ar X iv : h ep - l at / 9 21 00 37 v 1 2 8 O ct 1 99 2 The Shape of Inflated Vesicles

The conformation and scaling properties of self-avoiding fluid vesicles with zero extrinsic bending rigidity subject to an internal pressure increment ∆p > 0 are studied using Monte Carlo methods and scaling arguments. With increasing pressure , there is a first-order transition from a collapsed branched polymer phase to an extended inflated phase. The scaling behavior of the radius of gyration, the asphericities, and several other quantities characterizing the average shape of a vesicle are studied in detail. In the inflated phase, continuously variable fractal shapes are found to be controlled by the scaling variable x = ∆pN 3ν/2 (or equivalently , y = < V >/N 3ν/2), where N is the number of monomers in the vesicle and V the enclosed volume. The scaling behavior in the inflated phase is described by a new exponent ν = 0.787 ± 0.02.