Self-Diffusion in Viscous Liquids: Pulse NMR Measurements

Abstract

It is shown that measurement of the nuclear magnetic resonance (NMR) relaxation times in viscous media can lead to a determination of the coefficient of self-diffusion, D. Of particular value is the measure of the spin-lattice relaxation time in the rotating frame T1p as a function of the applied rf field, H1. Depending upon the particular system under study, the method may be used to measure proton self-diffusion in the range 10−8 cm2/sec ≳ D ≳ 5 × 10−13 cm2/sec and is, therefore, applicable to the study of very viscous liquids. By employing nuclei other than protons, both limits of this range may be decreased by two orders of magnitude or more. In contrast to other NMR techniques which measure properties of slow molecular motion, this technique measures the coefficient of self-diffusion rather than the correlation time for diffusive motion. As an illustration of the method, measurement of the self-diffusion constant in glycerol has been extended to a value more than an order of magnitude smaller than that measured by conventional NMR techniques.