Concentration Profiles in Creaming Oil-in-Water Emulsion Layers Determined with Stray Field Magnetic Resonance Imaging

Abstract

We report the first use of stray field magnetic resonance imaging in the determination of concentration profiles in layers (with submillimeter thickness) of coarse oil-in-water emulsions that are undergoing creaming. We compare our results for emulsions having various oil contents 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, however, the predictions of the model deviate substantially from the observed profiles. Whereas the model assumes that the concentration of oil in 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 explaining our findings, we consider the effects of polydispersity and the presence of gum xanthan in the continuous phase and also the possibility of gradual compaction of oil droplets in the cream layer (a phenomenon not considered in the model).

Long-term stability of sodium caseinate-stabilized nanoemulsions

“…From the CI data it is apparent that the full extent of creaming takes about a week to form, thereafter compaction of cream layer begins which stopped when no more oil droplets and proteins can be packed in the top cream layer. Similar behavior of compaction/compression of cream layer was observed in emulsions with excess unadsorbed polymers in the continuous phase (Fillery-Travis et al 1993;Newling et al 1997). It was proposed that the droplets in the cream layer underwent compression/compaction under the influence of gravity by gradually re-arranging with time leaving the serum layer squeezed out (Newling et al 1997).…”

“…Similar behavior of compaction/compression of cream layer was observed in emulsions with excess unadsorbed polymers in the continuous phase (Fillery-Travis et al 1993;Newling et al 1997). It was proposed that the droplets in the cream layer underwent compression/compaction under the influence of gravity by gradually re-arranging with time leaving the serum layer squeezed out (Newling et al 1997). The weak attractive force among the droplets in the cream later also allowed them to re-arrange under the influence of gravity (McClements 2007).…”

Flocculation of protein-stabilized oil-in-water emulsions

“…In practice, the presence (and extent) of flocculation is commonly inferred from emulsion creaming behaviour [7], either qualitatively from simple visual observations, or more quantitatively using a non-invasive technique such as turbidity scanning [25], ultrasound velocity scanning [26][27][28] or magnetic resonance imaging [29][30][31]. Away from the dilute Stokesian limit, creaming slows down as a consequence of hydrodynamic interactions between droplets.…”

Wide-gap Couette flows of dense emulsions: Local concentration measurements, and comparison between macroscopic and local constitutive law measurements through magnetic resonance imaging

“…Actually, A third way also used to study the creaming of an emulsion [38], consists in preparing a water-oil emulsion based on deuterium oxide instead of normal water. Because proton NMR is only sensitive to 1H nuclei, NMR or MRI measurements then bring exclusive information on the oil phase.…”