Thermal Conductivity Of Composites Research Articles

Lightweight, Thermally Conductive Liquid Metal Elastomer Composite with Independently Controllable Thermal Conductivity and Density.

Lightweight and elastically deformable soft materials that are thermally conductive are critical for emerging applications in wearable computing, soft robotics, and thermoregulatory garments. To overcome the fundamental heat transport limitations in soft materials, room temperature liquid metal (LM) has been dispersed in elastomer that results in soft and deformable materials with unprecedented thermal conductivity. However, the high density of LMs (>6 g cm-3 ) and the typically high loading (⩾85 wt%) required to achieve the desired properties contribute to the high density of these elastomer composites, which can be problematic for large-area, weight-sensitive applications. Here, the relationship between the properties of the LM filler and elastomer composite is systematically studied. Experiments reveal that a multiphase LM inclusion with a low-density phase can achieve independent control of the density and thermal conductivity of the elastomer composite. Quantitative design maps of composite density and thermal conductivity are constructed to rationally guide the selection of filler properties and material composition. This new multiphase material architecture provides a method to fine-tune material composition to independently control material and functional properties of soft materials for large-area and weight-sensitiveapplications.

Performance study of adsorption refrigeration system with composite adsorbent

As an effective way to improve the performance of heat and mass transfer, Composite adsorbent used in adsorption refrigeration has attracted increasing research attention. The aim of the research is to reveal composite theory of silica gel composite adsorbent and to understand adsorption refrigeration system mechanism running by above composite adsorbent. Coarse porous silica gel with different particle diameters was selected as the matrix of composite adsorbent and calcium chloride was selected as additive. The results showed that composite adsorbent's thermal conductivity and adsorption capacity increased significantly compared with pure silica gel. The thermal conductivity could be increased by 58.2%, and the adsorption capacity could be increased by 4–10 times. Finally, the adsorption refrigeration system using silica gel-calcium chloride composite adsorbent was studied. A two-bed adsorption refrigeration cycle running by above composite adsorbent was adopted. The experimental results showed that the optimal values of system cooling capacity and COP were not at the same time. The system cooling capacity reached its maximum at 1500 s and the system COP reached its maximum at 1200 s. The best heat recovery time was 20 s. The SCP of the system was up to 288.1 W kg−1, which could reduce the volume of the adsorption refrigeration system effectively.

Mechanical, physical and thermoacoustic properties of lightweight composite geopolymers

This research evaluates the physical and mechanical properties of particulate composites, produced from geopolymer paste with the incorporation of different organic type wastes as expanded polystyrene (EP), corkwood (CK), tire rubber (RB); in percentages by volume of 2, 4, and 6%. Metakaolin was used as a precursor of the geopolymer produced by alkali activation from NaOH and sodium silicate. The geopolymer composites were cured at room temperature. Properties as density, porosity, absorption, compressive strength, thermal conductivity, and acoustic behavior were evaluated. As complementary techniques, light and scanning electron microscopy were used. It was observed that the high alkalinity of the geopolymer mixture causes deterioration of the CK particles. Composites with the incorporation of 4% of the EP and RB particles reported compressive strength of 32 and 45 MPa at 28 days, and apparent density of 1853 and 1922 kg/m3, respectively, which represents a reduction of 6.08% and 2.58% in comparison to the GP reference. The thermal conductivity for composites with 4% of EP and RB was 0.316 and 0.344 W/m.K and the sound absorption coefficient was evaluated at frequencies of 500 Hz, 0.70, and 0.50 respectively. The evaluated performance properties show the feasibility of using 4% of EP and RB for the manufacture of geopolymer composites for applications in thermal and sound insulating panels.

Improved thermal conductivity of poly(dimethylsiloxane) composites filled with well-aligned hybrid filler network of boron nitride and graphene oxide

Polymer composites have attracted considerable attention due to their easy processability, low cost, and various applications. However, intrinsic poor thermal, electrical properties of polymer always have been the bottlenecks of multifunctional technical development. In this study, fabrication of low dielectric loss and highly thermal conductive composites was investigated through hybridization of silane-treated reduced graphene oxide (rGO) and boron nitride (BN), sintering of silver nanoparticles (AgNPs) on the surface of two-dimensional fillers, and infiltration of poly(dimethylsiloxane) (PDMS). The well-ordered filler structure was achieved by aligned BN on the rGO surface. The aligned PDMS/BNA-SrGOA composites, which form heat transfer paths along the filler orientation of two-dimensional BN and GO, exhibited high thermal conductivities of 10.91 and 1.27 W/mK according to in-plane and through-plane direction in a 1:2 ratio of BN and rGO. In addition, the dielectric loss was decreased by interaction with BN compared to that with only the rGO composites. Finally, the treatment of a silane coupling agent on the rGO surface reduced the interface resistivity between the filler and matrix, which reinforced the thermal, electrical, mechanical properties.

Fabrication of actiniae-like atomically thin hydroxylation boron nitride@polyaniline hierarchical composites with adjustable high thermal conductivity and electrical conductivity

Polyaniline (PANI) has been studied as soft electronic materials, which is still subject to performance obstacles such as low thermal conductivity and undesirable electrical conductivity. Herein, we report the in situ preparation of an atomically thin hydroxylated boron nitride (HO-BNNS)@PANI actiniae-like layered composite. HO-BNNS@PANI composite obtains brilliant electrical and thermal conductivity without destroying the pH sensitivity of PANI. In this case, the test results show that when the HO-BNNS content is 15 wt%, the conductivity of the HO-BNNS@PANI composite is 10.8 S cm−1, and the thermal conductivity is 1.21 W m−1·K−1 (≈520% that of pure PANI). More strikingly, the HO-BNNS@PANI composite maintains the pH responsiveness of the intrinsic PANI. This greatly improves the application range of composite materials. Meanwhile, since actiniae-like structural factors simultaneously improve ion diffusion capability and optimize reaction area, after five times of doping and dedoping, the conductivity of the HO-BNNS@PANI composite can still be maintained above 60%.

A Novel Branched Al2O3/Silicon Rubber Composite with Improved Thermal Conductivity and Excellent Electrical Insulation Performance.

In this paper, we report a thermal conductive polymer composite that consists of silicone rubber (SR) and branched Al2O3 (B-Al2O3). Owing to the unique two-dimensional branched structure, B-Al2O3 particles form a continuous three-dimensional network structure by overlapping each other in the matrix, serving as a continuous heat conductive pathway. As a result, the polymer composite with a 70 wt% filler achieves a maximum thermal conductivity of 1.242 Wm−1 K−1, which is equivalent to a significant enhancement of 521% compared to that of a pure matrix. In addition, the composite maintains a high volume resistivity of 7.94 × 1014 Ω·cm with the loading of 70 wt%, indicating that it meets the requirements in the field of electrical insulation. Moreover, B-Al2O3 fillers are well dispersed (no large agglomerates) and form a strong interfacial adhesion with the matrix. Therefore, the thermal decomposition temperature, residual mass, tensile strength, modulus and modulus of toughness of composites are significantly improved simultaneously. This strategy provides new insights for the design of high-performance polymer composites with potential application in advanced thermal management in modern electronics.

Study on thermal conductivities and mechanical properties of silicone/expanded graphite composites

In this study, series of expanded graphite (EG)-filled silicone composites were prepared by the bulk mixing and the solution methods to investigate the effect of thermal conductive EG particles and preparation methods on thermal conductivity of resulting silicone composites. With increasing EG contents and sizes, the thermal conductivity increased, and the solution mixing method showed higher thermal conductivity than the bulk mixing method. At 10 wt% of EG 140 μm-filled silicone composites, the solution mixing method showed the thermal conductivity of 0.789 W/m·K, which was about 147% over one prepared by the bulk mixing method and 538% increase over the pure silicone polymer. FE-SEM experiment was carried out to explore the dispersion and network formation of EG fillers in the silicone matrix. Tensile and dynamic mechanical analysis were also performed to investigate the mechanical reinforcement of the silicone composites. All the results suggested that the network structure of EG with larger size could improve mechanical reinforcement by increasing the modulus and optimize mechanical properties while improving the thermal conductivity of composites.

Influence of Surface Defects on the Thermal Conductivity of Hexagonal Boron Nitride/Poly(dimethylsiloxane) Nanocomposites: A Molecular Dynamics Simulation.

In this simulation, the reverse nonequilibrium molecular dynamics simulation is employed to explore how the surface defects in hexagonal boron nitride (h-BN) influence the thermal conductivity of poly(dimethylsiloxane) (PDMS)-based composites. First, the interfacial thermal conductivity and the intrinsic thermal conductivity of h-BN are obtained by tuning the defect density, the inhomogeneity of the defect distribution, and the number of h-BN layers. The defects enhance the interfacial thermal conductivity, especially for h-BNs with high inhomogeneity of the defect distribution and multilayer. However, the intrinsic thermal conductivity of h-BN is declined significantly by the defects. They can be explained well by the vibrational density of states of PDMS and h-BNs and their overlap. Then, by combining the effective medium approximation model with the simulation, the overall thermal conductivity of composites is obtained. It exhibits a gradual decrease with increasing defect density or reducing the inhomogeneity of the defect distribution. Meanwhile, the enhancement extent of the overall thermal conductivity by improving the concentration and size of h-BNs depends on the defect density and the defect distribution. Finally, the comparison between the simulation and experiment is discussed. In summary, our work provides some valuable insights into how the defect density, the defect distribution, and the number of layers influence the thermal conductivity of the PDMS-based composite.

Thermal Conductivity of Copper Matrix Composites Reinforced with Multi-wall Carbon Nanotubes

Carbon nanotubes (CNTs) reinforced with metal matrix composites (MMCs) have attracted an increasing interest due to their promising properties. One of the challenges in metal matrix-CNTs composites research is producing a uniform dispersion of CNTs. A poor dispersion of CNTs within the matrix, attributed to strong CNTs entanglement caused by Van der Waals forces. In this study, Cu/CNTs composites have been successfully fabricated by the powder metallurgy (PM) route. The thermal conductivity of Cu/CNTs composites showed that the thermal conductivity decreased after the incorporation of CNTs. The analysis revealed that the interfacial thermal resistance between the Cu matrix and CNTs plays a significant role in determining the thermal conductivity performances. Besides, the influences of porosity and distribution of CNTs also affected the thermal conductivity results.

Variasi persen berat tempurung kelapa terhadap konduktivitas termal komposit silicone rubber

Experiments to know themal conductivities of silicone rubber composite were conducted. The sillicon rubber was mixed with coconut shells charcoal powder with weight variations. The weight presentage variations were 0, 10, 20 and 30%. Increasing the weight persentage was expected to increase the thermal conductivity of the composite. The speciment size was 50 mm x 50 mm x 5 mm. The speciments were tested according to the conduction heat transfer mode. To make sure that the temperatures were steady, the experiments were performed for about 6 hours. The results indicated that increasing the weight presentage raised the composite thermalconductivities. At 0% of wight, the composite had a thermalconductivity of 0.157 W/m°C, at 10%, 20% and 30% of weight compositions; the composite had thermal conductivities of 0.461 W/m°C, 0.58 W/m°C, and 0.73 W/m°C respectively.

Comparison of the Thermal and Electrical Conductivities of Pretreated Kenaf–Polyester Composites

Conductivity of a material is an important physical property that determines its suitability or otherwise in all engineering designs and construction. The aim of this study is to determine the effects of two pretreatment methods viz acetylation and permanganate on the thermal and electrical conductivities of pretreated kenaf bast fibres applied in polyester resin. Fully grown kenaf (hibiscus cannabalis) were manually retted from the stalk, washed, and cut into short fibre lengths of about 10 cm. One portion of the fibres was pretreated with 5%pbw NaOH solution before immersing it in glacial acetic acid and then in acetic anhydride. The second was also pretreated with5%pbw of NaOH before being pretreated with 0.125%of KMnO4. The third portion of fibres was untreated to serve as control. The ground fibre was incorporated into ortho unsaturated polyester rand cast with moulds of dumb-belland square shapes. The electrical conductivity of the composites was deduced by measuring the resistance of the composites using the high voltage insulation tester model 3122 and calculating from equations. The thermal conductivities were determined by analytical method. The results show that chemical pretreatments of fibres by acetylation and permanganate methods have no appreciable effect on the thermal conductivities of composites. Further findings show that the acetylated fibre composites have no effect on the electrical conductivities of the composites. The permanganate pretreated fibre composites however increased the electrical conductivities of the composites significantly.

Comparison of the Thermal and Electrical Conductivities of Pretreated Kenaf–Polyester Composites

Conductivity of a material is an important physical property that determines its suitability or otherwise in all engineering designs and construction. The aim of this study is to determine the effects of two pretreatment methods viz acetylation and permanganate on the thermal and electrical conductivities of pretreated kenaf bast fibres applied in polyester resin. Fully grown kenaf (hibiscus cannabalis) were manually retted from the stalk, washed, and cut into short fibre lengths of about 10 cm. One portion of the fibres was pretreated with 5%pbw NaOH solution before immersing it in glacial acetic acid and then in acetic anhydride. The second was also pretreated with5%pbw of NaOH before being pretreated with 0.125%of KMnO4. The third portion of fibres was untreated to serve as control. The ground fibre was incorporated into ortho unsaturated polyester rand cast with moulds of dumb-belland square shapes. The electrical conductivity of the composites was deduced by measuring the resistance of the composites using the high voltage insulation tester model 3122 and calculating from equations. The thermal conductivities were determined by analytical method. The results show that chemical pretreatments of fibres by acetylation and permanganate methods have no appreciable effect on the thermal conductivities of composites. Further findings show that the acetylated fibre composites have no effect on the electrical conductivities of the composites. The permanganate pretreated fibre composites however increased the electrical conductivities of the composites significantly.

Controllable Fe ion-anchored graphene heterostructures for robust and highly thermal conductive cellulose nanofiber composites

Developing the polymer-based thermal interface materials (TIMs) is one of the most promising approaches to address heat accumulation along with the functionalization, integration, and miniaturization of modern electronics, while it is still a great challenge to balance the thermal conductivity and mechanical properties. In this article, Fe ion-anchored graphene (FeG) is successfully fabricated by a facile in situ Fe reduction of graphene oxide (GO) approach, and then cellulose nanofibers (CNFs)/FeG composites are prepared by vacuum-assisted filtration. FeG exhibits excellent dispersion and exfoliation in CNFs/FeG composites, due to the strong interfacial interaction between CNFs and FeG, such as hydrogen bonds and “Fe–O” complex binding. Thus, CNFs/FeG composite has the largely improved thermal conductivity up to 30.2 W/mK at FeG content of 50 wt%, which is substantially increased by 1160% in comparison with that of pure CNFs. In addition, the mechanical performances of CNFs/FeG-50 are unexpectedly simultaneously enhanced to 244 MPa for tensile strength, 4.10% for elongation at break, and 9.5 GPa for Young’s modulus, outperforming pure CNFs with increase of 137%, 33%, and 121%, respectively. This study provides a significant strategy for the design and construction of high thermal conductivity and high-performance polymeric TIMs in flexible and portable electronics.Graphic Abstract

A Study on Thermal and Electrical Conductivities of Ethylene-Butene Copolymer Composites with Carbon Fibers

Abstract Ethylene-butene copolymer (EBC)/carbon-fiber (CF) composites can be utilized as an electromechanical material due to their ability to change electric resistance with mechanical strain. The electro-mechanical properties and thermal conductivity of ethylene butene copolymer (EBC) composites with carbon fibers were studied. Carbon fibers were introduced to EBC with various concentrations (5 to 25 wt%). The results showed that carbon fibers’ addition to EBC improves the electric conductivity up to 10 times. Increasing the load up to 2.9 MPa will raise the electric resistance change by 4 500% for a 25% fiber sample. It is also noted that the EBC/CF composites’ electric resistance underwent a dramatic increase in raising the strain. For example, the resistance change was around 13 times higher at 15% strain compared to 5% strain. The thermal conductivity tests showed that the addition of carbon fibers increases the thermal conductivity by 40%, from 0.19 to 0.27 Wm–1K–1.

Multiscale modeling and maximizing the thermal conductivity of Polyamide-6 reinforced by highly entangled graphene flakes

In this work, we have established a multiscale model to accurately calculate the effective thermal conductivity of the composite of graphene and polyamide-6 (PA-6) and use this model to search for the optimal orientation distribution of the graphene flakes to maximize the composite thermal conductivity. Compared with the direct results of large-scale molecular dynamics simulations on the validation case, our model shows 1% relative error for the effective thermal conductance of the standalone graphene network, and 4% for the overall composite thermal conductivity. Counterintuitively, our model predicts that, for the percolation-dominated composite structure, randomly entangled graphene network produces superior thermal conductivity, compared to the composite structure with certain graphene alignment. Our results show that, without increasing graphene loading, the composite thermal conductivity can be maximized by simply producing the optimal orientation distribution for the graphene flakes.

Synergistic Enhanced Thermal Conductivity and Dielectric Constant of Epoxy Composites with Mesoporous Silica Coated Carbon Nanotube and Boron Nitride Nanosheet.

Dielectric materials with high thermal conductivity and outstanding dielectric properties are highly desirable for advanced electronics. However, simultaneous integration of those superior properties for a material remains a daunting challenge. Here, a multifunctional epoxy composite is fulfilled by incorporation of boron nitride nanosheets (BNNSs) and mesoporous silica coated multi-walled carbon nanotubes (MWCNTs@mSiO2). Owing to the effective establishment of continuous thermal conductive network, the obtained BNNSs/MWCNTs@mSiO2/epoxy composite exhibits a high thermal conductivity of 0.68 W m−1 K−1, which is 187% higher than that of epoxy matrix. In addition, the introducing of mesoporous silica dielectric layer can screen charge movement to shut off leakage current between MWCNTs, which imparts BNNSs/MWCNTs@mSiO2/epoxy composite with high dielectric constant (8.10) and low dielectric loss (<0.01) simultaneously. It is believed that the BNNSs/MWCNTs@mSiO2/epoxy composites with admirable features have potential applications in modern electronics.

Effects of silicon carbide as a heat conductive filler in butyl rubber for bladder tire curing applications

Rubber composites are widely used in tires and their related applications. In the present study, butyl rubber/carbon black/silicon carbide (α-SiC) composites were prepared by melt blending. They are used in tire curing applications for utilization of silicon carbide for the development of heat conductive bladder. The effect of α-SiC micro particle loading on resin curing characteristics, tensile properties (normal and aged), hardness, tear strength and morphology were studies. We also investigated its effect on the thermal transport properties of carbon black filled butyl rubber such as its heat conductivity, heat diffusivity, and specific heat capacity. A heat transfer mathematical modeling and computer simulation were conducted using ABAQUS finite element software to simulate the effect of bladder composite heat diffusivity increment on temperature-time dependency for different points of a tire during curing process. The results showed an average increase of 72% in the thermal conductivity, an average increment of 45% in heat capacity, and an average increment of 13% in heat diffusivity coefficient of carbon black filled composite in the presence of 18 phr (part per hundred of rubber) of α-SiC, without significant loss of mechanical properties. Further addition of α-SiC to 28 phr while decreasing mechanical properties did not have a further improving effect on the composite thermal conductivity and its thermal diffusivity coefficients. The tire curing simulation results revealed that it is possible to reduce the steam pressure inside of curing bladder from 22 to 20 bar (9%) in the presence of 18 phr α-SiC in bladder formula.

Simple large-scale method of recycled graphene films vertical arrangement for superhigh through-plane thermal conductivity of epoxy composites

Highly thermal conductive polymer-based materials are essential for modern microelectronic devices. However, conventional thermal conductive polymer-based composites exhibit constrained thermal conductivity even at a high content of highly thermal conductive fillers due to the lack of significant thermal conductive paths. In this work, effective thermal conductive paths were constructed with macro recycled graphene film fragments that were vertically arranged by a method of area restricting in the vertical direction under mechanical force. The resulting composites with vertically arranged structure displayed highly through-plane thermal conductivity of 20.97 W m−1 K−1 at 32.63 wt% graphene film fragments loading. Another three contrast experiments in different adding ways of fillers were as well accomplished to confirm the excellent vertically arranged structure. This study not only provides a simple way to obtain highly thermal conductive composites but also offers a strategy of making full use of wastes from industrial applications. The facile method for obtaining the superhigh though-plane thermal conductivity enlightens us to practical application. The recycled graphene films as millimeter-particles in this study can be expanded to other millimeter-particles arrangements. The mechanical force used for vertically arranged structure can be broadened to other forces such as vacuum or hydraulic pressure.

Enhancing Thermal Transport in Silicone Composites via Bridging Liquid Metal Fillers with Reactive Metal Co-Fillers and Matrix Viscosity Tuning.

Polymer matrix composites containing room temperature liquid metal (LM) microdroplets offer a unique set of thermo-mechanical characteristics that makes them attractive candidates for high performance thermal interface materials. However, to achieve the desired level of the composite thermal conductivity, effective bridging of such fillers into interconnected percolation networks needs to be induced. Thermal percolation of the LM microdroplets requires two physical barriers to be overcome. First, the LM microdroplets must directly contact each other through the polymer matrix. Second, the native oxide shell on the LM microdroplet must also be ruptured. In this work, we demonstrate that both physical barriers can be penetrated to induce ample bridging of the LM microdroplets and thereby achieve higher thermal conductivity composites. We accomplish this through a synergistic combination of solid silver and LM fillers, tuning of the silicone oil "matrix" viscosity, and sample compression. We selected silver as the solid additive because it rapidly alloys with gallium to form microscale needles that could act as additional paths that aid in connecting the LM droplets. We systematically explore the impact of the composition (filler type, volume fraction, and matrix oil viscosity) and applied pressure on the thermal conductivity and multiscale structure of these composites. We reveal the microscopic mechanism underlying the macroscopic experimental trends and also identify an optimal composition of the multiphase Ag-LM-Silicone oil composite for thermal applications. The identified design knobs offer path for developing tunable LM-based polymer composites for microelectronics cooling, biomedical applications, and flexible electronics.

Fabrication, microstructure, and thermal conductivity of multilayered Cu mesh/AZ31 Mg foil composites

In this study, multilayered Cu mesh/AZ31 Mg foil composites were designed and fabricated by diffusion bonding in a closed graphite mold at 400–445 °C. The effects of temperature on the microstructure of the joints formed and the thermal conductivity of the composite was evaluated. The mechanism responsible for the observed improvement in thermal conductivity was analyzed. After diffusion bonding, the thermal conductivity of the multilayered composite was as high as 122.3 W/m·K at room temperature (25 °C), which is 109.4% higher than that of the AZ31 Mg alloy (58.4 W/m·K) fabricated using the same process. Moreover, the fabricated Mg matrix composites had a maximum density of 2.21 g/cm 3 , indicating that they were lightweight. A continuous film-like structure composed of intermetallic compounds and α-Mg region with good contribution to heat conduction has been found, which has a reference for the design and fabrication of high-thermal-conductivity Mg matrix composites.