X-ray scattering from liquid-liquid interfaces

Liquid-liquid interfaces play an important role in many chemical and biological systems in addition to being interesting model systems to study the statistical physics of interfaces and membranes. Water-oil interfaces are a model for the interaction of water with a hydrophobic molecular environment, important for protein folding and the formation of structures in complex fluids. Biological membranes exist at aqueous-aqueous interfaces and provide a dynamic platform for important cell processes. Recent advances in X-ray scattering measurements of liquid-liquid interfaces allow for the study of ordering and fluctuations on the molecular length scale. Several fundamental issues can be addressed, including (a) ordering of solvents (bulk liquids), surfactants, and electrolytes at liquid-liquid interfaces, and the influence of the solvents on surfactant ordering, and (b) the existence of monolayer domains at these interfaces, the issue of domain equilibrium (creation and annihilation of domains), and phase transitions in these domain phases. Studies of water-oil interfaces that address the first of these issues will be presented.