Chemical Exchange in Unstable Emulsions

10 July 2024, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Nuclear magnetic resonance (NMR) is a routine method to study chemical exchange in reactions and molecular rearrangements in solution. However, when it comes to exchange of molecular species in liquid-liquid, two phase systems like in phase-transfer catalysis, the rate becomes a function of the surface between two phases, which means that only stable emulsions could be studied with standard equipment. Here, a setup is described with which unstable emulsions can be produced and studied in-situ by solution NMR spectroscopy. The setup provides sufficient torque and spinning frequency for generating an unstable two-phase water/oil mixture by rapid stirring. The pneumatically driven stirrer in the probe head was designed using ideas borrowed from magic angle sample spinning and a prototype was produced by 3D printing. As proof of concept, the dynamics in an aniline water emulsion over the phase boundary are studied by regular exchange spectroscopy NMR experiments.

Keywords

emulsion
NMR
3D printing

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