STIFFENING OF FLUID MEMBRANES AND ENTROPY LOSS OF MEMBRANE CLOSURE - 2 EFFECTS OF THERMAL UNDULATIONS

The problem of membrane softening by thermal undulations is revisited. In contrast to general belief, fluid membranes are predicted to be st iffened, not softened, by their undulations. Equal values of the effec tive bending rigidity are calculated from the interplay of local mean curvature modes (hats) on the basically flat membrane and from the cou pling of spherical harmonic modes with spherical curvature. In additio n, a conjecture is made on the entropy of membrane closure. It relies on a similarity of membrane closure to periodic boundary conditions.