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 DELTAp > 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 = DELTApN3nu/2 (or, equivalently, y = [V]/N3nu/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 nu=0.787+/-0.02.