Thermal Conductivity Of Polymers Research Articles

Development and Perspectives of Biobased Thermal Conductive Polymer Composites

Development and Perspectives of Biobased Thermal Conductive Polymer Composites

Thermal Conductivity of Polymers: A Simple Matter Where Complexity Matters.

Thermal conductivity coefficient κ measures the ability of a material to conduct a heat current. In particular, κ is an important property that often dictates the usefulness of a material over a wide range of environmental conditions. For example, while a low κ is desirable for the thermoelectric applications, a large κ is needed when a material is used under the high temperature conditions. These materials range from common crystals to commodity amorphous polymers. The latter is of particular importance because of their use in designing light weight high performance functional materials. In this context, however, one of the major limitations of the amorphous polymers is their low κ, reaching a maximum value of ≈0.4 W/Km that is 2-3 orders of magnitude smaller than the standard crystals. Moreover, when energy is predominantly transferred through the bonded connections, κ ⩾ 100 W/Km. Recently, extensive efforts have been devoted to attain a tunability in κ via macromolecular engineering. In this work, an overview of the recent results on the κ behavior in polymers and polymeric solids is presented. In particular, computational and theoretical results are discussed within the context of complimentary experiments. Future directions are also highlighted.

Conversion of hazardous waste into thermal conductive polymer: A prediction and guidance from machine learning

The preparation methods and thermal conductivity (TC) of the reported thermal conductive polymers vary significantly. A method to clarify the relationship between TC and influencing factors and to reach consistent conclusions is needed. In this study, we compiled 403 sets of data from the literature. Six typical features and three machine learning (ML) algorithms were selected and optimized. XGBoost algorithm achieved the best prediction of TC of thermal conductive polymer (correlation coefficient with 0.855). To further investigate the influence of the 6 features on the TC of thermal conductive polymer, we conducted the SHapley Additive exPlanations (SHAP) analysis. Based on the above results, pyrrhotite tailings were determined as the filler and the corresponding process parameters were also determined. However, the above model built based on literature was still unsatisfactory. We further optimized XGBoost and built XGBoost-Exp through data from the real experiment. Finally, a small percentage (23%) of real experimental data can significantly improve the prediction power of XGBoost-Exp for unseen data (correlation coefficient with 0.815). To summarize, XGBoost-Exp exhibits exceptional predictive performance for the TC of the unseen data, offering valuable insights into the influence of various features. Meanwhile, this method provides a new perspective for the utilization of hazardous sulfide minerals.

Insights into Thermal Conductivity at the MOF-Polymer Interface.

Understanding the thermal conductivity in metal-organic framework (MOF)-polymer composites is crucial for optimizing their performance in applications involving heat transfer. In this work, several UiO66-polymer composites (where the polymer is either PEG, PVDF, PS, PIM-1, PP, or PMMA) are examined using molecular simulations. Our contribution highlights the interface's impact on thermal conductivity, observing an overall increasing trend attributable to the synergistic effect of MOF enhancing polymer thermal conductivity. Flexible polymers such as PEG and PVDF exhibit increased compatibility with the MOF, facilitating their integration with the MOF lattice. However, this integration leads to a moderated enhancement in thermal conductivity compared to polymers that remain separate from the MOF structure, such as PS or PP. This effect can be attributed to alterations in phonon transport pathways and shifts in interfacial interactions between the polymer and MOF. Specifically, the infiltration of the polymer like PEG and PVDF into the MOF disrupted the MOF's ordered network, introducing defects or barriers that hindered phonon propagation. In contrast, nonpolar and rigid polymers like PP, PMMA, PS, and PIM-1 exhibited greater improvements in thermal conductivity when combined with MOFs compared to the flexible polymers PVDF and PEG. Most notably, our analysis identifies a critical interface region within approximately 30-50 Å that profoundly influences thermal conductivity. The interface region, as indicated by the density profile and radius of gyration, is notably shorter but plays a pivotal role in modulating the thermal properties. The sensitivity of the system to these interface characteristics underscores the crucial role of this particular interface area in dictating the thermal conductivity. Our findings emphasize the sensitivity of thermal conductivity in polymer matrices to interface characteristics and highlight the critical role of a specific interface region in modulating thermal properties.

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.

Smart Polymer Solution and Thermal Conductivity: How Important Is an Exact Polymer Conformation?

Smart Polymer Solution and Thermal Conductivity: How Important Is an Exact Polymer Conformation?

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.

Dual regulation of thermal conductivity and mechanical performance of nano cellulose-based composite via mimicking plant cell wall structure

Combining thermal conductive fillers and flexible polymers is an agile approach to fabricating composites with heat-conducting performance. However, the thermal conductivity of the composites is hard to reach an equal level to the functional fillers. The mainspring is that the thermally conductive pathways within the composite could not be well-constructed due to the air-induced interface thermal resistance. Herein, inspired by the plant cell wall structure, polyvinyl alcohol (PVA) with abundant hydroxyl groups was adopted as a binder for boosting the thermally conductive pathways construction between cellulose nanofiber (CNF) and alkalized hexagonal boron nitride (BN-OH), also for strengthening the mechanical performance of the composite. The results showed that the tensile strength and through-plane thermal conductivity of the composite were high up to 91.0 MPa and 2.2 W m−1 K−1 at 40 wt% PVA content, exhibiting 121 % and 450 % enhancements compared to pure CNF film (41.2 MPa and 0.4 W m−1 K−1). Moreover, the composite also presented high thermal stability (decomposition temperature of onset was 218 °C) and good hydrophobicity properties. Overall, this study innovatively proposes an idea for enhancing the thermal conductivity and improving the mechanical properties of the composite, which is indispensable for developing thermal management materials for next-generation electronics.

Unification of thermal conductivity, electrical insulation, and electromagnetic shielding: A bulk thermal conductive polymer from solid waste

In the context of the ongoing advancements in high-performance chips, heat dissipation, and electromagnetic shielding within electrical and electronic equipment are becoming increasingly intricate. Plastics have garnered widespread usage in electrical and electronic equipment as prevalent framework materials. However, the challenge persists in achieving a unification of electromagnetic interference (EMI) shielding, thermal conductivity (TC), and electrical insulation performance for plastics. Herein, we capitalize on the styrene–butadiene–styrene (SBS) copolymer to integrate the merits of polymers and magnetic minerals. Utilizing pyrrhotite (Pyr) tailings and waste polystyrene (PS) as raw materials, a formable block material denoted as PS-S@SBS/Pyr has been formulated. This material exhibits commendable performance in terms of TC, electrical insulation, and EMI shielding performance concurrently. The bidirectional bridging effect of SBS effectively reduces the interfacial thermal resistance between PS and Pyr. The TC of PS-S@SBS/Pyr can reach a maximum of 1.36 W/m‧K with a resistivity greater than 108 Ω‧m. Moreover, PS-S@SBS/Pyr consistently demonstrates a stable EMI shielding effectiveness of 33.1 dB within the 8–12 GHz frequency range, with absorption shielding predominating as the underlying mechanism. This green preparation method makes efficient utilization of two main solid wastes while increasing the added value of the material.

Influence of microscopic ordered arrangement and high-voltage directional molding in epoxy liquid crystal dispersed membranes on intrinsic thermal conductivity

Flexible epoxy liquid crystal dispersed membranes (ELCMs) with high thermal conductivity (TC) were successfully prepared by using high-voltage directional molding. Epoxy liquid crystal monomers (Epoxy-LC1 and Epoxy-LC2) were uniformly dispersed into flexible epoxy polymers cured by pentaerythritol tetra (3-mercaptopropionate). TC of ELCM1 and ELCM2 reached 1.27 W·(m·K)−1 and 2.36 W·(m·K)−1 with 30 wt% content of Epoxy-LC1 and Epoxy-LC2, which were 4.5 times and 8.43 times higher than that of pure epoxy polymer, respectively. Tensile strength and elongation at break of ELCM1 and ELCM2 were up to 8.1 MPa, 23 % and 23.8 MPa, 46.7 %, respectively. On the one hand, the favorable results are attributed to the molecular chains’ microscopic ordered arrangement by using high-voltage directional molding. On the other hand, the more important reason is that the hydrogen-bond interactions between −C=O and –OH of molecular chains in Epoxy-LC2 and epoxy polymer. This work offers a new way to design flexible epoxy resins and intrinsic thermal conductive polymers.

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.

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

Modulating thermal and electrical conductivities in polymers: An approach toward extracting molecular design rules through atomistic simulations

Polymers are extensively employed in diverse industries, including electrical equipment and electronic devices. Recent technological advancements have intensified the demand for dielectric polymers with both high insulation resistance and high thermal conductivity. We employed molecular dynamics simulations to clarify the intricate relationship between molecular structures, thermal conductivity, and ionic mobility from an atomistic point of view. Examined polymers include polyethylene, polyvinyl alcohol, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polychlorotrifluoroethylene, polyoxymethylene, and polyethylene oxide. Based on the elucidated correlations among force field parameters, we found that the parameters can be clustered into four groups: group 1 (atomic and bond parameters and force constant of the bond angle), group 2 (equilibrium angle and force constant of dihedral angle), and group 3 (side chain atom charges). Thermal conductivity showed relationships with parameters in group 1, with correlation coefficients mostly exceeding 0.7 in the absolute value. Considering the correlations between the parameters, we systematically altered the parameters within each group and computed thermal conductivity and ionic mobility. When altering the force field parameters of groups 1 and group 2, a trade-off relationship between thermal conductivity and ionic mobility becomes evident. Conversely, altering the force field parameters in group 3 increased thermal conductivity while decreasing ionic mobility, breaking the trade-off relationship. The proposed clustered-parameter variation method can predict the changes in the electrical and thermal conductivity of polymers through molecular structure modifications. The method, being a general and first-principles approach, is likely to have significant advantages in the molecular design across a diverse range of polymers.

Enhanced thermal conductivity in thermoplastic polyether ester elastomer vitrimer composite foams via cell growth-induced orientation and lap of hybrid fillers

Lightweight thermal conductive polymer foams own a great potential application in some weight sensitive fields such as aerospace and encapsulation. Herein, the enhancement of thermal conductivity of thermoplastic polyether ester elastomer (TPEE) vitrimer composites foams caused by cell growth inducing fillers orientation and lap was investigated with hybrid fillers of fixed 15 vol% h-BN and various SiC nanowires. First, the hybrid fillers orientation in TPEE vitrimer composites (TVC) characterized by SEM and XRD patterns showed that the hybrid fillers were induced to be through-plane orientation and no interfacial defects were observed owing to the increasing contact area among fillers caused by large specific area and length of SiC nanowires. Based on that, cells were generated into TVC through scCO2 foaming. The effect of through-plane orientation and lap of hybrid fillers caused by cell growth of different cell structures on the thermal conductivity of TVC foams was investigated using extended Hashin-Shtrikman model and Maxwell-Eucken I model. The results showed that the thermal conductivity of TVC foams could greatly be enhanced to be higher than that of TVC by cell growth of continuous cell structures as it contributed to the through-plane orientation and lap of hybrid fillers to increase the contact and lap ratio among fillers. Thereby, the thermal conductive networks favorable to heat transfer were constructed in TVC foams to enhance the thermal conductivity as well as merit of lightweight.

Core-sheath smart polymer fiber composites with high elasticity and thermal conductivity

Thermal conductive polymer fibers have broad development prospects because of its excellent thermal and mechanical properties. However, currently reported polymer fibers cannot simultaneously possess high thermal conductivity and high resilience, which greatly limits the application of thermal conductive polymer fibers. Therefore, preparing fibers with high thermal conductivity and high resilience is extremely challenging. The thermoplastic polyurethane/boron nitride liquid metal (TPU/BN-LMs) fiber with core sheath structure is prepared by coaxial wet spinning technology, the boron nitride (BN) doped in thermoplastic polyurethane elastomer (TPU) as sheath and the liquid metal (LMs) as core. The maximum tensile strength of the fiber is 3.9 MPa, and the elongation can reach 400 %. After multiple cycles of stretching, it can return to its original state. In addition, the thermal conductivity of the fiber in the horizontal direction and the vertical direction are 10.0 W m−1 K−1 and 4.6 W m−1 K−1, respectively. This work solves the current problem of high thermal conductivity and high resilience of thermally conductive polymer fibers that are difficult to be compatible. And it provides a new research idea for the design and preparation of new high thermal conductivity and high resilience polymer fiber materials.

AI-assisted inverse design of sequence-ordered high intrinsic thermal conductivity polymers

Artificial intelligence (AI) promotes the polymer design paradigm from a traditional trial-and-error approach to a data-driven style. Achieving high thermal conductivity (TC) for intrinsic polymers is urgent because of their importance in the thermal management of many industrial applications such as microelectronic devices and integrated circuits. In this work, we have proposed a robust AI-assisted workflow for the inverse design of high TC polymers. By using 1144 polymers with known computational TCs, we construct a surrogate deep neural network model for TC prediction and extract a polymer-unit library with 32 sequences. Two state-of-the-art multi-objective optimization algorithms of unified non-dominated sorting genetic algorithm III (U-NSGA-III) and q-noisy expected hypervolume improvement (qNEHVI) are employed for sequence-ordered polymer design with both high TC and synthetic possibility. For triblock polymer design, the result indicates that qNHEVI is capable of exploring a diversity of optimal polymers at the Pareto front, but the uncertainty in Quasi-Monte Carlo sampling makes the trials costly. The performance of U-NSGA-III is affected by the initial random structures and usually falls into a locally optimal solution, but it takes fewer attempts with lower costs. 20 parallel U-NSGA-III runs are conducted to design the pentablock polymers with high TC, and half of the candidates among 1921 generated polymers achieve the targets (TC > 0.4 W m−1K−1 and SA < 3.0). Ultimately, we check the TC of 50 promising polymers through molecular dynamics simulations and reveal the intrinsic connections between microstructures and TCs. Our developed AI-assisted inverse design approach for polymers is flexible and universal, and can be extended to the design of polymers with other target properties.

Preparation of high thermal conductivity vat photopolymerization used UV-curable resin synergistically enhanced by silicon nitride and boron nitride

Additive manufacturing (3D printing) technologies, especially vat photopolymerization (VPP), provide a cost-effective and efficient approach for the fabrication of heat dissipation devices with complex geometric designs. The incorporation of inorganic thermal conductive fillers into resin matrix is widely recognized as an effective way to enhance thermal conductivity. Notably, the synergistic effect of hybrid fillers can further enhance thermal conductivity. However, the consequent drastic increase in viscosity of the UV-curable resin may decrease the success rate and accuracy of printing on commercial VPP 3D printers. In this work, hexagonal boron nitride (h-BN) platelets and spherical h-BN together with β-Si3N4 are introduced into the UV-curable resin system. Corresponding results proved that h-BN together with β-Si3N4 provide a synergistic effect on the thermal conductivity enhancement compared to the filler in single morphology only. Moreover, owing to the spherical structure, low-viscosity UV-curable resin with high solid content can be prepared. In specific, a thermal conductive polymer composite material with a solid content of 60 wt% is prepared, which exhibits high thermal conductivity (1.42 W/mK), representing an enhancement of up to 610 % compared to neat resin. In subsequent application demonstrations, 3D printed heat dissipation devices with as-prepared resin composite material have been shown to effectively enhance the heat dissipation rate for the heating device.

Thermal performance of polymer gyroid heat exchangers combined with phase change materials as a latent heat thermal energy storage system: An experimental investigation

Latent heat thermal energy storage (LHTES) systems utilizing phase-change materials (PCMs) in conjunction with heat exchangers (HXs) have been widely investigated for efficient thermal energy utilization. This study experimentally evaluated the heat transfer performance and pressure loss of a PCM-based gyroid HX fabricated using a polymer 3D printer. Initially, the study compared the phase change time, heat storage and release characteristics, and pressure drop of the gyroid HX with those of a conventional shell-and-tube HX (S&T HX). The results demonstrate that the gyroid HX achieved up to 20 % shorter thermal charge and discharge times than the S&T HX, which is attributed to a higher heat transfer rate. Additionally, the measured pressure drop of the gyroid HX was up to 44 % lower than that of the S&T HX. Consequently, considering both the heat transfer rate and pressure drop, the gyroid HX showed an average improvement of 57 % and 31 % in the overall enhancement factor during charging and discharging, respectively, compared to the S&T HX. Further, metal gyroid HXs fabricated from steel and aluminum using metal 3D printing were experimentally compared with the polymer gyroid HX. Despite the polymer thermal conductivity being only 1/90 and 1/790 that of steel and aluminum, respectively, the heat transfer rate per unit mass of the polymer gyroid HX was 1.7 times that of the steel gyroid HX and approximately half that of the aluminum gyroid HX. This finding suggests that the polymer gyroid HX is suitable for LHTES applications where lightweight characteristics are crucial.