry was used to determine the temperature dependence of the equilibrium surface tension and surface excess, while the self-diffusion coefficient for monomeric di-(C6-Glu) was obtained by pulsed-field-gradient spin-echo NMR (D = 2.7 × 10-10 m2 s-1 at 25 °C). With these measured values, the final stages of the DST decays are shown to be consistent with an activation−diffusion controlled adsorption mechanism, and an apparent activation energy Ea of about 80 kJ mol-1. This conclusion supports the arguments of Liggieri et al. (J.Colloid Interface Sci. 1993, 156, 109).