Hydration-Driven Interfacial Behaviors of Nanoconfined Sodium Montmorillonite

Sodium montmorillonite (Na-MMT), frequently encountered in engineered and natural environments, exhibits pronounced swelling upon hydration─a response governed by hydration dynamics and interfacial mechanics at nanometer scales. In this study, we employ an all-atom (AA) molecular dynamics (MD) simulation framework, enhanced by GPU-accelerated hybrid Grand Canonical Monte Carlo (GCMC), to investigate how varying relative humidity conditions govern the adsorption behavior and interfacial responses of Na-MMT. By explicitly coupling water adsorption from an infinite reservoir to a constrained clay system with fixed interlayer spacing, this approach enables a quantitative analysis of hydration-driven structural transitions and local stress redistribution under increasing relative humidity (RH). At the nanoscale, these hydration-driven transformations give rise to pronounced changes in surface tension σ and disjoining pressure Π, both of which exhibit distinct dependence on RH. By quantitatively linking hydration-induced interfacial changes to relative humidity, we uncover how humidity modulates stress redistribution and ion mobility in nanoconfined Na-MMT. Specifically, we identify a hydration induced transition from discrete, surface-bound water clusters to a more continuous interfacial hydration network that facilitates cation delocalization and enhances stress homogeneity across the interlayer. The surface tension obtained from the hybrid GCMC/MD simulations exhibits thermodynamic consistency with that derived from integration of the Gibbs isotherm. These findings open new avenues for leveraging the GPU-accelerated hybrid GCMC/MD framework to explore interfacial energetics in non-swelling systems subjected to humidity variations.