Low temperature charge transport study of MWCNT/PEDOT:PSS composites: insulating to metallic regime

Abstract

Multiwall carbon nanotube (MWCNT)/poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) composites have been examined for their temperature and magnetic field dependent conductivity behavior. The conductivity ratio, σ r (σ 300 K/ σ 2 K), is significantly impacted by the sulfuric acid post-treatment of the composites and a slight alteration in MWCNTs loading. By adjusting the loading of MWCNTs in the composites, the charge transport is tuned from insulating to metallic regime. For the low loading of MWCNTs (0.04 wt%), charge transport of the composite lies in the insulating regime and follows a variable range hopping model. At moderate loading of MWCNTs, the transport of the composites lies in the critical regime and the temperature dependent conductivity follows a power law model. As the MWCNTs loading increases to 4 wt%, transport of the composites shifts to the metallic regime with σ r ∼ 2.8. The temperature dependent conductivity has been explained by using electron-electron interactions and weak localization effects and the conductivity follows ∼T 1/2 and ∼T 3/4 dependence in different temperature regimes. Wave function shrinkage and forward interference effects have been used to evaluate the magnetoconductance (MC) of the samples located in the insulating regime. For the composites lying in the metallic regime, a dominant contribution from weak localization explains the behaviour of the MC. However, for those in the critical regime a combined effect of weak localization and electron-electron interactions has been observed.