Direct encapsulation of nanoclusters into carbon nanotube microfibers for thermal engineering applications

The encapsulation of nanomaterials into carbon nanotubes (CNTs) has garnered considerable attention for its potential to enhance the intrinsic physical properties of CNTs. Although various encapsulated CNTs have been synthesized, modulation of their thermal transport properties remains largely uninvestigated, primarily due to the experimental challenges at the nanoscale. In addition, such modulation has not yet been archived in macroscopic CNT assemblies, such as fibers or films. In this study, we propose a direct encapsulation of inorganic clusters into highly aligned CNT microfibers and demonstrate the modulation of the electrical conductivity (σ) and thermal conductivity (κ) through the incorporation of Mo4S4 nanoclusters. Commercially available CNT microfibers were used as the host material, and the encapsulation was confirmed by Raman spectroscopy. As a result, both κ and σ were reduced by approximately 50% and 30%, respectively, compared to pristine microfibers at room temperature. This modulation contributes to an improvement in the thermoelectric figure of merit. The methodology indicates the potential of nanomaterial encapsulation for tuning the thermal transport properties of CNT-based bulk materials, offering a promising strategy for advanced thermal engineering applications.