Electronic transport properties of disordered metallic flake packings

The electronic transport properties of disordered packings of conducting, high aspect ratio flakes are of interest in the context of printed electronics where 2D nanoparticles such as graphene can be used to create conducting pathways made from nanosheet networks. The electrical conductivity depends strongly on the porosity of the sheet network and can be tuned via compression. Here, we use packings of macroscopic metallic flakes to elucidate the relationship between the packing fraction and the electrical conductivity which is anisotropic. This granular model experiment allows precise control over particle polydispersity, the contact resistance from the oxide layer and packing fraction. We use a strain-controlled compression cell to measure the axial and lateral conductivity of a disordered packing of thin aluminium flakes with particle aspect ratios of up to ~1300 as a function of packing fraction. We find that the conductivity increases by up to 6 orders of magnitude with compression. In the loosely packed state, the conductivity is approximately isotropic while in the highly jammed state, where the flakes align, the axial and lateral conductivities differ by 3 orders of magnitude. We employ a semi-empirical model to explain our results.