Coexistence of lamellae and vesicles in multi-stacked fluid membranes with polymer lipids

A continuum model for multi-stacked fluid membranes with polymer lipids is proposed, and a Monte Carlo calculation is carried out to observe defect structures in multi-lamellar membranes. We find three different phases: (1) undulating lamellae; (2) vesicles; and (3) coexisting undulating lamellae and vesicles. The phase diagram is determined by the calculation, and the coexistence states are characterized by the proportion of vesicle area. There are two qualitatively different coexistence states. In one, the vesicle regions and lamellar regions are rather clearly separated, and in the other the vesicle regions are entangled with lamellae in a complex way.