(409b) Transport of Lipid Amphiphiles to Fluid Interfaces from a Vesicle Dispersion

Poorly water-soluble amphiphiles, such as phospholipids, can assemble in excess water to form liquid crystals above their solubility limit. Extrusion of phospholipid lamellar liquid crystals allows for the formation of dispersed, kinetically stable unilamellar vesicles. We are interested in understanding how the presence of such dispersed colloidal assemblies influence the rate of formation of a surfactant monolayer at fluid interfaces. Adsorption dynamics were tracked using dynamic surface tension measurements for dilauroyl or dimyristoyl phosphatidylcholine (DLPC or DMPC) contained within monodisperse vesicles. Dispersed vesicles can deliver lipids to an interface over time, with delivery potentially taking place through two adsorption pathways: (1) direct interfacial disassembly of vesicles or (2) through a vesicle-to-monomer reaction beneath the interface, followed by monomer diffusion and adsorption. The overall kinetics are determined by the fastest pathway, with the slowest step within that pathway controlling the rate at which the pathway proceeds. From our work thus far, DLPC and DMPC appear to generate a monolayer at a fluid interface through pathway 2. It has become clear that the monomer solubility plays a key role in the adsorption pathway and that the effect of monomer/assembly properties on the adsorption dynamics are complex. Understanding the mechanistic landscape for monolayer formation is important in a variety of practical applications, including the stabilization of foams and emulsions in the food and cosmetic industries, and lipid migration in physiological and environmental settings. The theory and approach that we have developed to investigate this mechanistic landscape is transferable to similar systems of colloidal assemblies and is useful for identifying controlling mechanisms and effects of external variables on the system.