Mutual diffusion coefficients from NMR imaging

Abstract

• A method of studying diffusion of dissolved gases in liquids is presented. • The concentration field of the diffusing dissolved gas is monitored by NMR imaging. • Selective excitation enables quantitative measurements at low concentrations. • The mutual diffusion coefficient is determined from modeling the diffusion process. • The results agree well with reference data. In the present work, we use nuclear magnetic resonance imaging (MRI) to measure the mutual diffusion coefficient of methane in toluene at 298 K. The concentration field obtained upon dissolving gaseous methane in liquid toluene was monitored with two-dimensional MRI. To cope with the low concentration of methane, a chemical shift-selective pulse sequence was employed. The diffusion coefficient was determined from the resulting temporally and spatially resolved concentration data based on Fick’s second law. The resulting diffusion coefficient is in good agreement with reference data. We conclude that MRI experiments are well-suited for quantitative studies of mutual diffusion in liquid mixtures, also in challenging applications as the one studied here.