NMR on emulsions: characterisation of liquid dispersed systems

Abstract

Pulsed field gradient NMR (PFG-NMR) is an important method for the characterisation of emulsions. Apart from its application in quality control and process development, especially high-field NMR methods can be applied to investigate emulsions properties on the molecular level. Meanwhile, complex emulsion structures such as double emulsions have been developed and require analytical tools especially for the determination of droplet size distributions. This contribution provides an overview on the possibilities and methods of PFG-NMR referring to measurement, data processing and interpretation of droplet size distributions. Comparison of techniques and measurements on double emulsions are presented.

Microfluidic preparation and self diffusion PFG-NMR analysis of monodisperse water-in-oil-in-water double emulsions

“…The main drawback of the analysis of NMR data of emulsions is that it normally involves assuming a certain characteristic shape for the droplet size distribution, such as a log-normal distribution [9]. PFG-NMR has also been applied to double emulsions [11][12][13] and while the models used are quite sophisticated, in terms of their ability to account for the possible presence of water transport within the double emulsion, they still assume a certain shape for the size distribution of the inner water droplets.…”

Interpretation of NMR diffusometry data regarding droplet size distributions in micro- and nanoemulsions

“…This predominantly is, however, a question of software implementation rather than a question of measurement and restrictions on principle. An emulsion known to show a bimodal DSD was analysed 11 . Figure 2 shows the logarithmic signal decay log (S/S 0 ) over q 2 = g 2 · g 2 · d 2 of this emulsion as a function of diffusion time, with the usual monomodal fit (Figure 2a), and a two component fit (Figure 2b), according to Murday-Cotts with a monoand a bimodal lognormal distribution.…”

“…Bimodal emulsions were produced and measured as described in ref. 11. O/W emulsions with small droplet size below 1 µm were produced using 10%-vol squalene oil (≥98% Sigma-Aldrich), bi-distilled water, phospholipid E80 contributed by Lipoid GmbH as emulsifier from egg source containing 80% phosphatidylcholine, dispersed with ultrasonication using a Branson 450 sonotrode.…”

Effect of oil globule size on water exchange mechanism in water-in-oil-in-water emulsions

“…1. Hereby, P v is usually modelled by a lognormal volume-weighted particle size distribution 2,6,10 , I 0 is the echo intensity in the absence of a magnetic field and q is a function of the gyromagnetic ratio g (2.675 × 10 8 s -1 T -1 ), the gradient duration d and the gradient strength G according to…”

“…1a). The apparent water volume fractions p¢ 1,2 and apparent diffusion coefficients of the inner and outer water compartments D¢ 1,2 are functions 10,12 of their real values (p 1,2 and D 1,2 ) and the mean residence time (t 1,2 ) of water in the inner and outer water pool. Hereby, D 1 is related to the inner compartmental size distribution P v and p 1 equals EV.…”