title: Effect of molecular exchange on water droplet size analysis as determined by diffusion NMR: The W/O/W double emulsion case.
abstract: OBJECTIVE
  The accuracy of the inner water droplet size determination of W/O/W emulsions upon water diffusion measurement by diffusion NMR was evaluated. The resulting droplet size data were compared to the results acquired from the diffusion measurement of a highly water soluble marker compound with low permeability in the oil layer of a W/O/W emulsion, which provide a closer representation of the actual droplet size. Differences in droplet size data obtained from water and the marker were ascribed to extra-droplet water diffusion.
  
  
  METHODS
  The diffusion data of the tetramethylammonium cation marker were measured using high-resolution pulsed field gradient NMR, whereas the water diffusion was measured using both low-resolution and high-resolution NMR. Different data analysis procedures were evaluated to correct for the effect of extra-droplet water diffusion on the accuracy of water droplet size analysis.
  
  
  RESULTS
  Using the water diffusion data, the use of a low measurement temperature and diffusion delay Δ could reduce the droplet size overestimation resulting from extra-droplet water diffusion, but this undesirable effect was inevitable. Detailed analysis of the diffusion data revealed that the extra-droplet diffusion effect was due to an exchange between the inner water phase and the oil phase, rather than by exchange between the internal and external aqueous phase. A promising data analysis procedure for retrieving reliable size data consisted of the application of Einstein's diffusion law to the experimentally determined diffusion distances. This simple procedure allowed determining the inner water droplet size of W/O/W emulsions upon measurement of water diffusion by low-resolution NMR at or even above room temperature.
authors.affiliation: Particle and Interfacial Technology Group, Department of Applied Analytical and Physical Chemistry, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium. Electronic address: Lien.Vermeir@UGent.be.
authors.forename: Lien
authors.initials: L
authors.lastname: Vermeir
authors.affiliation: Particle and Interfacial Technology Group, Department of Applied Analytical and Physical Chemistry, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium; NMR and Structure Analysis Unit, Department of Organic Chemistry, Faculty of Sciences, Ghent University, Krijgslaan 281 S4, B-9000 Ghent, Belgium. Electronic address: P.Sabatino@yahoo.it.
authors.forename: Paolo
authors.initials: P
authors.lastname: Sabatino
authors.affiliation: Particle and Interfacial Technology Group, Department of Applied Analytical and Physical Chemistry, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium. Electronic address: Mathieu.Balcaen@UGent.be.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Balcaen
authors.affiliation: Particle and Interfacial Technology Group, Department of Applied Analytical and Physical Chemistry, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium. Electronic address: Arnout.Declerck@UGent.be.
authors.forename: Arnout
authors.initials: A
authors.lastname: Declerck
authors.affiliation: Laboratory of Food Technology and Engineering, Department of Food Safety and Food Quality, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium. Electronic address: Koen.Dewettinck@UGent.be.
authors.forename: Koen
authors.initials: K
authors.lastname: Dewettinck
authors.affiliation: NMR and Structure Analysis Unit, Department of Organic Chemistry, Faculty of Sciences, Ghent University, Krijgslaan 281 S4, B-9000 Ghent, Belgium. Electronic address: Jose.Martins@UGent.be.
authors.forename: José C
authors.initials: JC
authors.lastname: Martins
authors.affiliation: Pro(2)NMR, MVM and IBG-4, Karlsruher Institut für Technologie, Adenauerring 20b, DE-76131 Karlsruhe, Germany. Electronic address: Gisela.Guthausen@kit.edu.
authors.forename: Gisela
authors.initials: G
authors.lastname: Guthausen
authors.affiliation: Particle and Interfacial Technology Group, Department of Applied Analytical and Physical Chemistry, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium. Electronic address: Paul.VanderMeeren@UGent.be.
authors.forename: Paul
authors.initials: P
authors.lastname: Van der Meeren
mesh_terms: D004058:Diffusion; D004655:Emulsions / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D010316:Particle Size; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D013499:Surface Properties; D014867:Water / Q000032:analysis*
chemical_list: D004655:Emulsions; D000644:Quaternary Ammonium Compounds; D014867:Water; C027917:tetramethylammonium
keywords: Diffusion NMR (Nuclear Magnetic Resonance); High-resolution NMR; Low-resolution NMR; Molecular exchange; Tetramethylammonium chloride; W/O/W emulsion (water-in-oil-in-water); Water droplet size analysis; Water exchange; pfg-NMR diffusometry (pulsed field gradient)