Dynamic surface tension in concentrated solutions of CnEm surfactants:: A comparison between the theory and experiment

Dynamic surface tension (DST) measurements have been carried out with a series of CnE6-type surfactants with varying alkyl chain length (n = 10-16). Major emphasis has been placed on the DST relaxation in complex solutions containing both the micellar and monomer forms of surfactant. This paper also provides a step-by-step guidance to the theoretical interpretation of DST data for micellar solutions. Distributions of monomers and micelles in the vicinity of the gas/liquid interface, adsorption kinetics, and DST relaxation curves have been simulated in the framework of the Fainerman theory (Fainerman, V. B. Kolloid Z. 1981, 43, 94) explicitly allowing for monomer/micelle interconversation. A thorough numerical analysis has shown that although the Fainerman theory can follow the general experimental trends, it clearly lacks the flexibility needed to provide a self-consistent and quantitatively correct description of the process. Possible reasons for this disagreement are discussed.