THERMALLY INDUCED BUDDING OF PHOSPHOLIPID-VESICLES - A DISCONTINUOUS PROCESS

The process of thermally induced budding is studied for DMPC vesicles. With increasing temperature a pear shaped vesicle changes discontinuo usly into a pair of spherical vesicles connected by a narrow neck. In the course of the cooling process a thermal hysteresis in a stepwise m anner is observed. The size of the daughter vesicle diminishes by repe ated widening and narrowing of the neck until it finally remains open and the vesicle attains the pear shape again. These experimental findi ngs are difficult to rationalize within the bare bilayer couple model of phospholipid vesicles. To model the discontinuous behavior in the h eating process the expansion of the elastic energy of the bilayer up t o the third order in the area difference of the two monolayers is empi rically introduced. The van der Waals forces between mother and daught er vesicles are shown to be responsible for the repeated widening and narrowing of the neck in the cooling process.