Interactions between bilayer membranes and latex

The interaction between sulfate polystyrene latex and bilayer vesicles is described from the point of view of membrane-induced latex deflocculation and theoretical colloid stability for bilayer-covered particles from a DLVO model without free parameters. Unilamellar cationic or anionic vesicles were prepared from dioctadecyldimethylammonium bromide (DODAB) or asolecithin (ASO), respectively, and allowed to interact with sulfate polystyrene microspheres of several sizes. Mean zeta-average diameters for latex particles in the interacting mixtures decreases as a function of interaction time between sulfate polystyrene particles and asolecithin vesicles attaining a final size compatible with a negatively charged asolecithin monolayer deposited onto the anionic latex surface. In contrast to the ASO behaviour, the cationic DODAB was previously reported to deposit as a bilayer onto the sulfate latex. The occurrence of an ordered amphiphile assembly deposited onto the latex is highly dependent on the proportion of total surface areas for vesicles and particles. From zeta-potential measurements and a DLVO model, theoretical colloid stabilities are calculated as a function of monovalent salt concentration or particle size and found to be much higher than experimentally measured stabilities. DLVO expectations are not fulfilled in spite of the presumably ideal nature of the bilayer-covered polystyrene microsphere as a colloid. (C) 1999 Elsevier Science B.V. All rights reserved.