SPINODAL FLUCTUATIONS OF BUDDING VESICLES

We report the first systematic observations of precursor effects in Sh ape transitions of phospholipid-bilayer vesicles in aqueous solution. Vesicles change abruptly, as temperature T is raised, from a prolate e llipsoidal shape to a ''budded'' shape consisting of two unequal Spher es connected by a narrow neck. On the low-T side of this transition, w e see large thermal shape fluctuations (quasicritical fluctuations) an d long relaxation times (quasicritical slowing down), which may be int erpreted, in the context of a phi(6) Landau theory, as the fluctuation s of a metastable state near its spinodal instability.