Restricted self-diffusion of water in a highly concentrated W/O emulsion studied using modulated gradient spin-echo NMR

Restricted diffusion of water in a highly concentrated w/o emulsion was studied using pulsed field gradient spin echo techniques. The standard two-pulse version of this technique, suitable for analysis in the time domain, fails to investigate the short time-scale for diffusion inside a single emulsion droplet with radius 0.7 mum. With a pulse-train technique, originally introduced by Callaghan and Stepisnik, shorter time-scales are accessible. The latter approach is analyzed in the frequency domain and yields frequency dependent diffusion coefficients. Predictions for the outcome of the experiment were calculated in the time domain using the Gaussian phase distribution and the pore hopping formalism expressions for the echo attenuation. The results of these calculations were transformed to the frequency domain via a numerical inverse integral transform in order to compare with the experimental results. (C) 2002 Elsevier Science (USA).