Nanoindentation and nanoscratch of sub-micron polymer nanocomposite films on compliant substrate

Polymer thin films are deposited onto rigid materials for testing mechanical properties. However, the functionality of nanocomposites typically requires compliant substrates. Hence, it is important to investigate the nanomechanical properties of these films deposited on both substrates. This study compares the nanoindentation and nanoscratch behavior of Polyvinylamine (PVAm)/ Graphene oxide (GO) nanocomposite films on rigid silicon and compliant Polyethylene Terephthalate (PET) substrates. Contrary to the indentation rule of adhering to 10% of film depth, we obtain different measured hardness and reduced modulus on each film/substrate system with reduced modulus and hardness values of the PVAm/GO film on Silicon being 2 and 1.3 times higher than the film on PET at 10% film thickness. Experimenting on both substrates showed that extremely shallow indentation depths (< 4% of total film thickness) are necessary to measure comparable substrate independent film properties. The results also indicated that compliant substrate-based films exhibit better scratch resistance and higher adhesion strength of the film. Additionally, finite element analysis showed that using a rigid substrate concentrates the stress and deformation near the film surface. Using the compliant PET substrate results in larger elastic strain zone indicating deformation of the film and substrate alike.