THEORY OF RIPPLE PHASES OF LIPID BILAYERS

A wide variety of lecithins exhibit a ''rippled'' intermediate phase-the P(beta') phase, in addition to the common L(alpha) and L(beta') phases of hydrated phospholipids. We describe a continuum Landau theory that can account for all of the observed phases, including the asymmetric ripple phase observed in chiral bilayers. We predict the possible existence of more than one distinct ripple phase made possible by the two-dimensional nature of the tilt order parameter. Furthermore, we show that chiral bilayers can exhibit phase transitions from symmetric to asymmetric ripples as, for example, the temperature is lowered.