Dynamics of Water Intrusion in Polyelectrolyte-Bound Kaolinite: An Insight into Durability Mechanisms via Atomistic Modeling.

ABSTRACT

This research addresses interaction mechanisms of water-soluble polymers used as soil mineral stabilizers via atomistic classical molecular dynamics (MD). Specifically, this study addresses polyelectrolyte interactions with kaolinite, a ubiquitous clay mineral, in soils. The two water-soluble polymeric species evaluated are PSS poly(4-sodium styrenesulfonate) and PDADMAC poly(diallyldimethylammonium chloride). The primary focus is the evaluation of water migration through a polymer-kaolinite composite system, the resulting molecular arrangement and interactions, and the extents of water migration through the polymeric phase-binding kaolinite interfacial planes. Mean square displacement (MSD) analysis was used to quantify the motion of the system species from the MD trajectories by calculation of self-diffusion coefficients and comparison of the curves obtained. The MD results indicate that water infiltrates the polyelectrolyte phase adhering to the mineral interfaces. Nevertheless, the MSD analysis results indicate a 55.8% reduction in water self-diffusion with respect to pure mineral-confined water. This is a compelling indication that polyelectrolytes can hinder water movement. Most importantly, MSD analysis of both polyelectrolyte species shows that the movement of the chains is negligible relative to that of water. These results strongly suggest that the movement of polymer phases is restricted only to local chain mobility and a rather bound state to the mineral surfaces prevails.