Anomalous Water Penetration in $\text{Al}^{3+}$ Dissolution

TL;DR

This study uses advanced machine learning force fields to uncover a novel water penetration mechanism during the dissolution of $ ext{Al}^{3+}$, revealing complex hydration dynamics beyond the second shell.

Contribution

It introduces a new microscopic understanding of trivalent ion solvation dynamics using machine learning-based simulations.

Findings

Water beyond the second hydration shell penetrates and coordinates with $ ext{Al}^{3+}$.

Hydrogen bonding causes synchronized secondary water motion.

A new hydration penetration mechanism is identified.

Abstract

The physicochemical characterization of trivalent ions is limited due to a lack of accurate force fields. By leveraging the latest machine learning force field to model aqueous $\text{AlCl}_{3}$, we discover that upon dissolution of $\text{Al}^{3+}$, water molecules beyond the second hydration shell involve in the hydration process. A combination of scissoring of coordinating water is followed by synchronized secondary motion of water in the second solvation shell due to hydrogen bonding. Consequently, the water beyond the second solvation penetrates through the second solvation shell and coordinates to the $\text{Al}^{3+}$. Our study reveals a novel microscopic understanding of solvation dynamics for trivalent ion.