Mechanical properties investigation of bilayer graphene/poly(methyl methacrylate) thin films at macro, micro and nanoscale

Abstract

Mechanical properties of bilayer graphene/poly(methyl methacrylate) (GR/PMMA) and reference PMMA thin films are investigated using various macro, micro and nano mechanical test methods. The GR/PMMA bilayer film consists of the CVD graphene layer (1 nm thick) spin coated with 1 μm thick PMMA layer. Small punch test, Berkovich nanoindentation, AFM nanoindentation, AFM nanoscratch, and spherical-conical stylus nanoscratch are used as mechanical characterization techniques. The freestanding films behave as 2D-membranes and high stretching is achieved at slower tests due to the dissipation of energy during elongation. The bilayer film is more brittle with lower fracture strength, strain and toughness than the PMMA film, due to interfacial delamination between the GR and the PMMA layers at large strain. The surface elastic modulus is higher than the bulk tensile modulus due to the scale effect. The graphene layer contributes to the improvements of hardness and resistance to scratch for both freestanding and supported GR/PMMA films. Critical normal force of adhesive failure of the bilayer films is identified as an important parameter characterizing intrinsic adhesion properties of the graphene/PMMA interfaces. The GR/PMMA thin films have potential in future shielding applications for protection of electronic devices.