Correlated conformation and charge transport in multiwall carbon nanotube-conductingpolymer nanocomposites

Abstract

The strikingly different charge transport behaviours in nanocomposites of multiwall carbonnanotubes (MWNTs) and conducting polymer polyethylenedioxythiophene–polystyrene-sulfonic-acid(PEDOT–PSS) at low temperatures are explained by probing their conformationalproperties using small-angle x-ray scattering (SAXS). The SAXS studies indicate theassembly of elongated PEDOT–PSS globules on the walls of nanotubes, coatingthem partially, thereby limiting the interaction between the nanotubes in thepolymer matrix. This results in a charge transport governed mainly by smallpolarons in the conducting polymer despite the presence of metallic MWNTs. AtT > 4 K, hopping of the charge carriers following one-dimensional variable range hopping is evidentwhich also gives rise to a positive magnetoresistance (MR) with an enhanced localization length (∼5 nm) due to the presence of MWNTs. However, atT < 4 K, the observation of an unconventional positive temperature coefficient of resistivity isattributed to small polaron tunnelling. The exceptionally large negative MR observed inthis temperature regime is conjectured to be due to the presence of quasi-1D MWNTs thatcan aid in lowering the tunnelling barrier across the nanotube–polymer boundary resultingin large delocalization.