Berlin 2024 – scientific programme
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O: Fachverband Oberflächenphysik
O 16: Surface Dynamics & Electron-Driven Processes
O 16.1: Talk
Monday, March 18, 2024, 15:00–15:15, MA 141
Role of hydration and electrostatics in salt precipitation — •Adyant Agrawal1, Simon Gravelle2, Christian Holm1, and Alexander Schlaich3 — 1Institute for Computational Physics, University of Stuttgart — 2Univ. Grenoble Alpes, CNRS, LIPhy, 38000 Grenoble, France — 3SC SimTech, University of Stuttgart
The precipitation of salt leading to the formation of a salt crust is a crucial process in the environment, yet it is still not fully resolved at the molecular scale. We perform an extensive molecular dynamics simulation study of supersaturated solutions of simple salts in contact with their crystal surface to understand the precipitation mechanism. For NaCl, we found that the sodium ions have a larger preference to be adsorbed at a crystal surface than the chloride ions, which results in a buildup of positive charge on the crystal. An excess of sodium ions then drives the adsorption of chloride ions at the surface. This leads to a depletion in the charge distributions above the surface as the crystal grows. This mechanism is different from other common salts we tested. We also obtain the dependence of the free energy for adsorbed ions on the defect topology to capture the thermodynamics of crystal surface formation. We identify a complex competition between hydration and electrostatic interactions at the interface that controls the precipitation process and the interfacial topology. The grown surface can be anomalously patterned since some sites can be more favourable for water molecules than ions. We discuss these competing effects in the context of different common salts.
Keywords: Salt precipitation; Hydration; Crystal growth; Molecular Dynamics; Atomistic model