Pressure-induced topological phase transitions in membranes

Some highly unusual features of a lipid-water liquid crystal are revealed by high pressure x-ray diffraction, light scattering and dilatometric studies of the lamellar (bilayer [ital L][sub [alpha]]) to nonlamellar inverse hexagonal ([ital H][sub II]) phase transition: (i) The size of the unit cell of the [ital H][sub II] phase increases with increasing pressure; (ii) the transition volume, [Delta][ital V][sub [ital b][ital h]], decreases as the pressure is increased; and (iii) the intensity of scattered light increases as [Delta][ital V][sub [ital b][ital h]] decreases. Data are presented which suggest that this increase is due to the formation of an intermediate cubic phase, consistent with theoretical suggestions of an underlying universal phase sequence.