Size dependence, stability, and the transition to buckling in model reverse bilayers

Molecular dynamics simulations of a model bilayer made of surfactant dimers in a Lennard-Jones solvent are reported for three sizes of the systems up to an area of 100sigma x 100sigma and for a large interval of the specific areas: from hole formation under tension deep into the floppy state of a buckling compressed bilayer. The transition to the floppy state appears quite abrupt and discontinuous; in the floppy state the lateral tension is negative and scales with size while vanishing from below. The structure factor was also determined for all three sizes and all areas; for most part the apparent tension is larger than the lateral tension whereas the apparent rigidity constant--always positive--is low in the floppy state and increasing in the tensioned state. Both do not scale visibly with size. The replacement of the 1q(2) capillary-wave divergence by another pole is accounted for and explained.