Reactive molecular dynamics simulations of thermal and shear-driven oligomerization

Mechanochemical reactions play a critical role in many manufacturing, tribological, and synthesis processes. Often, these reactions happen at a sliding interface which makes them difficult to study experimentally. Such reactions are not fully understood since the reactant species are subject to frictional heating and mechanical stress simultaneously. Here, reaction pathways driven by heat, normal stress, and shear stress were investigated using reactive molecular dynamics simulations of mechanochemical oligomerization of α-pinene molecules on silica. Results identified shear stress as the key driver of oligomerization reactions under tribological conditions. Normal stress alone was ineffective in inducing any reactions and oligomerization could be driven thermally only at very high temperatures. Analysis of the reaction pathways showed that shear can activate multiple mechanisms that are not accessible thermally. Calculations of bond lengths and dihedral angles revealed that such activation is accompanied by physical deformation of reacting species. The findings from reactive molecular dynamics simulations provide critical insights into the activation mechanisms underlying mechanochemical reactions that can guide design of materials and processes with optimized and potentially tunable shear-induced reactions.