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.
Highlights
Quasi-Elastic Neutron Scattering (QENS) experiments are performed [12,28] to probe the diffusive motions of the confined water molecules and their orientational dependence regarding the clay surface
The results of this study showed that the time-evolution of the concentration gradient of interlayer Ca2+ was the main driving force interpreting exchange rates measured at all aqueous reservoir salinity investigated, while limitation at the solid/liquid interface, due to diffusion in the aqueous reservoir, can acts as a limiting factor to interpret exchange rates measured at low salinity conditions
This review focuses on dynamical properties of the water molecules and neutralizing counterions confined within clay particles
Summary
Ca2+ -saturated montmorillonite only exhibits crystalline swelling (see Figure 2) because inter-ionic correlation forces strongly reduce the swelling pressure of these charged interfaces [58,59] For that reason, these dynamical experiments require the use of purified clay samples to avoid coexistence of swollen and unswollen phases within heterogeneous samples. The purpose of that study is to exploit such a multi-scale analysis of the dynamical properties of ions and water molecules diffusing within clay sediments in order to develop a bottom-up approach of such complex interfacial dynamical processes In such analysis, we avoid to use fitted parameters derived from empirical models by performing realistic numerical modeling exploiting structural or dynamical properties, such as average residence time or local mobility, extracted from preliminary studies performed on a smaller scale
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