The Conformation of Fluid Vesicles

Abstract

The conformations and scaling properties of self-avoiding fluid vesicles with (i) an extrinsic bending rigidity κ and (ii) subject to an internal pressure increment Δp ≥ 0 are studied using Monte Carlo methods and scaling arguments. For κ = 0 and Δp = 0, our results are consistent with branched polymer behavior at large length scales. There is a smooth crossover from the crumpled to an extended state with increasing κ, with a peak in the specific heat when the persistence length reaches the system size. The scale-dependent effective bending rigidity is a decreasing function of system size for all bare rigidities so that for Δp = 0, fluid vesicles are always crumpled at sufficiently long length scales. For finite Δp, and κ = 0, there is a first-order transition from a low pressure, branched polymer phase to a high pressure, inflated phase. The behavior in the inflated phase is analyzed using a generalization of de Gennes’ “blob” picture, and it is shown that the mean square radius of gyration within the blobs scales with a new, independent exponent ν = 0.787 ± 0.020, where ~ N b v , and N b is the number of monomers in a blob.