Thermal and Electrical Transport in Ultralow Density Single‐Walled Carbon Nanotube Networks

Zhang, Ke Jia; Yadav, Abhishek; Kim, Kyu Hun; Oh, Youngseok; Islam, Mohammad F.; Uher, Ctirad; Pipe, Kevin P.

doi:10.1002/adma.201300059

Cited by 43 publications

(37 citation statements)

References 43 publications

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“…For a CNT aerogel, taking G ¼ 40 pW/K (Fig. 2), L ¼ 1 lm, q ¼ 8 kg/m 3 , and D ¼ 0.81 nm, we obtain 0.015 W/mÁK, which is of the same order of magnitude as the measurements of Schiffres et al 4 and Zhang et al 5 The prediction is likely an underestimate, as the average junction thermal conductance will be higher due to different CNT orientations, as shown in Fig. 3.…”

supporting

confidence: 75%

“…2,3 For a CNT aerogel in vacuum at a temperature of 300 K, Schiffres et al report a thermal conductivity of 0.025 W/mÁK (q ¼ 8 kg/m 3 , which corresponds to a volume fraction of 0.006), 4 while Zhang et al report a value of 0.055 W/mÁK (q ¼ 6.6 kg/m 3 ). 5 These values are much lower than the 12 W/mÁK predicted from an effective medium approximation for a random network of cylinders using a single-walled CNT thermal conductivity of 3000 W/mÁK. 4 This result indicates that the thermal conductance of the junctions between CNTs must be taken into account when predicting thermal conductivity.…”

mentioning

confidence: 84%

“…7 Some estimates of the thermal conductance of the junction between single walled CNTs from thermal conductivity measurements on different network materials suggest values between 2 and 12 pW/K, 4,8,9 while Zhang et al estimate 60 pW/K. 5 Molecular dynamics (MD) simulations 8,10 and atomistic Green's function calculations 8,11 of perpendicular junctions between single-walled CNTs predict thermal conductances between 10 and 100 pW/K at a temperature of 300 K that increase with increasing CNT diameter. The origin of these larger values compared to the majority of the experimental estimates will be discussed later in the paper.…”

mentioning

confidence: 99%

“…(1)], 11 we predict a thermal conductivity for a CNT aerogel of the same order of magnitude as previous experimental measurements. 4,5 These thermal conductances will be useful as input to network-level thermal transport models.…”

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confidence: 99%

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Thermal conductance of the junction between single-walled carbon nanotubes

McGaughey

2014

Applied Physics Letters

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The thermal conductances of the carbon nanotube (CNT) junctions that would be found in a CNT aerogel are predicted using molecular dynamics simulations. At a temperature of 300 K, the thermal conductance of a perpendicular junction converges to 40 pW/K as the CNT lengths approach 100 nm. The key geometric parameter affecting the thermal conductance is the angle formed by the two CNTs. At pressures above 1 bar, the presence of a surrounding gas leads to an effective increase in the junction thermal conductance by providing a parallel path for energy flow. Networks of carbon nanotubes (CNTs) (e.g., aligned films, mats, and aerogels) are candidates for use in electronic and optoelectronic devices, as thermal interface materials, and for thermal insulation.1 Thermal management is a key issue in all of these applications. Our focus here is related to single-walled CNT aerogels, which are a high-porosity material (densities q of 6-20 kg/m 3 ) where the individual CNTs form a random network held together by van der Waals interactions.2,3 For a CNT aerogel in vacuum at a temperature of 300 K, Schiffres et al. report a thermal conductivity of 0.025 W/mÁK (q ¼ 8 kg/m 3

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supporting

confidence: 75%

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confidence: 84%

mentioning

confidence: 99%

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confidence: 99%

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Thermal conductance of the junction between single-walled carbon nanotubes

McGaughey

2014

Applied Physics Letters

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“…While the latter dependence has been discussed in terms of the characteristics of the inter-shell phonon transport in the multi-walled CNTs [63], the former observation suggests a strong sensitivity of the effective thermal conductivity of CNT materials to their structural organization. It also puts into question the reliability of the estimations of the inter-tube contact conductance based on the experimental values of the effective conductivity of CNT materials [47,51,64,65]. These estimations typically rely on analytical equations derived for idealized systems composed of randomly dispersed straight nanotubes [57,60,62,66], whereas the arrangement of CNTs into bundles in real CNT materials has been shown to have a dramatic effect on the inter-tube heat exchange and the effective thermal conductivity [60,62].…”

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confidence: 99%

Thermal conductance of carbon nanotube contacts: Molecular dynamics simulations and general description of the contact conductance

Salaway

Zhigilei

2016

Phys. Rev. B

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The contact conductance of carbon nanotube (CNT) junctions is the key factor that controls the collective heat transfer through CNT networks or CNT-based materials. An improved understanding of the dependence of the inter-tube conductance on the contact structure and local environment is needed for predictive computational modeling or theoretical description of the effective thermal conductivity of CNT materials. To investigate the effect of local structure on the thermal conductance across CNT-CNT contact regions, non-equilibrium molecular dynamics (MD) simulations are performed for different inter-tube contact configurations (parallel fully or partially overlapping CNTs and CNTs crossing each other at different angles) and local structural environments characteristic of CNT network materials. The results of MD simulations predict a stronger CNT length dependence present over a broader range of lengths than has been previously reported and suggest that the effect of neighboring junctions on the conductance of CNT-CNT junctions is weak and only present when the CNTs that make up the junctions are within the range of direct van der Waals interaction with each other. A detailed analysis of the results obtained for a diverse range of inter-tube contact configurations reveals a non-linear dependence of the conductance on the contact area (or number of interatomic inter-tube interactions) and suggests larger contributions to the conductance from areas of the contact where the density of interatomic inter-tube interactions is smaller. An empirical relation accounting for these observations and expressing the conductance of an arbitrary contact configuration through the total number of interatomic inter-tube interactions and the average number of interatomic inter-tube interactions per atom in the contact region is proposed. The empirical relation is found to provide a good quantitative description of the contact conductance for various CNT configurations investigated in the MD simulations and is suitable for incorporation into mesoscopic models capable of predicting the effective thermal transport properties of CNT materials.

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Joule Heating Characteristics of Emulsion‐Templated Graphene Aerogels

Menzel

Barg

Miranda

et al. 2014

Adv Funct Materials

103

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The Joule heating properties of an ultralight nanocarbon aerogel are investigated with a view to potential applications as energy-efficient, local gas heater and other systems. Thermallyreduced graphene oxide (rGO) aerogels (10 mg cm -3 ) with defined shape are produced via emulsion-templating. Relevant material properties, including thermal conductivity, electrical conductivity and porosity, are assessed. Repeatable Joule heating up to 200°C at comparatively low voltages (~ 1V) and electrical power inputs (~2.5 W cm -3 ) is demonstrated.The steady-state core and surface temperatures are measured, analyzed and compared to analogous two-dimensional nanocarbon film heaters. The assessment of temperature uniformity suggests that heat losses are dominated by conductive and convective heat dissipation at the temperature range studied. The radial temperature gradient of an uninsulated, Joule-heated sample is analyzed to estimate the aerogel's thermal conductivity (around 0.4 W m -1 K -1 ). Fast initial Joule heating kinetics and cooling rates (up to 10 K s -1 )were exploited for rapid and repeatable temperature cycling, important for potential 2 applications in catalysis and for the thermal regeneration of solid adsorbers. These principles may be relevant to wide range of nanocarbon networks and applications.

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Thermal and Electrical Transport in Ultralow Density Single‐Walled Carbon Nanotube Networks

Cited by 43 publications

References 43 publications

Thermal conductance of the junction between single-walled carbon nanotubes

Thermal conductance of the junction between single-walled carbon nanotubes

Thermal conductance of carbon nanotube contacts: Molecular dynamics simulations and general description of the contact conductance

Joule Heating Characteristics of Emulsion‐Templated Graphene Aerogels

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