  Morphological transitions of phase separation associated with the asymmetry
of lipid composition were investigated using micrometer-sized vesicles of lipid
bilayers made from a lipid mixture. The complete macro-phase-separated
morphology undergoes a transition to a micro-phase-separation-like morphology
via a lorate morphology as a metastable state. The transition leads to the
emergence of monodisperse nanosized domains through repeated domain scission
events. Moreover, we have numerically confirmed the transitions using the
time-dependent Ginzburg-Landau model describing phase separation and the
bending elastic membrane, which is quantitatively consistent with experimental
results by fixing one free parameter. Our findings suggest that the local
spontaneous curvature due to the asymmetric composition plays an essential role
in the thermodynamic stabilization of micro-phase separation in lipid bilayers.
