Recent developments and applications of NSE in soft matter

Bilayer undulation dynamics in unilamellar phospholipid vesicles: effect of temperature, cholesterol and trehalose

We report a combined dynamic light scattering (DLS) and neutron spin-echo (NSE) study on the local bilayer undulation dynamics of phospholipid vesicles composed of 1,2-dimyristoyl-glycero-3-phosphatidylcholine (DMPC) under the influence of temperature and the additives cholesterol and trehalose. The additives affect vesicle size and self-diffusion. Mechanical properties of the membrane and corresponding bilayer undulations are tuned by changing lipid headgroup or acyl chain properties through temperature or composition. On the local length scale, changes at the lipid headgroup influence the bilayer bending rigidity κ less than changes at the lipid acyl chain: We observe a bilayer softening around the main phase transition temperature Tm of the single lipid system, and stiffening when more cholesterol is added, in concordance with literature. Surprisingly, no effect on the mechanical properties of the vesicles is observed upon the addition of trehalose.

Perfluorooctanoic acid rigidifies a model lipid membrane

We report a combined dynamic light scattering and neutron spin-echo (NSE) study on vesicles composed of the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine under the influence of varying amounts of perfluorooctanoic acid. We study local lipid bilayer undulations using NSE on time scales up to 200 ns. Similar to the effect evoked by cholesterol, we attribute the observed lipid bilayer stiffening to a condensing effect of the perfluorinated compound on the membrane.

A theoretical study of rotational and translational diffusion dynamics of molecules with a six-fold point symmetry adsorbed on a hexagonal lattice by neutron scattering

A complete analytical model for the rotational and translational diffusion of molecules with a six-fold point symmetry on a hexagonal lattice is presented. It can be applied, in particular, to the diffusion of benzene molecules adsorbed flat on the basal plane of graphite in the case of incoherent scattering. Under the weak hindered approximation, the classical mechanics framework and making use of the van Hove formalism of correlation functions, the intermediate scattering function and its Fourier transform, the scattering law, are both obtained. They can be expressed as sums of exponential decays or Lorentzian functions, respectively, containing the contribution of each of the dynamical processes taking place. In the case of benzene lying flat on the substrate we expect translational diffusion, continuous rotations of isolated molecules and hindered rotations of molecules within clusters. Each particular diffusive mechanism can be recognized owing to its particular signature in the dependence of the quasi-elastic broadening on the momentum transfer.