Monitoring the formation of oil–water emulsions with a fast spatially resolved NMR spectroscopy method**Project supported by the Natural Science Foundation of Fujian Province, China (Grant Nos. 2016J01078 and 2017J05011), the Fundamental Research Funds for the Central Universities of China (Grant Nos. 20720160125 and 20720150018), and the National Natural Science Foundation of China (Grant No. 11705068).

Abstract

In the present study, a fast chemical shift imaging (CSI) method has been used to dynamically monitor the formation of oil–water emulsions and the phase separation process of the emulsion phase from the excessive water or oil phase on the molecular level. With signals sampled from series of small voxels simultaneously within a few seconds, high-resolution one-dimensional (1D) 1H nuclear magnetic resonance (NMR) spectra from different spatial positions for inhomogeneous emulsion systems induced by susceptibility differences among components can be obtained independently. On the basis of integrals from these 1H NMR spectra, profiles obtained explicitly demonstrate the spatial and temporal variations of oil concentrations. Furthermore, the phase separation time and the length of the oil–water emulsion phase are determined. In addition, effects of oil types and proportions of the emulsifier on the emulsification states are also inspected. Experimental results indicate that 1D PHASICS (Partial Homogeneity Assisted Inhomogeneity Correction Spectroscopy) provides a helpful and promising alternative to research on dynamic processes or chemical reactions.