Nanoscale NMR velocimetry by means of slowly diffusing tracer particles

The resolution of NMR velocimetry is inherently limited by random displacements due to molecular self-diffusion, and has so far not extended below a few tens of microns. We report here an extension to the nanoscale domain, a result achieved by the use of slowly diffusing, NMR-visible core-shell latex particles. These particles comprise an oil core surrounded by a solid polymer shell, making spheres of diameter 370 nm. Using these particles in the annulus of a concentric cylinder Couette cell, we have measured flow-induced displacements down to a few hundreds of nanometers, allowing the observation of the solid-to-liquid transition of a glassy system. We envisage new possibilities for NMR velocimetry as an experimental tool for colloidal chemistry and physics.