Collective Dynamics of Lipid Membranes studied by Inelastic Neutron Scattering

TL;DR

This study investigates the collective short wavelength dynamics of deuterated DMPC lipid bilayers using inelastic neutron scattering, revealing phase coexistence effects and confirming the presence of an optical mode predicted by simulations.

Contribution

It provides new dispersion relations for lipid bilayers in gel and fluid phases, clarifies phase coexistence effects, and confirms the optical mode predicted by molecular dynamics simulations.

Findings

Deeper minimum in dispersion relation in gel phase.

Identification of an additional optical mode.

Temperature-dependent phase coexistence evidence.

Abstract

We have studied the collective short wavelength dynamics in deuterated DMPC bilayers by inelastic neutron scattering. The corresponding dispersion relation $\hbar\omega$(Q) is presented for the gel and fluid phase of this model system. The temperature dependence of the inelastic excitations indicates a phase coexistence between the two phases over a broad range and leads to a different assignment of excitations than that reported in a preceding inelastic x-ray scattering study [Phys. Rev. Lett. {\bf 86}, 740 (2001)]. As a consequence, we find that the minimum in the dispersion relation is actually deeper in the gel than in the fluid phase. Finally, we can clearly identify an additional non-dispersive (optical) mode predicted by Molecular Dynamics (MD) simulations [Phys. Rev. Lett. {\bf 87}, 238101 (2001)].