Molecular diffusion in porous media by PGSE ESR

Area of Science:

• Materials Science
• Physical Chemistry
• Biophysics

Background:

• Diffusion in porous media is crucial across chemistry, biology, and materials science.
• Pulsed-gradient spin-echo Nuclear Magnetic Resonance (PGSE NMR) is standard for characterizing diffusion in larger porous structures (≥2-3 µm).
• Electron Spin Resonance (ESR) offers higher sensitivity and faster timescales (ns-µs) suitable for smaller features but has faced technical limitations for porous media research.

Purpose of the Study:

• To demonstrate the first application of PGSE ESR for characterizing molecular diffusion in porous media.
• To overcome technical constraints hindering PGSE ESR adaptation for porous media research.
• To enable the study of diffusion in systems with features down to the nanometer scale.

Main Methods:

• Utilized Pulsed-gradient spin-echo Electron Spin Resonance (PGSE ESR).
• Employed a novel ESR resonator, efficient gradient coils, and fast gradient current drivers.
• Investigated molecular restricted diffusion in liquid solutions within a model porous system of sub-micron glass spheres.

Main Results:

• Successfully adapted PGSE ESR for porous media research, demonstrating its capability for the first time.
• Characterized molecular restricted diffusion in a model porous system.
• Showcased the potential of PGSE ESR to probe diffusion in features as small as 10 nm.

Conclusions:

• PGSE ESR is a viable and powerful technique for studying diffusion in sub-micron and nanometric porous media.
• This advancement opens new avenues for research in fields relying on understanding nanoscale transport phenomena.
• Future applications can extend to diverse areas involving dynamical processes in finely structured materials.