Homogeneous nucleation mechanism of NaCl in aqueous solutions

TL;DR

This study uses molecular dynamics simulations to reveal that NaCl nucleation in water occurs via aggregation driven by hydrophobic interactions, lowering the nucleation barrier and differing from classical theories.

Contribution

It demonstrates a homogeneous nucleation mechanism involving solute aggregation, contrasting with traditional two-step models and classical nucleation theory.

Findings

NaCl ions tend to aggregate at higher concentrations.

Aggregation is driven mainly by hydrophobic interactions.

Aggregation lowers the nucleation energy barrier.

Abstract

In this study, molecular dynamic simulations are employed to investigate the nucleation of NaCl crystal in solutions. According to the simulations, the dissolved behaviors of NaCl in water are dependent on ion concentrations. With increasing NaCl concentrations, the dissolved Na$^+$ and Cl$^-$ ions tend to be aggregated in solutions. In combination with our recent studies, the aggregate of dissolved solutes is mainly ascribed to the hydrophobic interactions. Thermodynamically, no barrier is needed to overcome in the formation of the solute aggregate. This is different from the two-step nucleation mechanism. In comparison with the classical nucleation theory (CNT), due to the aggregate of dissolved solutes, this lowers the barrier height of nucleation, and affects the nucleation mechanism of NaCl crystal in water.