Fluctuations and phase behavior of fluid membrane vesicles

We consider the behavior of a dilute phase of bilayer surfactant vesicles. We show that the free energy of a single vesicle increases logarithmically with vesicle size, due to a previously unappreciated finite-size contribution to the fluctuation free energy, in contrast to previous studies, which assumed a logarithmic decrease of the free energy due to thermal softening of the bending rigidity. This result leads to qualitatively different predictions for the behavior of an equilibrium vesicle phase.