Thermal Conductivity Of Graphene Research Articles

Modulating Thermal Conductivity via Targeted Phonon Excitation.

Thermal conductivity is a critical material property in numerous applications, such as those related to thermoelectric devices and heat dissipation. Effectively modulating thermal conductivity has become a great concern in the field of heat conduction. Here, a quantum modulation strategy is proposed to modulate the thermal conductivity/heat flux by exciting targeted phonons. It shows that the thermal conductivity of graphene can be tailored in the range of 1559 W m-1 K-1 (decreased to 49%) to 4093 W m-1 K-1 (increased to 128%), compared with the intrinsic value of 3189 W m-1 K-1. The effects are also observed for graphene nanoribbons and bulk silicon. The results are obtained through both density functional theory calculations and molecular dynamics simulations. This novel modulation strategy may pave the way for quantum heat conduction.

Effect of Defect on Thermal Conductivity of Graphene

Effect of Defect on Thermal Conductivity of Graphene

Thermal Properties of Engine Oils through the Integration of Graphene Nanoparticles: A Greener Approach for Sustainable Mechanical Systems

Tribology is a high demand mechanical system with friction and wear. Mechanical systems lose efficiency as a result. One answer for this issue is to utilize an oil that can limit contact and wear, bringing about improved effectiveness. The advancement of effective lubricating added substances for tribological properties improvement and improved thermal conductivity has gotten huge modern and scholarly consideration. By and large, nano-sized particles scattered in lubricants, referred to as nano-based lubricant, are utilized in mechanical structures to lessen heat and forces of frictions. Moreover, new guidelines will empower the utilization of greener lubrication advancements in oils. To resolve this issue, lubricants should satisfy guidelines while able to give exceptional oil characteristics. As another green material, this research will investigate the dissolving of Graphene nanoparticles in lubricants. The objective of this study is to perceive what Graphene added 10W40 motor oil means for the thermal properties and tribological characteristics. Graphene, which was added to 10W40 lubricant, was used to study the best design. Graphene nanoparticles were distributed in baseline engine oil in a two-step process. In the preparation of Graphene-based motor oil with a low volume mixture in the scope of 0.01% to 0.07% was used. Thermal conductivity and viscosity are estimated for all volume mixtures. Testing uncovered that Graphene added 10W40 motor oil were steady all through the review, with very little deposits in the following 30 days. The thermal conductivity of Graphene in SAE 40 motor oil expanded as the volume mixture is added.

A graphene@Cu-MOF hybrid synthesized by mechanical ball milling method and its flame retardancy and smoke suppression effect on EP

The traditional method of preparing graphene will cause serious environmental pollution, and the combustion of polymer materials will seriously harm people's health. In this paper, a Cu-MOF-coated graphene composite flame retardant (G@Cu-MOF) rich in flame retardant elements such as B and N was synthesized through green mechanical ball milling method. Flame retardants reduce the threat to the environment and people's lives and property. After adding 6 wt% G@Cu-MOF, the peak heat release rate, total heat release rate, CO production and CO2 production of epoxy resin (EP) composite samples decreased by 55, 14, 59, and 55%, respectively. This type of Cu-MOF releases incombustible gases such as boron trifluoride (BF3) and ammonia (NH3) during combustion, diluting the concentration of combustible gases and producing copper borate in the condensed phase. Cu2+ is reduced to Cu, and boron compounds are converted into boron oxides. The thermal conductivity of graphene can reduce the temperature of the matrix, and has good flame retardancy. It synergistically acts with Cu-MOF to promote the formation of high-quality residual char, and can significantly inhibit the heat and smoke release of EP. It plays a role in flame retardancy and protecting the substrate from fire. This study provides a new approach for preparing graphene hybrid flame retardants through mechanical ball milling, in order to improve the flame retardancy of EP and suppress the release of smoke and toxic gases.

Theoretical study on structural, electronic, transport and thermoelectric properties of Si/Ge doped graphene

First-principles simulations are used in this study to show the structural, electronic, transport, and thermoelectric features of silicon and germanium-doped monolayer graphene. We employed a supercell of 2 × 2 × 1 graphene that contains 8 C atoms. One C atom was substituted by Si/Ge at a doping concentration of 12.5 %. The results obtained show that the band gap of pure graphene may be effectively opened and converted into a direct bandgap semiconductor material by replacing the C atom with Si/Ge atoms. Phonon dispersion provides a representation of the dynamical stability of all three structures. Graphene's thermal conductivity is also decreased when heteroatoms are added. Additionally, the Seebeck coefficient, the power factor, the electrical conductivity, and the figure of merit of pure, silicon, and germanium-doped graphene were investigated. This study offers a theoretical basis for using a heteroatom-doping process to improve the performance of graphene's electronic, transport, and thermoelectric characteristics.

Model Approach to Thermal Conductivity in Hybrid Graphene-Polymer Nanocomposites.

The thermal conductivity of epoxy nanocomposites filled with self-assembled hybrid nanoparticles composed of multilayered graphene nanoplatelets and anatase nanoparticles was described using an analytical model based on the effective medium approximation with a reasonable amount of input data. The proposed effective thickness approach allowed for the simplification of the thermal conductivity simulations in hybrid graphene@anatase TiO2 nanosheets by including the phenomenological thermal boundary resistance. The sensitivity of the modeled thermal conductivity to the geometrical and material parameters of filling particles and the host polymer matrix, filler's mass concentration, self-assembling degree, and Kapitza thermal boundary resistances at emerging interfaces was numerically evaluated. A fair agreement of the calculated and measured room-temperature thermal conductivity was obtained.

The Effect of Sonication Time on Thermal Conductivity and Stability of Graphene (Gr) and Aluminium Nitride (AlN)

Nanolubricants are a critical topic currently due to their outstanding thermal conductivity and system performance. A highly stable nanolubricant dispersion is extremely useful for good lubrication performance. However, maintaining their dispersion stability over time is still a major challenge in this field. As a result, the goal of this paper is to evaluate the influence of sonication duration on the stability and thermal conductivity of nanolubricants. In this work, 0.1 vol% concentrations of graphene (Gr) and aluminium nitride (AlN) nanoparticles and polyolester oil (POE) as the base fluid are used. The duration of mechanical stirrer is constant however the ultrasonication time is varied. The stability of nanolubricants are observed by using visual observation technique for 21 days and measured by thermal conductivity and Zeta potential. The results show that the 45 min of sonication time for AlN and 15 min of sonication time for Gr are the optimum time for the ultrasonication.

Thermal conductivity of monolayer graphene: Convergent and lower than diamond

Thermal conductivity of monolayer graphene: Convergent and lower than diamond

Heat transfer mechanism in graphene reinforced PEEK nanocomposites.

The thermal conductivity of graphene is in the range of 3000-5000 W m-1 K-1, showing great potential in high thermal conductivity devices. However, the thermal conductivity of graphene-reinforced polymer is typically lower than 10 W m-1 K-1, which is far from theoretical expectations. To understand the mechanisms of heat transfer in graphene-reinforced polymers, this work investigated the effect of graphene addition on the thermal conductive performance of polyetheretherketone (PEEK) matrix. The study examined the number of layers, deflection angles, and interlayer distances using molecular dynamics (MD) simulations. The results showed that the improvement of thermal conductivity of PEEK nanocomposite was not only related to the content of graphene but also to the angle between the benzene ring in the molecular chain of PEEK and the transfer direction of heat flow. Increasing the number of graphene layers is more beneficial to the enhancement of thermal conductivity. In particular, the enhancement of thermal conductivity is most significant when the number of graphene layers is the same, and the interlayer distance is less than the truncation radius.

Molecular dynamics study on the thermal conductivity and ballistic resistance of twisted graphene

The twist as a new degree of freedom induces several angle dependent properties in twisted graphene, such as electronic and optical properties. However, the ballistic resistance and thermal conductivity of twisted graphene remain not well understood and experimentally challenging. Therefore, the effect of interlayer twist angle on the thermal conductivity and ballistic resistance of bilayer graphene (BLG) has been explored using molecular dynamics simulation herein. Results show that the thermal conductivity of graphene is very sensitive to the twist angle of the interlayer plane. As the twist angle increases from 0° to 60°, the in-plane thermal conductivity of twisted bilayer graphene (t-BLG) first decreases and then increases with a periodic interval of 30°, exhibiting an asymmetric double V-shaped curve. And the cross-plane thermal conductivity of t-BLG gradually first decreases from 0° to 30° and then increases from 30° to 60°, also showing an asymmetric V-shaped curve. In contrast, the interlayer twist angle has a limited influence on the ballistic resistance of t-BLG. With the change of the twist angle, the ballistic limit velocity does not change much, and the fluctuation range is less than 1.56%; the relative kinetic energy also changes little with the fluctuation less than 4%. Such a slight difference is insufficient to make a significant change in its ballistic resistance and its impact resistance is mainly affected by the number of membrane layers. Each additional layer increases its ballistic limit speed by about 8%. This study will provide some theoretical guidance for the study of heat dissipation in the anti-ballistic process of twisted graphene and the design of advanced protective materials.

Polydopamine coating grown on the surface of fluorinated polymer to enhance the self-lubricating properties of lignin-cellulose based composites

In this paper, a novel ethanol-water Tris buffer system was developed to construct a polydopamine (PDA) protective layer on the surface of polytetrafluoro-wax (PFW) to obtain PFW@PDA with excellent hydrophilicity. The wood-based slurry was obtained by solvent encapsulation and lignin-cellulose assisted ball milling process using waste poplar powder and flake graphite as raw materials. PFW@PDA exhibited excellent dispersion stability in such aqueous slurry and the water was removed from the slurry by vacuum filtration to obtain paper-based composite films. Based on the self-reinforcement of the lignin-cellulose cross-linked network, construction of graphene thermal conductivity network, and the effectiveness of PFW@PDA for wear reduction and self-lubricating. This composite film exhibits excellent water resistance, good thermal stability, and superior mechanical properties. The friction coefficient and wear rate were reduced by 71.3 % and 166.7 %, respectively, compared with the unmodified material. Besides, the end-of-life products can be recycled by mechanical crushing in water, which exhibits a good balance between wear resistance and sustainability, providing a new idea for improving the hydrophilicity of fluorinated polymers and enhancing paper-based friction materials.

Structural, electronic, and transport properties of Ge doped graphene: A DFT study

Using the study of first principles, the structural, electronic, and transport characteristics of a monolayer graphene supercell doped with germanium are investigated. The effect of dopant on the aforementioned properties is examined as the germanium concentration ranges from 12.5% to 25%. It has been observed that hetero atom-like germanium doping can increase the band gap in graphene, enhancing its potential use as a thermoelectric material. We observed the semiconducting and zero band gap semiconducting behaviour of graphene due to variations in doping concentration. It is found that the Seebeck coefficient of pure graphene (C8) is positive, While the doped graphene structures (C7Ge1, C6Ge2) have negative Seebeck coefficients. The ZT of pure graphene is very low, but ZT can be improved by doping the Ge atom to the graphene structure. Also, it is shown that the concentration of doping has a significant impact on the graphene's thermal conductivity.

Thermal conductivity of quasi-bilayer graphene without and with perfluorophenylazide molecules

The obstacles in further improving the heat-transport performance of the graphene-based films root in the random stacking configuration of the graphene flakes and their agglomeration in solvents. In order to overcome these obstacles, we design one kind of quasi-bilayer graphene device composed of one upper narrow nanoribbon and one lower wide nanoribbon with absorbed perfluorophenylazide (PFPA) molecules. By investigating the thermal conductivity (TC) of the quasi-bilayer graphene without absorbed PFPA molecules, we find the TC will increase as the length and width increase, while the TC will decrease with the increase of the layer number. This indicates that a quasi-bilayer graphene flake of a large area and a small layer number will be beneficial to increasing its TC. Furthermore, in the presence of the PFPA molecules, the TC of the quasi-bilayer graphene, albeit suppressed by the PFPA molecules, is found to decrease slowly with the increase of the PFPA molecule number. This demonstrates a feasible way to fabricate the high-quality graphene-based films based on the technology of absorbing PFPA molecules. This research should be an important reference for designing the graphene-based thermal functional devices.

Dependence of thermal conductivity of graphene on the coefficient of linear expansion and temperature

Graphene attracts particular interest recently due to its extraordinary properties. Xu et al. have studied length-dependent thermal conductivity in suspended single-layer graphene. They observed that the thermal conductivity of graphene increases and remains logarithmic divergence with sample length. Yoon et al. observed that the coefficient of linear expansion (α) for graphene is always negative between at least up to 2500 K. In this paper, we study the dependence of thermal conductivity of graphene on the coefficient of linear expansion (CLE). We find that the thermal conductivity of graphene bears an exponential relationship with its CLE and is directly proportional to the sample length. Using the Slack equation, we have also found that the thermal conductivity of graphene is inversely proportional to the temperature and verified the relationship between the thermal conductivity of graphene and CLE. Due to this property graphene can be utilized to remove fish plates in railroads which can increase the efficiency of railway tracks.

Improved Electrical and Thermal Conductivities of Graphene–Carbon Nanotube Composite Film as an Advanced Thermal Interface Material

Thermal management has become a crucial issue for the rapid development of electronic devices, and thermal interface materials (TIMs) play an important role in improving heat dissipation. Recently, carbon−based TIMs, including graphene, reduced graphene oxide, and carbon nanotubes (CNTs) with high thermal conductivity, have attracted great attention. In this work, we provide graphene−carbon nanotube composite films with improved electrical and thermal conductivities. The composite films were prepared from mixed graphene oxide (GO) and CNT solutions and then were thermally reduced at a temperature greater than 2000 K to form a reduced graphene oxide (rGO)/CNT composite film. The added CNTs connect adjacent graphene layers, increase the interlayer interaction, and block the interlayer slipping of graphene layers, thereby improving the electrical conductivity, through−plane thermal conductivity, and mechanical properties of the rGO/CNT composite film at an appropriate CNT concentration. The rGO/CNT(4:1) composite film has the most desired properties with an electrical conductivity of ~2827 S/cm and an in−plane thermal conductivity of ~627 W/(m·K). The produced rGO/CNT composite film as a TIM will significantly improve the heat dissipation capability and has potential applications in thermal management of electronics.

Size-dependent interfacial thermal transport in supported platinum nanocatalysts

An approach-to-equilibrium molecule dynamics simulation was used to study the heat transfer process and corresponding thermal conductivity of graphene and TiO2-supported platinum (Pt) nanoparticles. The results showed that the larger the number of supported Pt atoms, the faster the particles and support reached the thermal equilibrium. The increased number of supported atoms and the enhanced metal-support interactions (MSIs) led to increased interfacial thermal conductance. According to the analysis of the phonon density of states, the increased interfacial thermal conductance was attributed to the vibrational frequencies of the particles and TiO2 support (strong MSI) being concentrated in the low-frequency region, improving the degree of coupling and promoting heat transfer. In addition, by combining a large amount of simulation data and existing models, we established a simple prediction model for evaluating the interfacial thermal conductance of supported Pt catalysts.

Recent advances in thermal conductivity and thermal applications of graphene and its derivatives nanofluids

• Seven factors should be considered in the study of graphene thermal conductivity. • Significant research gap exists in factors of graphene thermal conductivity. • Positive and negative effects both exist when graphene nanofluids are applied. • Economics and environment must be considered in application of graphene nanofluids. • More thermal studies on the graphene nanofluids are warranted. With the rapid development of industrial technology, more and more high-power-consumption devices are utilized, resulting in significant challenges to the durability, reliability, and efficiency of devices, facilities, and systems. Developing efficient thermal management systems for high power consumption application scenarios has evolved as a prominent research topic. Graphene nanomaterials are suitable candidates for nanofluids because of their excellent physical properties and high thermal conductivity. Although there are many studies on graphene nanofluids, there is no comprehensive review article about the influencing factors of thermal conductivity and the applications of graphene nanofluids, especially in economic and environmental analysis. This paper reviews the influencing factors of the graphene nanofluid thermal conductivity, including temperature, nanoparticle size and shape, base fluid, concentration, pH, surface modification, and ultrasonication. Moreover, the applications of graphene nanofluids in heat pipes, heat exchangers, solar collectors, and pool boiling devices are presented. Their applications are also discussed in terms of economics and the environment. In addition, the findings of thermal research on graphene nanofluids are summarized, and available opportunities and challenges are demonstrated. It is concluded that graphene nanomaterials significantly improve the thermal conductivity of the base fluid by 1.2% to 83.4%. Graphene nanofluids significantly improved the performance of thermal management devices. This comprehensive review is necessary to promote the research and effective application of graphene nanofluids in the context of sustainable development and carbon neutrality.

Superior Thermal Conductivity of Graphene Film/Cu-Zr Alloy Composites for Thermal Management Applications.

As the power density of electronic devices continuously increases, there is a growing demand to improve the heat conduction performance of thermal management materials for addressing heat dissipation issues. Single-/few-layer graphene is a promising candidate as a filler of a metal matrix due to its extremely high thermal conductivity (k); however, the well-arranged assembly of 2D-component graphene with a high volume fraction remains challenging. Herein, we integrated a novel graphene-based macroscopic material of graphene film (GF) into a Cu matrix by infiltrating molten Zr-microalloyed Cu into a spirally folded and upright-standing GFs skeleton. The microstructure of the GF/Cu composites was regulated by an interface modification strategy. The GF/Cu composites with a spirally layered microstructure exhibit a superior k of 820 W/m K in the axial direction, much higher than that of Cu-matrix composites reinforced with graphene nanosheets (generally <500 W/m K) and twice that of Cu. The thermal transfer mechanisms were investigated by experiments and theoretical calculations. The results reveal that the excellent performance is attributed to the construction of high-heat conduction channels and a positive coordinating effect at the Zr-modified GF/Cu interface. Meanwhile, the relation between interfacial microstructure and heat transfer is established in the composites using interfacial thermal resistance as a bridge. This work yields in-depth insight into the heat conduction mechanism in highly oriented structures and provides a promising solution for the thermal management issues of high-power electronics.

Anisotropic Enhancement in Thermal Conductivity of Graphene Foam/Polymer Composites Based on Uniaxial Compression

Front Cover: A novel structural optimization of graphene foam through uniaxial compression is proposed in article 2200373 by Jiaqi Zhu and co-workers, and leads to controllable and superior anisotropic thermal conductivity. The mechanism of this anisotropy is revealed and the effective thermal conductivity (ETC) prediction model is established, broadening the application scope of ETC prediction models in 3D thermal conductive fillers.

Controlling the Thermal Conductivity of Monolayer Graphene with Kirigami Structure

In this work, the thermal conductivity performance of graphene kirigami (GK) was systematically investigated via molecular dynamics (MD) simulations. The results indicate that the degree of defects (DD) on GK has a significant influence on thermal conductivity. Reducing the DD is the most effective way to decrease the thermal conductivity of GK. For zigzag-incised GK sheets, the change rate of thermal conductivity can reach up to 1.86 W/mK per 1% change in DD by tuning the incision length. The rate of changing thermal conductivity with DD can be slowed down by changing the width among incisions. Compared with the zigzag-incised GK sheets, heat transfer across the armchair-incised GK comes out more evenly, without significant steep and gentle stages along the heat transfer routes. More importantly, the GK structure can adjust the thermal conductivity by stretching, which the previously reported nanoporous graphene does not have. The change rate of thermal conductivity achieves about 0.17 W/mK with 1% stretching strain for simulated GK and can be further reduced at high tensile strain rates, benefiting the precise and variable control of the thermal conductivity of the monolayer graphene.