Comments on modelling the diffusion‐controlled adsorption of surfactants

Abstract

AbstractIn this study, dynamic interfacial tension data are obtained with a drop volume tensiometer at the mineral oil‐water interface for Triton X‐100 dissolved in the water phase, and for Span 80 dissolved in the oil phase. Surfactant adsorption is modelled under diffusion‐controlled conditions using either long or short diffusion time approximations. A dimensionless parameter relating adsorption time, ta, to a characteristic diffusion time of each surfactant, tD, is introduced in order to determine the general applicability of the diffusion approximations. In the case of Triton X‐100, the long time approximation is valid, and the ratio of ta/τD is found to be much greater than one. In the case of Span 80, the short time approximation provides a good fit to the experimental data, and the ratio ta/τD is found to be on the order of unity or less. A consideration of experimental data found in the literature for other surfactants leads to the general conclusion that the ratio ta/τD is useful in characterising diffusion‐controlled adsorption of surfactants.