X-ray scattering from liquid-liquid interfaces

We present our recent progress in using synchrotron x-ray surface scatterin g to study several different aspects of ordering at liquid-liquid interface s. (1) The interfacial width at the water-alkane interface has been measure d for a series of different chain length alkanes. The variation of interfac ial width with the carbon number can be described by combining the capillar y wave prediction for the width with a contribution from the intrinsic stru cture. (2) Under appropriate conditions, a surfactant monolayer forms at th e interface between water and a hexane solution of a fluorinated surfactant . Reflectivity measurements that probe the electron density profile normal to the interface provide information on the surfactant ordering. This monol ayer undergoes a solid to gas transition as a function of temperature. Diff use scattering near the transition reveals the presence of islands. (3) Equ ilibrium interfaces between two aqueous phases containing polyethylene glyc ol and potassium phosphate salts can be studied. We present studies of conf ormal capillary wave fluctuations between two interfaces of a thin him of t his biphase system. We also demonstrate that ferritin can be trapped and st udied at this aqueous-aqueous interface.