Temperature-dependent resistivity in multiscale tri-phase hierarchical carbon nanocomposites

The electrical properties of hierarchical carbon-based architectures, such as carbon nanotube fibers (CNTFs) embedded within CNT-based nanocomposites, emerge from a competition between multiple charge-transfer mechanisms. Understanding and tailoring this interplay is critical for designing advanced materials. We report the first systematic study of charge transport in hierarchical tri-phase materials comprising single-walled CNT (SWCNT) fibers infiltrated with SWCNT/polymer nanocomposites above the electrical percolation threshold. Temperature-dependent electrical characterization from −180°C to 90°C reveals that the hierarchical combination of uni-phase CNTF with a bi-phase nanocomposite amplifies hopping and scattering phenomena. This is manifested by an increase in absolute temperature coefficient of resistance (TCR) from −0.17 and −0.08%K⁻¹ for the uni- and bi-phase materials, respectively, to −0.96%K⁻¹ for the tri-phase material and an increase in relative resistivity change. The conductivity in CNT-based systems is controlled by a temperature-dependent competition between variable-range hopping (VRH) and a high-temperature (HT) metallic-like transport mechanism, both tunable via SWCNT concentration. Embedding CNTFs in an insulating polymer (bi-phase) enhances the VRH regime, raising the TCR by ∼130%, while introducing a percolated SWCNT network (tri-phase) amplifies it by up to ∼240%. At the highest CNTs concentration, emerging ohmic pathways in tri-phase material reduce resistivity of the CNTF by 23%. We develop a unified empirical model with parallel VRH and HT conductivity channels that quantitatively reproduces the resistivity and TCR behavior across all types of specimens. This study provides a quantitative framework for charge transport in hierarchical carbon materials, opening a route to temperature-compensated design of next-generation CNT-based sensors.