Direct calculation of the planar NaCl-aqueous solution interfacial free energy at the solubility limit

TL;DR

This study provides the first direct computational estimates of the interfacial free energy between NaCl crystals and saturated aqueous solutions, revealing high anisotropy across different crystal planes using advanced simulation techniques.

Contribution

It introduces a novel application of the Mold Integration method to directly calculate anisotropic interfacial free energies for NaCl-water interfaces at saturation.

Findings

Interfacial free energies range from 100 to 150 mJ/m2 across planes.

Average interfacial free energy is 137(20) mJ/m2.

Results align with previous nucleation extrapolations.

Abstract

Salty water is the most abundant electrolyte aqueous mixture on Earth, however, very little is known about the NaCl-saturated solution interfacial free energy. Here, we provide the first direct estimation of this magnitude for several NaCl crystallographic planes by means of the Mold Integration technique, a highly efficient computational method to evaluate interfacial free energies with anisotropic crystal resolution. Making use of the JC-SPC/E model, one of the most benchmarked force fields for NaCl/water solutions, we measure the interfacial free energy of four different planes, (100), (110), (111), and (11-2) with the saturated solution at normal conditions. We find high anisotropy between the different crystal orientations with values ranging from 100 to 150 mJ/m2 and the average value of the distinct planes being 137(20) mJ/m2. This value for the coexistence interfacial free energy is in reasonable agreement with previous extrapolations from nucleation studies. Our work represents a milestone in the computational calculation of interfacial free energies between ionic crystals and aqueous solutions.