Fluctuation of a bilayer composed by amphipathic molecules

We investigated the properties of bilayer fluctuations using molecular dynamics. We modeled the amphipathic molecules as a diatomic molecule, constructed a bilayer in the solvent, and observed the Fourier spectrum of its fluctuations. The results showed that $q^4$ behavior was dominant at the high temperature, whereas a crossover from $q^4$ to $q^2$ was observed at the low temperature. This behavior is complementary to the results for monolayer membranes, where $q^2$ behavior was dominant when the interfacial tension was high, whereas a crossover from $q^2$ to $q^4$ was observed when the interfacial tension was lowered~[S. Kikuchi and H. Watanabe, J. Chem. Phys., $\bm{158}$ 12 (2023)]. These results suggest that the restoring force is dominated by elasticity at high temperatures and by interfacial tension at low temperatures. We also observed radial distribution functions to investigate the structure of amphipathic molecules in bilayers. The structure of the amphipathic molecules depends on temperature in the direction horizontal to the interface, while it does not depend on temperature in the direction perpendicular to the interface. This result suggests that bilayers increase fluctuations while maintaining the membrane structure in high temperature.