DIFFUSION IN AQUEOUS GELS - MUTUAL DIFFUSION-COEFFICIENTS MEASURED BY ONE-DIMENSIONAL NUCLEAR-MAGNETIC-RESONANCE IMAGING

A simple, reliable method to measure mutual diffusion coefficients of paramagnetic species in aqueous gel media using one-dimensional nuclear magnetic resonance imaging is reported. The concentration variation with position of a paramagnetic marker yields a corresponding spatial variation in T1 relaxation times within the gel. The inversion recovery imaging sequence employed nulls the image intensity from points in the gel with a specified T1 value, which permits the position of any chosen marker concentration to be followed as a function of time. The experimental method minimizes the effect of T2 relaxation in the gel. A plot of the null position as a function of the square root of time yields, after simple manipulation, the diffusion coefficient. The null point is well resolved with a characteristic signal variation in the vicinity of the null point. Diffusion coefficients of both organic (4-amino-TEMPO) and inorganic (copper sulfate) paramagnetic tracers in 10% polyacrylamide, 1 % agarose, and silica gel media are reported.