Zeta potential of air bubbles in solutions of binary mixtures of surfactants (monodistributed nonionic/anionic surfactant mixtures)

The improved spinning tube electrophorometer is used to measure the zeta potential of air bubbles immersed in solutions of mono-distributed nonionic/anionic surfactant mixtures. zeta potential variations over time reflect the transient regime of the adsorption of the surfactants at the bubble/solution interface; for the explored surfactant concentrations and the studied surfactants, they show that nonionic molecules are the first to occupy the interface before being partially moved by ionic molecules. At equilibrium, the composition of the interfacial surfactant mixture is found to be close to the composition of the surfactant mixture in solution. Within the micellization diagram, the variation of the equilibrated zeta potential allows the detection of a steep change of the interfacial arrangement of the surfactant molecules at the crossing of the critical mixed micelle concentration curve. (C) 1998 Academic Press.