Pressure-induced structural phase transition of dense droplet microemulsions studied by small-angle x-ray scattering

A small-angle x-ray scattering (SAXS) study of dense water-in-oil droplet m icroemulsions composed of water, decane, and AOT [sodium bis(2-ethylhexyl) sulfosuccinate] was performed in order to clarify phase behavior with appli ed pressure and the corresponding structural phase transitions. SAXS spectr a were collected for pressures between ambient pressure (0.1 MPa) and 80 MP a and droplet volume fraction, phi, from 0.40 to 0.70. With increasing phi, the mean radius of droplets decreased slightly and polydispersity increase d. With increasing pressure, the droplet structure transformed to a two-pha se system with coexistence of lamellar and droplet structures, independent of the droplet volume fraction. These results suggest that, with increasing pressure, the increasing inter-droplet attractive force controls the press ure variation of the structure. (C) 2001 American Institute of Physics.