Influence of Strong Confinement on the Structure and Dynamics of Liquids: a Study of the Clay/Water Interface Exploiting ²H NMR Spectroscopy and Spin-Locking Relaxometry

²H NMR spectroscopy, multiquanta relaxation, and spin-locking relaxometry are used to investigate the structural and dynamical properties of water molecules confined within dense sediments of synthetic fluorohectorite. As shown by the large residual splitting of the ²H NMR resonance line, water molecules confined in the interlamellar space of the clay are strongly oriented to contact with the fluorinated basal surface of the clay. Multiquanta relaxation measurements are used to identify and quantify the contributions of the quadrupolar and heteronuclear dipolar couplings by monitoring the NMR relaxation of the confined water molecules. Finally, the average residence time of the water molecules confined within the interlamellar space of the clay platelets is quantified by detailed analysis of ²H spin-locking relaxometry measurements. Thanks to the significant contributions of both quadripolar and heteronuclear dipolar relaxation mechanisms, ²H spin-locking relaxation measurements probe a broad dynamical range, by sampling angular velocities ranging between 10² and 3 × 10⁵ rad/s