Activation Volume in Shear-Driven Chemical Reactions

Interfacial shear-driven or shear-assisted chemical reactions play an important role in many engineering processes, including reactions between lubricant additives and the surfaces of mechanical components and fabrication of surface topographic features. Mechanistic studies of shear-driven chemical reactions often employ a mechanically assisted thermal activation model from which a so-called activation volume can be defined. Activation volume is important because it quantifies the efficiency of interfacial shear to drive the reaction. Recent advancements have enabled calculation of activation volume from both nano- and macro-scale experiments as well as simulations. However, the calculated volumes differ by orders of magnitude, even for the same reactant species, and the physical interpretations vary correspondingly. Here, we review how activation volume has been measured and interpreted for shear-driven reactions in the literature with the goal of guiding future efforts to understand and use this important parameter for engineering design through tribochemistry. Graphical Abstract: [Figure not available: see fulltext.].