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Experimental characterization of emulsion formation and coalescence by nuclear magnetic resonance restricted diffusion techniques
Author(s) -
Lee H.Y.,
McCarthy M. J.,
Dungan S. R.
Publication year - 1998
Publication title -
journal of the american oil chemists' society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.512
H-Index - 117
eISSN - 1558-9331
pISSN - 0003-021X
DOI - 10.1007/s11746-998-0249-7
Subject(s) - emulsion , coalescence (physics) , pulmonary surfactant , chemistry , oil droplet , molecular diffusion , diffusion , isoelectric point , analytical chemistry (journal) , chemical physics , chemical engineering , chromatography , nuclear magnetic resonance , organic chemistry , thermodynamics , metric (unit) , biochemistry , physics , operations management , enzyme , astrobiology , engineering , economics
Nuclear magnetic resonance (NMR) is explored as a technique for noninvasively monitoring emulsion droplet formation and destabilization. The method makes use of the fact that the diffusion of oil molecules within oil‐in‐water emulsion droplets results in attenuation of a coherent magnetic signal that emanates from those molecules. If oil diffusion is limited by the size of the droplet, the shape of a plot of attenuation over time is directly affected by the droplet radius. We use this approach to determine noninvasively the effect of surfactant type, surfactant concentration, pH, and ionic strength on droplet sizes within a 40 wt% octane and water emulsion, stabilized by Tween 20 or β‐lactoglobulin (β‐Lg). We find that addition of the low‐molecular‐weight Tween 20 forms finer emulsion droplets than does addition of the protein, and that the Tween 20 emulsion is sensitive to surfactant concentration below a threshold “saturation” concentration. The droplet sizes in β‐Lg‐containing emulsions increase as pH increases above the isoelectric point and as ionic strength increases. The fact that the NMR technique does not mistake clusters of droplets for single large droplets makes the analysis of these effects unambiguous. We further extend the use of NMR diffusion techniques to monitor the effect of surfactant type, surfactant concentration, and convection on the rate of droplet coalescence. The ability of NMR methods to distinguish between large single droplets and droplet clusters makes it well‐suited to monitor coalescence processes independently from flocculation.