Observation of power-law behavior in temperature dependent conductivity of multiwall carbon nanotube/polystyrene composites

For last two decades, a pronounced temperature dependence of electrical conductivity (sigma) in the multiwall carbon nanotube (MWCNT) - based polymer composite (even above the percolation threshold) has been widely reported; the conduction mechanism has been understood by employing conventional models, namely variable range hopping and fluctuation induced tunneling. Herein, we report on the observation of a weak temperature dependence of sigma in the MWCNT/polystyrene composites above percolation threshold (0.7-7 wt %) at temperatures down to 1.4 K, with a conductivity ratio smaller than 3. The low temperature conductivity data follow power-law exhibiting two slope behavior, with exponent values beta(1) similar to 0.10-0.14 (at T > 5 K) and beta(2) similar to 0.23-0.36 (at T < 5 K). The observation of weak temperature dependence of sigma is attributed to high aspect ratio (more than 4000), achievement of high degree of dispersion, and excellent electrical properties of MWCNT as well as optimized composite processing. Further, all the samples exhibit negative magnetoresistance which can be explained within the framework of weak localization model. (C) 2018 Elsevier B.V. All rights reserved