The prediction of Marangoni convection in binary liquid–liquid systems with added surfactants

The theoretically predicted stability of various binary liquid–liquid interfaces in the presence of a transferring surfactant is examined and compared against experimental observations. It is found that the accuracy of some of the current stability criteria in predicting interfacial stability under such conditions is poor. To improve this, a Marangoni coefficient is proposed, the magnitude of which predicts well the presence of surfactant induced Marangoni convection in the systems studied. Plots of the variation of the interfacial tension with concentrations of the various surfactants investigated are presented and changes in its value are related to the surfactant induced Marangoni convection observed.