NEUTRON REFLECTIVITY AT LIQUID INTERFACES

Examples of the potential of neutron reflectivity techniques are presented with studies of thin layers at the air-water and oil-water interfaces. In the case of air-water interfaces, we have studied mixed polymer (polydimethyl-siloxane)-surfactant layers. Selective deuteration allowed us to show that the mixed film is a superposition of two layers, and to determine their degree of interpenetration. In the case of oil-water interfaces, we have used a surfactant system of low interfacial tension. The neutron reflectivity is then sensitive to both the surface roughness and the surfactant layer thickness. In each case, correlations with independent measurements using ellipsometry (light reflectivity) are discussed.