Pulsed field gradient magic angle spinning NMR self-diffusion measurements in liquids

Area of Science:

• Nuclear Magnetic Resonance (NMR) Spectroscopy
• Materials Science
• Physical Chemistry

Background:

• Combined pulsed field gradient (PFG) and magic angle spinning (MAS) NMR is increasingly used for molecular mobility analysis in heterogeneous materials.
• The influence of sample rotation-induced forces on self-diffusivity measurements in PFG MAS NMR remains underexplored.

Purpose of the Study:

• To investigate the impact of sample rotation on the reliability of self-diffusivity measurements using PFG MAS NMR.
• To establish conditions for accurate self-diffusion coefficient determination in liquids via PFG MAS NMR.

Main Methods:

• Calibration of gradient uniformity and absolute strength for a magic angle gradient coil.
• Investigation of magic angle spinning's effect on PFG MAS NMR diffusion measurements using 12 and 50 microL rotors.
• Analysis of self-diffusion coefficients in pure liquids.

Main Results:

• Accurate self-diffusion coefficients were determined for liquids using PFG MAS NMR under specific conditions.
• A 50 microL rotor yielded unreliable results, particularly for low-viscosity compounds.
• A 12 microL rotor enabled accurate determination of self-diffusion coefficients for both fast and slow-diffusing species.

Conclusions:

• PFG MAS NMR can reliably measure liquid self-diffusion coefficients when appropriate experimental parameters are employed.
• The choice of rotor volume significantly impacts the accuracy of diffusion measurements.
• This methodology enhances the reliability of MAS diffusion studies for homogeneous and heterogeneous media.