Self-diffusion measurements by a mobile single-sided NMR sensor with improved magnetic field gradient

Area of Science:

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

Background:

• Accurate measurement of self-diffusion coefficients is crucial for understanding material properties.
• Traditional NMR methods can be time-consuming and require complex setups.
• Protonated systems present unique challenges for diffusion measurements.

Purpose of the Study:

• To develop a simple, fast, and sensitive method for measuring self-diffusion coefficients.
• To utilize a mobile single-sided NMR sensor with a uniform magnetic field gradient.
• To validate the method across various organic solvents, polymers, and biological tissues.

Main Methods:

• Employing a mobile single-sided NMR sensor with a specialized magnet geometry for a uniform magnetic field gradient.
• Utilizing Hahn and stimulated echo sequences for diffusion coefficient measurement.
• Implementing a Carr-Purcell-Meiboom-Gill pulse sequence to enhance sensitivity and shorten experimental time.
• Measuring diffusion curves in under one minute.

Main Results:

• Successfully measured self-diffusion coefficients (D) for organic solvents and poly(dimethylsiloxane) of varying molar masses.
• Observed concentration-dependent diffusion of n-hexane in natural rubber, aligning with theoretical predictions.
• Applied stimulated-echo sequences to determine diffusion coefficients as a function of evolution time in restricted diffusion systems.
• Measured water diffusion in sandstones and sheep Achilles tendon, demonstrating applicability to biological and porous media.
• Eliminated the need to account for relaxation during pulse sequences due to a strong static gradient.

Conclusions:

• The developed NMR method offers a rapid and sensitive approach for self-diffusion coefficient measurement.
• The technique is versatile, applicable to a wide range of materials including polymers, porous media, and biological tissues.
• The method provides insights into pore geometry and surface-to-volume ratios in restricted diffusion systems.
• The strong static gradient simplifies measurements by negating relaxation effects.