  We investigated the thermodynamic relaxation of giant unilamellar vesicles
(GUVs) which contained small vesicles within their interior. Quenching these
vesicles from their fluid phase (T>Tm) through the phase transition in the gel
state (T<Tm) drives the inner vesicles to be expelled from the larger mother
vesicle via the accompanying decrease in vesicle area by ~25% which forces a
pore to open in the mother vesicle. We demonstrate that the proceeding time
evolution of the resulting efflux follows the relaxation of the membrane area
and describe the entire relaxation process using an Onsager-like nonequilibrium
thermodynamics ansatz. As a consequence of the volume efflux internal vesicles
are expelled from the mother vesicle. Although complete sealing of the pore may
occur during the expulsion, the global relaxation dynamics is conserved.
Finally, comparison of these results to morphological relaxation phenomena
found in earlier studies reveals a universal relaxation behaviour in GUVs. When
quenched from the fluid to gel phase the typical time scale of relaxation shows
little variation and ranges between 4-5 seconds.
