  We show that a metastable multilamellar vesicle (`onion'), in contact with
excess solvent, can spontaneously deplete solute molecules from its interior
through an unusual, entropy-driven mechanism. Fluctuation entropy is gained as
the uneven partition of solute molecules helps the onion relieve tension in its
lamellae. This mechanism accounts for recent experiments on the interaction
between uncharged phospholipid onions and dissolved sugars.
