Stability of Hydrated Clay Layers from Molecular Simulations

Clays adsorb water following discrete steps in which water is roughly structured in layers. The resulting discrete hydration states can be viewed as phases separated by unstable domains and the change of hydration state can be viewed as a phase transformation. Here, we identify stable basal spacings and the domains of (meta-) stability through the analysis of confining pressure isotherms obtained from molecular simulations performed in grand canonical ensemble. This ensemble mimics drained conditions. Through thermodynamic analysis, we can explain the coexistence of different hydration states at clay particle scale and provide kinetics arguments to the hysteresis observed with respect to traction and compression. The gained insights into the mechanical behavior of the elementary constituents of clays may lead to a better understanding of the behavior of clay-rich rocks and soils.