  The strikingly different charge transport behaviors in nanocomposites of
multiwall carbon nanotubes (MWNTs) and conducting polymer polyethylene
dioxythiophene - polystyrene sulfonic acid (PEDOT-PSS) at low temperatures are
explained by probing their conformational properties using small angle X-ray
scattering (SAXS). The SAXS studies indicate assembly of elongated PEDOT-PSS
globules on the walls of nanotubes, coating them partially thereby limiting the
interaction between the nanotubes in the polymer matrix. This results in a
charge transport governed mainly by small polarons in the conducting polymer
despite the presence of metallic MWNTs. At T > 4 K, hopping of the charge
carriers following 1D-VRH is evident which also gives rise to a positive
magnetoresistance (MR) with an enhanced localization length (~ 5 nm) due to the
presence of MWNTs. However, at T < 4 K, the observation of an unconventional
positive temperature coefficient of resistivity (TCR) is attributed to small
polaron tunnelling. The exceptionally large negative MR observed in this
temperature regime is conjectured to be due to the presence of quasi-1D MWNTs
that can aid in lowering the tunnelling barrier across the nanotube - polymer
boundary resulting in large delocalization.
