Water and Ion Dynamics in Confined Media: A Multi-Scale Study of the Clay/Water Interface

Abstract

This review details a large panel of experimental studies (Inelastic Neutron Scattering, Quasi-Elastic Neutron Scattering, Nuclear Magnetic Resonance relaxometry, Pulsed-Gradient Spin-Echo attenuation, Nuclear Magnetic Resonance Imaging, macroscopic diffusion experiments) used recently to probe, over a large distribution of characteristic times (from pico-second up to days), the dynamical properties of water molecules and neutralizing cations diffusing within clay/water interfacial media. The purpose of this review is not to describe these various experimental methods in detail but, rather, to investigate the specific dynamical information obtained by each of them concerning these clay/water interfacial media. In addition, this review also illustrates the various numerical methods (quantum Density Functional Theory, classical Molecular Dynamics, Brownian Dynamics, macroscopic differential equations) used to interpret these various experimental data by analyzing the corresponding multi-scale dynamical processes. The purpose of this multi-scale study is to perform a bottom-up analysis of the dynamical properties of confined ions and water molecules, by using complementary experimental and numerical studies covering a broad range of diffusion times (between pico-seconds up to days) and corresponding diffusion lengths (between Angstroms and centimeters). In the context of such a bottom-up approach, the numerical modeling of the dynamical properties of the diffusing probes is based on experimental or numerical investigations performed on a smaller scale, thus avoiding the use of empirical or fitted parameters.

Inelastic Neutron Scattering of Methane Hydrate Confined in Hydrophilic and Hydrophobic Porous Model Carbons

“…Evidently, the vibrational modes of water molecules, encompassing both translational and librational zones, undergo alterations induced by the adsorption potential of the pore wall, with these effects being more pronounced in the confined environment. In agreement with previous studies indicating the existence of nonfreezable water in confinement, the spectrum for sample HOMC-10%H 2 O in Figure a is, undoubtedly, the INS spectral fingerprint of the nonfreezable water at the carbon pore wall, also called the interface water′ by some authors. The dynamic properties of low-density amorphous ice and high-density amorphous differ considerably from the nonfreezable water presented here …”

Role of Cationic Organization on Water Dynamics in Saponite Clays

“…This swelling regime, referred to as crystalline swelling, provides an elegant way to control water confinement in the structure, as, depending on humidity, confinement accounts for either one or two statistical layers of water molecules corresponding to the so-called monolayer and bilayer states. Numerous experimental and simulation studies have investigated the structure and dynamics of water in this swelling regime. − Convincing results were obtained by focusing on synthetic clay minerals such as saponite and hectorite that are less heterogeneous than natural samples, a significant advantage from both experimental (less hydration heterogeneities) and simulation (more realistic models) points of view. − In all the studies dealing with the structure of confined water, it appeared crucial to collate experimental results with simulation ones to test extensively the suitability of the various force fields used in the simulations. Furthermore, as far as dynamics are considered, considering motion anisotropy by working on oriented samples proved to be particularly fruitful.…”

Role of cationic organisation on water dynamics in saponite clays

“…A vast body of literature shows that the structure and dynamics of water are significantly a↵ected by confinement and numerous reviews on this topic have been published (e.g. [1][2][3][4] ).…”

“…Numerous experimental and simulation studies have investigated the structure and dynamics of water in this swelling regime. 1,[10][11][12][13] Convincing results were obtained by focusing on synthetic clay minerals such as saponite and hectorite that are less heterogeneous than natural samples, a significant advantage on both experimental (less hydration heterogeneities) and simula-tion (more realistic models) points of view. [14][15][16][17][18][19] In all the studies dealing with the structure of confined water, it appeared crucial to collate experiments results with simulation ones to test extensively the suitability of the various force fields used in the simulations.…”