Emulsion stability probed by low field NMR

Emulsions are dispersed multiphase systems, where droplets of one liquid are distributed in a secondary immiscible liquid, with typical radii of the order of tens of microns. Most emulsions are thermodynamically unstable and will separate into their constituent phases given sufficient time. As they have a significant industrial importance (food, agriculture, conventional energy) the properties of an emulsion need to be well understood. The droplet size distribution is the main characteristic of such systems, which will give insight to other relevant functionalities (e.g., viscosity, stability, and turbidity). Hence an ability to experimentally determine this size distribution is essential [1, 2].

Application of NMR techniques for emulsion characterization has provided many unique and valuable insights. Here we present recent developments using bench-top low field NMR applied for sizing of water-in-crude oil emulsions. Using different bench-top NMR equipment and a combination of NMR relaxometry, diffusion and spectroscopy we will report on the following recent developments:
(i) Automation of emulsion droplet sizing and its use to probe various emulsion breaking strategies.
(ii) The impact of flow on emulsion droplet sizing and the extraction of quantitative fundamental droplet dispersion data to characterise enhanced emulsion droplet collisions under flow.
(iii) The use of emulsion droplet sizing to quantify the microstructural changes that occur following the transition of such w/o droplets into cyclopentane hydrate particles.
(iv) The impact of CO2 at low pressures on the emulsion stability, probing different proposed mechanisms for emulsion breaking via this route.



References:
1. M.L. Johns, NMR studies of emulsions, Current Opinion in Colloid and Interface Science 14 (2009) 178-183
2. M.L. Johns and L. F. Gladden, Sizing emulsion droplets under flowing conditions using Magnetic Resonance
methods, JMR 154 (2002) 142-145