Decoupling between the Temperature-Dependent Structural Relaxation and Shear Viscosity of Concentrated Lithium Electrolyte

Relationship between Viscosity and Acyl Tail Dynamics in Lipid Bilayers

Membrane viscosity is a fundamental property that controls molecular transport and structural rearrangements in lipid membranes. Given its importance in many cell processes, various experimental and computational methods have been developed to measure the membrane viscosity, yet the estimated values depend highly on the method and vary by orders of magnitude. Here we investigate the molecular origins of membrane viscosity by measuring the nanoscale dynamics of the lipid acyl tails using x-ray and neutron spectroscopy techniques. The results show that the membrane viscosity can be estimated from the structural relaxation times of the lipid tails.

Collective Mesoscale Dynamics of Liquid 1-Dodecanol Studied by Neutron Spin-Echo Spectroscopy with Isotopic Substitution and Molecular Dynamics Simulation

The collective dynamics of liquid 1-dodecanol was investigated at a length scale matching the mesoscale structure arising from the segregation of hydrophilic and hydrophobic domains. To this end, neutron spin-echo experiments were performed on a series of partially deuterated samples and the relevant collective dynamics of the hydroxyl groups with respect to the alkyl chains was extracted from the linear combination of the intermediate scattering functions of these samples. The resulting collective dynamics is slower than the single particle dynamics as determined by the measurement on the nondeuterated sample. The experimental results are in excellent agreement with molecular dynamics simulation, which allows further insight into the mechanism of the molecular motions. The results indicate that two factors are responsible for the slower collective dynamics. The first one is the slower dynamics of the hydroxyl group, with respect to the alkyl chains, owing to hydrogen bonding, and the second one is the presence of mesoscale structuring.