Application of PFG NMR in spectral resolution mode to study water-oil emulsions

UDK: 622.276.8:543.422.25
Key words: emulsion, nuclear magnetic resonance (NMR), diffusion, pulsed field gradient (PFG)
Authors: D.L. Melnikova, O.I. Gnezdilov, V.D. Skirda (Kazan Federal University, RF, Kazan)
The main purpose of current work is the detailed investigation of the opportunities of modern PFG NMR methods for studying the dynamic and structural properties of emulsions. As the example of emulsion for this study, the sample of direct emulsion “MC-90”, which contains 8, 90 and 2 % of oil, water and surfactant (SAS) respectively, has been created. The molecular composition of this mixture is similar to the composition of direct water-oil emulsion, which allows to use obtained results on real water-oil emulsions. To determine nuclear magnetic relaxation times 2D relaxometry methods have been used. It has been defined, that all molecular components have similar values of corresponding relaxation times (T1/T2~1). Thereby, all components satisfy the high-temperature approximation, i.e. have small correlation times of molecular motion. In particular, it has been found, that the equal diffusion coefficients for surfactant and water components - is the necessary and sufficient condition for existence of direct emulsion in the system. At the same time, by PFG NMR in spectral resolution mode it has been shown, that the feature of the investigated emulsion structure is a bimodal size distribution of dispersed in water oil-SAS formations. These results demonstrate the unique capabilities of PFG NMR for studies of complex disperse molecular structures, which include water-oil emulsions.
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