Thermal Conductivity Of Polymer Composites Research Articles

Discussion on the thermal conductive network threshold of Al2O3/Co-continuous phase polymer composites

Achieving high thermal conductivity in polymer composites with micro or nanoparticle fillers are challenging. Typically, over 50 ​vol% filler loading is necessary to form a thermal conductive network. However, even with such a network in place, the increase in thermal conductivity may not be significant compared to that in electrically conductive composites. To clarify the ideal filler network structure, we endeavored to selectively disperse nano-sized Al₂O₃ nanoparticles at the interface of co-continuous SEBS/PA6 blends, with and without various filler surface modification methods. A thermal conductive network forms when all interface areas are fully covered by 2.56 ​vol% of Al2O3 nanoparticles (very close to theoretical loading content 2.29 ​vol%). In this case, the Al2O3 nanoparticle has the highest thermal conductive contribution (TCC). However, the absolute TCC values are extremely low because of the interfacial thermal resistance and it will decrease when the filler content exceeds 2.56 ​vol%, indicating that some nanoparticles are dispersed separately out of the existed thermal conductive network. These findings suggest that the construction of a connected thermal conductive network, relatively lower interfacial thermal resistance and the precise positioning of fillers within this network are essential for achieving high thermal conductivity composites.

Development and Perspectives of Biobased Thermal Conductive Polymer Composites

Development and Perspectives of Biobased Thermal Conductive Polymer Composites

Significant enhancement of bi-directional ultrahigh thermal conductivity in polymer composites fabricated via Polyetherimide@Silver core–shell structured microspheres

Nowadays, the polymer-based composites with excellent thermal-conductive ability and ideal electromagnetic interference shielding performance are in great demand with the advent of developing modern electronic technology. However, most conventional thermal-conductive materials were typically designed to enhance thermal conductivity in just one single direction (through-plane or in-plane direction), which will be inadequate to meet increasing heat-dissipation requirements. Hence, polyetherimide/Silver (PEI/Ag) composites with unique segregated thermal-conductive network were fabricated via hot-pressing the core–shell (PEI@Ag) particles, which was endowed with superior thermal-conductive ability in bi-directions. By this process, the Ag shell was deposited on the surface of various polymer microsphere, and diverse morphology of composite particles would lead to different findings. The results show the PEI@Ag composites with filler content of 18.9 vol% exhibited high in-plane thermal conductivity and through-plane thermal conductivity of 19.9 and 14.0 W/mK, respectively. Particularly, these results achieved obvious improvements of 331 % and 1264 % higher than the composites with filler random distribution, indicating the composite materials obtained outstanding advantage in both horizontal and vertical direction. The research also found that the composites prepared from PEI@Ag core–shell structures possess better properties than those prepared with Ag nanoparticles growing on polymers, indicating the importance of continuous heat-transfer path, and their heat transfer behavior was further demonstrated by finite element analysis. Besides, the composites also exhibited remarkable EMI shielding performance (40.1 dB)). In a word, this study provides viable strategies to enhance the thermal conductivity of composites based on organic solvent-soluble polymer with EMI capability for the development of electronic devices.

Thermal conductivity enhancement of epoxy by a 3D Si3N4 crystal rod/grain skeleton fabricating from photovoltaic silicon waste

Silicon nitride (Si3N4) is one of the preferred fillers for the preparation of high thermal conductivity polymer composites because of its intrinsic high thermal conductivity and good electrical insulation. To maximize the thermal conductivity enhancement effect of the fillers in the composites, it is necessary to pre-construct a three-dimensional (3D) thermally conductive filler network. Herein, surfactant foaming was applied to pre-construct a 3D Si-containing framework from photovoltaic silicon waste (PSW), which was subsequently transformed into a porous skeleton consisting of Si3N4 rods and grains by in-situ nitridation reaction sintering. And finally, thermal conductive Si3N4/epoxy (EP) composites were fabricated after infiltrating EP into the network skeleton. When the filler content of Si3N4 was 41.00 vol%, the obtained Si3N4/EP composite showed the highest thermal conductivity of 2.99 W·m-1·K-1, which was 13.95 times higher than that of pure EP. Tests on running CPU and heating table showed that the Si3N4/EP substrate had excellent heat dissipation performance compared to the pure EP substrate. The 3D continuous network formed by "bridging" between two different morphologies of Si3N4 microcrystals contributed to providing effective multi-directional heat transfer paths and thereby improving the thermal conductivity of the composites. Overall, the low cost of raw silicon source originating from industrial waste as well as the simple and practical construction of heat-conducting filler network demonstrate the promising application of the Si3N4/EP composites fabricated in our work.

Hydrogen-peroxide intercalated expanded graphite facilitates large enhancement in thermal conductivity of polyetherimide/graphite nanocomposites

In this work, we prepared expanded graphite (EG) filler using hydrogen peroxide (H2O2) as an oxidizing agent to study its impact on the thermal conductivity (k) of polyetherimide (PEI) composite, compared to EG prepared using sodium chlorate (NaClO3). Sulfuric acid was used as the primary intercalating agent for both synthesis routes. The use of H2O2 prepared EG (EG-H2O2) led to a remarkable ∼4030% enhancement (9.5 Wm−1K−1) in k of the PEI/EG composite, while the use of NaClO3 prepared EG (EG-NaClO3) led to a much smaller enhancement of ∼2190% (5.3 Wm−1K−1), at 10 wt% EG composition compared to kPEI (∼0.23 Wm−1K−1). Such findings exceed the current state-of-art in EG-based polymer composites. Detailed characterization was performed to understand the properties of EG-H2O2 and EG-NaClO3. Raman analysis revealed that H2O2 resulted in relatively defect-free EG (ID/IG ratio ∼0.04), thus preserving the k of graphite (∼2000 Wm−1K−1). Use of NaClO3, however, led to a large defect density (ID/IG ratio ∼0.25), yielding graphite with significantly diminished k. Furthermore, through-plane thermal diffusivity of EG-H2O2 paper was measured to be 9.5 mm2s-1 while that of NaClO3 case was measured to be 6.7 mm2s-1, thus directly confirming the beneficial impact of H2O2 in preserving the high k of graphene. X-ray photoelectron spectroscopy (XPS) revealed that the higher number of defects in EG-NaClO3 are due to the higher degree of oxidation induced by NaClO3. The results demonstrate the potential of EG-H₂O₂ as an efficient filler for achieving high thermal conductivity polymer composites.

Anisotropically enhanced thermal conductivity of polymer composites based on segregated nanocarbon networks

Anisotropically enhanced thermal conductivity of polymer composites based on segregated nanocarbon networks

Thermal Conductive Polymer Composites: Recent Progress and Applications.

As microelectronics technology advances towards miniaturization and higher integration, the imperative for developing high-performance thermal management materials has escalated. Thermal conductive polymer composites (TCPCs), which leverage the benefits of polymer matrices and the unique effects of nano-enhancers, are gaining focus as solutions to overheating due to their low density, ease of processing, and cost-effectiveness. However, these materials often face challenges such as thermal conductivities that are lower than expected, limiting their application in high-performance electronic devices. Despite these issues, TCPCs continue to demonstrate broad potential across various industrial sectors. This review comprehensively presents the progress in this field, detailing the mechanisms of thermal conductivity (TC) in these composites and discussing factors that influence thermal performance, such as the intrinsic properties of polymers, interfacial thermal resistance, and the thermal properties of fillers. Additionally, it categorizes and summarizes methods to enhance the TC of polymer composites. The review also highlights the applications of these materials in emerging areas such as flexible electronic devices, personal thermal management, and aerospace. Ultimately, by analyzing current challenges and opportunities, this review provides clear directions for future research and development.

Exploring the Impact of Visual Heat Conduction Paths on Thermal Conductivity of Polymer Composites and the Practical Applications.

The theory of heat conduction paths has been widely recognized and widely studied in the research about the thermal conductivity of thermal conductive polymer composites at present. Encapsulating polymer pellets with thermally conductive fillers and processing them into thermally conductive polymer composites is a simple and effective method for constructing heat conduction paths. It is meaningful to investigate the related heat conduction mechanism of this method. Otherwise, this approach can significantly preserve the performance of the polymer substrate, making it highly valuable for practical material applications. In this work, polyethylene-octene elastomer (POE) pellets were encapsulated with thermal conductive fillers by physical absorption. Subsequently, the composite films containing heat conduction paths were fabricated using the encapsulated POE pellets through a heating press. Alumina (Al2O3), boron nitride (BN), and alumina/boron nitride hybrid (Al2O3/BN) fillers were used to prepare Al2O3@POE, BN@POE, and BN/Al2O3@POE composite films to investigate the influence of filler shapes on heat conduction path construction. The influence of the constitute and density of heat conduction paths on the thermal conductivity of composite films was analyzed by infrared thermal imaging, finite element analysis, and thermal resistance theory in detail. Owing to the reserved good adhesion and flexibility of the POE substrate, the composite films could be directly used as thermal interface materials for chip cooling, which presented a good heat dissipation effect. Furthermore, a series of integrated composite materials were prepared by the combination of encapsulated pellets with various functional films (copper foil, aluminum foil, and graphite sheet) through a one-pot heating press, exhibiting a good electromagnetic shielding effect. The performance of the composites and the corresponding preparation method demonstrate the strong significance of this research for practical applications.

Highly thermal conductivity polymer composites reinforced by BNNS/UHMWPE fabric for reliable electronic thermal protection and management

With the rapid development of 5G communication and microelectronics technology, the heat accumulation of high-power electronic devices puts forward an urgent demand for high thermal conductivity (TC) composites. However, it's still a great challenge through electrically insulating polymer to achieve good comprehensive performance of high TC, flexibility, and safety reliability. Herein, ultra-high molecular weight polyethylene (UHMWPE) fabric was coated with boron nitride nanosheets (BNNS) by dispersion and interfacial reinforcement of cellulose nanofibers (CNFs), and the BNNS/UHMWPE fabric-reinforced polymer composite (B/UF-PC) with 3D continuous thermal pathway was obtained by further composite with polydimethylsiloxane (PDMS). The continuous thermal pathways of highly aligned UHMWPE fibers in the fabric and the synergistic effect of the BNNS network enhance the out-of-plane and in-plane TC to 6.02 and 11.78 W/m K, respectively. Moreover, B/UF-PC exhibits flexible, lightweight (0.89 g/cm3), and significantly higher tensile strength (87.40 MPa) and energy absorption efficiency (98 %) than those of polymer composites, which allows it to be used in reliable electronic thermal management to prevent heat accumulation and external mechanical impact. This work provides a strategy for efficiently preparing flexible polymer composites with high TC and insulation properties.

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.

Role of four-phonon processes in thermal conductivity of two-dimensional materials and thermal-transport enhancement arising from interconnected nanofiller networks in polymer/nanofiller composites.

Recent research has shed light on the importance of four-phonon scattering processes in the thermal conductivity (k) of 2D materials. The inclusion of 4 phonon scattering processes from first-principles has been shown to lead to a thermal conductivity of ∼1290 W m-1 K-1 in graphene at 300 K, significantly lower than the values predicted to be in excess of 4000 W m-1 K-1 based only on 3 phonon scattering processes. Four phonon processes are shown to be most significant for flexural ZA phonon modes, where the reflection symmetry selection rule (RSSR) is less restrictive for 4-phonon than 3-phonon scattering processes. This combined with the low frequencies of ZA phonon modes, leading to high populations, leads to higher 4-phonon than 3-phonon scattering of low frequency ZA phonon modes in graphene at 300 K. In this review, the role of parameters such as atomic structure, phonon dispersion and temperature on 4-phonon scattering processes in a wide range of 2D materials is reviewed. Materials such as graphene nanoplatelets (GnPs) have been extensively investigated for enhancement of the thermal conductivity of polymer composites. However, such enhancement is limited by the poor interfacial thermal conductance between the polymer and filler material. Interconnected filler networks overcome this issue through highly efficient continuous percolative heat transfer paths throughout the composite. Such 3D networks have been shown to enable ultra-high polymer thermal conductivities, approaching ∼100 W m-1 K-1, and even exceeding those of several metals. In this review, different techniques used to achieve such interconnected 3D filler networks, namely, aerogels, foams, ice-templating, expanded graphite, hot pressing of filler coated polymer particles, the synergistic effect between multiple fillers, and the stitching of filler sheets, are discussed and their impact on thermal conductivity enhancement are presented.

Achieving low dielectric constant and high thermal conductivity polymer composites by using larger POSS functionalized boron nitride nanosheets

A series of larger POSS-functionalized boron nitride nanosheets were prepared and utilized to address the trade-off between low dielectric constants and high thermal conductivity in polymer composites.

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.