Adhesion-induced phase behavior of multicomponent membranes.

Biomimetic membranes that contain several molecular components are studied theoretically. In contact with another surface, such as a solid substrate or another membrane, some of these intramembrane components are attracted by the second surface and, thus, act as local stickers. The cooperative behavior of these systems is characterized by the interplay of (i) attractive binding energies, (ii) entropic contributions arising from the shape fluctuations of the membranes, and (iii) the entropy of mixing of the stickers. A systematic study of this interplay, which starts from the corresponding partition functions, reveals that there are several distinct mechanisms for adhesion-induced phase separation within the membranes. The first of these mechanisms is effective for flexible stickers with attractive cis interactions (within the same membrane) and arises from the renormalization of these interactions by the confined membrane fluctuations. A second, purely entropic mechanism is found for rigid stickers without attractive cis interactions and arises from a fluctuation-induced line tension. Finally, a third mechanism is present if the membrane contains both stickers and repellers, i.e., nonadhesive molecules that protrude from the membrane surface. This third mechanism is based on an effective potential barrier and becomes less effective if the shape fluctuations of the membrane become more pronounced.