Phase inversion in emulsions studied by low field NMR

Abstract

Phase inversion phenomenon is studied using two novel low field NMR-based methods. The first method monitors the variation of the apparent spin-spin relaxation time (T2*) of the emulsions. It is based on the difference of the spin-spin relaxation time of water molecules inside a water droplet and within an aqueous bulk phase. The second method uses a diffusion measurement to distinguish between the water signal from droplets and the bulk. The relative distribution of water in droplets and in bulk can be measured. Moreover, droplet size distribution of water can be determined based on this method. Both methods were tested on the phase inversion of a model emulsion. A semi-batch process was used to perform the emulsification in situ. The information obtained through these methods is correlated to optical microscopy and conductivity measurements. When the phase inversion from w/o to o/w is induced by adding a hydrophilic surfactant to the nonionic Span® 80 the inversion seems to pass a double emulsion state before reaching the o/w state. This is an important observation to a mechanical understanding of the phase inversion.