Graphene and other 2-dimensional materials are materials that have thickness on the atomic scale, which makes them ideal solid lubricants for small length scale devices such as micro-electro-mechanical-systems (MEMS). Graphene is also known to possess an extraordinary property called superlubricity, where friction between two material layers becomes vanishingly small. Most of these superlubric phenomena, however, have been observed in well-prepared laboratory conditions for very small flakes. This award supports research on the mechanics of friction mechanisms of 2-dimensional materials at the atomic scale using a novel predictive computational method based on molecular dynamics called hyperdynamics. This method will allow the researchers to study large 2-dimensional layers such as those grown with the chemical vapor deposition method. An enhanced understanding about superlubricity achieved in this research will pave the way for realization of frictionless sliding on macroscopic scales. Since friction is one of the primary causes of energy dissipation or waste, the research will potentially enhance sustainability and efficiency efforts in transportation, manufacturing, and other sectors where moving parts consume a lot of energy. All computer codes developed in this project will be made freely available to the research community. The project will provide training to graduate students as well as research opportunities to undergraduate students as part of the University of Cincinnati's co-op program. An outreach program for science and engineering education based on computer simulations will also be organized for local high schools in the Greater Cincinnati area.
Graphene synthesized by the chemical vapor deposition method and other 2-dimensional materials are characterized by a multi-grain structure with defects, which has been hypothesized to cause detrimental effects on their mechanical and frictional properties. In this project, theoretical and computational models which can reliably predict mechanical and frictional properties of multi-grain graphene and other 2-dimensional materials such as molybdenum disulfide and hexagonal boron nitride will be constructed. A novel atomistic simulation method called hyperdynamics will be applied to overcome the limitations of conventional methods enabling simulations under spatio-temporal conditions close to actual experiments. Various sliding objects and defected structures comprising grain boundaries, stacking, and surface steps will be investigated under several chemical environments and externally applied conditions, such as temperature, sliding velocity, normal force. This systematic research will greatly enhance our understanding of the underlying atomic-level frictional and energy dissipation mechanisms operative in 2-dimensional materials, which is critical in developing efficient macroscopic devices.
