The formation of a boundary film by reaction with a gas-phase lubricants or lubricant additives formally occurs in several steps that involve the  initial adsorption and reaction of the lubricant molecule on the surface, followed by shear-induced decomposition and formation of the boundary film.   Fully understanding this sequence of reaction steps will enable the structure of the additive molecule to be related to the nature of the resulting boundary lubricating film.  The approach is illustrated using the gas-phase lubrication of copper by dimethyl disulfide (DMDS).  DMDS initially reacts with copper at ~300 K to form thiolate species and shear at the interface causes sulfur and some carbon to penetrate the substrate to form a boundary film that reduces friction.  The kinetics of the shear-induced rate of thiolate decomposition is measured in ultrahigh vacuum from the amount of methane that is formed as the surfaces rub, where the reaction rate increases by about six orders of magnitude compared to the thermal decomposition rate.  Models for the increase in shear-induced decomposition rate will be discussed.

Shear-induced chemical reaction pathways on copper

248th National Meeting (2014)

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