Carbon Nanotubes Modified Oil-based Nanofluids: Electrical Conduction Mechanism Analysis

This paper reports research on the electrical conduction mechanisms of nanofluids, formed by adding carbon nanotube (CNT) and 0.5 wt% of graphite (Gt) particles to engine oil, in the range of temperatures up to 400 K. An analysis of the dc conductivity of nanofluids versus CNT concentration and temperature, have shown a percolation threshold of 0.6 wt% and revealed the PTCR (Positive Temperature Coefficient of Resistivity) effect for temperatures below the critical value Tc approximate to 350 K and concentrations above the critical percolation threshold. The ac conductivity of all samples was fitted in the range of frequency from 100 Hz to 1 MHz using the Jonscher power law, which allows for the specification of the appropriate electrical conduction mechanism using the exponent s in that law. The electric modulus has shown two dielectric relaxations for the nanofluid-based CNT fillers; the first one at low frequency is related to interfacial polarization, while the second one at high frequency is attributed to the interaction between CNT nanoparticles and dipolar molecules of commercial oil additives. The modulus spectra were fitted using the Havriliak-Negami model.