Chapter 5 - Orthotropic friction at the edges and interior of graphene and graphene fluoride and frictional anisotropy of graphene at the nanoscale

Abstract

We provide evidence that the friction of graphene films has a directional dependence in the interior and at the edges of the graphene sheets. Graphene fluoride was shown to have lower friction coefficients than graphene at almost all angles either inside or at the edges of the samples. At the edges, graphene and graphene fluoride were shown to have a dependence on the scan direction. It is unexpected with respect to all reported results as of today. We have experimentally proven that graphene and graphene fluoride manifest different coefficients of sliding friction at the edges (graphene fluoride from 5.8×10−3 to 4.9×10−1; graphene from 8.2×10−3 to 3.3×10−1) of a sheet sample versus the interior (graphene fluoride from 5.1×10−3 to 1.5×10−1; graphene from 2.5×10−2 to 2.3×10−1) under ambient humidity conditions (~60%). Atomic force microscopy (AFM) was used to prove the friction coefficients have distinct directional dependence between graphene and graphene fluoride. It is assumed that differences in friction coefficients between those in literature and our results for graphene fluoride were due to ambient experimental conditions. Further investigation of the effects of water on friction between the AFM tip and graphene fluoride is warranted.