Chemical reactions are the basis of many manufacturing processes and play important roles in their performance and energy utilization. Many manufacturing processes involve heating source materials to drive reactions to form desired products. However, another way to drive reactions is through the use of mechanical force. This project focuses specifically on reactions driven by friction force at sliding interfaces. Such tribochemical reactions underpin manufacturing processes including chemical mechanical polishing and the formation of protective films on the surface of mechanical components. As such, a fundamental understanding of tribochemical reactions can lead to the development of more energy efficient, sustainable manufacturing processes. This research topic lies at the intersection of chemical and mechanical engineering and, as such, the students involved in the research necessarily receive interdisciplinary training. This research is integrated into undergraduate and graduate courses and engages students from underrepresented groups.
In mechanistic studies of shear-driven chemical reactions, researchers often employ a mechanically assisted thermal activation model from which a parameter referred to as the ‘critical activation volume’ can be defined. Recent advancements in experimental techniques have enabled measurement of this activation volume for various tribochemical reactions and the measured values have been compared with a variety of physical volumes. However, such comparisons are unfounded since the thermal activation model describes an energy difference between the reactant and transition states of a reaction and does not contain molecular information of a molecular description associated with these states. This work hypothesizes that activation volume is determined by the propensity of molecules or surface atoms to deform relative to their equilibrium geometries under interfacial shear, and that its magnitude is governed by the geometric structure of precursor molecules, chemisorption to the sliding substrate or formation of interfacial bonds across a shear plane, and environmental conditions such as co-adsorbates, temperature, etc. This hypothesis is investigated through complementary tribochemical experiments and reactive molecular dynamics simulations using model systems with controlled molecular parameters that enable isolation of the individual contributions to the specific set of independent variables and their synergistic effects.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
