Saturated Sodium Chloride Solution under an External Static Electric Field: a Molecular Dynamics Study

TL;DR

This study uses molecular dynamics simulations to explore how external electric fields influence the crystallization process of saturated sodium chloride solutions, revealing acceleration, retardation, and phase transition behaviors depending on field strength.

Contribution

It provides new insights into the effects of static electric fields on salt solution crystallization and identifies a threshold field strength for phase transitions.

Findings

Moderate electric fields accelerate nucleation.

Strong electric fields inhibit or prevent crystallization.

A threshold electric field exists for phase transition, increasing with concentration.

Abstract

The behavior of saturated aqueous sodium chloride solutions under a constant external electric field (E) was studied by molecular dynamics (MD) simulation. Our dynamic MD simulations have indicated that the irreversible nucleation process towards crystallization is accelerated by a moderate E, but retarded or even prohibited under a stronger E, which can be understood by the competition between self-diffusion and drift motion. The former increases with E resulting in the acceleration of the nucleation process, and the latter tears oppositely charged ions more apart under a stronger E leading to the deceleration of nucleation. Moreover, our steady-state MD simulations have indicated that a first-order phase transition happens in saturated solutions only when the applied E is below a certain threshold Ec, and the ratio of crystallized ions does not change with the electric field. The magnitude of Ec increases with concentration, because larger clusters are easy to form in a more concentrated solution and require a stronger E to dissociate them.