Molecular structure and environment dependence of shear-driven chemical reactions: Tribopolymerization of methylcyclopentane, cyclohexane and cyclohexene on stainless steel

Abstract

Abstract Tribochemistry, which is another name of mechanochemistry driven by shear, deals with complex and dynamic interfacial processes that can lead to facilitation of surface wear or formation of beneficial tribofilms. For better mechanistic understanding, we investigated the reactivity of tribopolymerization of organic molecules with different internal ring strain energy (methylcyclopentane, cyclohexane, and cyclohexene) on a stainless steel (SS) surface in inert (N2), oxidizing (O2), and reducing (H2) environments. On the clean SS surface, precursor molecules were found to physisorb with a broad range of molecular orientations. In inert and reducing environments, the strain-free cyclohexane showed the lowest tribochemical activity among the three tested. Compared to the N2 environment, the tribochemical activity in H2 was suppressed. In the O2 environment, only cyclohexene produced tribofilms and methylcyclopentane and cyclohexane did not. When tribofilms were analyzed with Raman spectroscopy, the spectral features of diamond-like carbon (DLC) or amorphous carbon (a-C) were observed due to photochemical degradation of triboproducts. Based on infrared spectroscopy, tribofilms were found to be organic polymers containing oxygenated groups. Whenever polymeric tribrofilms were produced, wear volume was suppressed by orders of magnitudes but not completely to zero. These results supported the previously suggested mechanisms which involved surface oxygens as a reactant species of the tribopolymerization process.