Measurement of self-diffusion coefficients of water in smectite by stimulated echo 1H nuclear magnetic resonance imaging

1H nuclear magnetic resonance (NMR) imaging was performed for the measurement of self-diffusion coefficients of water molecules (1H2O) in smectite. We measured two smectite samples (saponite and montmorillonite) with 96.6 wt.% of water at 23.8°C. A stimulated echo imaging sequence with magnetic field gradient pulses for the diffusion measurement was applied to the samples at a static magnetic field of 2.35 T. Eight NMR images were obtained with systematically changing the strength of field gradient pulses. The statistics of 225 diffusion data for each sample showed that the average diffusion coefficient was 2.06×10−9 m2/s for saponite and 1.52×10−9 m2/s for montmorillonite. The standard deviation was 0.02×10−9 m2/s for saponite and 0.05×10−9 m2/s for montmorillonite. The measurement time for the eight NMR images was 2.8 h, which is much shorter than that for conventional methods. Therefore, NMR imaging is suitable for the quick measurement of water diffusion in clay.