Direct Calculation of the Interfacial Free Energy between NaCl Crystal and its Aqueous Solution at the Solubility Limit

Salty water is the most abundant electrolyte aqueous mixture on Earth, however, very little is known about the NaCl-saturated solution interfacial free energy (gamma s). Here, we provide the first direct estimation of gamma s 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 gamma s of four different crystal planes, (100), (110), (111), and (112 over bar ) with the saturated solution at normal conditions. We find high anisotropy between the different crystal orientations with values ranging from 100 to 150 mJ m-2, and the average value of the distinct planes being gamma over bar s = 137(20) mJ m-2. This value for the coexistence interfacial free energy is in reasonable agreement with previous extrapolations from nucleation studies. Our Letter represents a milestone in the computational calculation of interfacial free energies between ionic crystals and aqueous solutions.

Automated summary

This study provides the first direct estimation of the interfacial free energy of NaCl-saturated solution on several crystallographic planes. The results show high anisotropy between different crystal orientations, with values ranging from 100 to 150 mJ m-2.