CONCENTRATION PROFILES IN CREAMING OIL-IN-WATER EMULSION LAYERS DETERMINED WITH STRAY FIELD MAGNETIC-RESONANCE-IMAGING

We report the first use of stray field magnetic resonance imaging in t he determination of concentration profiles in layers (with submillimet er thickness) of coarse oil-in-water emulsions that are undergoing cre aming. We compare our results for emulsions having various oil content s to the predictions of a numerical model. In emulsions having low oil content(12 and 23 vol %), we find that the model adequately predicts the profile shape and time-dependent change in the lower region of the emulsion. In the cream layer at the top of each of the samples, howev er, the predictions of the model deviate substantially from the observ ed profiles. Whereas the model assumes that the concentration of oil i n the cream layer is constant as the layer increases in thickness, we observe that there is a concentration gradient in the cream layer and that the concentration of oil in the layer increases with time. In exp laining our findings, we consider the effects of polydispersity and th e presence of gum xanthan in the continuous phase and also the possibi lity of gradual compaction of oil droplets in the cream layer (a pheno menon not considered in the model).