New insights for accurate chemically specific measurements of slow diffusing molecules

Area of Science:

• Materials Science
• Physical Chemistry
• Analytical Chemistry

Background:

• Molecular transport is crucial for materials used in batteries, membranes, and fuel cells.
• Nuclear magnetic resonance (NMR) is a powerful tool for probing molecular motion and material properties.
• Robust diffusion measurements are essential for accurately characterizing molecular transport.

Purpose of the Study:

• To identify and address artifacts in pulsed-field-gradient (PFG) NMR diffusion measurements.
• To develop strategies for obtaining reliable diffusion data, particularly for challenging samples.
• To improve the accuracy of molecular transport characterization in various materials.

Main Methods:

• Utilized standard PFG NMR calibration protocols with deuterium oxide (2H2O).
• Investigated diffusion of hydrogen-1 (1H)-glycerol and identified experimental artifacts.
• Performed mathematical analysis of NMR signals considering PFG transients and nuclear properties.

Main Results:

• Observed significant artifacts in 1H-glycerol diffusion measurements not seen with 2H2O.
• Demonstrated that artifacts are more pronounced for nuclei with high gyromagnetic ratios (γ).
• Showed that reducing sample dimension along the gradient direction effectively minimizes non-ideal NMR signal behaviors.

Conclusions:

• Artifacts in PFG NMR diffusion measurements can be significant and are dependent on nuclear properties.
• A quantitative strategy is provided for minimizing errors in diffusion measurements, especially for slow-diffusing species.
• The findings enhance the reliability of NMR for studying molecular transport in diverse materials.