High Thermal Conductive Filler Research Articles

Magnetically-accelerated photo-thermal conversion and energy storage based on bionic porous nanoparticles

Recently, the technology of mixing phase change materials with high thermal conductivity fillers was developed, which has allowed thermal energy storage to be implemented in a wide range of industrial technologies and processes. In the present study, a hierarchical bionic porous nano-composite was prepared, which efficiently merged the nanomaterial characteristics of magnetism and high thermal conductivity in order to form a magnetically-accelerated solar-thermal energy storage method. The morphology and thermo-physical properties of materials were analysed. The experimental outcomes of phase change heat transfer demonstrated that the maximum storage efficiency increases by 102.7% when the hierarchical bionic porous structure is used, and a further 27.1% improvement can be achieved with the magnetic field. At the same time, the heat transfer process of energy storage in hierarchical porous composites under external physical fields is explained by simulation. Therefore, this magnetically-accelerated method demonstrated the superior solar-thermal energy storage characteristics within a hierarchical bionic porous structure which is particularly beneficial for the utilisation of solar direct absorption collectors and energy storage technology.

Bi-directional high thermal conductive epoxy composites with radially aligned boron nitride nanosheets lamellae

Hexagonal boron nitride (h-BN), as a high thermal conductive filler, has been widely used to construct thermal transport network in polymers. However, anisotropic thermal property of BN and its conventional thermal conductive network usually lead to high thermal conductivity in one direction that limits the overall heat dissipation effect. Herein, we report a novel radially aligned three-dimensional boron nitride nanosheets/epoxy composite for thermal interface materials via radial freeze-casting method. The as-prepared composite with radially aligned boron nitride nanosheets lamellae exhibits bidirectional high thermal conductivity, with 4.02 W m−1 K−1 in the through-plane direction and 3.87 W m−1 K−1 in the in-plane direction even at low BNNS loading (e.g., 15 vol%), respectively. Besides, excellent electronic insulation property and shape stability can also meet the requirements of isotropic TIM in thermal management.

Enhancing thermal conductivity in graphene-loaded paint: Effects of phase change, rheology and filler size

High thermal-conductivity coatings have garnered much attention in fields such as the automotive and aerospace industries. Commonly used filler-loaded coatings are limited either by the high viscosity of the coating paint or by the intrinsic properties of the filler. In this study, we used graphene as a high thermal conductivity filler to enhance the properties of paint used in the automotive industry. The effects of filler size on the thermal conductivity and viscosity of stable liquid dispersion (paint) are studied and modeled in graphene nanoplatelet-loaded paint (2.47 vol%), which exhibits enhanced thermal conductivity of 160% (1.6 vs. 0.6 W (m K)−1 for the neat commercial paint) and low viscosity. Furthermore, the filler with the optimum performance (in the paint) is studied in solid state, where it elicits a 720% enhancement in thermal conductivity (14.4 vol%).

Dynamic tuning of magnetic phase change composites for solar-thermal conversion and energy storage

Photo-thermal conversion and energy storage using phase change materials are now being applied in industrial processes and technologies, particularly for electronics and thermal systems. This method relies on adding high thermal conductivity fillers, such as nanoparticles, to enhance the phase change process. In the long term, dynamic tuning heat transfer provides a superior means of tuning control the heat transfer efficiency and speed. In this study, a nanofluid phase change material was prepared by adding magnetic nanoparticles, effectively combining the properties of high thermal conductivity and magnetism, in an attempt to develop a magnetically enhanced approach for dynamic tuning of photo-thermal conversion charging. Our results showed that the phase change efficiency of magnetic phase change material can be improved by magnetic field application. With the increasing magnetic strength, the photo-thermal storage efficiency was enhanced, and storage capacity was improved by more than 48%. Meanwhile the steady temperature of the magnetic phase change material increased, enhancing the open-circuit voltage in photo-thermoelectricity experiments. Thus, the proposed method demonstrated in this study achieved superior phase change heat transfer characteristics within a photo-thermal conversion process by dynamically controlling the magnetic field distribution, which should be especially useful for direct solar energy utilisation.

Thermal polymer composites of hybrid fillers

Thermal polymer composite materials for heat dissipation purposes have been widely researched over the previous decade due to their ease of processing, electric insulating, low cost and lightweight. These materials, which embedded with high thermal conductive fillers in the polymer matrix, exhibit high electrical insulation and thermal conductivity properties. These materials, however, are very hard to manage because usually it contains more than 70% volume of filler in order to be able to rapidly dissipate heat. Several approaches have been conducted by different research groups to enhance heat transfer through polymers while decreasing its filler contents. This paper presents a systematic review on several approaches which are used for enhancing the thermal properties of polymer composites by incorporating various types of fillers. The primary goal of this review is to identify any future trends in thermal polymer composites that regulate and dictate the method of thermal conduction.

Latent heat and thermal conductivity enhancements in polyethylene glycol/polyethylene glycol-grafted graphene oxide composites

Although high-thermal conductivity fillers can enhance the thermal conductivity of organic phase change materials (PCMs), it is still difficult to simultaneously prevent the loss in latent heat. The realization of enhanced thermal conductivity without adversely affecting the latent heat of polymeric PCMs remains challenging. We report experimental results demonstrating that polyethylene glycol (PEG)-based PCM composites exhibit large latent heats beyond the expected values and significantly improved thermal conductivities. Latent heat and thermal conductivity enhancements are achieved by optimizing the interaction between the filler and PCM in the PEG/graphene oxide (GO) composites. PEG-grafted GO (PEG-g-GO) is synthesized and introduced into the PEG to regulate the interaction between the PEG base and GO. The result can be largely attributed to the enhanced GO dispersion and heightened mobility of the PEG chains. The grafted PEG in the PEG-g-GO acts as a plasticizer, leading to a considerable effect on the crystallization kinetics of the PEG in the composite PCMs, and thus the improved crystallizability.

Thermal conductivity of filled composite materials considering interactions between fillers

Adding high thermal conductive fillers to base materials has been recognized as an efficient way to increase the thermal conductivity of composites materials. The heat conductive path is formed by filler contacts, this is a key point. In this paper, the effects of filler contacts are investigated based on generalized model and isolated model. The results indicate that the thermal conductivity is always linearly increased with the sphere filler contents. However, for cube filler, when the volume content exceeds 10%, the growth of thermal conductivity is accelerated along with filler contents. The 10% filler content is the inflection point and percolation threshold for cube filler. It is much lower than previously reported. The effect of filler contacts is very small for sphere fillers. Meanwhile, the deviation of thermal conductivity between two-dimensional and three-dimensional model is also very small for sphere filler. The cube fillers have substantial effects on the consequently thermal conductivity than sphere fillers. A series of new three-dimensional generalized model are proposed by numerical method. The filler contacts are considered in this model, the deviation with the experiment tested is in an acceptable range at wide filler contents.

Anisotropic thermally conductive flexible polymer composites filled with hexagonal born nitride (h-BN) platelets and ammine carbon nanotubes (CNT-NH2): Effects of the filler distribution and orientation

High thermal conductive filler (hexagonal boron nitride and carbon nanotube) reinforced polymer composites have obtained a growing attention in the microelectronic industry for their good thermal conductivity but electrical insulating. In this work, a synergistic hybrid structure of two fillers with different dimensions had been designed and prepared by taking hexagonal born nitride (h-BN) platelets and ammine carbon nanotubes (CNT-NH2) into the flexible polymer matrix. Using cycloaliphatic epoxy resin (CER) as the polymer matrix, a serious of (a) h-BN/CER based, (b) hybrid filler h-BN@CNT-NH2/CER based, and (c) mixed filler CNT-NH2 and h-BN/CER based composites were prepared. In this structure, h-BN (and h-BN@CNT-NH2) platelets stacked along the horizontal direction under the assistance of gravity force and interactivity between the fillers. The orientation of the h-BN platelets was investigated by scanning electron microscope (SEM) of the cracked cross-section of the composite film and XRD measurement via calculating the orientation function (f). The CNT-NH2 was embedded within the network to improve the filler-filler contact or network-density. Due to the anisotropic properties of h-BN platelets and dispersion states of CNT-NH2, the composites with different structures presented different and special properties, including thermal/electrical conductivity properties, mechanical properties, and thermal decomposition properties. The analysis of structure and mechanism of thermal decomposition were then proposed to explain those interesting properties. The incorporation and dispersion states of CNT-NH2 in the composites played an important effect on the enhancement of the thermal conductivity properties both included in-plane (∼1.76 W/m·K) and through-plane (∼1.09 W/m·K) thermal conductivity. Additionally, the good electrical insulating properties and mechanical properties of the composites provided a potential application in the thermal management areas. The solvent-free procedure was environment friendly, easy operation, and suitable for the practical application in large scale.

Multifunctional anisotropic flexible cycloaliphatic epoxy resin nanocomposites reinforced by aligned graphite flake with non-covalent biomimetic functionalization

High thermal conductive filler (graphite flake) reinforced polymer composites have obtained a growing attention in the microelectronic industry. In order to overcome the obstacles in surface modification, in this study, dopamine chemistry was used to achieve the facile modification of graphite flake via forming a polydopamine (PDA) shell on the surface in a solvent-free aqueous condition. The strong π-π interaction between the hexagonal structural graphite flake and aromatic dopamine molecules ensured the effective modification. The PDA coating on graphite flake enhanced the compatibility between the filler and the flexible cycloaliphatic epoxy resin (CER) matrix via hydrogen bond, and promoted the epoxy curing process by forming covalent bond. Under the assistance of gravity, the PDA@graphite flake stacked along the horizontal direction in the polymer matrix. The procedure of filler alignment and mechanism of thermal decomposition were investigated by XRD measurement and thermodynamic/kinetics analysis, respectively. The dynamic mechanical analysis (DMA) was also used to investigate the relationship between microstructure and performance. Due to the combination of surface modification and alignment of PDA@graphite flake, the prepared CER/PDA@graphite has higher in-plane thermal conductivity. In addition, excellent adhesion property and thermal stability demonstrated that the CER/PDA@graphite composites was a good candidate as thermal interface material (TIMs), which could be applied in the thermal management areas. The procedure was environment friendly, easy operation, and suitable for the practical application in large scale.

Dynamic tuning of optical absorbers for accelerated solar-thermal energy storage

Currently, solar-thermal energy storage within phase-change materials relies on adding high thermal-conductivity fillers to improve the thermal-diffusion-based charging rate, which often leads to limited enhancement of charging speed and sacrificed energy storage capacity. Here we report the exploration of a magnetically enhanced photon-transport-based charging approach, which enables the dynamic tuning of the distribution of optical absorbers dispersed within phase-change materials, to simultaneously achieve fast charging rates, large phase-change enthalpy, and high solar-thermal energy conversion efficiency. Compared with conventional thermal charging, the optical charging strategy improves the charging rate by more than 270% and triples the amount of overall stored thermal energy. This superior performance results from the distinct step-by-step photon-transport charging mechanism and the increased latent heat storage through magnetic manipulation of the dynamic distribution of optical absorbers.

Enhanced thermal transport performance for poly(vinylidene fluoride) composites with superfullerene

High thermal conductive polymer composites have recently attracted much attention, along with the quick development to the electronic devices toward higher speed. The addition of high thermal conductive fillers is an efficient method to solve this problem. Here, we introduced superfullerene (SF), a novel zero-dimensional carbon-based filler, and incorporated into PVDF by a solution method. The effects of SF filler on the thermal conductivity of PVDF composites were systematically investigated. It was found that PVDF composites exhibited an improvement in thermal conductivity at a low SF loading. PVDF composites with only 5 wt% SF filler present the thermal conductivity value of 0.365 Wm-1K-1, which is as much as 121 % enhancement in comparison with that of neat PVDF. In view of the excellent thermal transport performance, the composites may enable some applications in thermal management in the future.

High thermal conductivity phase change composite with a metal-stabilized carbon-fiber network

To enhance the thermal conductivity of phase change materials (PCM) such as sugar alcohol and molten salts, the preparation of a phase change composite (PCC) with a PCM and a filler with high thermal conductivity has been widely investigated. Although many reported PCCs have high thermal conductivity, the stability during thermal cycling endurance is often too low for practical use. This paper describes the development of a PCC with both high thermal conductivity and high cyclic durability. The PCCs were prepared by a hot-pressing method. Erythritol (melting point: 118°C, thermal conductivity: 0.73Wm−1K−1) was used as a PCM, and carbon fiber (thermal conductivity: 900Wm−1K−1 in the fiber direction) and indium particles (thermal conductivity: 82.8Wm−1K−1) were used as the high thermal conductivity fillers. The effective thermal conductivity of the PCC was measured using the laser flash method and the network structures were analyzed using energy dispersive spectroscopy and scanning electron microscopy. Thermal cycling tests through the melting and solidification phases of the erythritol were performed to investigate the cyclic durability of the PCCs. We found that the indium particles melted during hot pressing, welding together the carbon fiber to produce a stable percolating network, which significantly enhanced the thermal conductivity and cyclic endurance of the PCCs.

A reconstruction of Maxwell model for effective thermal conductivity of composite materials

Composite materials consisting of high thermal conductive fillers and polymer matrix are often used as thermal interface materials to dissipate heat generated from mechanical and electronic devices. The prediction of effective thermal conductivity of composites remains as a critical issue due to its dependence on considerably factors. Most models for prediction are based on the analog between electric potential and temperature that satisfy the Laplace equation under steady condition. Maxwell was the first to derive the effective electric resistivity of composites by examining the far-field spherical harmonic solution of Laplace equation perturbed by a sphere of different resistivity, and his model was considered as classical. However, a close review of Maxwell’s derivation reveals that there exist several controversial issues (deficiencies) inherent in his model. In this study, we reconstruct the Maxwell model based on a potential mean-field theory to resolve these issues. For composites made of continuum matrix and particle fillers, the contact resistance among particles was introduced in the reconstruction of Maxwell model. The newly reconstructed Maxwell model with contact resistivity as a fitting parameter is shown to fit excellently to experimental data over wide ranges of particle concentration and mean particle diameter. The scope of applicability of the reconstructed Maxwell model is also discussed using the contact resistivity as a parameter.

High thermal conductivity phase change composite with percolating carbon fiber network

Abstract Latent heat storage (LHS) using phase change materials (PCM) is a promising technology for the effective use of solar and industrial exhaust heat. However, the heat transfer rate of an LHS system is severely limited by the low thermal conductivity of the PCM. Therefore, this paper describes the development of a high thermal conductivity phase change composite (PCC) with a percolating network of a high thermal conductivity filler. The relationship between the effective thermal conductivity of the PCC and the network structure of the filler was investigated. The PCC were prepared by the conventional melt-dispersion (MD) method and a novel hot-press (HP) method. Erythritol (melting point: 118 °C, thermal conductivity: 0.73 W m−1 K−1) was used as the PCM, and carbon fiber (thermal conductivity: 900 W m−1 K−1 in the fiber direction) was used as the high thermal conductivity filler. The effective thermal conductivity of the PCC was measured by the laser flash method and the network structures were observed by energy dispersive spectroscopy using a scanning electron microscope. As a result, we observed that the percolating filler network in the PCC could be easily formed by the HP method, presenting a higher thermal conductivity with less filler additive than the PCC fabricated by the MD method. Additionally, we found that PCM raw materials with a high packing ratio accelerated the formation of the percolating filler network.

Thermal conductivity of polypropylene composites with hybrid fillers of boron nitride and vapor‐grown carbon fiber

High thermal conductivity fillers of boron nitride (BN) and vapor‐grown carbon fiber (VGCF) were used alone or incorporate to prepare polypropylene (PP) composites. The effects of filler content, particle size and shape, and single vs. hybrid BN/VGCF fillers were investigated with respect to the thermal conductivity of the PP composites. The thermal conductivity of PP/BN composites depended upon the content and particle size of the BN. Increased content and length of VGCF had the effect of increasing the thermal conductivity of the PP composites. Hybrid fillers were created with a mixture of medium‐sized BN and long‐length VGCF; hybrid BN/VGCF fillers enhanced the thermal conductivity of PP composites with a lower total content compared with PP composites containing only medium‐sized BN particles. POLYM. COMPOS., 37:936–942, 2016. © 2014 Society of Plastics Engineers

Heat dissipation performance of a high-brightness LED package assembly using high-thermal conductivity filler

This paper presents a thermal analysis and experimental validation of natural convective heat transfer of a high-brightness light-emitting diode (LED) package assembly. The substrate materials used in the LED package assembly were filled and doped using boron nitride (BN) filler. The thermal conductivity of the BN-filled substrate was measured. The temperature distribution and heat flow of the LED package were assessed by thermal profile measurement using an infrared (IR) camera and thermocouples. In addition, the heat transfer process of the LED package assembly in natural convection was also simulated using the computational fluid dynamics method. The optical performance of the LED package was monitored and investigated with various filler contents. The heat conduction mechanism in the substrate was analyzed. IR thermogram showed that the BN-doped substrate could effectively lower the surface temperature of the LED package by 21.5°C compared with the traditional FR4 substrate. According to the IESNA LM 80 lifetime testing method, reduction in LED temperature can prolong the LED's lifetime by 19,000h. The optical performance of the LED package assembly was also found to be improved significantly in lighting power by 10%. As a result, the overall heat dissipation capability of the LED package to the surrounding is enhanced, which improves the LED's efficacy.

Exfoliated hexagonal boron nitride-based polymer nanocomposite with enhanced thermal conductivity for electronic encapsulation

Hexagonal boron nitride (h-BN) nanosheet is a novel high thermal conductivity and high aspect ratio filler that has the potential to substantially enhance the thermal conductivity of polymer composites. We prepared h-BN nanosheet by liquid exfoliation of bulk h-BN flakes, and demonstrated the enhanced thermal conductivity of its epoxy composite. It is found that the enhancement of thermal conductivity by using h-BN nanosheet is substantial at low filler loadings. At a loading of 5 wt%, the thermal enhancement factor is 113% for exfoliated h-BN nanosheets, and is only 28% for h-BN control. It is also noted that the effect of using h-BN nanosheets becomes less obvious at high filler loading probably due to the large thermal boundary resistance. Infrared thermal imaging measurement confirmed that the resulting h-BN nanosheet/epoxy nanocomposite can successfully reduce the thermal resistance between Cu–Si interfaces when being used as thermal conductivity adhesives. Further, detailed characterizations on the flowability, thermomechanical properties and moisture adsorption, etc. revealed the promising application of the BN nanosheet/epoxy nanocomposite for electronic encapsulation.

Preparation and properties of polyamide 6 thermal conductive composites reinforced with fibers

The majority of inorganic particles-filled thermal conductive composites highlight thermal conductivity in detriment of mechanical properties. In this work, magnesium hydroxide (Mg(OH)2), alumina (Al2O3) and flake graphite-filed polyamide 6 (PA6) composites prepared by twin-screw extruder, were reinforced with carbon and glass fibers separately. Effects of fiber type and content on thermal conductivity, mechanical properties and heat deflection temperature (HDT) of the PA6-based composites were investigated. The results showed that the thermal conductivity of the composites improved with increasing carbon fiber content, while decreased slightly with glass fiber loading. Furthermore, strength, modulus and HDT of the PA6-based composites increased with the increase of fiber content. The reinforcing effects of the two fibers on the thermal and mechanical properties of the composites were compared and interpreted in this paper. By incorporating simultaneously high thermal conductive fillers and high-strength fibers, the combined composites hold a good potential in heat dissipation applications.

Thermal properties and moisture absorption of nanofillers‐filled epoxy composite thin film for electronic application

This current study aimed to enhance the thermal conductivity of thin film composites without compromising other polymer qualities. The effect of adding high thermal conductivity nanoparticles on the thermal properties and moisture absorption of thin film epoxy composites was investigated. Three types of fillers in nanosize with high thermal conductivity properties, boron nitride (BN), synthetic diamond (SD), and silicon nitride (Si3N4) were studied. SN was later used as an abbreviation for Si3N4. The contents of fillers varied between 0 and 2 vol.%. An epoxy nanocomposite solution filled with high thermal conductivity fillers was spun at 1500–2000 rpm to produce thin film 40–60 µm thick. The effects of the fillers on thermal properties and moisture absorption were studied. The addition of 2 vol.% SD produced the largest improvement with 78% increment in thermal conductivity compared with the unfilled epoxy. SD‐filled epoxy thin film also showed good thermal stability with the lowest coefficients of thermal expansion, 19 and 124 ppm, before and afterTg, respectively, which are much lower compared with SN‐filled and BN‐filled epoxy thin film composites. However the SD‐filled epoxy film has its drawback as it absorbs more moisture compared with BN‐filled and SN‐filled epoxy film. Copyright © 2012 John Wiley & Sons, Ltd.

High thermal conductivity epoxy composites with bimodal distribution of aluminum nitride and boron nitride fillers

High thermal-conductivity fillers of aluminum nitride (AlN) and boron nitride (BN) were incorporated in the epoxy matrix in order to identify the effects of the particle size and the relative composition on the thermal conductivity of composites. In the bimodal distribution of polygonal AlN and planar BN particles, the optimal thermal conductive path was strongly affected by the packing efficiency and interfacial resistance of the particles in a sensitive way and, consequently, the maximum thermal conductivity was achieved up to 8.0W/mK in the 1:1 volume ratio of AlN:BN particles. In the optimal volume ratio of the two fillers at 1:1, the relative filler size, which was represented by the shape factor (or the diameter ratio of the two filler particles, RD), also influenced the thermal conductivity giving the maximum conductivity at the shape factor RD≈1. The optimal morphology and composition of the AlN/BN composite systems were clearly visualized and thoroughly discussed in the filler distribution curves plotting the filler-appearance frequency as a function of particle size. The developed methodology validated that two different particles should be packed well to fill up the interstitial space and, simultaneously, the contact resistance and the contact area of the fillers should be optimized to maximize the thermal conductivity.