Effect of ionic surfactants on drainage and equilibrium thickness of emulsion films

This paper presents new theoretical and experimental results that quantify the role of surfactant adsorption and the related interfacial tension changes and interfacial forces in the emulsion film drainage and equilibrium. The experimental results were obtained with plane-parallel microscopic films from aqueous sodium dodecyl sulphate solutions formed between two toluene droplets using an improved micro-interferometric technique. The comparison between the theory and the experimental data show that the emulsion film drainage and equilibrium are controlled by the DLVO interfacial forces. The effect of interfacial viscosity and interfacial tension gradient (the Marangoni number) on the film drainage is also significant.

Unlike foam films, the effect of ionic surfactant on the drainage of the toluene–water–toluene films stabilized by 0, 1, 10 and 30 μM SDS was found to be satisfactorily described by the DLVO surface forces—no extension of the DLVO theory to include hydrophobic or hydrophilic interaction is required. Interfacial viscosity and interfacial tension gradient are also important.Figure optionsDownload as PowerPoint slide