Screened Pair Interaction of Charged Colloidal Particles in Liquid-Liquid Interfaces

The interaction of charged colloidal particles adsorbed to oil-water interfaces is still a subject of intensive research and scientific debate. The relative stability of such particles against aggregation compared to particles in aqueous bulk solution or in air-water interfaces has led to the controversial proposition that particles can sustain electric surface charges on the surface portion in contact with the oil phase, even if the latter has a very low electric permittivity. We show that this notion is supported by liquid-structure analysis of interfacial particle ensembles observed with digital video microscopy. Interaction measurements in the presence of surfactant micelles in the oil phase in fact suggest the surprising possibility of screening electrostatic interaction through the oil with the help of non-ionic surfactants.