Dynamics of purely coherent tail-tail correlation in lipid bilayers

Lipid molecules are a basic building block for biological membranes. We have studied the collective membrane fluctuations by neutron spin echo and extracted bending and area compressibility moduli and membrane viscosity. The latter is one of two important parameters to characterize transport properties in membranes. The other important parameter, the molecular diffusion constant, was measured by us using neutron backscattering. Interestingly we observe that the temperature and molecular size dependence of the viscosity and diffusion constant are different, despite expecting them to both be dictated by the same frictional force. To understanding the differences we would like to measure the dynamics of the lipid tail-tail correlations as a main source of friction comes from the lipid packing. As the signal is weak and purely coherent, we need LET with polarized neutron option.