  As a model of soft confinement for polymers, we investigated equilibrium
shapes of a flexible vesicle that contains a phase-separating polymer solution.
To simulate such a system, we combined the phase field theory (PFT) for the
vesicle and the self-consistent field theory (SCFT) for the polymer solution.
We observed a transition from a symmetric prolate shape of the vesicle to an
asymmetric pear shape induced by the domain structure of the enclosed polymer
solution. Moreover, when a non-zero spontaneous curvature of the vesicle is
introduced, a re-entrant transition between the prolate and the dumbbell shapes
of the vesicle is observed. This re-entrant transition is explained by
considering the competition between the loss of conformational entropy and that
of translational entropy of polymer chains due to the confinement by the
deformable vesicle. This finding is in accordance with the recent experimental
result reported by Terasawa, et al.
