Charge Transport in Functionalized Octopus-Shaped Multi-Walled Carbon Nanotube/Graphene Hybrids: Implications for Extremely Stretchable Conductors

There is a challenge to achieve the maximum feasible charge transport property for conductive polymer nano-composites containing graphitic nanoparticles. Multi-walled carbon nanotube (MWCNT) and graphene hybridization is a commonly investigated solution for enhancing the electron conduction in these nanocomposites. In this work, we present the functionalized octopus-shaped hybrid of MWCNT/graphene (FOS-hybrid), where the nanotube ends and graphene edges are stitched together by ethylenediamine and are subsequently functionalized by octadecylamine (ODA). At the identical total weight percentages of nanoparticles, the poly[styrene-b-(ethylene-co-butylene)-b-styr-ene] (SEBS)-based nanocomposites of the FOS-hybrid demon-strate superior electrical conductivity, sigma dc, compared to SEBS-based nanocomposites of ODA-functionalized MWCNT or graphene and even their physically incorporated hybrid. The synergistic ratio equal to the ratio of "sigma dc of the hybrid nanoparticles composite" to "sigma dc of the single nanofiller composite" with higher sigma dc is approximately 15.6 for the FOS-hybrid. This obtained synergistic ratio is the highest reported value for hybrid systems comprising MWCNT and graphene so far. In contrast to the majority of previous investigations, the improvement in the dispersion state is not the main reason for synergism in this work, and the observed remarkable synergism is attributed to the extremely structured networks of octopus-shaped particles with low tunneling resistivity at MWCNT/graphene junctions. The Monte Carlo simulation shows that the significant "average number of active neighboring particles" for the conducting network of FOS-hybrid is what makes their network very efficient, which is not just originated from the expected complexity imposed by hybridization. Additionally, the SEBS-based nanocomposite with 5 wt % FOS-hybrid particles displays high elongation at break (765%) and low electromechanical sensitivity (Delta R/R0 = 0.52 at 100% strain). This result is attributed to the superb dispersion affected by ODA-functionalization and covalent bonding between hybrid components in octopus-shaped particles, which does not break under strain. Therefore, strain-insensitive stretchable conductors can be produced by FOS-hybrid nanocomposites.