Diffusion on a molecular scale as observed using PGSE NMR

Abstract

For half a century, pulsed-gradient Spin-Echo NMR based on the Stejskal-Tanner equation has been used to infer Fick's-Law diffusion coefficients of solutes in simple liquids and complex fluids. The decades since the original papers have seen vast advances in instrument technology and pulse sequence design, all leading to improved measurements of diffusion coefficients. However, just as the last half-century has brought major advances in instrument technology, so also it has also brought major advances in scientific understanding of diffusion on molecular distance and time scales. This article discusses implications of these advances in molecular hydrodynamics for the interpretation of PGSE NMR attenuation curves. The results here are particularly significant for studies on complex fluid systems that have relaxations on the time and distance scales that are observed in PGSE NMR experiments.