PENETRATION OF INSOLUBLE LIPID MONOLAYERS AT THE AIR-WATER-INTERFACE BY WATER-SOLUBLE BLOCK-COPOLYMERS AND HOMOPOLYMERS

We used scanning angle reflectometry to directly measure the extent of water-soluble polymer adsorption to insoluble dipalmitoylphosphatidyl choline monolayers at the air-water interface. Although high molecular weight polystyrene-b-poly(ethylene oxide) (PS-PEO) diblock copolymers are kinetically prevented from forming adsorbed brushes on solid surf aces, they did manage to adopt a more extended or brushy conformation at the fluid interfaces examined here. For both PS-PEO and PEO homopol ymer, the ability of the adsorbing polymer to drive the Liquid expande d-to-liquid condensed monolayer phase transition facilitated monolayer penetration. The significance of this excluded area sink effect in th e monolayer penetration mechanism depended on the polymer architecture . PS-PEO was a more effective monolayer penetrator than PEO homopolyme r owing to its ability to increase the PEO block extension when penetr ating denser monolayers. Thus, both polymer architecture and excluded area effects determine the effectiveness of monolayer penetration.