The air-solution equilibrium and dynamic surface tensions, g eq solution for the surface tension decay g(t) cannot be oband g(t), respectively, of different nonionic C i E j and glucamide tained. Instead, for where g(t) is close to either that for the surfactants have been studied as a function of concentration c, pure solvent g 0 , or the equilibrium value of the solution above and below their CMCs. DuNouy tensiometry was used to g eq , limiting laws can be used. For neutral molecules these determine g eq , CMCs, and the surface excesses G. The g(t) decays approximations have been given by Miller et al. as (5) were measured in the range 2 ms-12 s using a maximum bubble pressure instrument and analyzed in terms of asymptotic solutions to the Ward and Tordai equation. At the start the g(t) curves short times
were all consistent with a diffusion-controlled adsorption. However, toward the end good evidence was found for a mixed mechanism with an adsorption barrier of between 5 and 12 kJ mol 01 . and
This barrier does not seem to depend on the CMC, surfactant type [2] or the presence of micelles up to 100 1 CMC. The results support theoretical predictions (L. Liggieri et al., J. Colloid Interface Sci. 156, 109 (1993)) of the diffusion-activation adsorption kinetics long times g(t) t rฯฑ ร
g eq / RTG 2 2c อฉ p Dt อช 1/2 . for nonionic surfactants.