The Shape of Inflated Vesicles

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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=Δp N³ν/² (or equivalently, y = <V>/ N³ν/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.