Dynamic surface tensions of nonionic surfactant solutions

The air-solution equilibrium and dynamic surface tensions, gamma(eq) and gamma(t), respectively, of different nonionic CiEj and glucamide surfactants have been studied as a function of concentration c, above and below their CMCs. DuNouy tensiometry was used to determine gamma(eq), CMCs, and the surface excesses Gamma. The gamma(t) decays 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 gamma(t) curves 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(-1) This barrier does not seem to depend on the CMC, surfactant type or the presence of micelles up to 100 x CMC. The results support theoretical predictions (L. Liggieri et al., J. Colloid Interface Sci. 156, 109 (1993)) of the diffusion-activation adsorption kinetics for nonionic surfactants. (C) 1997 Academic Press.