Effects of temperature and pressure on phase transitions in a ternary microemulsion system

Temperature variation experiments of small angle neutron scattering ~SANS! and neutron spin echo ~NSE! were carried out in order to compare effects of temperature and pressure on a structural formation in a ternary microemulsion system composed of AOT ~Aerosol-OT; dioctyl sulfosuccinate sodium salt!, D2O, and n-decane. From SANS measurements, a phase transition from one-phase dense water-in-oil droplet to two-phase coexistence with a lamellar and a disordered structure was observed with increasing temperature, similar to the case of pressure variation. Another phase transition was observed at a higher temperature above the lamellar phase, although such a subsequent phase transition has not been observed at higher pressure. The characteristic features of structural phase transitions by temperature and by pressure were compared by introducing a reduced temperature and pressure. The dynamical property observed from the NSE measurement was different between the high-temperature phase and the high-pressure phase. These results indicate that the mechanism of the phase transition induced by temperature is different from that by pressure. © 2001 American Institute of Physics. @DOI: 10.1063/1.1415459#