Kinetics and Dynamics of Pressure-induced Phase Transition in Amphiphilic Systems

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Amphiphilic molecules such as surfactants and lipids conform various semi-microscopic scale structures with oil and water. A ternary microemulsion composed of AOT (Aerosol-OT), water and decane has a water-in-oil droplet structure at ambient temperature and pressure, and separates into two phases with increasing either temperature or pressure. In order to clarify the mechanisms of these transitions, neutron spin echo experiments have been carried out. The results could be interpreted that the microscopic origins of pressure-induced and temperature-induced transitions are different.We also investigated the system composed of non-ionic surfactant C_<12>E_5, D_2O, and octane by mean of small-angle neutron scattering. The effects of temperature and pressure were opposite unlike the case of AOT. A pressure-induced hexagonal phase was shown for the first time.A structural change of an aqueous solution of DPPC with adding ethanol and varying temperature and pressure were investigated by means of small-angle neutron scattering and small-angle X-ray scattering. A swollen gel phase, in which the lamellar repeat distance is slightly larger than the known phase, was identified at moderate temperature and pressure for the first time.