Phononic Friction in Monolayer/Bilayer Graphene

Herein, frictional phonon dissipation in monolayer/bilayer graphene was modeled using phonon spectra based on molecular dynamics simulations. The results indicate that the number of excited acoustic phonon modes is the primary reason for increased friction. Specifically, the frequencies of flexural acoustic modes shifted to high levels as thickness increased during the sliding process, resulting in increased friction. The increase in friction with sliding velocity is caused by an increase in the number of in-plane acoustic modes. Higher normal loads can increase both the in-plane and flexural acoustic modes, leading to increased friction. Our observations further suggest that the variation in temperature at the friction interface results from the competition between frictional energy and thermal conductivity. Both high normal loads and thick layers increase the thermal conductivity, ultimately improving the friction dissipation efficiency. Hence, it can be concluded that the increase in thermal conductivity is the reason for the counterintuitive decrease in the interfacial temperature resulting from high friction.