ELECTROSTATIC EFFECTS ON INTERFACIAL FILM FORMATION IN EMULSION SYSTEMS

The adsorption at silica from dilute emulsion systems was studied with in situ ellipsometry. In particular, the effects of electrostatic int eractions on the adsorption rate and the adsorbed layer structure and formation were investigated by varying the emulsion droplet and surfac e charge, as well as the electrostatic screening, accomplished by vary ing pH and the excess electrolyte concentration. Electrostatic interac tions were found to markedly affect the adsorption rate, but not the a dsorbed layer structure or the mechanism for the adsorbed layer format ion. For all cases investigated, the adsorbed layer thickness correspo nds to emulsion droplets or multilamellar liposomes, and the adsorbed layer formation proceeds through attachment of emulsion droplets and/o r multilamellar liposomes at the surface without extensive droplet spr eading or liposome collapse. When the droplets and the surface are sim ilarly charged, the adsorption is facilitated by increasing the electr ostatic screening or by decreasing the emulsion droplet and surface ch arge, accomplished by increasing the excess electrolyte concentration and decreasing pH, respectively. When the droplets and the surface are oppositely charged, the adsorption rate is much higher than that obse rved when the droplets and the surface are similarly charged, although the adsorbed layer structure and the mechanism for the adsorbed layer formation are similar, Qualitatively, these effects may be understood by considering only electrostatic and van der Waals interactions. (C) 1996 Academic Press, Inc.