Thermal Conductivity Of Single-walled Carbon Nanotubes Research Articles

Phenomenological model of thermal transport in carbon nanotube and hetero-nanotube films

The thermal properties of individual single-walled carbon nanotubes (SWCNTs) have been well documented in the literature following decades of intensive study. However, when SWCNTs form a macroscale assembly, the thermal transport in these complex structures usually not only depends on the properties of the individual tubes, but also is affected and sometimes dominated by inner structural details, e.g. bundles and junctions. In this work, we first performed an experimental measurement of the thermal conductivities of individual SWCNT bundles of different sizes using a suspended micro-thermometer. The results, together with the data that we obtained from a previous work, give a complete experimental understanding of the effect of bundling on the thermal conductivity of SWCNTs. With these quantitative understandings, we propose a phenomenological model to describe the thermal transport in two-dimensional (2D) SWCNT films. The term ‘line density’ is defined to describe the effective thermal transport channels in this complex 2D network. Along with experimentally obtained geometric statistics and film transparency, the thermal conductance of SWCNTs is estimated, and the effects of bundle length, diameter, and contact conductance are systematically discussed. Finally, we extend this model to explain thermal transport in 2D networks of one-dimensional van der Waals heterostructures, which are coaxial hetero-nanotubes we recently synthesized using SWCNTs as the template. This extended model suggests that the contribution of boron nitride nanotubes (BNNTs) to the overall performance of a SWCNT–BNNT heterostructured film depends on the transparency of the original SWCNT film. The increase in the thermal conductance of a highly transparent film is estimated to be larger than that of a less transparent film, which shows a good agreement with our experimental observations and proves the validity of the proposed phenomenological model.

Anharmonic Effects in Single-Walled Carbon Nanotubes Analyzed through Low-Temperature Raman Imaging

The high thermal conductivity of single-walled carbon nanotubes (SWCNTs) has gained much attention for their applications in potential thermal devices. Here, we investigate anharmonic effects, originated from phonon interactions, of SWCNT bundles by temperature dependent Raman imaging using our home-built mini cryostat system. The cryostat system is small enough to be mounted on a piezo scanner that suppresses thermal drift, enabling Raman imaging at different temperatures. We obtained Raman spectral images of several SWCNT bundles with a spatial resolution of a few hundred nanometers at different temperatures. We found that different bundles show different temperature dependences of Raman peak intensity, shift, and width. The temperature dependence was further elucidated by considering the sample topography observed by atomic force microscopy, where bundle effects seem to play an important role to influence the anharmonicity. The temperature-dependent Raman analysis based on spatially resolved imaging will be a powerful tool to investigate anharmonic effects of advanced carbon nanomaterials as well as to realize in situ visualization of thermal properties for future thermal devices.

Thermal Transport in Multi-Walled Carbon Nanotubes

Studies on heat conduction in nano-dimensional structures have raised numerous interests not only because of geometry dependent thermal transport but also apparently controllable heat dissipation in confined regions including the role of defects and impurity atoms. On reducing the structural size from bulk-to-nanoscale dimension, there will be significant alteration of specific heat capacity. So, thermal conductivity goes different in different temperature regimes approaching to a maximal value at 300 K for carbon nanotubes (CNTs). It may be noted that, unlike electronic contribution to the specific heat capacity, the lattice contribution in a 1D system varies as ~T (as compared to ~T3 trend for a 3D system). Though theoretically and practically thermal conductivity measurements have been carried out for SWCNT but no such theoretical works have been performed for double and triple wall carbon nanotube. We first established the theoretical calculation of thermal conductivity of DWCNT and TWCNT which matches with the experimental observations. The novelty of our work lies with the fact that we first found that as the no of walls increase in CNT from single to double to triple, thermal conductivity values decreases due to van der Waals interaction between the atoms of different walls. We see that thermal conductivity of single-wall CNT is very high (~3500 WmK-1), but it gets reduced to ~700 WmK-1 for a double-wall CNT. This drop is ascribed to incoherent heat dissipation owing significantly to the van der Waals interaction among the atoms of different co-axial walls

Chirality and Diameter Influence on Thermal Conductivity of Single-Walled Carbon Nanotubes.

Influence of chirality and diameter on thermal conductivity of Single-Walled Carbon Nanotube (SWNT) with different tube lengths have been investigated using non-equilibrium molecular dynamics (NEMD) method. The tube lengths of the SWNTs studied here are 20, 50 and 100 nm, respectively, and at each length the relationship between chiral angle and thermal conductivity of SWNT has been revealed; the dependence of thermal conductivity on diameter has also been studied. We find that chirality impact on thermal conductivity of SWNT is more obvious when tube length is relatively shorter, while diameter effect is more noticeable when tube gets longer. With larger chiral angle, thermal conductivity of chiral SWNTs is greater than that with smaller chiral angle and thermal conductivity increases with diameter.

Influence of chirality on the thermal conductivity of single-walled carbon nanotubes

The influence of chirality on the thermal conductivity of single-walled carbon nanotubes (SWNTs) is discussed in this paper, using a non-equilibrium molecular dynamics (NEMD) method. The tube lengths of the SWNTs studied here are 20, 50, and 100 nm, respectively, and at each length the relationship between chiral angle and thermal conductivity of a SWNT is revealed. We find that if the tube length is relatively short, the influence of chirality on the thermal conductivity of a SWNT is more obvious and that a SWNT with a larger chiral angle has a greater thermal conductivity. Moreover, the thermal conductivity of a zigzag SWNT is smaller than that of an armchair one. As the tube length becomes longer, the thermal conductivity increases while the influence of chirality on the thermal conductivity decreases.

Thermal Conductivity of Single-Walled Carbon Nanotube with Internal Heat Source Studied by Molecular Dynamics Simulation

The thermal conductivity of (5, 5) single-walled carbon nanotubes (SWNTs) with an internal heat source is investigated by using nonequilibrium molecular dynamics (NEMD) simulation incorporating uniform heat source and heat source-and-sink schemes. Compared with SWNTs without an internal heat source, i.e., by a fixed-temperature difference scheme, the thermal conductivity of SWNTs with an internal heat source is much lower, by as much as half in some cases, though it still increases with an increase of the tube length. Based on the theory of phonon dynamics, a function called the phonon free path distribution is defined to develop a simple one-dimensional heat conduction model considering an internal heat source, which can explain diffusive-ballistic heat transport in carbon nanotubes well.

Investigation of thermal conductivity of single-wall carbon nanotubes

In this paper, the thermal conductivity of Single-wall carbon nanotubes (SWCNTs) is determined by lattice vibrations (phonons) and free elections. The thermal conductivity of SWCNTs is modeled up to 8-300 K and the observed deviations in K-T figures of SWCNTs are explained in terms of phonon vibrations models. An suitable theoretical model is shown for thermal conductivity behavior with respect to temperature and is generalized for experimental results. This model enables us to calculate thermal conductivity SWNTs and Thermal Potential Energy (TPE).

Computational modeling of the thermal conductivity of single-walled carbonnanotube–polymer composites

A computational model was developed to study the thermal conductivity of single-walledcarbon nanotube (SWNT)–polymer composites. A random walk simulation was used tomodel the effect of interfacial resistance on the heat flow in different orientations of SWNTsdispersed in the polymers. The simulation is a modification of a previous model taking intoaccount the numerically determined thermal equilibrium factor between the SWNTs andthe composite matrix material. The simulation results agreed well with reportedexperimental data for epoxy and polymethyl methacrylate (PMMA) composites. Theeffects of the SWNT orientation, weight fraction and thermal boundary resistance on theeffective conductivity of composites were quantified. The present model is a useful tool forthe prediction of the thermal conductivity within a wide range of volume fractions of theSWNTs, so long as the SWNTs are not in contact with each other. The developedmodel can be applied to other polymers and solid materials, possibly even metals.

Experimental and theoretical study of the length-dependent thermal conductivity of individual single-walled carbon nanotubes

We report measurements on the length-dependent thermal conductivity of individual single-walled carbon nanotubes (SWNTs) on a substrate using a four-pad 3ω method with the consideration of heat loss between the sample and substrate. An increase in thermal conductivity with length (0.5—7μm) was observed at room temperature. The length-dependence of thermal conductivity was theoretically predicted by the modified WV model with consideration of second order-3-phonon process. The predicted phonon mean free path is about 175nm. Both the measurement and the prediction show the scale effect of the length on the thermal conductivity of SWNTs.

Length-dependent thermal conductivity of single-wall carbon nanotubes: prediction andmeasurements

In this paper, we propose a modified wavevector (WV) model that takes accountof the N-process relaxation time and second-order three-phonon process topredict the length dependence of the thermal conductivity of single-wallcarbon nanotubes (SWNTs). The model is validated by length-dependentthermal conductivities of individual SWNTs measured using the four-pad3ω method. The fitted Grüneisen parameter is close to 2 for SWNTs. These results indicatethat the effect of the second-order three-phonon process cannot be neglectedat room temperature. Both the experimental and theoretical results prove thatthe thermal conductivity increases with length of SWNTs over the range of0.5–7 µm.

Length Dependence of Thermal Conductivity of Single-WalledCarbon Nanotubes

Dependence of the thermal conductivity on the length of two armchairsingle-walled carbon nanotubes (SWNTs) is studied by the nonequilibriummolecular dynamics (MD) method with Brenner II potential. The thermalconductivities are calculated for (5, 5) and (7, 7) SWNTs with lengthsranging from 22 to 155 nm. The results show that the thermalconductivity of SWNTs is sensitive to the length and it does notconverge to a finite value when the tube length increases up to 155 nm,however it obeys a power law relation.