title: Homogeneous length scale of shear-induced multilamellar vesicles studied by diffusion NMR.
abstract: A recently developed protocol for pulsed gradient spin echo (PGSE) NMR is applied for the size determination of multilamellar vesicles (MLVs). By monitoring the self-diffusion behavior of water, the technique yields an estimate of the homogeneous length scale λ(hom), i.e. the maximum length scale at which there is local structural heterogeneity in a globally homogeneous material. A cross-over between local non-Gaussian to global Gaussian diffusion is observed by varying the experimentally defined length- and time-scales. Occasional observation of a weak Bragg peak in the PGSE signal attenuation curves permits the direct estimation of the MLV radius in favorable cases, thus yielding the constant of proportionality between λ(hom) and radius. The microstructural origin of the Bragg peak is verified through Brownian dynamics simulations and a theoretical analysis based on the center-of-mass diffusion propagator. λ(hom) is decreasing with increasing shear rate in agreement with theoretical expectations and results from (2)H NMR lineshape analysis.
authors.affiliation: Physical Chemistry, Center of Chemistry and Chemical Engineering, Lund University, Lund, Sweden. ingrid.aslund@fkem1.lu.se
authors.forename: Ingrid
authors.initials: I
authors.lastname: Aslund
authors.forename: Bruno
authors.initials: B
authors.lastname: Medronho
authors.forename: Daniel
authors.initials: D
authors.lastname: Topgaard
authors.forename: Olle
authors.initials: O
authors.lastname: Söderman
authors.forename: Claudia
authors.initials: C
authors.lastname: Schmidt
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D017666:Deuterium Oxide / Q000737:chemistry; D004058:Diffusion; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005026:Ethylene Glycols; D007202:Indicators and Reagents; D009227:Myristic Acids; D016011:Normal Distribution; D010316:Particle Size; D011336:Probability; D014867:Water / Q000737:chemistry
chemical_list: D005026:Ethylene Glycols; D007202:Indicators and Reagents; D009227:Myristic Acids; C542169:triethyleneglycol mono n-tetradecyl ether; D014867:Water; D017666:Deuterium Oxide