Hydrophobic surfactants are used in a variety of practical applications, including the stabilization of microbubbles, formulation of wetting agents and cosmetics, and the design of flavor delivery enhancers. Understanding the kinetics of film formation for these hydrophobic surfactants are important for the improvement of manufacturing processes in these fields. Mixtures of long chain phospholipids are hydrophobic surfactants that are commonly used as stabilizers in the food and cosmetic industries. We investigated the mechanisms of adsorption of two purified long chain phospholipids, dilauroyl or dimyristoyl phosphatidylcholine (DLPC or DMPC). Adsorption from a dispersion of small unilamellar vesicles onto a clean air-water surface was studied using drop profile tensiometry. Adsorption rates were found to be proportional to vesicle concentration for both phospholipids, indicating a clear mechanistic role for vesicles. Theoretical expressions for possible contributing mechanisms and pathways, via molecular and/or vesicle transport, were developed, and used to predict an associated flux towards the interface. These flux expressions were compared to experimentally measured adsorption rates for a variety of lipid concentrations, temperatures, vesicle diameters, and convection rates. Our results indicated that the formation of a DLPC monolayer arises from a molecular transport mechanism that is enhanced by vesicle-to-monomer exchange beneath the interface. Adsorption rates of DMPC were an order of magnitude smaller, which we attribute to the decreased monomer solubility. The influence of the phase transition temperature on the adsorption behavior was also considered. We will discuss our approach to investigating the adsorption kinetics for potential application to a wider range of hydrophobic surfactants.<br/>

Mechanism of adsorption of phosphatidylcholine from a dispersion of vesicles onto a clean air-water interface

255th National Meeting (2018)

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