Chemical exchange in unstable emulsions.

Area of Science:

• Chemistry
• Spectroscopy
• Chemical Engineering

Background:

• Nuclear Magnetic Resonance (NMR) is a standard technique for studying chemical reactions in solution.
• Studying molecular exchange in unstable two-phase liquid-liquid systems, such as those in phase-transfer catalysis, is challenging due to rapid demixing.
• Standard NMR equipment cannot analyze rapidly demixing emulsions, limiting the study of interfacial phenomena.

Purpose of the Study:

• To develop and demonstrate a novel in-situ Nuclear Magnetic Resonance (NMR) setup capable of studying unstable emulsions in two-phase systems.
• To overcome the limitations of standard NMR equipment in analyzing systems that require continuous shear forces.
• To investigate the dynamics of molecular species across phase boundaries in rapidly stirred emulsions.

Main Methods:

• A custom-designed, pneumatically driven stirrer integrated into an NMR probe head was developed.
• The stirrer design was inspired by magic angle sample spinning principles and realized using 3D printing.
• The setup generates and maintains unstable water/oil emulsions with sufficient shear forces for in-situ NMR analysis.
• Exchange spectroscopy NMR experiments were performed on an aniline-water emulsion to validate the setup.

Main Results:

• The developed setup successfully generated and sustained unstable two-phase emulsions within the NMR probe.
• The system provided adequate torque and spinning frequency to maintain the emulsion during NMR measurements.
• In-situ NMR exchange spectroscopy allowed for the study of molecular dynamics across the phase boundary in the aniline-water emulsion.
• The feasibility of studying interfacial chemical exchange in unstable emulsions using NMR was demonstrated.

Conclusions:

• A novel 3D-printed, pneumatically driven stirring setup enables in-situ NMR studies of unstable emulsions.
• This technique expands the scope of NMR spectroscopy to include dynamic processes in challenging two-phase systems.
• The setup facilitates the investigation of interfacial phenomena and chemical exchange in systems relevant to phase-transfer catalysis and beyond.