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

Rivecourt_water-desorption

This file corresponds to an image sequence of neutron transmission images of a fossil wood during drying. The wood comes from Rivecourt (Parisian Basin, Oise, Paleogene

Rivecourt_water-sorption

This file corresponds to a sequence of neutron transmission images recorded during humidification of a fossil wood sample coming from Rivecourt (Parisian Basin, France, paleogene

Angeac_water-desorption

This file corresponds to a sequence of neutron transmission images recorded on a fossil wood during drying. The wood comes from Angeac (Aquitanian basin, Cretaceous:Paleocene

Angeac_water-sorption

This file corresponds to a sequence of neutron transmission images recorded during humidification of a fossil wood sample coming from Angeac (Aquitanian Basin, France, cretaceous:paleocene

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