Thermal Conductivity Of Polymer Composites Research Articles

Significantly Enhanced Thermal Conductivity of hBN/PTFE Composites: A Comprehensive Study of Filler Size and Dispersion.

High-temperature polymers are attractive for applications in extreme temperatures, where they maintain their mechanical flexibility and electrical insulating properties. However, their heat dissipation capability is limited due to their intrinsically low thermal conductivities. Hexagonal boron nitride (hBN) is a chemically inert, thermally stable, and electrically insulative compound with a high thermal conductivity, making it an ideal candidate as a filler within a high-temperature polymer matrix to increase the thermal conductivity. This study evaluates the effect of filler size and dispersion on thermal conductivity by producing homogeneous composite samples using a combination of solvent mixing and resonant acoustic mixing (RAM). We carefully characterized our samples, including the spread of the size distribution, and observed that the smaller sized hBN centered around 5 μm was able to integrate more seamlessly into the polytetrafluoroethylene (PTFE) matrix with particle size in the 15 μm range and hence outperformed 30 μm, in contrast to the conventional wisdom, which asserts that larger fillers universally perform better than smaller ones. Our thermal conductivity of hBN/PTFE composites at 30 wt % is 2× higher than the literature values. Notably, we reached the record-high value of 3.5 W/m K at 40 wt % with an onset of percolation at 20 wt %, attributed to optimized hBN dispersion that facilitates the formation of thermal percolation. Our findings provide general guidelines to enhance the thermal conductivity of polymer composites for thermal management, ranging from power transmission to microelectronics cooling.

An Effective Approach for the Preparation of High Performance Thermal Conductive Polymer Composites Containing Liquid Metal

An Effective Approach for the Preparation of High Performance Thermal Conductive Polymer Composites Containing Liquid Metal

Preparation and thermal conductivity of bimodal diamond particles reinforced phenolic resin composites

AbstractThermal conductive polymer composites have broad application prospects in the field of thermal management. However, due to intrinsically low thermal conductivity of polymers, even if fillers with high mass fraction are filled, the thermal conductivity of polymer composites cannot be significantly improved. In this paper, bimodal diamond particles (70 wt.% 150 μm and 22 wt.% 25 μm) were incorporated into phenolic resin to construct continuous heat transfer pathways by close packing, thereby enhancing its thermal conductivity. The results indicated that diamond particles with smaller particle size can effectively bridge the gaps between larger ones, forming a continuous for heat conduction. As a result, a maximum thermal conductivity value of 12.45 W/(m·K) can be achieved, which is 65.5 times, 9.8 times and 8.4 times higher than pure phenolic resin, 25 μm diamond particles reinforced phenolic resin composite and 150 μm diamond particles reinforced phenolic resin composite, respectively. Furthermore, heat dissipation and water cooling experiments also confirm the superior heat dissipation performance of phenolic resin composites reinforced with bimodal diamond particles. When the heating voltage is 10 V and the water cooling rate is 30 mL/min, the upper surface temperature of bimodal diamond composites is 129.2°C lower than that of pure phenolic resin. This investigation provides a new type of polymer composite with high thermal conductivity, which has promising prospects for application in thermal management. It also provides new insights for preparing polymer composites with high thermal conductivity by close packing of bimodal particles.Highlights Surface modification of the filler enhances its combination with resin. The interfacial bonding will be enhanced by D–OH bond on diamond surface. Bimodal diamond particles lead to the formation of a closely packed structure. This special structure can form a three‐dimensional heat conduction network. The highest TC of the DD/PR composite is 12.45 W/(m·K).

Application of machine learning in predicting the thermal conductivity of single-filler polymer composites

Polymer composites with superior thermal conductivity and low electrical conductivity are pivotal in the cooling of electronic devices. Despite their prevalence, the accurate prediction of the thermal conductivity of these composites remains a challenge. The emergence of machine learning (ML) provides a groundbreaking approach to solving this issue. In this study, we constructed a comprehensive dataset collected from previous experimental papers and successfully predicted the thermal conductivity of single-filler polymer composites using four ML regression algorithms: random forest regression (RFR), gradient boosting decision tree (GBDT), extreme gradient boosting (XGBoost), and Gaussian process regression (GPR). By employing feature engineering to select pertinent features from the original datasets, the accuracy of the four models on the test set was improved, among which GBDT exhibited the highest accuracy with the Pearson correlation coefficient value of 0.981. Factors such as filler volume fraction and matrix thermal conductivity significantly influence the thermal conductivity of composite materials, while the thermal conductivity of the fillers has a relatively minor impact. Additionally, we identified the topological polar surface area (TPSA) as a crucial descriptor for surface modifications, quantifying diverse surface-modifying agents. Due to the incorporation of more descriptors, ML models exhibit higher precision and broader applicability compared to empirical formulas. Our study provides an effective tool for predicting the thermal conductivity of polymer composites with single fillers and underscores the potential of machine learning in accelerating materials design.

Enhancing Thermal Conductivity in Polymer Composites through Molding-Assisted Orientation of Boron Nitride.

Incrementing thermal conductivity in polymer composites through the incorporation of inorganic thermally conductive fillers is typically constrained by the requirement of high filler content. This necessity often complicates processing and adversely affects mechanical properties. This study presents the fabrication of a polystyrene (PS)/boron nitride (BN) composite exhibiting elevated thermal conductivity with a modest 10 wt% BN content, achieved through optimized compression molding. Adjustments to molding parameters, including molding-cycle numbers, temperature, and pressure, were explored. The molding process, conducted above the glass transition temperature of PS, facilitated orientational alignment of BN within the PS matrix predominantly in the in-plane direction. This orientation, achieved at low filler loading, resulted in a threefold enhancement of thermal conductivity following a single molding time. Furthermore, the in-plane alignment of BN within the PS matrix was found to intensify with increased molding time and pressure, markedly boosting the in-plane thermal conductivity of the PS/BN molded composites. Within the range of molding parameters examined, the highest thermal conductivity (1.6 W/m·K) was observed in PS/BN composites subjected to five molding cycles at 140 °C and 10 MPa, without compromising mechanical properties. This study suggests that compression molding, which allows low filler content and straightforward operation, offers a viable approach for the mass production of polymer composites with superior thermal conductivity.

Modelling effective thermal conductivity in polymer composites: A simple cubic structure approach

In this study, we propose the simple cubic model, a distinctive thermal-conductive mathematics for modelling the effective thermal conductivity in polymer composites, taking both filler size and interface thermal resistance into account. This model is constructed by delineating heat transport paths within simple cubic structural units, leveraging principles involving Fourier's law, minimum thermal resistance, specific equivalent thermal conductivity, and thermal resistance network. Demonstrating broad applicability, the simple cubic model accurately predicts effective thermal conductivity within a 0–40 % volume fraction range of filler in polymer composites, maintaining less than 15 % error. Its robustness is validated across over 100 experimental datasets, encompassing various polymer matrices and granular filler types. This extensive validation underscores the model's efficacy, both with our experimental data and existing literature. The simple cubic model's insightful predictions make it valuable in designing and preparing thermally conductive polymer composites.

Polyimide-assisted fabrication of highly oriented graphene-based all-carbon foams for increasing the thermal conductivity of polymer composites

Graphene and its derivatives are often preferentially oriented horizontally during processing because of their two-dimensional (2D) layer structure. As a result, thermal interface materials (TIMs) composed of a polymer matrix and graphene-derived fillers often have a high in-plane (IP) thermal conductivity (K), however, the low through-plane (TP) K makes them unsuitable for practical use. We report the development of high-quality polyimide/graphite nanosheets (PG) perpendicular to the plane using a directional freezing technique that increase the TP K of polymer-based composites. Graphene-derived nanosheets (GNs) were obtained by the crushing of scraps of highly thermally conductive graphene films. A water-soluble polyamic acid salt solution was used to disperse the hydrophobic GNs filler to achieve directional freezing. The polyimide, which facilitated the directional alignment of the GNs, was then graphitized. The introduction of the GNs increases the order and density of the PG, thus improving the strength and heat transfer performance of its polydimethylsiloxane (PDMS) composite. The obtained PG/PDMS composite (21.1% PG, mass fraction) has an impressive TP K of 14.56 W·m−1·K−1, 81 times that of pure PDMS. This simple polyimide-assisted 2D hydrophobic fillers alignment method provides ideas for the widespread fabrication of anisotropic TIMs and enables the reuse of scraps of graphene films.

The effect of different GNP/BNNP foam structures in the infiltration of epoxy resin: A fundamental study

AbstractHierarchical 3D architecture of nanoplatelets, also known as foams, has arisen as a promising alternative to overcome agglomeration and promote mechanical reinforcement and electrical and thermal conductivity of polymer composites. Freeze‐drying is a cost‐effective method to manufacture foams with different structures and tailored thermal and electrical properties. This study used freeze‐drying to produce graphene (GNP), boron‐nitride (BNNP), and hybrid foams of different ratios. The interaction between these structures and high‐temperature epoxy grade was investigated via contact angle analysis. The foams were also infiltrated with epoxy to achieve a fully dense nanocomposite. The contact angle monitoring reveals solid loading content, composition, and structure as the main factors affecting wettability. Despite the slight variation in porosity among the foams, all the samples achieved a densification above 96%, suggesting that the epoxy viscosity of 2.34 Pa∙s combined with optimized infiltration parameters can successfully produce dense nanocomposites. The contact angle analysis is a suitable method to compare the infiltration quality of freeze‐dried foams and can be applied to evaluate the production feasibility of other polymer/foam nanocomposites. Furthermore, preliminary thermal data shows a clear temperature increase for the epoxy/foam structures, with GNP and 50:50 GNP:BNNP being the most thermally conductive compositions. This study serves as a starting point for freeze‐dried foams/polymer nanocomposite investigation and may broaden the possibilities for manufacturing and future application of these structures.Highlights The freeze‐dried foams were successfully fabricated and infiltrated with high‐temperature epoxy, obtaining densifications above 96%. The main factors affecting infiltration are foam morphology, porosity, and chemical affinity between polymer and foam platelets. Thermal conductivity has significantly improved by adding GNP and BNNP foam network to epoxy matrix.

Enhance thermal conductivity via constructing a low heat resistance interface with quaternized graphene

Interfacial thermal resistance of fillers in thermal conductive polymer composites is a barrier restricting heat dissipation function. In-situ graft of quaternary ammonium group on the surface of graphene can form cation-π interaction, providing a medium for heat transfer between graphene layers. Accordingly, we fabricate polyvinyl alcohol (PVA)-based heat conductive composite containing quaternized graphene stacking structure. With the assistance of non-covalent bonding, the in-plane thermal conductivity of the composite formed by self-precipitation method reaches 9.97 W m−1 K−1 at a filling content of 30 vol%. Molecular dynamics (MD) simulation further explores the promoting effect of the interfacial structure constructed between the charged group and graphene on the interfacial heat transfer. The optimized interfacial structure not only alleviates the bottleneck of interface thermal resistance but also enhances the mechanical properties of composite. This strategy provides an ideal solution to preparation of high-performance thermal management materials for electronic equipment.

Numerical analysis on the direction to improve thermal conductivity of polymer composites filled with spherical particles

The research on thermal conductivity of insulating polymer-matrix composites filled with spherical particles (PMCs-SP) is far below the requirements for industrial utility. To find the improving direction for the thermal conductivity of PMCs-SP (KPMCs-SP), a series of PMCs-SP models filled with randomly distributed spherical particles were established. The PMCs-SP models were validated by comparing the calculated KPMCs-SP with the experimental data. It is found that KPMCs-SP increases with the increasing volume fraction of spherical particles, and the influence of filler size and interfacial thermal resistance on KPMCs-SP shows a significant synergistic effect. The formation of heat conduction chains could effectively improve KPMCs-SP. Increasing the number of heat conduction chains and decreasing the spacing of spherical particles can both increase the KPMCs-SP. To quantify the effect of heat conduction chains on KPMCs-SP, the concept of compactness of heat flow chains (C) was creatively proposed. The KPMCs-SP-C curve presences a threshold value, C0 = 0.6372, beyond which KPMCs-SP could be significantly enhanced. In addition, the theoretical specific thermal resistance of PMCs-SP (Rλ,PMCs-SP) was first calculated. For PMCs-SP with the default parameters, the theoretical minimum Rλ,PMCs-SP converged to ∼ 0.72 m·K·W−1.

Facile synthesis of functionalized boron nitride nanosheets for photo‐cured 3D printing of high thermal conductive composites

AbstractAddressing the concern of heat accumulation in electronic devices, considerable research efforts have been dedicated to develop composites that are thermally conductive yet electrically insulative. Incorporating hexagonal boron nitride (h‐BN) as fillers shows promise in enhancing the thermal conductivity of polymer composites. However, notable challenges arise from difficulties in achieving well dispersion and establishing efficient three‐dimensional thermal conductive networks. This work demonstrated an efficient photocurable direct ink writing (DIW) printing method to fabricate functional h‐BN nanosheets (A‐BNNS)/epoxy acrylate (EA) resin‐based thermal conductive composites (A‐BNNS/EA). Apple polyphenol‐assisted ball milling was employed to fabricate functionalized BN nanosheets (A‐BNNS). Subsequently, A‐BNNS/EA inks were 3D printed using DIW to create thermally conductive composites, which were then UV‐cured. The composite containing 55 wt% A‐BNNS demonstrated an impressive thermal conductivity (TC) of 3.44 W/(m K). The utilization of 3D printing technology enables an onion‐like dispersion of A‐BNNS within the polymer matrix, effectively constructing three‐dimensional thermal conductive networks. This contribution significantly enhances the overall thermal conductivity.Highlights The functional BNNS (A‐BNNS) was achieved by apple polyphenol‐assisted ball milling. The utilization of photocurable 3D printing technology for producing high thermal conductivity materials are efficient. A‐BNNS exhibited an onion‐like distribution and effectively constructed a 3D thermal conductive network within the polymer matrix The composites demonstrate excellent thermal conductivity and favorable heat dissipation property.

A comprehensive study on enhancing effective thermal conductivity of polymer composites with randomly distributed triple fillers

This paper describes a comprehensive study on the effective thermal conductivity (ETC) of triple-filled polymer composites. A very complicated behavior was revealed under various effective factors, such as thermal conductivity (TC), volume fraction (VF), particle distribution, particle size, and filler arrangement. Consequently, some prediction models, which were well validated with numerical results, are first developed. Additionally, the ETC of polymer composite dramatically and non-linearly depends on TC ratios, VF ratios, particle distribution, filler arrangement, and particle size of the triple filler. The mountain shape of the ETC forms and depends on a variety of effective factors. The maximum ETC exists at the given optimum TC ratios ranging from approximately 0.1 to 100. It was also found that the ETC increases with the increase of the VF ratio for a threshold TC ratio; however, this trend changes when TC ratios go beyond the threshold values. Particularly, the ETC of the particle-filled polymer composite also depends on the filler arrangement, even though particles are straightly arranged along the direction of thermal flow. This effect becomes more significant when the difference in VF and TC between particles is larger. The results obtained are very useful in enhancing and maximizing the ETC of polymer composites with triple fillers and even multiple fillers in general.

Metal coordination in polymer drives efficient phonon transfer through self-assembled microstructures

Molecular interactions such as hydrogen bond, van der Waals force, covalent bond in association with heat transfer in polymeric materials have been reported, while the relationship between metal-polymer coordination and thermal conduction has not been studied yet. In this work, the molecularly-assembled microstructure of the composites produced by metal coordination with polyvinyl alcohol (PVA) reveals a qualitative correlation between microstructure and thermal conductivity (TC). The ellipsoid-shaped domain and increased coil size create stable phonon transmission channels, which are beneficial for boosting TC by lengthening the mean free path of phonon propagation. Strong coordination between the metal ions and the hydroxyl groups in the polyvinyl alcohol chains results in competition between the inter- and intra-molecular OH–OH hydrogen bonds, which eventually takes precedence. Such coordination structure creates distinctive micro-crystal domains and is discovered to be essential for TC enhancement. Moreover, the power generation value of thermal conversion using PVA-H/2.0Fe(NO3)3 film is twice that of pure PVA-H film, which has higher and faster conversion efficiency. These materials have been demonstrated as excellent candidates for improving the conversion efficiency of thermoelectric devices. In summary, this work offers a new strategy for regulating TC through metal coordination and a fundamental comprehension of the link between metal coordination, microstructure, and TC in polymer composites.

Recent Progress in Fabrication and Structural Design of Thermal Conductive Polymer Composites

Recent Progress in Fabrication and Structural Design of Thermal Conductive Polymer Composites

Numerical study on effective thermal conductivity of polymer composites with randomly distributed multi-fillers

This paper presents a numerical investigation of the effective thermal conductivity (hereafter, ETC) of polymer composites with randomly distributed multi-fillers. A finite element method combined with a user-defined code was proposed to predict the ETC under various effects. Consequently, the polymer composite structure was well generated for single, hybrid, and particularly triple fillers. The numerical results were thoroughly validated by comparing them with the prediction models, as well as numerical and experimental results in the literature. The highly complex behavior of the ETC in terms of effective parameters is first explored. The ETC of the triple-filled polymer composite improves compared with single and hybrid fillers only if the different filler‟s TCs are used. Otherwise, the ETC slightly reduces if the filler‟s TCs have the same value. The results obtained are very useful in understanding the complex behavior of the ETC of polymer composites with multiple fillers.

Preparation and construction mechanism of thermal conductive epoxy‐based composite via magnetic field induced orientation

AbstractBN was modified with Fe3O4 to confer it with paramagnetic responsivity. The scanning electron microscopy and energy dispersive spectrometer (EDS) results demonstrated that with the assistance of an external magnetic field, the paramagnetic BN particles within an epoxy matrix are effectively aligned along the direction of the magnetic field during the curing process of epoxy resin, hence forming continuous thermal conduction pathways. Therefore, the thermal conductivity of the epoxy‐based composite filled with 30 wt% of BN and externally applied with a 50 mT magnetic flux density was 0.7417 (W/m·K), an improvement of 207.89% relative to the pure epoxy resin. The establishment of continuous thermal pathways facilitates effective phonon conduction, thereby further enhancing the thermal conductivity of the material. Meanwhile, this study investigates the chain formation mechanism of Fe3O4‐modified BN under the influence of a magnetic field. When subjected to an applied magnetic field, the magnetic BN embedded in an epoxy resin matrix undergoes magnetization, rotation, and contact. Subsequently, multiple particles initially form short chains, then aggregate into longer chains aligned with the direction of the magnetic field. The findings indicate that the magnetic field induced particle alignment method holds significant potential in the fabrication of high thermal conductivity polymer composites with low filler loading.

Effect of Nanoscale in Situ Interface Welding on the Macroscale Thermal Conductivity of Insulating Epoxy Composites: A Multiscale Simulation Investigation.

Insulating thermally conductive polymer composites are in great demand in integrated-circuit packages, for efficient heat dissipation and to alleviative short-circuit risk. Herein, the continuous oriented hexagonal boron nitride (h-BN) frameworks (o-BN@SiC) were prepared via self-assembly and in situ chemical vapor infiltration (CVI) interface welding. The insulating o-BN@SiC/epoxy (o-BN@SiC/EP) composites exhibited enhanced thermal conductivity benefited from the CVI-SiC-welded BN-BN interface. Further, multiscale simulation, combining first-principles calculation, Monte Carlo simulation, and finite-element simulation, was performed to quantitatively reveal the effect of the welded BN-BN interface on the heat transfer of o-BN@SiC/EP composites. Phonon transmission in solders and phonon-phonon coupling of filler-solder interfaces enhanced the interfacial heat transfer between adjacent h-BN microplatelets, and the interfacial thermal resistance of the dominant BN-BN interface was decreased to only 3.83 nK·m2/W from 400 nK·m2/W, plunging by over 99%. This highly weakened interfacial thermal resistance greatly improved the heat transfer along thermal pathways and resulted in a 26% thermal conductivity enhancement of o-BN@SiC/EP composites, compared with physically contacted oriented h-BN/EP composites, at 15 vol % h-BN. This systematic multiscale simulation broke through the barrier of revealing the heat transfer mechanism of polymer composites from the nanoscale to the macroscale, which provided rational cognition about the effect of the interfacial thermal resistance between fillers on the thermal conductivity of polymer composites.

One-pot upcycling strategy achieved in Bi-continuous thermal conductive polymer composites

Though upcycling post-consumer polymers into high-value materials is appealing, it faces challenges including complex, costly processes and difficulties to achieve a circular lifecycle. To address these issues, we have developed a novel approach that involves designing a unique bi-continuous phase morphology with selective distribution of the conductive fillers in the semi-crystalline polymer phase. As a result, these composites exhibited excellent thermal conductivity (7.07 W m−1·K−1) and stable environmental longevity (thermal aging and 500 h UV irradiation) and can be upcycled as effective flame retardant (vertical combustion grade V-0) and smoke suppressed materials (smoke density grade 64.1) after their service life as a thermal conductive material has ended. Rather than being discarded or undergo molecular upcycling, they could be straightforwardly repurposed through melt processing and even displayed better processability, suggesting a one-pot but effective upcycle strategy for polymeric materials.

Enhanced Electrical and Thermal Conductivities of Polymer Composites with a Segregated Network of Graphene Nanoplatelets.

Introducing a segregated network constructed through the selective localization of small amounts of fillers can be a solution to overcome the limitations of the practical use of graphene-based conductive composites due to the high cost of fillers. In this study, polypropylene composites filled with randomly dispersed GNPs and a segregated GNP network were prepared, and their conductive properties were investigated according to the formation of the segregated structure. Due to the GNP clusters induced by the segregated structure, the electrical percolation threshold was 2.9 wt% lower than that of the composite incorporating randomly dispersed GNPs. The fully interconnected GNP cluster network inside the composite contributed to achieving the thermal conductivity of 4.05 W/m∙K at 10 wt% filler content. Therefore, the introduction of a segregated filler network was suitable to simultaneously achieve excellent electrical and thermal conductivities at a low content of GNPs.

Magnetic-induced dynamically enhanced in-plane or out-of-plane thermal conductivity of BN/Ag NWs@Ni/epoxy composites

The thermal conductivity of polymer composites could be improved through the orientation of fillers in specific directions. Here, a novel strategy to fabricate BN/Ag nanowires@Ni/epoxy composites (BN/Ag NWs@Ni/EP) to dynamically improve the in-plane or out-of-plane thermal conductivity of the composites in real-time by changing the direction of the magnetic field was investigated. The thermal conduction path was constructed by Ag NWs bridging between BN flakes. Ag NWs@Ni would be oriented in the in-plane or out-of-plane direction by changing the direction of the magnetic field. The out-of-plane or in-plane thermal conductivities of the composites were 0.824 and 0.723 W m−1K−1 at 40 wt% BN/Ag NWs@Ni content, and the corresponding TCEs were 429% and 359% respectively when Ag NWs@Ni was oriented in the out-of-plane or in-plane direction. Meanwhile, BN/Ag NWs@Ni/EP exhibited good mechanical and dielectric properties, which were beneficial for its industrial application in electronic packaging. This strategy provides the possibility for the applications that required the adjustment of the heat conduction direction in real-time.