Pressure-induced hexagonal phase in a ternary microemulsion system composed of a nonionic surfactant, water, and oil.
The pressure-induced phase transition in a microemulsion, consisting of pentaethylene glycol mono-n-dodecyl ether, water, and n-octane, was investigated by means of small-angle neutron scattering. A pressure-induced phase transition from a lamellar structure to a hexagonal structure was observed. The temperature-pressure phase boundary shows a positive slope with dTdP approximately 0.09 KMPa. The structure unit of the high-pressure hexagonal phase was an oil-in-water cylinder with the membrane thickness of 15.5 A, identical to the low-temperature hexagonal phase. Pressurizing was found to have the same effect by decreasing temperature. This behavior was satisfactorily explained with the pressure dependence of the spontaneous curvature of surfactant membranes. That is, the volume change of surfactant tails plays a dominant role in the structure change of the microemulsion with applying pressure.
Nagao
Michihiro
M
Institute for Solid State Physics, The University of Tokyo, 106-1 Shirakata, Tokai 319-1106, Japan. mnagao@issp.u-tokyo.ac.jp
Seto
Hideki
H
Ihara
Daisuke
D
Shibayama
Mitsuhiro
M
Takeda
Takayoshi
T