  We propose a model describing liquid-solid phase coexistence in mixed lipid
membranes by including explicitly the occurrence of a rippled phase. For a
single component membrane, we employ a previous model in which the membrane
thickness is used as an order parameter. As function of temperature, this model
properly accounts for the phase behavior of the three possible membrane phases:
solid, liquid and the rippled phase. Our primary aim is to explore extensions
of this model to binary lipid mixtures by considering the composition
dependence of important model parameters. The obtained phase diagrams show
various liquid, solid and rippled phase coexistence regions, and are in
quantitative agreement with the experimental ones for some specific lipid
mixtures.
