ENTROPY-DRIVEN TENSION IN VESICLE MEMBRANES AND UNBINDING OF ADHERENT VESICLES

In recent years, it has become apparent that condensed-fluid membranes behave similar to linear-flexible polymers. Thermal motions act to randomize surface conformations; thus, constraints posed by closed capsule volumes or binding to stiff substrates lead to entropy-driven steric forces. With micromechanical methods, entropy-driven tension (and thereby curvature elasticity) in vesicle membranes and properties of vesicle-vesicle "unbinding" in the weak adhesion regime have been measured. Although thermal fluctuations only become visible when bilayer tensions fall below 10(-3) dyn/cm, entropy effects significantly "soften" surface expansion and adhesion properties at levels of tension and binding energy that are orders of magnitude higher. Thus, a self-consistent field approximation has been developed to capture the essential features of the continuous unbinding transition and to provide a useful method to predict the renormalization of underlying long-range interaction.