Chemical shift imaging of molecular transport in colloidal systems: visualization and quantification of diffusion processes

Magnetic resonance imaging with chemical shift resolution is demonstrated to provide detailed information about molecular transport on the macroscopic scale in complex colloidal systems. The concentrations of species with distinct 1H resonance lines can be quantified from spatially resolved, high-resolution, 1H nuclear magnetic resonance spectra. The method is demonstrated by experiments on three systems with multiple simultaneous transport processes where the diffusion coefficients depend on position and/or on the concentration of other species: (1) release of poly(ethylene glycol) and imidazole from a hydrogel into an external reservoir of water, (2) migration of acetic acid and tetramethylammonium ions in a highly concentrated water-in-oil emulsion with initially non-uniform concentration of solutes, and (3) release of tetramethylammonium ions loaded into a hydrogel triggered by the diffusion of methyl green into the gel matrix.