The self-wetting properties of ionic crystal surfaces are studied, using NaCl(100) as a prototype case. The anomalously large contact angle measured long ago by Mutaftschiev is well reproduced by realistic molecular dynamics simulations. Based on these results, and on independent determinations of the liquid-vapor and the solid-vapor interface free energy, an estimate of the solid-liquid interface free energy is extracted. The solid-vapor surface free energy turns out to be small and similar to the liquid-vapor one, providing a direct thermodynamic explanation of the reduced wetting ability of the ionic melt.
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