Abstract
An important and often discussed question in emulsion science is the structure of (multiple) emulsions because of the direct correlation of structure and emulsion properties. The well known W1/O/W2 type of double emulsions consists of a quasi continuous water phase (W2), in which an emulsion, consisting of oil- (O) and inner water phase (W1), is dispersed. As these systems are often opaque and dilution additionally influences the system’s equilibrium states, NMR is exploited for its use to give insight into the geometrical structure as well as into the composition.Pulsed Field Gradient NMR (PFG-NMR) is known for determination of droplet size distributions. Signals of the different phases, for example oil and water, can be discriminated either by chemical shift, relaxation or diffusion. Regarding multiple emulsions, molecular dynamics interferes, and often the phases cannot be considered as being independent. Molecular exchange can be observed, which is confirmed independently by PFG-NMR, NMR-relaxometry and Confocal Laser Scanning Microscopy (CLSM).Apart from size distribution, also the composition, that is the concentration of the dispersed phases, is of interest, especially in the context of process development and storage stability. In the case of single emulsions, it can be determined by NMR spectroscopy, also by the recently re-investigated low-field NMR spectroscopy. Concerning multiple emulsions, diffusion or relaxation offers the additional differentiation of chemically similar phases.
Published Version
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