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

TL;DR

This study uses Molecular Dynamics simulations to explore how size affects the stability, transition, and buckling behavior of model reverse bilayers made of surfactant dimers, revealing a discontinuous transition to a floppy, buckling state with negative tension.

Contribution

It provides new insights into size-dependent stability, the nature of the transition to buckling, and the modification of capillary wave behavior in model bilayers.

Findings

Transition to floppy state is abrupt and discontinuous.

Lateral tension becomes negative in the buckling state.

Finite size influences apparent rigidity and surface tension.

Abstract

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 $100\sigma \times 100\sigma$ and for a large interval of specific areas:from hole formation under tension to the floppy state of a compressed bilayer. The transition to the floppy state appears quite abrupt and discontinuous; in the floppy state the lateral tension is negative. Lateral tension and the structure factor were determined for all 3 sizes and all areas; the apparent rigidity constant and apparent surface tension are determined and correlated with the specific area and the finite size. The replacement of the $1/q^2$ capillary-wave divergence by a pole is accounted for and explained. The derivative of the lateral tension jumps from a high value in a flat bilayer to a low value in the floppy, rough, and buckling state, where the tension itself is negative.