GIANT VESICLES AT THE PROLATE-OBLATE TRANSITION - A MACROSCOPIC BISTABLE SYSTEM

Giant phospholipid vesicles are shown to exhibit thermally activated t ransitions between a prolate and an oblate shape on a time scale of se veral seconds. From the fluctuating contour of such a vesicle we extra ct ellipticity as an effective reaction coordinate whose temporal prob ability distribution is bimodal. We then reconstruct the effective pot ential from which we derive an activation energy of the order of k(B)T in agreement with theoretical calculations. The dynamics of this tran sition is well described within a Kramers model of overdamped diffusio n in a bistable potential. Thus, this system can serve as a model for macroscopic bistability.