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 Δp>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=Δ${\mathit{pN}}^{3\nu /2\mathrm{}}$ (or, equivalently, y=〈V〉/${\mathit{N}}^{3\nu /2\mathrm{}}$), 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.