Molecular Dynamics Simulations of Nanoscale Friction on Illite Clay: Effects of Solvent Salt Ions and Electric Double Layer

TL;DR

This study uses molecular dynamics simulations to explore how different salt ions affect nanoscale friction on illite clay, revealing mechanisms that could inform greener stabilization methods for quick clay.

Contribution

It provides a detailed molecular-level understanding of how monovalent and divalent salts influence friction and electric double layer structure in clay, aiding development of eco-friendly stabilizers.

Findings

Divalent cations increase friction and sit higher on the surface.

Monovalent cations sit closer to the surface and cause less friction.

Electric double layer structure mediates the salt-induced friction changes.

Abstract

Quick clay is a highly sensitive soil that transforms rapidly from solid to liquid under minor stress, as a result of long-term salt leaching that drastically reduces shear strength. Stabilizing it is both costly and carbon-intensive, significantly impacting construction emissions in regions like Norway. Developing greener stabilization methods is challenging due to limited understanding of the weakening mechanisms and the specific roles of different salts. In this study, we use molecular dynamics (MD) simulations to investigate the sliding behavior of illite platelets, the key component in Norwegian quick clay, and how it is affected by the different ions in the solution surrounding the surface. We examine the impact of monovalent (NaCl, KCl, CsCl) and divalent (MgCl2 and CaCl2) salts on platelet-surface interactions, focusing on the friction enhancement brought by divalent salts and how the electric double layer (EDL) structure mediates frictional behavior. We find that divalent cations sit higher on top of the surface, and lead to an increase in friction, while monovalent cations sit closer to the surface. By providing a detailed analysis of these interactions, the study offers a novel framework for understanding the role of salts in clay mechanics and highlights opportunities to design environmentally friendly stabilizers as alternatives to traditional lime and cement.