Determination of mean droplet sizes of water-in-oil emulsions using an Earth's field NMR instrument

The use of the Earth's magnetic field (EF) to conduct nuclear magnetic resonance (NMR) experiments has a long history with a growing list of applications (e.g. ground water detection, diffusion measurements of Antarctic sea ice). In this paper we explore whether EFNMR can be used to accurately and practically measure the mean droplet size ((a)) of water-in-oil emulsions (paraffin and crude oil). We use both pulsed field gradient (PFG) measurements of restricted self-diffusion and T-2 relaxometry, as appropriate. T-2 relaxometry allows the extension of droplet sizing ability below the limits set by the available magnetic field gradient strength of the EFNMR apparatus. A commercially available bench-top NMR spectrometer is used to verify the results obtained using the EFNMR instrument, with good agreement within experimental error, seen between the two instruments. These results open the potential for further investigation of the application of EFNMR for emulsion droplet sizing. (C) 2012 Elsevier Inc. All rights reserved.