CURVATURE INSTABILITY IN FLUID MEMBRANES WITH POLYMER LIPIDS SUBJECT TO TENSION

Shape transformations of a flat fluid membrane with polymer lipids sub ject to lateral tension are studied as an approximation far multimembr ane systems. Using Monte Carlo simulations, we find several characteri stic structures of membranes, such as thermal fluctuations, large loca lized deformations, and undulations due to a curvature instability. Th e effect of thermal fluctuations on the curvature instability is inves tigated, and the undulations are characterized by a single-mode approx imation for unstable modes. It is shown that thermal fluctuations, the curvature instability and vesiculation determine the parameter region in which an undulating membrane is observed. The phase diagram of und ulation obtained through simulations closely resembles that measured e xperimentally for ''biogels.'' This suggests that the undulation corre sponds to defects in multimembrane systems and that the curvature inst ability is the main cause of defect formation in ''biogels.''