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Graphene nanoplatelets (GNPs) have attracted considerable attention in the field of thermal management materials due to their unique structure and exceptional thermal conductive properties. In this work, we demonstrate a significant synergistic effect of GNPs, alumina (Al2O3), and magnesia (MgO) in improving the thermal conductivity of polycarbonate/acrylonitrile-butadiene-styrene polymer alloy (PC/ABS) composites. The thermal conductivity of the composites prepared through partial replacement of Al2O3 and MgO with GNPs could increase dramatically compared with that without GNPs. The maximum thermal conductivity of the composite is 3.11 W mK−1 at total mass fraction of 70% with 0.5 wt% GNPs loading. It increases 60% compared with that without GNPs (1.95 W mK−1). The synergistic effect results from the compact packing structure formed by Al2O3/MgO and the bridging of GNPs with Al2O3/MgO, thus promoting the formation of effective thermal conduction pathways within PC/ABS matrix. More importantly, together with the intrinsically high thermal conductivity of GNPs, boosted and effective pathways for phonon transport can be created, thus decrease the thermal resistance at the interface between fillers and PC/ABS matrix and increase the thermal conductivity of composites. [ABSTRACT FROM AUTHOR]

The development of thermal conductive polymer composite is necessary for the application in thermal management. In this paper, the experimental and theoretical investigations have been conducted to determine the effect of copper nanowires (CuNWs) and copper nanoparticles (CuNPs) on the thermal conductivity of dimethicone nanocomposites. The CuNWs and CuNPs were prepared by using a liquid phase reduction method, and they were characterized through scanning electron microscopy (SEM) and X-ray diffraction (XRD). The experimental data show that the thermal conductivity of composites increases with the increase of filler. With the addition of 10 vol.% CuNWs, the thermal conductivity of the composite is 0.41 W/m/K. The normalized thermal conductivity enhancement factor is 2.73, much higher than that of the analogue containing CuNPs (1.67). These experimental data are in agreement with Nan’s model prediction. Due to the high aspect ratio of 1D CuNWs, they can construct thermal networks more effectively than CuNPs in the composite, resulting in higher thermal conductivity. [ABSTRACT FROM AUTHOR]

Epoxy resin based thermal interfacial materials (TIMs) with high thermal conductivity have been obtained by filling Ag nanoparticle-decorated graphene nanosheets (GNSs) as thermal conductive fillers. The thermal conductivity ( k ) enhancement of epoxy resin based TIMs increases with the thermal filler loading. The more decoration of Ag nanoparticles on the GNS surfaces, the higher thermal conductivity enhancement of epoxy resin based TIM is. It is proposed that the bigger Ag nanoparticles acting as “spacers” increase the distance between the graphene sheets more than the smaller ones. It is not easy for graphene sheets to form stacked graphitic structures and the high specific surface area as well as other unique properties exhibited by 2D graphene are retained. Furthermore, the larger particle size is desired to minimize the scattering of phonons because of low interfacial thermal barrier. The obvious enhancement of thermal properties should be also attributed to the high intrinsic k of graphene and the effective thermal conductive networks forming by graphene and Ag nanoparticles. The synergistic effects including the stronger phonon Umklapp scattering, better phonon transmission trough the interfaces, decreasing Kapitza resistance, and decreasing ability of heat transfer by electrons result in the slight variation of k with the temperature. The weak temperature dependence of k is beneficial for TIM applications and can be obtained by controlling the addition of hybrid thermal fillers and quantity of decorated silver nanoparticles. [ABSTRACT FROM AUTHOR]

We experimentally investigated the thermal transport behaviors of suspended single-layer graphene (SLG) and graphene sheets with different sizes. The length of graphene sheet suspended on a groove of SiO 2 /Si substrate is equal to the groove width (508 μm). Laser cutting technology is used to tailor SLG to obtain graphene sheets with different widths. A one-dimensional steady-state method is applied to measure the thermal conductivity, k , of graphene sheet and SLG at different conditions. k of the graphene sheets with different widths is much higher than that of SLG and increases with the decrease of graphene sheet width, and the increase in k appears significant when the width decreases greatly. We proposed that the Umklapp scattering may become dominant in phonon transport with the increasing of graphene sheet width, resulting in the thermal conductivity decrease. Another anomalous behavior is that k increases firstly and then decreases with an increase in temperature, and has a peak value at around 50 °C. The competition effects of boundary scattering, point defect scattering, grain-boundary phonon scattering, and Umklapp scattering in phonon transport may contribute to this phenomenon. A maximum k value of 2450.55 W m −1 K −1 is obtained under the condition of 50 °C when the SLG is cut for the fourth times. The electrical conductivity of graphene sheets with different widths at room temperature is in the range of 0.7584–2.7002 × 10 6 Ω −1 m −1 . The graphene sheet with small width exhibits better thermal and electronic properties that make them attractive for the fabrication of nanoscale electronics and promising for the application in thermal management. [ABSTRACT FROM AUTHOR]

This letter reports on the measurements of the thermal conductivity along a long free-standing graphene nanoribbon (GNR) by a one-dimensional steady-state method. The GNR was cut from a single layer graphene sheet and it has the length and width of 508 and 385 μm, respectively. It is observed from the measurements that the GNR has highly temperature dependent thermal conductivities. The values increase from 126.21 W·m-1·K-1 to 877.32 W·m-1·K-1 in the temperature range from -75 to 100 °C, with an exception of an abruptly large value of 1044.41 W·m-1·K-1 at 50 °C. The electrical resistances of the GNR decrease linearly with the temperature and the absolute resistance-temperature coefficient was determined to be a pretty large value of 0.004148 K-1, indicating obvious temperature dependent electrical conductive behavior. [ABSTRACT FROM AUTHOR]

Abstract: Stable water based nanofluids containing multi-walled carbon nanotubes (MWNTs) were prepared using cationic gemini surfactant as stabilizer. Zeta potential measurements and Fourier transformation infrared spectra were employed to study the absorption mechanisms of the surfactants on the MWNT surfaces. The stability of the nanofluids was obtained using UV–vis absorption method. Results of thermal conductivity indicate that higher concentration of cationic gemini surfactant is a negative factor in improving the thermal conductivity of nanofluids. Increase of spacer chain length of cationic gemini surfactant gives rise to the sediment of MWNTs in the nanofluids, resulting in decrease of thermal conductivity enhancement of MWNT nanofluids. Mechanical ball-milling technology would be a new method to pretreat the pristine MWNTs, and using this method nanofluids with optimized thermal properties can be obtained. [Copyright &y& Elsevier]

Abstract: Single-walled carbon nanotubes (SWNTs) and double-walled carbon nanotubes (DWNTs) have been functionalized through the wet-mechanochemical reaction method. Results from the infrared spectrum and zeta potential measurements show that the hydroxyl groups have been introduced onto the treated SWNT and DWNT surfaces. Transmission electron microscope observations revealed that the SWNTs and DWNTs were cut short after being milled. SWNTs and DWNTs with optimized aspect ratio can be obtained by adjusting the ball milling parameters. Thermal conductivity enhancement of water-based nanofluids containing treated carbon nanotubes (CNTs) shows augmentation with the increase of temperature mainly due to the effects of an ordering liquid layer forming around the chemical surfaces of CNTs. Moreover, the thicker interfacial layer of water molecules on the surfaces of CNTs with smaller diameter, such as SWNTs, is in favor of greater thermal conductivity enhancement compared with the thinner one on the surfaces of DWNTs or MWNTs with larger diameter. [Copyright &y& Elsevier]

Abstract: Multiwalled carbon nanotubes (MWNTs) were treated by concentrated acid combined with mechanical ball mill technology. The treated multiwalled carbon nanotubes (TCNTs) with functionalized surfaces and controlled morphologies were used to prepare silicon oil based nanofluids by using hexamethyldisiloxane as dispersant. Thermal conductivity results of the obtained nanofluids show that the collective effects, involving straightness ratio, aspect ratio, and aggregation of TCNTs, play a key role in the thermal conductivity of CNT nanofluids. This study suggests that the thermal characteristics of nanofluids might be manipulated by means of controlling the morphology of the additions, which also provide a promising way to conduct investigation on the mechanism of heat transfer in nanofluids. Reliable rheological properties of the prepared nanofluids were provided. It is important when the nanofluids are used in the potential heat exchange areas. The silicone oil based fluids behave in Newtonian manner in all the studied MWNT volume fractions and temperatures. The hexamethyldisiloxane added in silicone oil, in addition to decreasing the silicone oil viscosity, has little effect on the nanofluid rheological properties. [Copyright &y& Elsevier]

Abstract: Homogeneous and stable nanofluids have been produced by suspending well dispersible multi-walled carbon nanotubes (CNTs) into ethylene glycol base fluid. CNT nanofluids have enhanced thermal conductivity and the enhancement ratios increase with the nanotube loading and the temperature. Thermal conductivity enhancement was adjusted by ball milling and cutting the treated CNTs suspended in the nanofluids to relatively straight CNTs with an appropriate length distribution. Our findings indicate that the straightness ratio, aspect ratio, and aggregation have collective influence on the thermal conductivity of CNT nanofluids. [Copyright &y& Elsevier]

Abstract: Multi-walled carbon nanotubes (CNTs) were treated by using mechanochemical reaction method to enhance their dispersibility for producing CNT nanofluids. The thermal conductivity was measured by a short hot wire technique and the viscosity was measured by a rotary viscometer. The thermal conductivity enhancement reaches up to 17.5% at volume fraction of 0.01 for an ethylene glycol based nanofluid. Temperature has no obvious effects on thermal conductivity enhancement for the as prepared nanofluids. With an increase in thermal conductivity of the base fluid, the thermal conductivity enhancement of a nanofluid decreases. At low volume fractions (<0.4vol%), nanofluids have lower viscosity than corresponding base fluid due to lubricative effect of nanoparticles. When the volume fraction is higher than 0.4vol%, the viscosity increases with nanoparticle loadings. The prepared nanofluids, with no contamination to medium, good fluidity, stability, and high thermal conductivity, would have potential applications as coolants in advanced thermal systems. [Copyright &y& Elsevier]

Abstract: A green method was applied to prepare composites of multi-walled carbon nanotubes (MWNTs) decorated with silver nanoparticles (Ag-NPs). The MWNTs were functionalized by using mechanical ball milling technology in the presence of ammonium bicarbonate. The functionalized MWNTs were decorated with Ag-NPs by the traditional method of using a silver mirror reaction. Scanning electron microscopy (SEM) characterization showed that Ag-NPs distributed uniformly on the walls of MWNTs. The content and size of Ag-NPs could be controlled by adjusting the reducing time. The X-ray diffraction (XRD) patterns demonstrated that the Ag-NPs crystallized well. The resulting Ag/MWNT composites were used to prepare a water based nanofluid. The nanofluid showed higher thermal conductivity compared to that of a nanofluid containing MWNTs with functionalized surfaces. [Copyright &y& Elsevier]

Graphene papers (GP) modified with alkaline earth metal ions (Mg 2 + , Ca 2 + ) were prepared by reduction of graphene oxide papers, which were obtained through a facile vacuum filtration of graphene oxide solution aqueous. The thermal conductive properties of graphene paper and its modified analogues were measured with a laser flash method. The thermal diffusivities of Mg-modified GP and Ca-modified GP are 1003.4 mm 2 /s and 2232.2 mm 2 /s, respectively, which is significantly improved compared with unmodified graphene paper (694.9 mm 2 /s). The corresponding thermal conductivities are 100.4 W/mK (GP), 147.7 W/mK (Mg-GP) and 331.8 W/mK (Ca-GP), respectively, from which a substantial enhancement in thermal conductivity of M-modified GP is also observed. It is found that the ion chelating between carboxyl groups of graphene oxide and alkaline earth metal ions will bridge the small graphene oxide sheets, and it will decrease the thermal resistance of the boundary and increase the contact surface of graphene sheets. The reduction of M-modified graphene oxide can partly recover the structure of graphene, thus can further improve the heat transfer property of graphene paper. [ABSTRACT FROM AUTHOR]

Abstract: Two kinds of silicone grease containing graphene nanoplatelets or reduced graphene oxide were prepared, and their thermophysical properties have been investigated. When the volume fraction was 1%, the reduced graphene oxide was the most effective additive to enhance the heat transfer properties of silicone, and graphene nanoplatelet was slightly inferior to the former. While when the concentration was enhanced, the viscosity of silicone grease containing reduced graphene oxide became very large due to its rich pore structure. Graphene nanoplatelet was efficient for the thermal conductivity enhancement of silicone grease, and it provided a thermal conductivity enhancement was up to (loading of ). The experimental result is in excellent agreement with the recently developed theoretical model analyzing the thermal conductivity of isotropic composites containing randomly embedded GNPs, and it validates that graphene is an effective thermally conducting filler to let grease have high thermal conductivity with low filler content. [Copyright &y& Elsevier]

Abstract: Phase-transfer method has been applied for preparing stable kerosene based Fe3O4 nanofluids. Oleic acid was successfully grafted onto the surface of Fe3O4 nanoparticles by chemisorbed mode, which let Fe3O4 nanoparticles have good compatibility with kerosene. Pure cubic-phase Fe3O4 nanoparticles with an average diameter of 15nm were obtained. The nanoparticles in nanofluids had the tendency to form larger clusters with the diameter of about 155nm, and ultrasonication could not decrease the size of the clusters. The Fe3O4 nanofluids prepared by phase-transfer method do not show the previously reported “time-dependence of the thermal conductivity characteristic”, which indicates the stability of the nanofluids. In the temperature range from 10 to 60°C, the thermal conductivities of the nanofluids track the thermal conductivities of the base liquid and the enhanced ratios are almost constant for the same loading. There is no clear behavior of the previously reported “the temperature dependence of the thermal conductivity”. The enhancement of the thermal conductivity increases linearly with the volume fraction of Fe3O4 nanoparticles and the value is up to 34.0% for 1.0vol.% nanofluid. It is proposed that the soft cluster structure may be the reasonable explanation of the anomalously enhanced thermal conductivity. [Copyright &y& Elsevier]

Abstract: Stable ethylene glycol based copper nanofluids were prepared through a two-step method, using polyvinyl pyrrolidone as dispersant, which was vital for the long-term stability of nanofluids. The substantial thermal conductivity enhancements were seen for the obtained nanofluids. For ethylene glycol based copper nanofluids with 0.5vol.% at 50°C, the enhancement ratio was up to 46%. The thermal conductivities depended strongly on the temperature of fluid, and the enhancement ratios increased along with the increasing temperatures. Brownian motions of Cu nanoparticles would play the key role on determining the effects of the temperature on thermal conductivity enhancement of nanofluids. The measured apparent thermal conductivity showed the time-dependent characteristic within 15min. It indicated that the measurement should be made after 15min at least to obtain the true thermal conductivities of ethylene glycol based copper nanofluids. [Copyright &y& Elsevier]

Abstract: Ethylene glycol (EG) based nanofluids containing ZnO nanoparticles were prepared, and the thermal transport properties including thermal conductivity and viscosity were measured. The results show that the thermal conductivity of ZnO-EG nanofluids is independent of setting time from 20 to 360min. The absolute thermal conductivity increases with temperature for different temperatures ranging from 10 to 60°C, while the enhanced ratios are almost constant. The thermal conductivity of ZnO-EG nanofluids depends strongly on particle concentration, and it increases nonlinearly with the volume fraction of nanoparticles. The enhanced value of 5.0vol.% ZnO-EG nanofluid is 26.5%, consistent with the prediction values by the combination of the aggregation mechanism with the Maxwell and Bruggeman models. The facts indicate that there is no magic physics behind nanofluids and the classical theories predict the measurements well. The rheological behaviors of the nanofluids show that ZnO-EG nanofluids with low volume concentrations demonstrate Newtonian behaviors, and for higher volume concentrations nanofluids, the shear-shinning behavior will be observed, because the effective volume fraction of aggregates is much higher than the actual solid volume fraction. [Copyright &y& Elsevier]

In this study, we investigated the influence of nitrogen doping on thermal conductivity of carbon nanotubes (CNTs) experimentally and theoretically. The nitrogen-doped CNTs were synthesized by using thermal chemical vapor deposition method and were used to prepare silicone composites. The thermal conductivity of silicone composites with these CNTs improves greatly. A negative influence of nitrogen doping on thermal conductivity of CNT/silicone composites is observed. The calculated thermal conductivity of CNTs indicates that the thermal conductivity of nitrogen-doped CNTs decreases rapidly with the nitrogen content in CNTs. This is attributed to defects in nitrogen-doped CNTs, which act as phonon scattering centers. [ABSTRACT FROM AUTHOR]

A remarkable synergistic effect between graphene sheets and alumina particles in improving the thermal conductive properties of the novel thermal grease is demonstrated. The use of hybrid size alumina filler leads to compact packing structure in the silicone base and hinders the aggregation of graphene to form clusters. The two-dimensional graphene with superb thermal conductivity can bridge the alumina particles to form more compact packing structure and provide faster and more effective pathways for phonon transport in thermal grease. These synergistic effects decrease the thermal boundary resistance and enhance the thermal conductivity of the thermal grease. The addition of graphene is only 1 wt.%, and the maximum thermal conductivity of the novel thermal grease is 3.45 W/m K. It is significantly improved compared with the thermal grease without graphene (2.70 ± 0.10 W/m K). With respect to the silicone base, an enhancement in thermal conductivity of 2553% is obtained. Meanwhile, a correction theoretical model is proposed by modifying Burggeman asymmetric model, and the model predictions are in reasonable agreement with the experimental values. [ABSTRACT FROM AUTHOR]

Organic phase change materials (PCMs) composites with thermally induced flexibility, lower interfacial thermal resistance, excellent stability, photo-absorption, higher thermal conductivity, good photo-thermal conversion and storage properties present better prospects in solar thermal application. This research prepared flexible PCMs composite by taking palmitic acid (PA) as PCMs, olefin block copolymers (OBC) as carriers and graphene nanoplatelets (GNP) as additive by blending and hot-pressing method. The unique block structure of OBC, excellent performance of GNP and interaction between GNP and PA provide OBC/GNP/PA composites good flexibility, excellent stability and thermal reliability. GNP as effective solar trap and thermal conductive additive are attribute to the sunlight capture, high solar energy conversion and transportation. The photo-thermal conversion efficiency of OBC/GNP/PA PCMs composites with 4 wt % GNP reaches 86.21%. The thermal conductivity is 155% higher than PA/OBC. The phase change enthalpy is 145.52 J/g for adsorbing 77.6 wt% PAand 4 wt% GNP. PCMs composites show excellent energy storage properties. Practical and easy preparation method and excellent performances of OBC/GNP/PA composites provide a good idea and more possibility for flexible PCMs composites with enhanced thermal conductivity in low and medium temperature solar thermal application. • Thermal induced flexible PCM composites with enhanced thermal conductivity for high-efficiency solar thermal conversion and storage is developed. • The OBC/GNP/PA composites exhibit excellent thermally induced flexibility, good shape stability and thermal reliability. • The highest efficiency of photo-thermal conversion is up to 86.21%. • The thermal conductivity is 155% improvement over PA/OBC. • High photo-thermal energy storage and practical preparation show huge potential for solar thermal-energy applications. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an experimental investigation of rheological and heat transfer properties of Al2O3 nanofluids based on the mixture of 45vol.% ethylene glycol and 55 vol. % water. The Al2O3 nanofluids (volume fraction φ =0.02) over 45°C exhibit Newtonian behaviors, below 45°C, they will be non-Newtonian fluids. The enhanced thermal conductivity ratios of the nanofluids with the volume fraction 1.0%, 2.0% and 3.0% are 3.8%, 7.7%, and 11.6% respectively, slightly larger than those predicted by the classic theoretical models. The heat transfer coefficients of the nanofluids with 1.0vol.% and 2.0vol.% have been found an increase up to 57% and 106%, respectively, when the Reynolds number is 2000. [Copyright &y& Elsevier]

Abstract: Homogeneous and stable ethylene glycol based nanofluids containing low volume concentration diamond nanoparticles have been prepared. Diamond nanoparticles, purified and surface modified by the mixture acid, consist of the highly defective structure and the active functional groups on the surface. Ultrasound and the alkalinity of solution are beneficial to the deaggregate of soft diamond particle aggregation, and the diameters of purified nanodiamond are changed from 30–50nm to 5–10nm. The thermal conductivity enhancement decreases with elapsed time for 1.0vol.% DNP–EG nanofluid at pH=7.0. While for the stable nanofluids at pH=8.5, there is no obvious thermal conductivity decrease within 6 months. The thermal conductivity enhancement values are up to 17.23% for the 1.0vol.% nanofluid at 30°C. Viscosity measurements show that the nanofluids demonstrate Newtonian behavior, and the viscosity significantly decreases with the temperature. [Copyright &y& Elsevier]

Abstract: Multi-walled carbon nanotubes (CNTs) as produced are usually entangled and not ready to be dispersed into organic matrix. CNTs were treated by mechano-chemical reaction with ball milling the mixture of potassium hydroxide and the pristine CNTs. Hydroxide radical functional groups have been introduced on the CNT surfaces, which enabled to make stable and homogeneous CNT composites. Treated CNTs were successfully dispersed into the palmitic acid matrix without any surfactant. Transient short-hot-wire apparatus was used to measure the thermal conductivities of these nanotube composites. Nanotube composites have substantially higher thermal conductivities than the base palmitic acid matrix, with the enhancement increasing with the mass fraction of CNTs in both liquid state and solid state. The enhancements of the thermal conductivity are about 30% higher than the reported corresponding values for palmitic acid based phase change nanocomposites containing 1wt% CNTs treated by concentrated acid mixture. [Copyright &y& Elsevier]