Increasing water solubility with decreasing droplet size limits the use of water NMR diffusometry in submicron W/O-emulsion droplet size analysis

Mathieu Balcaen; Lorenz De Neve; Lien Vermeir; Timothee Courtin; Koen Dewettinck; Davy Sinnaeve; Paul Van der Meeren

doi:10.1016/j.jcis.2017.12.049

Increasing water solubility with decreasing droplet size limits the use of water NMR diffusometry in submicron W/O-emulsion droplet size analysis

J Colloid Interface Sci. 2018 Mar 15:514:364-375. doi: 10.1016/j.jcis.2017.12.049. Epub 2017 Dec 19.

Authors

Mathieu Balcaen¹, Lorenz De Neve², Lien Vermeir³, Timothee Courtin⁴, Koen Dewettinck⁵, Davy Sinnaeve⁶, Paul Van der Meeren⁷

Affiliations

¹ Particle and Interfacial Technology Group, Department Applied Analytical and Physical Chemistry, Ghent University, Coupure Links 653, B-9000 Gent, Belgium. Electronic address: Mathieu.Balcaen@UGent.be.
² Particle and Interfacial Technology Group, Department Applied Analytical and Physical Chemistry, Ghent University, Coupure Links 653, B-9000 Gent, Belgium. Electronic address: Lorenz.DeNeve@UGent.be.
³ Particle and Interfacial Technology Group, Department Applied Analytical and Physical Chemistry, Ghent University, Coupure Links 653, B-9000 Gent, Belgium. Electronic address: Lien.Vermeir@UGent.be.
⁴ NMR and Structure Analysis, Department Organic and Macromolecular Chemistry, Ghent University, Campus Sterre S4, Krijgslaan 281, B-9000 Gent, Belgium. Electronic address: Timothee.Courtin@UGent.be.
⁵ Laboratory of Food Technology and Engineering, Department Food Safety and Food Quality, Ghent University, Coupure Links 653, B-9000 Gent, Belgium. Electronic address: Koen.Dewettinck@UGent.be.
⁶ NMR and Structure Analysis, Department Organic and Macromolecular Chemistry, Ghent University, Campus Sterre S4, Krijgslaan 281, B-9000 Gent, Belgium. Electronic address: Davy.Sinnaeve@UGent.be.
⁷ Particle and Interfacial Technology Group, Department Applied Analytical and Physical Chemistry, Ghent University, Coupure Links 653, B-9000 Gent, Belgium. Electronic address: Paul.VanderMeeren@UGent.be.

PMID: 29278792
DOI: 10.1016/j.jcis.2017.12.049

Abstract

Hypothesis: Water droplet size analysis of water-in-oil emulsions using water NMR diffusometry yielded values that were, from a certain shear intensity onwards, independent from the shear which was used during production. It was assumed that the constant water droplet size, obtained for samples prepared at higher shear, were only apparent droplet diameters. Considering the well-known increased solubility of the dispersed phase in the continuous phase at smaller droplet sizes, it is hypothesized that water diffusion in the oil phase was responsible for the fact that apparent rather than real sizes were obtained.

Experiments: W/O-emulsions, prepared with a varying shear intensity, were characterized using dynamic light scattering, light microscopy, T₂-relaxometry and PFG-NMR diffusometry. The latter measurements were conducted on both a low- and a high-resolution device and was based on either water (LR- and HR-NMR) or a water-soluble marker (HR-NMR).

Findings: Low-resolution PFG-NMR is incapable of accurately determining the droplet size of W/O-emulsions containing (sub)micron sized droplets. On the other hand, using high-resolution PFG-NMR diffusometry and the addition of an oil insoluble marker to the water phase, the application window could be extended towards smaller droplet sizes. Finally, it was shown that T₂-relaxometry was capable of detecting differences in droplet size between (sub)micron sized W/O-emulsions.

Keywords: High-resolution NMR; Low-resolution NMR; NMR diffusometry; PFG-NMR; T(2)-relaxometry; W/O-emulsion.