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 L_α) to nonlamellar inverse hexagonal (HII) phase transition: (i) The size of the unit cell of the HII phase increases with increasing pressure; (ii) the transition volume, {Δ}Vbh, decreases as the pressure is increased; and (iii) the intensity of scattered light increases as {Δ}Vbh 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.