Monitoring The Formation Of Oil-water Emulsions With Spatially Resolved NMR Spectroscopy Methods

Nuclear magnetic resonance(NMR)as a noninvasive technique which can provide abundant information of experimental samples,it has become one of the most widely-used methods for structure and composition analyses in many research fields.Emulsions as a kind of common dispersion system,have widely applications in many fields.In present,studies of emulsions are focused on preparation methods,droplet size distribution(DSD),micromorphology and stability.The knowledge of the mechanism of emulsion formation has great significance in understanding the stability of emulsions and phase separation progress.In this thesis,two spatially resolution NMR methods were applied to investigate the mechanism of emulsion formation,by which chemical shift and the spatial information can be obtained at the same time.On the basis of integrals from these 1H NMR spectra,the portrayed oil concentration profiles explicitly demonstrate the spatial and temporal variations of oil concentrations.The main results are as follows:First,the preparation,properties and application for emulsion were briefly reviewed.The current research progress of emulsions and application of NMR technology in emulsions were introduced.Several recently emerged spatially resolved spectroscopy techniques including basic principles,technical features and applications were summarized.Second,a rapid chemical shift imaging method was used to dynamically monitor the formation of oil-water emulsions and the process of the emulsified phase separating from the excess water and oil phase.With signals sampled from series of small voxels simultaneously,high-resolution one-dimensional(1D)1H NMR spectra for the inhomogeneous emulsion systems can be obtained from different spatial positions independently induced by susceptibility differences among components.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 exact length of the oil-water emulsion phase have been determined.In addition,effects of oil types and proportions of the emulsifier on the emulsification process have also been inspected.Experimental results indicate that 1D PHASICS provides a helpful and promising alternative to research on dynamic processes or chemical-reactions.Third,the localized magnetic resonance spectroscopy was applied in monitoring the phase separation process of emulsions.In this chapter,the MRS method was also used to observe the emulsification process of water and oil systems.Experimental results show that during the process of phase separation after the emulsion formation,concentration variations of water and oil with time and space can also be obtained.Compared with the 1D PHASICS method,MRS present better spectral quality with a higher signal to noise ratio.However,since MRS can not simultaneously stimulate all voxels within the target zone,it is not possible to accurately observe all concentration variations at different levels at the same time.