title: Montmorillonite alignment induced by magnetic field: evidence based on the diffusion anisotropy of water molecules.
abstract: Diffusion coefficients of water in Na-montmorillonite (Na-mon) suspensions have been determined by pulsed-field gradient spin-echo (PGSE) NMR spectroscopy for three directions (x, y, and z), where x and y mean the directions perpendicular to the static magnetic field, and z the direction parallel to it. Diffusion anisotropy was observed in the suspensions with Na-mon weight fractions of 0.63, 1.82, and 3.32%; i.e., the diffusivity of water in the z direction is faster than that in the x or y direction. The largest diffusion anisotropy of water was observed at the Na-mon fraction of 3.32%. However, diffusion anisotropy disappeared in the suspensions with Na-mon fraction more than 5.02%. The fast diffusivity in the z direction was slightly enhanced in a stronger static magnetic field (14.1 T). These results indicate that the platelike Na-mon particles are aligned with their platelike faces parallel to the static magnetic field of NMR. We also measured diffusion coefficients of water for the z direction in the temperature range from 24 to 85 degrees C. The plot of diffusion coefficients of water against reciprocal temperature showed a refraction point at 65 degrees C. This phenomenon explicitly means that the alignment is gradually relaxed at higher temperatures.
authors.affiliation: Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 2-12-1-N1-34 O-okayama, Meguro-ku, Tokyo 152-8550, Japan. 04d19081@nr.titech.ac.jp
authors.forename: Takafumi
authors.initials: T
authors.lastname: Takahashi
authors.forename: Takahiro
authors.initials: T
authors.lastname: Ohkubo
authors.forename: Yasuhisa
authors.initials: Y
authors.lastname: Ikeda