NMR Studies of Gel-Emulsions; Diffusometry and Applications of Novel Field Gradient Techniques

Abstract: The aim of these studies has been to investigate what information that can be obtained on gel-emulsions with nuclear magnetic resonance, NMR, as the investigating tool. The gel-emulsions are important in many technical applications such as in food products, in cosmetic and pharmaceutical formulations, and in emulsion explosives, just to name a few applications. We have worked with the NMR diffusometry technique as developed by Stejskal, Tanner and Callaghan, and have loaded the gel-emulsion water phase with simple molecules acting as model drugs, as well as ordinary drugs such as lidocaine to clarify the usefulness of this technique. In porous materials the NMR diffusometry technique measures the mean square displacement, which gives information on structure and obstruction effects. This technique can also measure the emulsion break down process. To measure the diffusion on very short time scales, as in small emulsion droplets, we have used a novel technique with modulated field gradient spin echo pulse trains. We have also applied the chemical shift imaging technique of molecular transport in gel-emulsions. With this technique we can monitor the spatial distribution of solutes as a function of time. In the interpretation of data from the application of these techniques one often uses the short gradient pulse limit approximation, but the quality of the information is a matter of some uncertainty. We have provided some insight on this problem. The NMR diffusometry technique measures diffusion in a time-window from a few 100 µs up to several seconds, and the root mean square displacement in the µm range, and have many advantages as; it is rapid, does not require any isotopic labelling or addition of disturbing probes, only small amounts of sample is needed, and it is a non-destructive method (the same sample can be repeatedly studied).