STRUCTURE OF MICROEMULSIONS STUDIED BY NMR

We discuss the application of NMR to investigate microemulsion structu re. There are mainly two important NMR experiments; relaxation and sel f-diffusion studies. Of these two, self-diffusion studies have been fo und to be particularly informative in that it is the only technique wh ich can demonstrate bicontinuity in equilibrium microemulsions. Self-d iffusion coefficients of water, oil and surfactant can be obtained in the same experiment. For droplet microemulsions, the self-diffusion co efficients of the surfactant and enclosed solvent correspond to the dr oplet diffusion coefficient, which in turn depends on its hydrodynamic radius and on interactions. The self-diffusion coefficient of the con tinuous solvent is slightly reduced due to obstruction effects, which depends on the droplet shape. For bicontinuous structures, the solvent diffusion on both sides of the surfactant film as well as the surfact ant diffusion within the film is monitored. In particular the diffusio n of the two solvents depends on how the surfactant film curves. NMR r elaxation is found to be useful in the studies of droplet microemulsio ns. It is very sensitive to the droplet size while at the same time be ing insensitive to interactions. The latter allows for reliable size i nformation even at higher droplet concentrations.