Effect of Gas Environment on Mechanochemical Reaction: A Model Study with Tribo-Polymerization of Α-Pinene in Inert, Oxidative, and Reductive Gases

Mechanically induced or assisted chemical reactions readily occur in many tribological interfaces; however, the reactants involved in such reactions are often not well understood. Using the tribo-polymerization of α-pinene as a model system, this study investigated how the surround gas environment influences the surface chemistry of substrate controlling the tribochemical reactivity. Based on the hypothesis that oxidative chemisorption of α-pinene at the sliding solid surface plays critical role, inert (dry N ₂ ), oxidative (dry air), and reductive (10% H ₂ in Ar) gas environments were chosen to alter the degree of surface oxidation in the sliding contact. Comparing the tribo-polymerization yield of α-pinene on two highly reactive substrates (Pd and CuO) and two relatively inert substrates (diamond-like carbon and silicon oxide), it was found that the oxidative gas significantly enhances the tribochemical reactivity of α-pinene. Infrared spectroscopy analysis was employed to confirm that the chemisorption of α-pinene on the surface in the oxidative gas environment plays a critical role. The gas environment was also found to affect the chemical composition and elastic modulus of the tribo-polymer products.