Revealing Transition States during the Hydration of Clay Minerals

Abstract

A molecular-scale understanding of the transition between hydration states in clay minerals remains a challenging problem because of the very fast stepwise swelling process observed from X-ray diffraction (XRD) experiments. XRD profile modeling assumes the coexistence of multiple hydration states in a clay sample to fit the experimental XRD pattern obtained under humid conditions. While XRD profile modeling provides a macroscopic understanding of the heterogeneous hydration structure of clay minerals, a microscopic model of the transition between hydration states is still missing. Here, for the first time, we use molecular dynamics simulation to investigate the transition states between a dry interlayer, one-layer hydrate, and two-layer hydrate. We find that the hydrogen bonds that form across the interlayer at the clay particle edge make an important contribution to the energy barrier to interlayer hydration, especially for initial hydration.

Large-Scale Molecular Dynamics Simulation of the Dehydration of a Suspension of Smectite Clay Nanoparticles

“…This evidence that energetic barriers to swelling or dehydration are relatively weak beyond the 2-layer hydrate is consistent with MD simulation predictions of the free energy of swelling of a pair of Na-smectite nanoparticles in bulk liquid water. 104 The results presented above validate various experimental hypotheses based on calorimetric, X-ray diffraction, and gravimetric water sorption experiments regarding the ordering of hydration and dehydration and the coexistence of different hydration environments in smectite films. 42,43,96,105−109 Specifically, our results show that smectite dehydration proceeds through the following sequence of partially overlapping steps:…”

Ion exchange selectivity in clay is controlled by nanoscale chemical–mechanical coupling

“…This behavior contrasts with ion diffusion-limited exchange in anhydrous phyllosilicates (11), which increases appreciably with temperature through the Arrhenius behavior of the diffusion coefficient (12). Interlayer water diffusion has a strong temperature dependence (13), while species exchange, including water, between bulk solution and the interlayer is essentially barrierless (14,15), indicating that neither process limits collapse.…”

Engineered Barrier System Research Activities at LBNL (FY2020 Progress Report)

“…We used the Weighted Histogram Analysis Method (WHAM) code (Grossfield) to extract the PMF profile from the umbrella sampling results. Ho et al (2019) showed that the ClayFF parameter set does not predict the dry to onewater layer (0W -1W) hydration process well. The authors of the study modified ClayFF to capture the dry to hydrated state transition.…”