Structural and Dynamical Properties of Water Molecules Confined within Clay Sediments Probed by Deuterium NMR Spectroscopy, Multiquanta Relaxometry, and Two-Time Stimulated Echo Attenuation

The structure and multiscale dynamics of water molecules confined within dense clay sediments are investigated by deuterium (²H) NMR spectroscopy, relaxometry, and two-time correlation measurements. The splitting of the ²H NMR resonance line quantifies the specific ordering of water molecules confined within the clay interlamellar space. The angular distribution of clay aggregates within the sediment is evaluated from variation of the transverse ²H NMR relaxation rates as a function of orientation of the clay film within the static magnetic field. The average residence time of the water molecules within clay aggregates is determined by multiquanta spin-locking relaxometry. Finally, water exchange between different aggregates is extracted from the attenuation of ²H two-time stimulated echo. These simultaneous NMR dynamical investigations cover a broad range of characteristic times (between 10 μs and 100 ms) appropriate to investigate the multiscale dynamical behavior of water molecules confined within heterogeneous porous networks

Anisotropic Features of Water and Ion Dynamics in Synthetic Na- and Ca-Smectites with Tetrahedral Layer Charge. A Combined Quasi-elastic Neutron-Scattering and Molecular Dynamics Simulations Study

The temperature- and orientation-dependent dynamics of water molecules and sodium or calcium cations confined in the interlayer space of synthetic saponite with contrasting layer charge were analyzed through the combination of three-axis neutron spectroscopy and molecular dynamics (MD) simulation. We first show that it is possible to generate MD simulated quasi-elastic spectra that are equivalent to the experimental ones. As a consequence, the analysis of spectra in terms of Lorentzian decomposition can be advantageously replaced by a direct exploitation of MD results. We show that such strategy provides classical information on the influence of clay crystal chemistry on water and ion dynamical features as well as reliable additional information on (i) dynamics associated to different types of water molecules (bonded or not to interlayer cations) and (ii) interlayer cation dynamics. The same strategy applied to data obtained at higher temperature provided further confirmation of the validity of the atomic potentials used in simulations while allowing the extraction of activation energies for water and cations translational motions

Long-Time Dynamics of Confined Water Molecules Probed by ²H NMR Multiquanta Relaxometry: An Application to Dense Clay Sediments

The structural and dynamical properties of water molecules confined within dense clay sediment are investigated by ²H NMR spectroscopy and multiquanta relaxometry. The relative contribution of both quadrupolar and paramagnetic NMR relaxation mechanisms is evaluated by carefully analyzing the variation of ²H multiquanta NMR relaxation rates as a function of the orientation of the clay sediment within the static magnetic field. The same analysis is successfully applied to ²H multiquanta NMR spin-locking relaxation measurements, significantly increasing the probed dynamical range. That procedure leads to an accurate determination of the average residence time of the water molecule confined within the interlamellar space of the clay lamellae

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