The superior effect of edge functionalization relative to basal plane functionalization of graphene in enhancing the thermal conductivity of polymer–graphene nanocomposites – a combined molecular dynamics and Green's functions study (original) (raw)
2022
To achieve high thermal conductivity (k) of polymer graphene nanocomposites, it is critically important to achieve efficient thermal coupling between graphene and its surrounding polymers through effective functionalization schemes. In this work, we demonstrate that edge-functionalization of graphene nanoplatelets (GnPs) can enable a larger enhancement of effective thermal conductivity in polymer-graphene nanocomposites, relative to basal plane functionalization. Effective thermal conductivity for edge case is predicted, through molecular dynamics simulations, to be up to 48% higher relative to basal plane bonding for 35 wt.% graphene loading with 10 layers thick nanoplatelets. This unique result opens up promising new avenues for achieving high thermal-conductivity polymer materials, which is of key importance for a wide range of thermal management technologies. The anisotropy of thermal transport in single layer graphene leads to very high in-plane thermal conductivity (~2000 W/mK...
In this work, we demonstrate that edge-oxidation of graphene nanoplatelets (GnPs) can enable a larger enhancement of effective thermal conductivity (k) in polyetherimide (PEI)-graphene nanocomposites, relative to basal plane functionalization. Edge oxidation is achieved in this work by using a chemical scheme (recently introduced) involving oxidizing graphene in presence of sodium chlorate and hydrogen peroxide, introducing an excess of carboxyl groups on the edge of graphene. Edge oxidation offers the advantage of preserving the high in-plane thermal conductivity of graphene (kin > 2000 W/mK)), while also coupling polymer to this high-in plane thermal conduction pathway of graphene. Carboxyl-moieties on edge-oxidized graphene enhance interfacial thermal transport by interacting with oxygen groups on polyetherimide through hydrogen bonding, resulting in enhancement of overall composite thermal conductivity. Basalplane oxidation of graphene, on the other hand, achieved through modified Hummers method, distorts sp 2 carbon-carbon network of graphene lowering its intrinsic thermal conductivity. The resulting thermal conductivity of edge-oxidized GnP/PEI composite is found to be enhanced by 18%, whereas that of basal-plane functionalized GnP/PEI composite is diminished by 57%, with respect to pristine GnP/PEI composite for 10 weight% filler content. 2-dimensional Raman spectroscopy of individual graphene nanoplatelets is used to confirm and distinguish the location of oxygen functional groups on graphene. Presented results can lead to fundamentally novel pathways for achieving high thermal-conductivity polymer composites.
Model Approach to Thermal Conductivity in Hybrid Graphene–Polymer Nanocomposites
Molecules
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.
Duality of the interfacial thermal conductance in graphene-based nanocomposites
Carbon, 2014
The thermal conductance of graphene-matrix interfaces plays a key role in controlling the thermal properties of graphene-based nanocomposites. Using atomistic simulations, we found that the interfacial thermal conductance depends strongly on the mode of heat transfer at graphene-matrix interfaces: if heat enters graphene from one side of its basal plane and immediately leaves it through the other side, the corresponding interfacial thermal conductance, G across , is large; if heat enters graphene from both sides of its basal plane and leaves it at a position far away on its basal plane, the corresponding interfacial thermal conductance, G non-across , is small. For a single-layer graphene immersed in liquid octane, G across is 150MW/m2KwhileGnon−acrossis150 MW/m 2 K while G non-across is 150MW/m2KwhileGnon−acrossis5 MW/m 2 K. G across decreases with increasing multi-layer graphene thickness (i.e., number of layers in graphene) and approaches an asymptotic value of 100 MW/m 2 K for 7-layer graphenes. G non-across increases only marginally as the graphene sheet thickness increases. Such a duality of the interface thermal conductance for different probing methods and its dependence on graphene sheet thickness can be traced ultimately to the unique physical and chemical structure of graphene materials. The ramifications of these results in areas such as the optimal design of graphene-based thermal nanocomposites are discussed.
Nanomaterials, 2020
Thermal conductivity (k) of polymers is usually limited to low values of ~0.5 Wm−1K−1 in comparison to metals (>20 Wm−1K−1). (100)T3//(926)T4 The goal of this work is to enhance thermal conductivity (k) of polyethylene–graphene nanocomposites through simultaneous alignment of polyethylene (PE) lamellae and graphene nanoplatelets (GnP). Alignment is achieved through the application of strain. Measured values are compared with predictions from effective medium theory. A twin conical screw micro compounder is used to prepare polyethylene–graphene nanoplatelet (PE-GnP) composites. Enhancement in k value is studied for two different compositions with GnP content of 9 wt% and 13 wt% and for applied strains ranging from 0% to 300%. Aligned PE-GnP composites with 13 wt% GnP displays ~1000% enhancement in k at an applied strain of 300%, relative to k of pristine unstrained polymer. Laser Scanning Confocal Microscopy (LSCM) is used to quantitatively characterize the alignment of GnP flakes...
Thermal transmittance in graphene based networks for polymer matrix composites
Graphene nanoribbons (GNRs) can be added as llers in polymer matrix composites for enhancing their thermo-mechanical properties. In the present study, we focus on the eect of chemical and geometrical characteristics of GNRs on the thermal conduction properties of composite materials. Congurations consisting of single and triple GNRs are here considered as representative building blocks of larger ller networks. In particular, GNRs with dierent length, relative orientation and number of cross-linkers are investigated. Based on results obtained by Reverse Non-equilibrium Molecular Dynamics simulations, we report correlations relating thermal conductivity and thermal boundary resistance of GNRs with their geometrical and chemical characteristics. These eects in turn aect the overall thermal transmittance of graphene based networks. In the broader context of eective medium theory, such results could be benecial to predict the thermal transport properties of devices made of polymer matrix composites, which currently nd application in energy, automotive, aerospace, electronics, sporting goods, and infrastructure industries.
Thermally Conductive Graphene-Polymer Composites: Size, Percolation, and Synergy Effects
The rapidly increasing device densities in electronics dictate the need for efficient thermal management. If successfully exploited, graphene, which possesses extraordinary thermal properties, can be commercially utilized in polymer composites with ultrahigh thermal conductivity (TC). The total potential of graphene to enhance TC, however, is restricted by the large interfacial thermal resistance between the polymer mediated graphene boundaries. We report a facile and scalable dispersion of commercially available graphene nanoplatelets (GnPs) in a polymer matrix, which formed composite with an ultrahigh TC of 12.4 W/m K (vs 0.2 W/m K for neat polymer). This ultrahigh TC was achieved by applying high compression forces during the dispersion that resulted in the closure of gaps between adjacent GnPs with large lateral dimensions and low defect densities. We also found strong evidence for the existence of a thermal percolation threshold. Finally, the addition of electrically insulating boron-nitride nanoparticles to the thermally conductive GnP-polymer composite significantly reduces its electrical conductivity (to avoid short circuit) and synergistically increases the TC. The efficient dispersion of commercially available GnPs in polymer matrix provides the ideal framework for substantial progress toward the large-scale production and commercialization of GnP-based thermally conductive composites.
Heat conduction in graphite-nanoplatelet-reinforced polymer nanocomposites
Applied Physics Letters, 2006
Heat transport in polymer nanocomposites reinforced with graphite nanoplatelets (GNPs) is studied using high-precision thermal conductivity measurements. The resistance to heat conduction across interfaces between GNPs and the polymer matrix has a strong effect on energy transport in the nanocomposites. The thermal conductivity is observed to increase when GNPs are pretreated with nitric acid to improve interfacial bonding. The improvement in the thermal conductivity, however, is much smaller than the corresponding improvement in mechanical properties. The thermal interface resistance extracted from the present thermal conductivity data is comparable to that obtained from the previously reported data on carbon nanotube suspensions. (
Nanoscale, 2017
The effect of simultaneous alignment of polyethylene (PE) lamellae and graphene nanoplatelets (GnP) on the thermal conductivity (k) of PE-GnP composites is investigated. Measurements reveal a large increase of 1100% in k of the aligned PE-GnP composite using 10 wt% GnPs relative to unoriented pure PE. The rate of increase of k with applied strain for the pure PE-GnP composite with 10 wt% GnP is found to be almost a factor of two higher than the pure PE sample, pointing to the beneficial effect of GnP alignment on k enhancement. Aligned GnPs are further found to be 3 times as effective in enhancing k as in the randomly oriented configuration. Enhancement in k is correlated with the alignment of PE lamellae and GnPs through wide-angle X-ray scattering and polarized Raman spectroscopy. At the maximum applied strain of 400% and using 10 wt% GnPs, a composite k of 5.9 W mK(-1) is achieved. These results demonstrate the great potential of simultaneous alignment effects in achieving high k...
Enhanced thermal conductivity of graphene nanoplatelets epoxy composites
Materials Science-Poland
Efficient heat dissipation from modern electronic devices is a key issue for their proper performance. An important role in the assembly of electronic devices is played by polymers, due to their simple application and easiness of processing. The thermal conductivity of pure polymers is relatively low and addition of thermally conductive particles into polymer matrix is the method to enhance the overall thermal conductivity of the composite. The aim of the presented work is to examine a possibility of increasing the thermal conductivity of the filled epoxy resin systems, applicable for electrical insulation, by the use of composites filled with graphene nanoplatelets. It is remarkable that the addition of only 4 wt.% of graphene could lead to 132 % increase in thermal conductivity. In this study, several new aspects of graphene composites such as sedimentation effects or temperature dependence of thermal conductivity have been presented. The thermal conductivity results were also com...
Functionalization mediates heat transport in graphene nanoflakes
Nature communications, 2016
The high thermal conductivity of graphene and few-layer graphene undergoes severe degradations through contact with the substrate. Here we show experimentally that the thermal management of a micro heater is substantially improved by introducing alternative heat-escaping channels into a graphene-based film bonded to functionalized graphene oxide through amino-silane molecules. Using a resistance temperature probe for in situ monitoring we demonstrate that the hotspot temperature was lowered by ∼28 °C for a chip operating at 1,300 W cm(-2). Thermal resistance probed by pulsed photothermal reflectance measurements demonstrated an improved thermal coupling due to functionalization on the graphene-graphene oxide interface. Three functionalization molecules manifest distinct interfacial thermal transport behaviour, corroborating our atomistic calculations in unveiling the role of molecular chain length and functional groups. Molecular dynamics simulations reveal that the functionalizatio...
Modeling issues regarding thermal conductivity of graphene-based nanocomposites
2018
Modeling thermal conductivity of graphene-based nanocomposites is analyzed from an effective medium approximation point of view, where interfacial thermal resistance and arbitrary shape of the fillers are considered. Two approximations, Maxwell-Garnett and coherent potential approximation, are used to show that the usual oblate spheroidal shape approximation of graphene nanodots is not satisfactory to model thermal conductivity in graphene-based composites. Key-words: Composites, graphene, graphene-based composites, thermal conductivity, thermal interface materials, Maxwell-Garnett approximation, coherent potential approximation.
Thermal Transport in Graphene Composites: The Effect of Lateral Dimensions of Graphene Fillers
2021
We report on the investigation of thermal transport in non-cured silicone composites with graphene fillers of different lateral dimensions. Graphene fillers are comprised of few-layer graphene flakes with lateral sizes in the range from 400 nm to 1200 nm and number of atomic planes from one to ~100. The distribution of the lateral dimensions and thicknesses of graphene fillers has been determined via atomic force microscopy statistics. It was found that in the examined range of the lateral dimensions the thermal conductivity of the composites increases with the increasing size of the graphene fillers. The observed difference in thermal properties can be related to the average gray phonon mean free path in graphene, which has been estimated to be around ~800 nm at room temperature. The thermal contact resistance of composites with graphene fillers of 1200-nm lateral dimensions was also smaller than that of composites with graphene fillers of 400-nm lateral dimensions. The effects of ...
Thermal conductivity of graphene nanoplatelet/cycloaliphatic epoxy composites: Multiscale modeling
Carbon, 2018
Composite materials using cycloaliphatic epoxy (CE) resins are used in some structural applications that require resistance to aggressive environments. Specifically, CE-based composites are used for structural reinforcement in aluminum conductor composite core (ACCC) high-voltage power lines. However, CE resins have a relatively low thermal conductivity, which makes it difficult to dissipate localized heating due to transmission line faults. Graphene nanoplatelet (GNP) reinforcement can potentially improve the thermal conductivity of CE composites (~0.2 W/m-K) due to its superior in-plane thermal conductivity (~5,300 W/m-K). In this study, the thermal conductivities of GNP/CE composites are investigated by multiscale modeling using molecular dynamics (MD) and micromechanics simulation techniques. Different levels of GNP dispersion and aspect ratio are studied and compared to experimental data established herein and in the literature. The thermal conductivity of GNP/CE composites increases with increased GNP content, dispersion, and aspect ratio. Additionally, covalently functionalized GNP/CE systems are simulated to determine the effect of functionalization on thermal conductivity. The transverse thermal conductivity of GNP/CF/CE hybrid composites is further investigated and validated with experimental values. This study establishes a unique multiscale modeling approach for predicting thermal conductivity of polymer nanocomposite materials (and hybrid composite materials) based on molecular structure of the nanoreinforcement/polymer interface.
Thermal behavior of thermoplastic polymer nanocomposites containing graphene nanoplatelets
Journal of Applied Polymer Science, 2017
Polypropylene (PP), acrylonitrile butadiene styrene (ABS), and thermoplastic polyurethane (TPU) nanocomposites filled with 5 wt % of two different kinds of commercially available graphene nanoplatelets (GNPs) were prepared. Composites materials were characterized in terms of thermal properties (thermal conductivity and thermal stability) in order to study the effect of different fillers within different thermoplastic matrices. The exfoliation process and the mechanical properties were also investigated. We chose three different thermoplastic polymers (polyolefin, copolymer and elastomer) to cover a wide range of thermoplastic materials and identify a guideline in the use of GNPs for nanocomposite materials. No drastic differences were observed in terms of mechanical properties when the same matrices were filled with different GNPs. Concerning thermal conductivity, it was observed that the GNPs plane dimensions play a crucial role in the increase of conductive properties.
Polymer Composites, 2018
In-plane alignment of graphene nanoplatelets (GNPs) in thin thermal interface material layers suppresses the through-plane heat transport, which limits the performance of materials. In order to suppress the in-plane alignment of the GNP filler within polypropylene (PP) and increase the through-plane component, modification of GNP (MG) was performed in this study. For this aim, GNP was treated with diallyldimethylammonium chloride solution and filled with PP at different weight fractions by using a laboratory type high-speed thermo-kinetic mixer. The effect of MG loading into PP on thermal conductivity and surface resistivity of PP was measured. With using MG as a conductive filler for PP, instead of GNP, through-plane conductivity increased by 11%, however in-plane conductivity decreased by 33%. Modified GNP-filled PP showed better through-plane conductivity and surface resistivity than those of unmodified GNP-filled PP. Tensile and three point bending tests were performed to determine tensile and flexural properties of composites. Dynamic mechanical analysis was carried out to evaluate viscoelastic properties, such as storage modulus and loss modulus of composites. The thermal properties of samples were measured by using a differential scanning calorimetry, thermogravimetric analysis, and thermo-mechanical analysis. Scanning electron microscopy was utilized to observe the fracture surfaces of the composites after tensile tests. POLYM.
We investigate the thermal conductivity of fluorinated graphene using molecular dynamics simulations. We find that fluorination reduces the thermal conductivity of graphene, with the amount of reduction strongly depending on both distribution and coverage of fluorination. The thermal conductivity shows a somewhat U-shaped change with coverage from 0% to 100%. At the same coverage, random fluorination results in a larger reduction in thermal conductivity than patterned fluorination, and the patterned strips oriented perpendicular to heat flux cause a stronger reduction than the strips parallel to heat flux. We also find that fluorination makes the thermal conductivity less sensitive to strain.
Thermal Transport in Graphene Nanostructures: Experiments and Simulations
Graphene, Ge/iii-V, and Emerging Materials For Post-Cmos Applications 2, 2010
Thermal transport in graphene and graphene nanostructures have been studied experimentally and theoretically. Methods and previous work to measure and calculate the thermal conductivities of graphene and related nanostructures are briefly reviewed. We demonstrate that combining Raman spectroscopy for thermometry and electrical transport for Joule heating is an effective approach to measure both graphene thermal conductivity and graphenesubstrate interface thermal resistance. This technique has been applied to a variety of exfoliated or CVD-grown graphene samples (both suspended and substrate-supported), yielding values comparable with those measured using all-optical or all-electrical techniques. We have also employed classical molecular dynamics simulation to study thermal transport in graphene nanostructures and suggest such structures may be used as promising building blocks for nanoscale thermal engineering.
Multiscale modeling of thermal conductivity of polymer/carbon nanocomposites
International Journal of Thermal Sciences, 2010
Molecular dynamics simulation was used to estimate the interfacial thermal (Kapitza) resistance between nanoparticles and amorphous and crystalline polymer matrices. Bulk thermal conductivities of the nanocomposites were then estimated using an established effective medium approach. To study functionalization, oligomeric ethylene-vinyl alcohol copolymers were chemically bonded to a single wall carbon nanotube. The results, in a poly(ethylene-vinyl acetate) matrix, are similar to those obtained previously for grafted linear hydrocarbon chains. To study the effect of noncovalent functionalization, two types of polyethylene matrices. --aligned (extended-chain crystalline) vs. amorphous (random coils) were modeled. Both matrices produced the same interfacial thermal resistance values. Finally, functionalization of edges and faces of platelike graphite nanoparticles was found to be only modestly effective in reducing the interfacial thermal resistance and improving the composite thermal conductivity.