Molecular Aspect Ratio Effect on Axial Thermal Transport in Solution-Spun Carbon Nanotube Fibers

Neat, densely packed, and highly aligned carbon nanotube fibers (CNTF) have appealing room-temperature axial thermal conductivity () and thermal diffusivity ( for applications in lightweight axial heat spreading or flexible thermal connections. Although increasing the molecular aspect ratio (i.e., ratio of nanotube length to nanotube diameter) of the constituent single-wall and few-wall carbon nanotubes (CNTs) is expected to improve and by reducing the number of interfaces along the axial direction per unit length, no prior work has quantified the molecular aspect ratio effect on thermal transport for solution-spun CNTF. Here, we perform self-heated steady-state and three-omega thermal measurements at room temperature on suspended CNTF in vacuum. The CNT molecular aspect ratios range from 960 to 5600, as quantified by rheological measurements of liquid crystalline CNT solutions. The thermal measurement results show that increases from to with increasing . The axial electrical conductivity also increases from to with increasing , and the Wiedemann–Franz law predicts the electronic contribution to is for the highest sample. CNTF made with varying volume fraction of constituent high- and low- CNTs generally fall within typical macroscopic rule-of-mixtures bounds for and . The thermal diffusivity scales with , leading to a sample-averaged volumetric heat capacity of 1.5±0.1 . Thus, this work shows that increasing the molecular aspect ratio enhances and of solution-spun CNTF, motivating further investigation into thermal transport mechanisms and applications of carbon nanotube fibers.