Unlike thermal, photochemical, and electrochemical reactions which are initiated by electronic excitation or transition within or among reactant molecules, tribochemical reactions are initiated by mechanical actions imposed onto the molecules by the solid surface. Here, the key question is how mechanical energy is channeled into chemical reaction coordinates. This question is related to the magnitude of the critical activation volume which can be obtained from Arrhenius-type analysis of the load or shear stress dependence of reaction yields or rates. We have addressed this question through carefully designed experiments and collaborations with computational groups. This talk will focus on the effects of chemical structures of the adsorbed molecules that are being sheared at the interface and the critical role of surface chemistry determining overall reaction yields. By studying a series of homologous organic molecules consisting of 10 carbon atoms (alpha-pinene, pinane, n-decane), it was found that molecules with internal strains more readily undergo tribochemical polymerization reactions, compared to the ones without any internal strain. Studying the reactivity of alpha-pinene on various solid materials under tribological sliding conditions without wear of substrate, it was discovered that the surfaces capable of oxidative chemisorption and activation of interfacial molecules can greatly increase tribochemical polymerization reactions. This data suggests that without chemisorption, the inert surface cannot efficiently transfer mechanical energy to molecules for reactions. Further insights into molecular details during tribochemical reactions were revealed through molecular dynamics simulations using ReaxFF reactive forces. Based on these results, the physical meaning of the critical activation volume in tribochemical reactions is proposed.

Constituents of tribochemistry – molecule and surface at shearing interface: How would their chemical structure affect the critical activation volume of mechanochemical reaction?

255th National Meeting (2018)

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