Peaked bulk crystal nucleation in charged sphere melts from salt concentration dependent crystallization experiments at very low metastability

TL;DR

This study investigates how electrolyte concentration influences crystal nucleation rates in charged sphere suspensions, revealing a peak in nucleation rate and unusually low energy barriers, with implications for understanding colloidal crystallization.

Contribution

It provides the first detailed experimental analysis of salt concentration effects on nucleation in charged colloids, highlighting a peaked nucleation rate and low energy barriers.

Findings

Nucleation rate exhibits a pronounced initial peak.

Nucleation barriers are below thermal energy.

Nucleation rate scales with metastability times particle density.

Abstract

We determined bulk crystal nucleation rates in aqueous suspensions of charged spheres at low metastability. Experiments were performed in dependence on electrolyte concen-tration and for two different particle number densities. The time-dependent nucleation rate shows a pronounced initial peak, while post-solidification crystal size distributions are skewed towards larger crystallite sizes. At each concentration, the nucleation rate density initially drops exponentially with increasing salt concentration. The complete data set, however, shows an unexpected scaling of the nucleation rate densities with met-astability times the number density of particles. Parameterization of our results in terms of Classical Nucleation Theory reveals unusually low interfacial free energies of the nu-cleus surfaces and nucleation barriers well below the thermal energy. We tentatively attribute our observations to the presence of doublets introduced by the employed con-ditioning technique and acting as nucleation seeds.