Collective Dynamics of Lipid Membranes studied by Inelastic Neutron Scattering

Abstract

We have studied the collective short wavelength dynamics in deuterated DMPC bilayers by inelastic neutron scattering. The corresponding dispersion relation $\hbarω$(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)].