Adhesion-induced lateral phase separation in membranes

Adhesion between membranes is studied using a phenomenological model, where the inter membrane distance is coupled to the concentration of sticker mol ecules on the membranes. The model applies to both adhesion of two flexible membranes and to adhesion of one flexible membrane onto a second membrane supported on a solid substrate. We mainly consider the case where the stick er molecules form bridges and adhere directly to both membranes. The calcul ated mean-field phase diagrams show an upward shift of the transition tempe rature indicating that the lateral phase separation in the membrane is enha nced due to the coupling effect. Hence the possibility of adhesion-induced lateral phase separation is predicted. For a particular choice of the param eters, the model exhibits a tricritical behavior. We also discuss the non-m onotonous shape of the inter-membrane distance occurring when the lateral p hase separation takes place. The inter-membrane distance relaxes to the bul k values with two symmetric overshoots. Adhesion mediated by other types of stickers is also considered.