Dehydration-Driven Ion Aggregation and the Onset of Gelation in ZnCl 2 Solution

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 drives two coordination-controlled structural changes: a crossover at Z = 2 from predominantly isolated Zn-containing species to Cl-bridged clusters and the onset of gelation near Z ≈ 3 . The model reproduces the concentration-dependent trends observed in the molecular dynamics simulations with two fitted parameters, while the cluster-size distribution at the highest concentration is consistent with three-dimensional percolation scaling over the accessible range of cluster sizes.