Theory on Formation of the Ripple Phase in Bilayer Membranes

Abstract

To discuss the phase transition from the L_α or L_β phase to the periodic ripple (P_β) phase, we propose a model free energy, which is a functional of two kinds of fields. One denotes the displacement of the polar head groups of lipid molecules and the other the order parameter describing the configuration of hydrocarbon chains. The free energy is noted to include no intrinsic lengths to generate the periodic pattern spontaneously. The ripple phase can be found to occur intermediately between two flat phases due to large fluctuations of the order parameter. The temperature dependence of the period and a qualitative phase diagram are also given.