Pressure-induced topological phase transitions in membranes

Abstract

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 ${\mathit{L}}_{\mathrm{\ensuremath{\alpha}}}$) to nonlamellar inverse hexagonal (${\mathit{H}}_{\mathrm{II}}$) phase transition: (i) The size of the unit cell of the ${\mathit{H}}_{\mathrm{II}}$ phase increases with increasing pressure; (ii) the transition volume, \ensuremath{\Delta}${\mathit{V}}_{\mathit{b}\mathit{h}}$, decreases as the pressure is increased; and (iii) the intensity of scattered light increases as \ensuremath{\Delta}${\mathit{V}}_{\mathit{b}\mathit{h}}$ 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.