Deciphering Ball Milling Mechanochemistry via Molecular Simulations of Collision-Driven and Liquid-Assisted Reactivity.

Mechanochemistry by ball milling proceeds through a series of discrete, high-energy collisions between milling balls and the sample, yet the molecular-level processes that govern the resulting chemical and physical transformations remain poorly understood. In this study, we develop a molecular dynamics simulation protocol to investigate a model mechanochemical reaction between potassium chloride (KCl) and 18-crown-6 ether, both under dry conditions and in the presence of water as a liquid additive. Our simulations reveal that the reaction is initiated by collision-induced fragmentation of the KCl crystal into individual ions. This process occurs when the absorbed energy per ion pair during a collision exceeds the crystal's cohesion energy. We further show that the addition of a small amount of water facilitates the formation of complexes between potassium ions and 18-crown-6 molecules. However, excessive water content stabilizes the reactants instead, thereby suppressing complex formation. These findings highlight a non-linear relationship between liquid additive concentration and the reaction outcome. Our approach offers a molecular-level perspective on mechanochemical reactivity, providing valuable insights that could guide the rational optimization of milling conditions-particularly the targeted selection and dosing of liquid additives-to improve reaction efficiency.