Dispersion relation of lipid membrane shape fluctuations by neutron spin-echo spectrometry

TL;DR

This study uses neutron spin-echo spectrometry to analyze mesoscopic shape fluctuations in lipid bilayers, revealing relaxation processes and phase transition effects on membrane mechanics.

Contribution

It provides the first detailed dispersion relation measurements of lipid membrane fluctuations across different phases using neutron spin-echo techniques.

Findings

Identified two relaxation processes at 10ns and 100ns.

Fitted dispersion relation to smectic hydrodynamic theory.

Observed mode softening near phase transition.

Abstract

We have studied the mesoscopic shape fluctuations in aligned multilamellar stacks of DMPC bilayers using the neutron spin-echo technique. The corresponding in plane dispersion relation $\tau^{-1}$(q$_{||}$) at different temperatures in the gel (ripple, P$_{\beta'}$) and the fluid (L$_{\alpha}$) phase of this model system has been determined. Two relaxation processes, one at about 10ns and a second, slower process at about 100ns can be quantified. The dispersion relation in the fluid phase is fitted to a smectic hydrodynamic theory, with a correction for finite q$_z$ resolution. We extract values for, the bilayer bending rigidity $\kappa$, the compressional modulus of the stacks $B$, and the effective sliding viscosity $\eta_3$. The softening of a mode which can be associated with the formation of the ripple structure is observed close to the main phase transition.