SMALL-ANGLE NEUTRON-SCATTERING FROM DIFFUSE INTERFACES .1. MONOLAYERS AND BILAYERS IN THE WATER OCTANE C12E5 SYSTEM

We have investigated the small-angle neutron scattering (SANS) of ternary microemulsions and a binary L3 phase. Of particular interest is the local structure of monolayers at the water-oil interface in microemulsions and of bilayers in the isotropic anomalous L3 phase of the binary water-nonionic surfactant system. In both cases the scattering is characteristic of a locally flat structure with a diffuse interface which arises from the penetration of solvent molecules. We interpret the data in terms of a Gaussian scattering length density profile which varies smoothly across the mono- and bilayers. From the scattering curves we obtain the width of the layers and the effective areas occupied by the surfactant molecules. Furthermore, we conclude that for the case of bilayers the hydrophobic tails of the surfactant molecules in the opposing monolayers interdigitate.