Dehydration-Driven Ion Aggregation and the Onset of Gelation in ZnCl$_2$ Solution

TL;DR

This study presents a minimal model for ionic aggregation in concentrated ZnCl₂ solutions, revealing dehydration-driven ion binding transitions and gelation, validated by molecular dynamics simulations and percolation theory.

Contribution

The paper introduces a new minimal model that captures dehydration effects, chloride binding, and loop formation in ZnCl₂ solutions, advancing understanding of ion aggregation and gelation.

Findings

Dehydration triggers ion binding transitions at specific Zn coordination numbers.

The model quantitatively matches molecular dynamics simulation results.

Cluster-size distribution follows percolation theory near gelation.

Abstract

A minimal model of ionic aggregation in concentrated ZnCl$_2$ is developed, guided by molecular dynamics simulations with a machine-learned potential. It explicitly incorporates solvent-site depletion, correlated chloride binding, and allows for loops within Zn-Cl clusters. Dehydration is shown to drive ion binding through two sharp transitions set by the Zn coordination number $Z$: a crossover at $Z=2$ from isolated ions to Cl-bridged clusters, and gelation near $Z\approx 3$. The model agrees quantitatively with MD results, and the critical exponent of the cluster-size distribution matches percolation theory.