Evidence for activation-diffusion controlled dynamic surface tension with a nonionic surfactant

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 degrees 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 x 10(-10) m(2) s(-1) at 25 degrees 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 E-a of about 80 kJ mol(-1). This conclusion supports the arguments of Liggieri et al.