Thermal Conductivity Of Carbon Nanotubes Research Articles

Vertical Single-Wall Carbon Nanotube Forests as Plasmonic Heat Pipes

High thermal conductivity of carbon nanotubes (NTs) is attractive for the heat removal applications. However, the problem of efficient thermal coupling to the heater/cooler still needs to be resolved. We study near-field electromagnetic tunneling as a mechanism of heat transfer across the interface. We report interface thermal (Kapitza) conductance between a low-density vertical metallic single-wall NT forest and a quartz substrate on the order of 50 MW/Km(2) and explain it by strong electromagnetic interaction and near-field entanglement between the surface phonon-polaritons in the polar dielectric and the NT plasmons. We predict that the thickness of the NT film can be tweaked to the resonance wavelength of these entangled modes for performance optimization of nanocarbon thermal interconnects.

Thermal and Thermoelectric Transport in Nanostructures and Low-Dimensional Systems

Significant progress has been made in recent studies of thermal and thermoelectric transport phenomena in nanostructures and low-dimensional systems. This article reviews several intriguing quantum and classical size effects on thermal and thermoelectric properties that have been predicted by theoretical calculations or observed in experiments. Attention is focused on the Casimir limit in phonon boundary scattering and the effect of phonon confinement on the lattice thermal conductivity of semiconductor nanowires (NWs) and nanomeshes; the effects of thickness, lateral size, and interface interaction on the lattice thermal conductivity of carbon nanotubes (CNTs) and graphene; and the phonon-drag thermopower and quantum size effects on the thermoelectric power factor in semiconductor NWs. Further experimental and theoretical investigations are suggested for better understanding of some of these nanoscale transport phenomena.

Thermal Conductivity of Polymer/Carbon Nanotube Composites

As one of the most important field of current nanoscience, the polymer nanocomposites is a promising and efficient way for new generation materials with high performances and multifunctionalities. The incorporating of nanofillers in a polymer matrix may improve mechanical, thermal, electrical or dielectric properties of the composites. The current paper focuses on the thermal conductivity of polymer/carbon nanotube composites. These last, are considered to be ideal candidates for the development of nanocomposite materials. Clarifying the role of the factors, influencing the properties of the composites, enable us to choose the suitable processing method for obtaining the composites and to improve the different properties of these systems. This article reviews the dependence of thermal conductivity of carbon nanotubes on the tube size and the effect of interface on the equivalent property. The relationship between the thermal conductivity and the nanostructure of composites are discussed.

Thermal conductivity of carbon nanotube nanofluid—Experimental and theoretical study

AbstractIn this work, thermal conductivity of carbon nanotubes' (CNTs) nanofluid is studied both experimentally and theoretically. CNT nanofluids were stabilized using gum arabic (GA). The concentration of CNTs was varied from 0.01–0.1 wt% while the concentration of GA was varied from 1–2.5 wt%, respectively. The effect of particle volume fraction and temperature on the thermal conductivity enhancement of the nanofluids was also studied. A simple thermal conductivity model which demonstrates the effect of diameter and aspect ratio of the CNTs and takes into account the effect of temperature on thermal conductivity enhancement is presented. Good agreement between experimental and estimated values proves that the proposed model can provide precise prediction of the thermal conductivity of fluid containing CNTs. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.20405

Research on the influences of point defects on the thermal conductivity of carbon nanotube by simulation with orthogonal array testing strategy

In the preparation process of carbon nanotubes, various point defects inevitably come into being in the lattice structures. The defects strongly affect the thermal transport properties of carbon nanotubes. Thermal conduction in carbon nanotube is simulated by using nonequilibrium molecular dynamics method with reactive bond order (REBO) potential. Thermal conductivities of carbon nanotubes with and without defects are calculated for comparison. An orthogonal array testing strategy is employed. In the calculation it greatly saves the experimental effort and identifies the degrees of influence of such structural factors as defect type, tube length, tube radius, etc. on thermal conductivity of tube. The effects of three types of point defects: vacancy, doping and adsorption are primarily studied, and the ambient temperature factor is also analyzed. Simulation results show that the thermal conductivity of carbon nanotubes with defects decreases significantly due to point defects compared with that of perfect carbon nanotubes. The defect type has the first greatest influence on the decrease of thermal conductivity, and hvae the second third greatest infuluences respeetively the radius and the length of carbon nanotubes. The degrees of influence of the above types of point defect are in the order of vacancydopingadsorption. Different types of point defects have different effects on tubes at different ambient temperatures.

Influence of Thermal Boundary Resistance and Interfacial Phonon Scattering on Heat Conduction of Carbon Nanotube/Polymer Composites

Polymer nanocomposites are one of the most promising applications of carbon nanotubes (CNTs). In order to improve their thermal properties, it is important to understand their heat conduction characteristics from a microscopic viewpoint. In this study, we have investigated the heat conduction of CNT/polyethylene composites by using molecular dynamics simulations. We particularly focused on the thermal boundary conductance across CNT/polyethylene interfaces and thermal conductivity of CNT in polyethylene matrix, which govern the overall thermal conductivity of CNT/polyethylene composites. We found relatively low thermal boundary conductance across CNT/polyethylene interfaces (～10 MWm-2K-1) and a moderate but non-negligible thermal conductivity reduction of CNT in polyethylene matrix (22 %). By the mode-dependent phonon transport analysis, the thermal conductivity reduction was identified to be mainly due to scattering of low frequency CNT phonons by polyethylene. The results obtained through an effective medium approximation model give overall thermal conductivity of the CNT/polyethylene composite that is in agreement with experiments.

Thermal Conductance of Buckled Carbon Nanotubes

Knowledge of thermal conductance of carbon nanotubes under mechanical deformation is important to characterize the robustness of carbon nanotube heat conduction. In this study, using molecular dynamics simulations, we have calculated thermal conductance of an elastically buckled single-walled carbon nanotube. A local buckle was formed by mechanically bending a carbon nanotube at an angle of 60°, and thermal conductance through the buckle was calculated by a nonequilibrium molecular dynamics approach. The thermal conductance exhibits strong diameter dependence, correlated with the strain energy generated in the buckle. Despite the highly strained deformation, the thermal resistance across a buckle is similar to that of a point defect and heterotube junction, revealing a robust nature of carbon nanotube heat conduction to buckling deformation.

Thermal conductivity of carbon nanotubes and graphene in epoxy nanofluids and nanocomposites

We employed an easy and direct method to measure the thermal conductivity of epoxy in the liquid (nanofluid) and solid (nanocomposite) states using both rodlike and platelet-like carbon-based nanostructures. Comparing the experimental results with the theoretical model, an anomalous enhancement was obtained with multiwall carbon nanotubes, probably due to their layered structure and lowest surface resistance. Puzzling results for functionalized graphene sheet nanocomposites suggest that phonon coupling of the vibrational modes of the graphene and of the polymeric matrix plays a dominant role on the thermal conductivities of the liquid and solid states.PACS: 74.25.fc; 81.05.Qk; 81.07.Pr.

Raman Characterization of Thermal Conduction in Transparent Carbon Nanotube Films

Using materials with high thermal conductivity is a matter of great concern in the field of thermal management. In this study, we present our experimental results on two-dimensional thermal conductivity of carbon nanotube (CNT) films obtained by using an optical method based on Raman spectroscopy. We use four kinds of CNTs in film preparation to investigate the effect of CNT type on heat spreading performance of CNT films. This first comparative study using the optical method shows that the arc-discharge single-walled carbon nanotubes yield the best heat spreading film. We also show that the Raman method renders reasonable thermal conductivity value as long as the sample is a transparent film by testing CNT films with various transmittance. This study provides useful information on characterization of thermal conduction in transparent CNT films and could be an important step toward high-performance carbon-based heat spreading films.

Tuning thermal transport in nanotubes with topological defects

Using the atomistic nonequilibrium Green’s function, we find that thermal conductance of carbon nanotubes with presence of topological lattice imperfects is remarkably reduced, due to the strong Rayleigh scattering of high-frequency phonons. Phonon transmission across multiple defects behaves as a cascade scattering based with the random phase approximation. We elucidate that phonon scattering by structural defects is related to the spatial fluctuations of local vibrational density of states (LVDOS). An effective method of tuning thermal transport in low-dimensional systems through the modulation of LVDOS has been proposed. Our findings provide insights into experimentally controlling thermal transport in nanoscale devices.

Atomistic Simulations of Heat Transport in Carbon Nanotubes Effected by Temperature and Stretch Strain

Carbon nanotubes (CNTs) is a well thermal transport nano materials, however, the thermal conductivity of CNTs has not been well established, only a few groups had reported experimental data and the existed simulation results ranged widely. Specially, the conclusions in low temperature section and dynamic structures were not very clearly. In this paper, the methods based on phonon scattering theory were applied to explore the thermal transport properties CNTs. The investigation was carried out under the conditions of temperature and axial strain. In the consideration of quantum effect, the thermal conductivity increased linearly with the growth of temperature in low-temperature section, and began to decrease gradually when the temperature exceeded a definite value. If an axial strain was concerned, there was an increasing trend of thermal conductivity as the stretch strain increases. However, after the strain exceeded a particular value the thermal conductivity decreased significantly. In addition, the high frequency phonon peak in PDOS was found to be an important parameter in describing thermal transport properties of dynamic structures.

Measurement of the Thermal Conductivity of Carbon Nanotube–Tissue Phantom Composites with the Hot Wire Probe Method

Developing combinatorial treatments involving laser irradiation and nanoparticles require an understanding of the effect of nanoparticle inclusion on tissue thermal properties, such as thermal conductivity. This information will permit a more accurate prediction of temperature distribution and tumor response following therapy, as well as provide additional information to aid in the selection of the appropriate type and concentration of nanoparticles. This study measured the thermal conductivity of tissue representative phantoms containing varying types and concentrations of carbon nanotubes (CNTs). Multi-walled carbon nanotubes (MWNTs, length of 900-1200nm and diameter of 40-60nm), single-walled carbon nanotubes (SWNTs, length of 900-1200nm and diameter <2nm), and a novel embodiment of SWNTs referred to as single-walled carbon nanohorns (SWNHs, length of 25-50nm and diameter of 3-5nm) of varying concentrations (0.1, 0.5, and 1.0mg/mL) were uniformly dispersed in sodium alginate tissue representative phantoms. The thermal conductivity of phantoms containing CNTs was measured using a hot wire probe method. Increasing CNT concentration from 0 to 1.0mg/mL caused the thermal conductivity of phantoms containing SWNTs, SWNHs, and MWNTs to increase by 24, 30, and 66%, respectively. For identical CNT concentrations, phantoms containing MWNTs possessed the highest thermal conductivity.

Thermal conductivity and thermal rectification in carbon nanotubes with geometric variations of doped nitrogen: Non-equilibrium molecular dynamics simulations

The thermal conductivity of carbon nanotubes with geometric variations of doped nitrogen is investigated. The phenomenon of thermal rectification shows that the heat transport is preferably in one direction. The asymmetric heat transport of the triangular single-nitrogen-doped carbon nanotubes (SNDCNTs) is larger than that of the parallel various-nitrogen-doped carbon nanotubes (VNDCNTs).

Diameter dependence of carbon nanotube thermal conductivity and extension to the graphene limit

Using an exact numerical solution of the phonon Boltzmann equation, we demonstrate a nontrivial evolution with diameter of the intrinsic lattice thermal conductivity, $\ensuremath{\kappa}$, of a wide range of achiral and chiral single-walled carbon nanotubes (SWCNTs) into that of graphene, ${\ensuremath{\kappa}}_{graphene}$. We find that $\ensuremath{\kappa}&lt;{\ensuremath{\kappa}}_{graphene}$ for all but the smallest diameter SWCNTs and that $\ensuremath{\kappa}$ exhibits a minimum for modest diameters. This behavior results because the inherent curvature in SWCNTs violates a selection rule in graphene arising from its reflection symmetry, which strongly restricts phonon-phonon scattering in that system.

Thermal conductivity of carbon nanotube reinforced aluminum composites: A multi-scale study using object oriented finite element method

In this study, object oriented finite element method (OOF) has been utilized to compute the thermal conductivity of plasma sprayed Al-12 wt.% Si containing 10 wt.% multiwall carbon nanotubes (CNTs). The computations have been made at micro- and macro-length scales which highlight the effect of CNT dispersion on thermal conductivity. Experimentally measured values at 50 °C indicate that CNT addition reduced the thermal conductivity of Al–Si matrix from 73 W m −1 K −1 to 25.4 W m −1 K −1 which is attributed to the presence of CNT clusters. OOF calculations at micro-length scale predicted an 81% increase in the conductivity of Al–Si matrix due to presence of well dispersed CNTs inside the matrix. At larger lengths scale, the decrease in the overall conductivity is related to the extremely low conductivity of CNT clusters. Thermal conductivity of CNT clusters could be up to three orders of magnitude lower than individual CNTs. OOF computed values match well with experimental results. OOF compute thermal conductivity of Al–CNT composite is also compared with theoretical two-phase models for CNT-composites at different length scales.

Dispersibility dependence of thermal conductivity of carbon nanotube based nanofluids

A differential effective medium theory together with Brownian motion is used to predict Effective Thermal Conductivity (ETC) of CNT nanofluids. ETC was influenced significantly by Brownian motion and enhancement was higher in dilute nanofluids. A theoretical model employing an effective volume fraction with dispersibility factor agrees well with experimental data.

Multiwalled carbon nanotubes as a contributing reinforcement phase for the improvement of thermal conductivity in copper matrix composites

The thermal conductivities of carbon nanotube (CNT)–copper (Cu) composites are greatly increased for compositions containing up to 1 vol.% CNT and remain above the value for pure Cu up to 3 vol.% CNT. The obtained enhancement was in good agreement with estimates based on Eshelby’s equivalent inclusion method. This agreement suggests that very low thermal resistance might be realized at the interface between CNTs and the Cu matrix, which consists of faceted and closely attached interface without any compounds.

The role of different parameters on the stability and thermal conductivity of carbon nanotube/water nanofluids

It is obvious that the applicability and efficiency of nanofluids (suspensions contained nanoparticles) are related to their high heat transfer coefficients, especially thermal conductivity. Many parameters affect this property including size, shape and source of nanoparticles, surfactants, power of ultrasonic, time of ultrasonication, elapsed time after ultrasonication, pH, temperature, particle concentration and surfactant concentration. Some of these parameters may have interaction effects. An accepted way for obtaining the optimized condition is based on the design of experiments and statistical analysis. In this paper we investigate the stability and thermal conductivity of carbon nanotube (CNT)/water nanofluids and propose the optimum condition for the production and application of nanofluids. It has been shown that the significant factors on the thermal conductivity and stability are not precisely similar to one another.

Thermal conductivity of carbon nanotubes

This paper addresses the problem of modeling the thermal conductivity of carbon nanotubes (CNTs) of submicron length that have relatively low point-defect concentrations. Point defects are taken into account at the ends of these CNTs to model the commonly encountered situation where point defects are introduced unintentionally at the ends of the CNT under prevailing fabrication methods. Herein, previous models for thermal transport in graphite are adapted to investigate the thermal transport properties of CNTs.

Thermal conductivity of carbon nanotubes with quantum correction via heatcapacity

The molecular dynamics simulation with the use of the empirical Tersoff potential isapplied to study the thermal characteristics of carbon nanotubes (CNTs). A thermalreservoir is devised to control the temperature and to exact the heat flux input. Thequantum effect defining the precise temperature from the absolute zero Kelvin and up isincluded by applying phonon (boson) statistics to the specific heat. At low temperature,the CNT thermal conductivity increases with increasing temperature. After reaching itspeak, which is limited by the length of the CNT, it decreases with temperature dueto phonon–phonon interactions. The scaling law of thermal conductivity as afunction of temperature and length is inferred from the simulation results, allowingprediction for CNTs of much longer length beyond what MD could simulate.