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

A simple, reliable method to measure mutual diffusion coefficients of paramagnetic species in aqueous gel media using one-dimensional nuclea r 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 recover y imaging sequence employed nulls the image intensity from points in t he gel with a specified T1 value, which permits the position of any ch osen marker concentration to be followed as a function of time. The ex perimental 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 yie lds, after simple manipulation, the diffusion coefficient. The null po int is well resolved with a characteristic signal variation in the vic inity of the null point. Diffusion coefficients of both organic (4-ami no-TEMPO) and inorganic (copper sulfate) paramagnetic tracers in 10% p olyacrylamide, 1 % agarose, and silica gel media are reported.