Conductivity Of Epoxy Composites Research Articles

Constructing house-of-cards-like networks with BNNS confined in interlocking Al2O3 platelet skeletons for thermally conductive epoxy composites

The construction of 3D filler networks is an effective strategy to improve the thermal conductivity of epoxy resins, yet it is still severely limited by the disconnection of conduction channels. In this contribution, an original interlocking hybrid skeleton with continuous conduction channels was developed by assembling BNNS into an in situ-formed interlocking Al2O3 platelet skeleton using commercial polyurethane as a template, where large intergranular contact areas of Al2O3 platelets were established by sintering to greatly decrease the contact thermal resistance. Besides, the interlocking Al2O3 skeleton coupled with BNNS under hydrogen bonding endowed further improvement of its thermal conductivity. The optimized Al2O3/BNNS/EP composite displayed an excellent thermal conductivity of 5.01 W/mK at 15.3 vol% of Al2O3 and 11.4 vol% of BNNS loading, far higher than that of neat epoxy resin by 1904.0 %. Meanwhile, the interlocking hybrid skeleton provided the epoxy resin with low dielectric loss, satisfactory thermal stability and flame retardancy.

Excellent thermal conductive epoxy composites via adding UHMWPE fiber obtained by hot drawing method

AbstractThe continuous updating and iteration of electronic devices brings about a significant accumulation of heat. It is urgent to enhance the thermal properties of polymer‐based composites to alleviate the heat dissipation problem in the microelectronics industry. In this paper, the hot drawing process was introduced to increase the crystallinity of ultra‐high molecular weight polyethylene (UHMWPE) fiber and improve its thermal conductivity. The ultra‐high molecular weight polyethylene fiber/epoxy resin (UHMWPE fiber/Epoxy) composites with high thermal conductivity were prepared by compositing UHMWPE fiber with epoxy resin under vacuum conditions. Due to the good crystallinity of the UHMWPE fiber (86%), an efficient thermal conduction path is provided for phonons in the axial direction along the fibers. The results show that the thermal conductivity of the composites reaches a maximum of 3.51 W/mK (in‐plane), which is 17.47 times higher than that of the epoxy resin (0.19 W/mK). The thermography pictures indicate that the composites have better heat transfer capacity with an increase in the draw ratio (λ). In addition, the composites also have the characteristics of low density and low electrical conductivity. These researches will provide a new idea for the preparation of all‐polymer composites with high thermal properties.Highlights A hot drawing process was introduced to increase the crystallinity of UHMWPE fiber for improving thermal conductivity. High crystallinity facilitates the reduction of phonon scattering and the transmission of thermal energy by phonons. The obtained polymer composites exhibit an ultra‐high in‐plane thermal conductivity.

Thioester-Based Latent Curing Agent for Thermally Conductive Epoxy Composites

Thioester-Based Latent Curing Agent for Thermally Conductive Epoxy Composites

Construction of alumina framework with a sponge template toward highly thermally conductive epoxy composites

AbstractCeramic‐based polymer composites are commonly utilized as thermal management materials due to their high thermal conductivity and electrical insulation properties. One efficient method to enhance the thermal conductivity of these composites is by constructing a three‐dimensional thermal conductive network within the polymer matrix. In this study, alumina was coated onto the surface of polyurethane (PU) foam, followed by high‐temperature removal of the PU foam and sintering of the alumina sheets to obtain a continuous alumina framework. Epoxy resin was then infiltrated into this alumina framework to fabricate highly thermally conductive EP/f‐Al2O3 composites. The EP/f‐Al2O3 composite achieved a thermal conductivity of 2.44 W m−1 K−1 when the filler content of 26.8 vol%, representing a 400% improvement compared to EP/Al2O3 composite with randomly dispersed fillers, and a remarkable 1180% enhancement compared to epoxy resin. Infrared thermal imaging also confirmed the excellent heat dissipation capability of the EP/f‐Al2O3 composites. Overall, this research presents an effective method for producing highly thermally conductive and electrically insulating composites that can be used in electronic thermal management applications.Highlights Fabrication of porous Al2O3 frameworks/epoxy composites. Porous Al2O3 frameworks were fabricated by polyurethane foam template. The obtained EP/f‐Al2O3 composite exhibited excellent thermal conductivity.

Advances in Liquid Crystal Epoxy: Molecular Structures, Thermal Conductivity, and Promising Applications in Thermal Management

Traditional heat conductive epoxy composites often fall short in meeting the escalating heat dissipation demands of large‐power, high‐frequency, and high‐voltage insulating packaging applications, due to the challenge of achieving high thermal conductivity (k), desirable dielectric performance, and robust thermomechanical properties simultaneously. Liquid crystal epoxy (LCE) emerges as a unique epoxy, exhibiting inherently high k achieved through the self‐assembly of mesogenic units into ordered structures. This characteristic enables liquid crystal epoxy to retain all the beneficial physical properties of pristine epoxy, while demonstrating a prominently enhanced k. As such, liquid crystal epoxy materials represent a promising solution for thermal management, with potential to tackle the critical issues and technical bottlenecks impeding the increasing miniaturization of microelectronic devices and electrical equipment. This article provides a comprehensive review on recent advances in liquid crystal epoxy, emphasizing the correlation between liquid crystal epoxy's microscopic arrangement, organized mesoscopic domain, k, and relevant physical properties. The impacts of LC units and curing agents on the development of ordered structure are discussed, alongside the consequent effects on the k, dielectric, thermal, and other properties. External processing factors such as temperature and pressure and their influence on the formation and organization of structured domains are also evaluated. Finally, potential applications that could benefit from the emergence of liquid crystal epoxy are reviewed.

Highly thermal conductive epoxy composites enabled by 3D graphene/Cu-based dual networks for efficient thermal management

With the increasing integration of electronic devices, efficient thermal management is urgently required. Herein, 3D graphene/Cu-based dual networks were developed for highly thermal conductive epoxy (Cu@hLIG/EP) composites. Using the honeycomb-like porous laser-induced graphene (hLIG) as 3D skeleton, the Cu layer was introduced by electroless plating. The Cu@hLIG/EP composite showed a high thermal conductivity up to 16.4 W m−1 K−1, which was almost 63 times that of neat EP and 6 times that of hLIG/EP composite with similar filler loading. This increase was attributed to the pre-constructed 3D network, phonon-electron dual thermal transfer channels and reduced phonon mismatch in composites. Furthermore, by using the reprocessable EP resin, the designability of thermal conductive composites was greatly enhanced, where layered composites could be easily fabricated by the simple stacking strategy. The material/process developed demonstrates wide promise in thermal management applications.

Synchronously enhancing thermal conductivity and dielectric properties in epoxy composites via incorporation of functionalized boron nitride.

Polymer-like dielectrics with superb thermal conductivity as well as high dielectric properties hold great promise for the modern electronic field. Nevertheless, integrating these properties into a single material simultaneously remains problematic due to their mutually limited physical connotations. In this study, we developed high-quality thermally conductive epoxy composites with excellent dielectric properties. This was achieved by incorporating surface-functionalized microscale hexagonal boron nitride (BN) along with N-[3-(Trimethoxysilyl)propyl]ethylene diamine (DN) and N-[3-(Trimethoxysilyl)propyl]aniline (PN). In the resulting epoxy composite, microscale BN serves as the primary building block for establishing the thermally conductive network, while silica particles act as bridges to regulate heat transfer and reduce interfacial phonon-scattering. The prepared composites were thoroughly examined across various filler contents (ranging from 10 to 80 wt%). Among them, the DNBN/epoxy composite exhibited higher thermal conductivity (in-plane: 47.03 W m-1 K-1) at 60 wt% filler content compared to BN/epoxy (39.40 W m-1 K-1) and PNBN/epoxy (33 W m-1 K-1) composites. These results highlight the usefulness of surface modification of BN in improving compatibility between fillers and epoxy, ultimately reducing composite viscosity. Furthermore, the DNBN/epoxy composite at 60 wt% demonstrated superb dielectric constant (∼6.15) without compromising on dissipation loss (∼0.06). The strategy adopted in this study offers significant insights into designing dielectric thermally conductive composites with superior performance outcomes.

Effect of small-sized modifier on boron nitride for efficient heat transfer through thermal conductive epoxy composites

Surface modification of a crystalline filler is a powerful method for increasing the thermal conductivity (κ) of filler-impregnated composites. Herein, boron nitride (BN) filler was functionalized with cationic molecules of different sizes to directly recognize the effect of an amorphous area on the filler-polymer matrix interface. Measured thermal conductivity and temperature rise for a polymer composite was up to 67.1 % and 15.3 % greater, respectively, in the sample to which the smallest molecule-modified BN was added, compared to the comparable sample with free BN. The smaller the size of the modifier molecule, the better it bonds with the resin and the smaller the non-crystalline area. Such changes improve the heat transfer at the interface by reducing interfacial thermal resistance. These findings can serve as a reference to develop alternative and effective strategies for filler modification, an alternative approach instead of focusing on functional groups and modifiers.

Ultrahigh in-plane thermal conductive epoxy composites by cellulose-supported GnPs@PDA skeleton under stress-induced orientation strategy

Designing anisotropic thermally conductive networks in thermal management materials can effectively exploit the high in-plane thermal conductivity of two-dimensional fillers to achieve high heat transfer efficiency along the predetermined direction, which is the hotspot for thermal management materials. However, constructing such an interconnected network with an orderly alignment structure through thermally conductive fillers has proved challenging. In this study, a high-density cellulose-supported GnPs@PDA skeleton with an interconnected and ordered structure was successfully prepared through the stress-induced strategy. After embedding into the epoxy resin, the EP/CGP composites with 22.1 vol% filler content exhibit an excellent in-plane thermal conductivity of 8.39 W/mK under a 75 % compression ratio, which is 12.3 times higher than that without compression. The enhancement of thermal conductivity for EP/CGP composites under the stress-induced orientation strategy is illustrated by the finite element analysis and metal foam theory. Furthermore, the transient heat transmission processes of the composites are recorded to verify their prospect in thermal management applications. This novel approach sheds light on the fabrication of thermally conductive networks with interconnected and ordered structures for next-generation thermal management materials.

Recent Progress on Multifunctional Thermally Conductive Epoxy Composite.

In last years, the requirements for materials and devices have increased exponentially. Greater competitiveness; cost and weight reduction for structural materials; greater power density for electronic devices; higher design versatility; materials customizing and tailoring; lower energy consumption during the manufacturing, transport, and use; among others, are some of the most common market demands. A higher operational efficiency together with long service life claimed. Particularly, high thermally conductive in epoxy resins is an important requirement for numerous applications, including energy and electrical and electronic industry. Over time, these materials have evolved from traditional single-function to multifunctional materials to satisfy the increasing demands of applications. Considering the complex application contexts, this review aims to provide insight into the present state of the art and future challenges of thermally conductive epoxy composites with various functionalities. Firstly, the basic theory of thermally conductive epoxy composites is summarized. Secondly, the review provides a comprehensive description of five types of multifunctional thermally conductive epoxy composites, including their fabrication methods and specific behavior. Furthermore, the key technical problems are proposed, and the major challenges to developing multifunctional thermally conductive epoxy composites are presented. Ultimately, the purpose of this review is to provide guidance and inspiration for the development of multifunctional thermally conductive epoxy composites to meet the increasing demands of the next generation of materials.

Enhanced Thermal Conductivity of Epoxy Composites Fabricated with Boron Nitride and Multi-Walled Carbon Nanotubes

Preparation of polymer-based packaging materials with rapid heat dissipation capacity is crucial for ensuring high-power equipment’s service life. To achieve this, boron nitride (BN) and multi-walled carbon nanotubes (MWCNTs) were used in different ratios to prepare thermally conductive epoxy composites. These composites were created through a simple mixing and curing process, resulting in a heat transmission path. Then, BN and MWCNTs were separately functionalized with dopamine and acid to enhance their dispersibility and interfacial compatibility within the epoxy resin. This was done to further explore their influence on the formation of serial heat transfer pathways. The BN/MWCNTs/epoxy composites with a filler ratio of 15:1 and a total filler loading of 30 wt % exhibited a thermal conductivity of 0.92 W/mK, which is 118% higher than pure epoxy. These composites also displayed favorable mechanical properties and thermal stability. This study provides guidance for designing high-performance epoxy composites to meet modern electronic devices’ thermal management requirements.

Thermally conductive epoxy composites with efficient heat transfer pathways by in-situ growth of CNTs on oriented BNNS

The rapid development of high-frequency electronic devices not only brings the rise of electronic information fields but also causes harm caused by a large amount of heat accumulation in the equipment. Herein, we build a continuous heat transfer framework formed by growing carbon nanotubes (CNTs) in an oriented boron nitride structure. The ice-dissolving complexation (IDC) method couples the orientation construction of boron nitride nanosheets (BNNS) and the surface localization of cobalt ions (Co2+) under mild conditions. The reduced Co on the surface of BNNS utilizes its catalytic ability to realize the in-situ conversion of styrene into CNTs, which link adjacent BNNS through covalent bonding to form a fluent heat transfer pathway. The oriented thermal conduction channel and low thermal resistance interface structure promote the through-plane and in-plane thermal conductivity of the composite to reach 4.83 W m−1 K−1 and 1.98 W m−1 K−1, respectively. Its light weight, compression resistance, and insulation give this composite a vaster application prospect. The design of such an efficient composite filler thermal conductivity network provides ideas for constructing of new thermal management materials.

Preparation of highly thermally conductive epoxy composites featuring self‐healing and reprocessability

AbstractEnhancing the thermal conductivity of epoxy resin is an urgent demand for its application in electronic packaging field. In this work, thermally conductive epoxy/graphite composite featuring excellent self‐healing and reprocessability is prepared based on covalent adaptable networks. The effect of graphite on the rheology, reprocessing, and self‐healing properties of epoxy have been studied. The result shows that the prepared composites can be easily reprocessed and have excellent self‐healing property. On the fundamental of the highly multifunctional performance of the epoxy composites, highly thermally conductive bulk composites are constructed via multilayered stacking up and self‐healing based on the film composites, which is prepared using a rolling method. It is demonstrated that the films can assemble into new substance bulk by stacking up through self‐healing. The high thermal conductivity is achieved by the highly aligned graphite induced by the rolling process. Result reveals that, being filled with 50% mass fraction of GR, the bulk composites possesses high thermal conductivity of 8.411 Wm−1 K−1. This work provides a new strategy to prepare recyclable and highly thermally conductive epoxy.

Highly thermally conductive and negative permittivity epoxy composites by constructing the carbon fiber/carbon networks

The geometry of electronic devices is shrinking, while electronic components are moving towards miniaturization, integration and high frequencies. Polymer composites with high thermal conductivity, low cost and light weight are urgently needed for thermal management areas such as clean energy, 5G mobile phones, artificial intelligence and so on. In this paper, pre-oxygenated fibers (POF) are firstly prepared into POF felt using air-flow netting and needling. The POF felts are graphitized to form carbon felts (CF). Finally, the CF/C felt are prepared by vacuum impregnation-lamination cured-carbonization-graphitization-purification. Epoxy resin/carbon fiber/carbon (EP/CF/C) composite prepared by a simple vacuum encapsulation method. Test results show that the prepared epoxy composites have a thermal conductivity of up to 2.83 W/mK and 0.57 W/mK in-plane and through-plane with 8.94 vol% CF/C. The maximum thermal conductivity enhancement of the epoxy composites is 1389% and 202% compared to the pure epoxy resin. The composite's maximum in-plane and through-plane conductivity can reach 0.17 S/cm and 0.04 S/cm respectively. Composites show a certain negative dielectric behavior. With increasing of graphitization, the negative permittivity appears in the low frequency region. Infrared imaging shows that the prepared epoxy composites have excellent thermal management properties. The carbon fiber thermally conductive composites prepared in the above manner may have promising applications in advanced thermal management.

Enhancing thermal conductivity of epoxy composites via f‐BN@f‐MgO hybrid fillers assisted by hot pressing

AbstractHigh thermal conductive polymeric composites are extremely desired for the thermal management of electronic devices due to the rapid development of the modern microelectronic industry. Herein, the functionalized boron nitride (BN) and magnesium oxide (MgO) hybrid fillers (f‐BN@f‐MgO) were synthesized and used to prepare the enhanced thermal conductive epoxy (EP) composites through the hot‐pressing method. The results demonstrated that the covalent binding of BN and MgO in the hybrid fillers reduced the interface thermal resistance effectively between fillers and matrix and the hot‐pressing induced force facilitated the construction of the continuous thermal conduction paths. Consequently, the as‐prepared epoxy composite at 40 wt% hybrid fillers loading had high thermal conductivity (TC) (1.97 W/[m·K]), outstanding insulating performance (6.9 × 1015 Ω cm) and excellent thermal stability. Furthermore, a probable thermal conduction mechanism was proposed to illustrate the high TC of the epoxy composite. Therefore, this study provides a new approach to preparing epoxy composites with outstanding performances.

Single‐walled Carbon Nanotubes Dispersed by CO2 Responsive Surfactants for Fabricating High Conductive Epoxy Composites

AbstractThe emerging nanomaterials single‐walled carbon nanotube (SWNTs) with large specific surface area, excellent electrical conductivity and high mechanical strength, has been used to fabricate electronic devices. However, the extremely strong π‐π interactions make SWNTs easy to agglomerate, thus limiting their application. In this work, a novel method was applied to disperse SWNTs by using rigid rosin‐based CO2 responsive surfactant rosin acid dimaleimide choline (R‐BMI‐C). When pH 10.4, SWNTs can be uniformly and stably dispersed, and at pH 6.3, SWNTs aggregated. The dispersed SWNTs was then integrated into diglycidyl ether of bis phenol A (DGEBA) to fabricate high conductive epoxy composites. Their properties were characterized by SEM, TG, high resistivity meters, etc.. The results showed that the modified SWNTs/DGEBA composites obtained an ultra‐low percolation threshold (0.025 wt.%). Compared with the original SWNTs/DGEBA composite, its tensile strength and elastic modulus were enhanced by 17 % and 96 %, respectively, when the SWNTs content was 0.5 wt.%.

Glucose-Assisted Exfoliation of Hexagonal Boron Nitride Nanosheets and Modification with Hyperbranched Polymers for Thermally Conductive Epoxy Composites: Implications for Thermal Management

Glucose-Assisted Exfoliation of Hexagonal Boron Nitride Nanosheets and Modification with Hyperbranched Polymers for Thermally Conductive Epoxy Composites: Implications for Thermal Management

Highly Thermally Conductive Epoxy Composites with AlN/BN Hybrid Filler as Underfill Encapsulation Material for Electronic Packaging.

In this study, the effects of a hybrid filler composed of zero-dimensional spherical AlN particles and two-dimensional BN flakes on the thermal conductivity of epoxy resin were studied. The thermal conductivity (TC) of the pristine epoxy matrix (EP) was 0.22 W/(m K), while the composite showed the TC of 10.18 W/(m K) at the 75 wt% AlN–BN hybrid filler loading, which is approximately a 46-fold increase. Moreover, various essential application properties were examined, such as the viscosity, cooling rate, coefficient of thermal expansion (CTE), morphology, and electrical properties. In particular, the AlN–BN/EP composite showed higher thermal stability and lower CTE (22.56 ppm/°C) than pure epoxy. Overall, the demonstrated outstanding thermal performance is appropriate for the production of electronic packaging materials, including next-generation flip-chip underfills.

Optimization of mechanical properties of recycled polyurethane waste microfiller epoxy composites using grey relational analysis and taguchi method

Mechanical properties and thermal conductivity of epoxy composites reinforced with recycled clamshell container waste as a micro filler (RCCF) were studied. The studies have been carried out to identify the influence of the two variables, the heating time periods (HT) within the range of 2, 4, 6 min., and wt % within the range of 1 %, 2 %, 4 % of recycled clamshell container waste that has been used as a reinforcing filler of epoxy composites. Recycling polyurethane waste aims to control and maintain a pollution-free environment, which is currently considered a difficult issue in addition to achieving low-cost aspects in preparing the composites. According to the method of no-combustion heating, the clamshell waste was converted from the natural plastic state into solids that were later made into 75 μm micro filler by grinding. Composites were ranked using grey relational analysis (GRA). The effect of each control parameter on response variables was analyzed by the Taguchi method. Using MINITAB 19 software, regression equations were obtained for each variable of mechanical properties and thermal conductivity to predict the properties of epoxy composites. The results of the addition of recycled clamshell container waste to epoxy resin show an improvement in the mechanical properties and thermal conductivity of the composites. The optimal value of the two factors was at HT2wt2, i.e. HT and wt % of 4 min and 2 %, respectively. The optimization values for the bending strength, impact strength, tensile strength, stiffness and thermal conductivity are 68.2 MPa, 10.348 kJ/m2, 21.08 MPa, 80 Shore D and 0.504 W/m·C°, respectively. The proposed Taguchi methodology based on grey relational analysis has been shown to be effective in solving multi-feature decision-making problems.

Epoxy-based composites with enhanced thermal properties through collective effect of different particle size fillers

Taking advantages of excellent adhesion and insulating properties, polymer-based thermal interface materials have been widely used in electrical and electronic industry. However, applications was limited due to the existence of high interfacial resistance and poor mechanical properties resulted from poor dispersion and weak interfacial adhesion of thermal conductive fillers in the polymer matrix. Herein, different sizes of aluminum oxide microparticle was used as thermal conductive fillers to fabricate a series of high thermal conductive epoxy composites, and the effect of fillers loading ratio on the properties of thermal conductive, mechanical, thermal stability was further analyzed. The optimum composite exhibits a high thermal conductivity (1.91 ± 0.02 W·m−1·K−1) at a loading ratio of 1: 2 (20-μm: 70-μm, mass ratio), which is equivalent to a thermal conductivity enhancement of 950% in comparison with pure epoxy resin. The outstanding properties of the as-prepared composite is mainly attributed to the effective conductive network formed by different size fillers that the smaller particles act as a bridge to connect the larger one. This work has proved by Agari model that combining different sizes Al2O3 as fillers is a workable way to obtain composite with high thermal conductivity and it is expected to provide a reliable route for the preparation of thermally conductive composites with different particle sizes.