Fluctuations in the flat and collapsed phases of polymerized membranes

Fluctuations in polymerized membranes are explored via extensive molecular dynamics simulations of simplified « tethered surface » models. The entropic rigidity associated with repulsive second-nearest-neighbor interactions leads to a flattening of « phantom surfaces ». An attractive interaction in the presence of distant self-avoidance leads to a collapsed membrane with fractal dimension three at sufficiently low temperatures. When the attractive interaction is turned off, the surface returns to the flat phase found in earlier simulations. A study of density profiles and hexatic internal order allows a simple physical interpretation of results for the structure function of oriented membranes