Divergent and Ultrahigh Thermal Conductivity in Millimeter-Long Nanotubes

Abstract

Low-dimensional materials could display anomalous thermal conduction that the thermal conductivity (κ) diverges with increasing lengths, in ways inconceivable in any bulk materials. However, previous theoretical or experimental investigations were plagued with many finite-size effects, rendering the results either indirect or inconclusive. Indeed, investigations on the anomalous thermal conduction must demand the sample length to be sufficiently long so that the phenomena could emerge from unwanted finite-size effects. Here we report experimental observations that the κ's of single-wall carbon nanotubes continuously increase with their lengths over 1 mm, reaching at least 8640 W/mK at room temperature. Remarkably, the anomalous thermal conduction persists even with the presence of defects, isotopic disorders, impurities, and surface absorbates. Thus, we demonstrate that the anomalous thermal conduction in real materials can persist over much longer distances than previously thought. The finding would open new regimes for wave engineering of heat as well as manipulating phonons at macroscopic scales.

Crossover from ballistic to normal heat transport in theϕ4lattice: If nonconservation of momentum is the reason, what is the mechanism?

“…Thus, these studies suggest that the ballistic thermal conduction in real (quasi-)1D materials can persist over macroscopic distances. In fact, it has been usually believed that in such materials heat is conducted ballistically by the low-frequency, longwavelength phonons [6], and hence the anomalous ballistic behavior can persist even with the presence of defects, isotopic disorders, impurities, and surface absorbates [7].…”

“…In those studies, this ballistic phonon transport has been found * Electronic address: phyxiongdx@fzu.edu.cn † Electronic address: saadatmand.d@gmail.com ‡ Electronic address: dmitriev.sergey.v@gmail.com for (quasi)-1D samples having length less than a threshold value, L * (usually characterized by the phonon mean free path), such as that for SiGe nanowires L * ≈ 8.3 µm [9], for carbon nanotubes L * ≈ 1 mm [7], and for holey silicon L * ≈ 200 nm [10]. Thus, these studies suggest that the ballistic thermal conduction in real (quasi-)1D materials can persist over macroscopic distances.…”

“…With the development of laser technology [4,5] which allows to probe the thermal properties of materials at reduced size and time scales, ballistic thermal conduction (α = 1) has been observed experimentally for Si 0.9 Ge 0.1 and Si 0.4 Ge 0.6 nanowires, carbon nanotubes, holey silicon, Al 0.1 Ga 0.9 N thin film, and others [6][7][8][9][10][11]. In those studies, this ballistic phonon transport has been found * Electronic address: phyxiongdx@fzu.edu.cn † Electronic address: saadatmand.d@gmail.com ‡ Electronic address: dmitriev.sergey.v@gmail.com for (quasi)-1D samples having length less than a threshold value, L * (usually characterized by the phonon mean free path), such as that for SiGe nanowires L * ≈ 8.3 µm [9], for carbon nanotubes L * ≈ 1 mm [7], and for holey silicon L * ≈ 200 nm [10].…”

Solitons as candidates for energy carriers in Fermi-Pasta-Ulam lattices

“…One of the most intriguing phenomena is the anomalous energy transport in momentum-conserving lattices, which is the divergence of the thermal conductivity with the increasing lengths of lattices . This has been experimentally verified in one dimensional (1D) carbon nanotubes [28,29] and two dimensional (2D) graphenes [30].…”

Carbon-Based Materials for Thermoelectrics

“…Indeed, theoretical models [130][131][132] and numerical simulations [133] have predicted a divergent L when the length of 1D and 2D crystals increases. Recent experiments on millimeter-long SWCNTs [134] and up to 9 m long singlelayer graphene [135] have demonstrated divergent L , with a maximum room-temperature L of 8,640 W/m-K and 1,813 ± 111 W/m-K, respectively, even though there are concerns regarding the existence of radiative heat loss during the measurement on SWCNTs [136]. Such high L , however, renders CNT and graphene inappropriate as TE materials in their raw forms.…”