Size determination of shear-induced multilamellar vesicles by rheo-NMR spectroscopy

A model for analyzing the deuterium ((2)H) NMR line shapes of D(2)O in surfactant multilamellar vesicle (MLV, "onion") systems is proposed. The assumption of the slow exchange of water molecules between adjacent layers implies that the (2)H NMR line shape is simply given by a sum of Lorentzians if the condition of motional narrowing is also fulfilled. Using the classical two-step model for the NMR relaxation in structured fluids allows us to calculate how the NMR line shape depends on the MLV size. The model is tested on two different MLV systems for which the NMR line shapes are measured as a function of the applied shear rate using rheo-NMR. The MLV sizes obtained are in good agreement with previous data from rheo-small-angle light scattering.