POLYMER SURFACTANT FILMS AT THE AIR-WATER-INTERFACE .2. A NEUTRON REFLECTIVITY STUDY

Mixed polymer-surfactant films at the air-water interface have been st udied using neutron reflectivity. When poly(dimethylsiloxane) is sprea d on the surface of a surfactant layer, the resultant mixed film is a superposition of two layers: one surfactant-rich and one polymer-rich. The composition and the degree of mixing of the layers depend on the nature of the surfactant. We find significant penetration of the polym er into a monolayer of single-chain nonionic surfactant, C10E6. For a double-chain anionic surfactant, AOT, no interpenetration of the two l ayers is detected. This difference is most probably due to the greater flexibility of the C10E5 Monolayer compared to that of AOT. The highe r degree of hydration of the nonionic surfactant layer could also play a role in the mixing behavior of the polymer and surfactant layers. T he molecular thickness of the polymer layer indicates a flat two-dimen sional conformation of the spread polymer. The results from this study together with those in part 1 our paper suggest that the wetting beha vior of the polymer is related to the degree of interpenetration of th e polymer and surfactant layers.