Conductivity of poly(methyl methacrylate) composite films filled with ultra-high aspect ratio carbon fibers

Abstract In this study, the poly(methyl methacrylate) (PMMA)/carbon fibers (CFs) composite films with different CFs concentrations have been prepared using the solution casting technique. CFs were modified using aqua regia to reduce aggregations. The residual aspect ratios (ARs) of CFs in the composite films are 49, 105, 227, 312, 417, 527 and 616, respectively. Light microscopy and SEM were applied to investigate the morphology of the composite films. The resistance of the film with different ARs of CFs was measured (1) perpendicularly and (2) along the in-plane direction. Both percolation thresholds ϕc,⊥ and ϕc,∥ were determined by fitting the Mclachlan GEM equation. The conductivity in both directions was presented in contour plot versus ARs of CFs and concentration of CFs. A huge amount of experimental data was obtained in this study, seven aspect ratio (AR) of CFs multiply 12 volume fraction of CFs with two measuring directions. Based on Balberg's excluded volume theory, for the first time the pre-factors K⊥ and K∥ were revealed, considering different measuring direction on the film.