Correlated conformation and charge transport in multiwall carbon nanotube - conducting polymer nanocomposites

TL;DR

This study explores how the conformational arrangement of PEDOT-PSS globules on MWNTs influences charge transport mechanisms in nanocomposites, revealing temperature-dependent behaviors and the role of nanotube-polymer interactions.

Contribution

It provides new insights into the correlation between nanostructure conformation and charge transport in MWNT-polymer composites, highlighting the impact of nanotube coating on transport properties.

Findings

Charge transport is dominated by small polarons despite metallic nanotubes.

Hopping conduction follows 1D-VRH above 4 K, with positive magnetoresistance.

Below 4 K, small polaron tunnelling and large negative MR are observed.

Abstract

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.