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Determination of electrical percolation threshold of carbon nanotube‐based epoxy nanocomposites and its experimental validation

The electrical conductivity of polymer nanocomposites plays a critical role in applications like aerospace and electromagnetic shielding. Electrical conductivity and other electromagnetic parameters of carbon nanotube (CNT)-based epoxy nanocomposites are being analysed in this work for their suitability in electromagnetic shielding. Unfilled epoxy and CNT epoxy nanocomposite samples with various filler loadings are prepared. Impedance measurements are conducted over the frequency range of 20 Hz–10 MHz. Micromechanics model is used for the theoretical estimation of electrical conductivity of CNT-based epoxy nanocomposites. Interface thickness in the conventional model is modified to avoid the overestimation of electrical conductivity. DC conductivity of nanocomposites determined experimentally is found to obey classical law of percolation theory and percolation threshold is determined to be 0.17 wt% which agrees well with theoretical value of 0.18 wt% obtained using modified micromechanics model. AC conductivity is found to obey universal dynamic response. Dipolar polarisation mechanism is prominent in the tested frequency range whose frequency of occurrence increases with CNT content due to a greater number of interfaces formed between CNT and epoxy. CNT epoxy nanocomposites are found to have negative permeability thus acting as absorbers in electromagnetic shielding.