Sequential Diffusion Spectra as a Tool for Studying Time-Dependent Translational Molecular Dynamics: A Cement...

Area of Science:

• Materials Science
• Physical Chemistry
• Chemical Engineering

Background:

• Translational molecular dynamics in porous materials are influenced by pore structure, affecting diffusion over different timescales.
• Longer timescales correlate with lower frequencies, while shorter timescales correspond to higher frequencies in molecular dynamics.

Purpose of the Study:

• To develop and apply a novel method for directly measuring diffusion at specific frequencies.
• To investigate the diffusion spectra and their evolution during white cement hydration.

Main Methods:

• Utilized Nuclear Magnetic Resonance (NMR) modulated gradient spin-echo (MGSE) pulse sequence for signal attenuation measurement.
• Calculated diffusion coefficients at specific frequencies derived from the inverse double inter-echo time.
• Analyzed diffusion spectra using a diffusion spectra model to extract time-dependent parameters.

Main Results:

• Successfully measured diffusion spectra, revealing the distribution of diffusion across a wide frequency range.
• Monitored the white cement hydration process through sequential acquisition of diffusion spectra.
• Obtained time-dependent changes in diffusion characteristics during hydration.

Conclusions:

• The novel NMR-MGSE method enables direct measurement of frequency-dependent diffusion in porous materials.
• This technique provides insights into the dynamic changes within materials like hydrating cement.
• The method is applicable to studying other systems exhibiting time-dependent structural evolution.