  Ever since the raft model for biomembranes has been proposed, the traditional
view of biomembranes based on the fluid-mosaic model has been altered. In the
raft model, dynamical heterogeneities in multi-component lipid bilayers play an
essential role. Focusing on the lateral phase separation of biomembranes and
vesicles, we review some of the most relevant research conducted over the last
decade. We mainly refer to those experimental works that are based on physical
chemistry approach, and to theoretical explanations given in terms of soft
matter physics. In the first part, we describe the phase behavior and the
conformation of multi-component lipid bilayers. After formulating the
hydrodynamics of fluid membranes in presence of the surrounding solvent, we
discuss the domain growth-law and decay rate of concentration fluctuations.
Finally, we review several attempts to describe membrane rafts as
two-dimensional microemulsion.
