Recent Advances in the Rational Design of Thermal Conductive Polymer Composites

Highly Interconnected Thermal Conduction Highway for Highly Thermally Conductive and Mechanically Strong Polymeric Composites

Industrial implementation of highly thermally conductive polymeric composites has been hindered by several hurdles, such as the low intrinsic thermal conductivity (TC) of polymers, the use of expensive thermally conductive fillers, and difficulty in processing composites with high filler loading. In this study, we introduce a straightforward fabrication method for a high TC polymeric composite with a programmed internal structure of a highly interconnected thermal conduction highway (HITCH) by the simple addition of partially cured resin fragments into the conventional filler/resin combination. Critical variables, such as the concentration of the added resin fragments and the local concentration of hexagonal boron nitride (hBN) in the HITCH, as well as the packing density of the fragments, were systematically tuned to maximize the TC with the use of the least amount of the filler. Careful choice of the compositions enabled a significant TC enhancement of the composite by 2.6 times (6.5 W/mK) compared to the value of the conventional composite at the same overall concentration of hBN (∼2.5 W/mK). Finally, a composite with high TC (∼12 W/mK) and strong tensile strength (∼22.6 MPa), which is good enough for most practical thermal management applications, could be successfully fabricated with the use of the least amount of the filler (∼34 wt %). The comprehensive study of the HITCH composite here can be easily extended to other combinations with various fillers and matrices and may provide a library to researchers looking for advanced materials for future thermal management systems.

Laser-Induced Damage of UHMW-PE-Based Layered Ballistic Materials

The laser-induced damage threshold properties of material structures play a key role in identifying and selecting optimum materials with the respective geometric configurations for laser shielding applications. The laser-induced damage mechanism is predominantly influenced by the absorption, thermal conductivity, and transition temperature characteristics of the materials. Ultrahigh-molecular weight polyethylene (UHMW-PE) ballistic composite sheet structures, traditionally employed for conventional ballistic purposes, merit examination for their laser shielding capabilities, leveraging their established use in conventional shielding applications. These materials can be configured into the desired geometries along with layer structures. In this study, we conducted both numerical modeling and experimental investigations to assess and analyze the laser-induced damage mechanism in layered UHMW-PE material structures. To the best of our knowledge, this is the first time that both numerical modeling and experimental investigations have been conducted to assess and analyze the laser-induced damage mechanisms in such layered UHMW-PE material structures for high-power laser exposure. Our laser-material interaction model takes into account the optical, thermal, and structural properties of such layered UHMW-PE composite materials. Our model-based numerical calculations consistently align with experimental results, providing validated analysis of the laser-induced damage mechanism concerning layered structure geometries, optical power, and density (i.e., up to 5 kW at 1075 nm wavelength), as well as revealing nonlinear behavior in certain cases.

Soft composites with liquid inclusions: functional properties and theoretical models

Soft materials containing liquid inclusions have emerged as a promising class of materials. Unlike solid inclusions, liquid inclusions possess intrinsic fluidity, which allows them to retain the excellent deformation ability of soft materials. This can prevent compliance mismatches between the inclusions and the matrix, thus leading to improved performance and durability. Various liquids, including metallic, water-based, and ionic liquids, have been selected as inclusions for embedding into soft materials, resulting in unique properties and functionalities that enable a wide range of applications in soft robotics, wearable devices, and other cutting-edge fields. This review provides an overview of recent studies on the functional properties of composites with liquid inclusions and discusses theoretical models used to estimate these properties, aiming to bridge the gap between the microstructure/components and the overall properties of the composite from a theoretical perspective. Furthermore, current challenges and future opportunities for the widespread application of these composites are explored, highlighting their potential in advancing technologies.

Self-Adaptive Rapid Thermal Conductive Fabrics Based on Hygroscopic Shrinkage Response for Personal Cooling and Drying

Advanced fabrics with thermal wet management capability as low energy consumption media contribute to personal cooling and drying. Nevertheless, it remains a great challenge to obtain intelligent fabrics with adjustable thermal conductivity (TC) capable of bridging the supply and demand between human body temperature and self-adaptive thermal conduction. Herein, we report hygroscopic-shrinkage nanofiber-based fabrics with excellent moisture sensitivity and significant volume shrinkage, which benefits the construction of high-density thermal conductive pathways by absorbing sweat, with a maximum sweat absorption rate reaching up to 1781%. The TC of the shrunken fabric is significantly increased from the initial 0.102 to 0.731 W·m-1 K-1 with a volume shrinkage rate of 89% due to the synergistic effect of van der Waals force, capillary force, viscous resistance, and gravity. Besides, an enhanced TC of the resulting fabrics facilitates rapid heat transfer to the environments. By capturing the surface temperature variations of the fabric after shrinkage and commercially available cotton/Coolmax, we obtained the fabric that releases the same amount of heat in a shorter period of time (3.3 s). With its exceptional personal thermal and wet management properties, this study paves the way for designing new-generation intelligent fabrics capable of creating more comfortable microclimates.

High-Performance Graphene Biocomposite Enabled by Fe3+ Coordination for Thermal Management

Emerging biocomposites with excellent heat dissipation capabilities and inherent sustainability are urgently needed to address the cooling issues of modern electronics and growing environmental concerns. However, the moisture stability, mechanical performance, thermal conductivity, and even flame retardancy of biomass-based materials are generally insufficient for practical thermal management applications. Herein, we present a high-performance graphene biocomposite consisting of carboxylated cellulose nanofibers and graphene nanosheets through an evaporation-induced self-assembly and subsequent Fe3+ cross-linking strategy. The Fe3+ coordination plays a critical role in stabilizing the material structure, thereby improving the mechanical strength and water stability of the biocomposite films, and its effect is revealed by density functional theory calculations. The hierarchical structure of the biocomposite films also leads to a high in-plane thermal conductivity of 42.5 W m-1 K-1, enabling a superior heat transfer performance. Furthermore, the resultant biocomposite films exhibit outstanding Joule heating performance with a fast thermal response and long-term stability, improved thermal stability, and flame retardancy. Therefore, such a general strategy and the desired overall properties of the biocomposite films offer wide application prospects for functional and safe thermal management.

Ladder-like Poly(methacryloxypropyl) silsesquioxane-Al2O3-polybutadiene Flexible Nanocomposites with High Thermal Conductivity

Ladder-like poly(methacryloxypropyl)-silsesquioxanes (LPMASQ) are photocurable Si-based gels characterized by a double-stranded structure that ensures superior thermal stability and mechanical properties than common organic polymers. In this work, these attractive features were exploited to produce, in combination with alumina nanoparticles (NPs), both unmodified and functionalized with methacryloxypropyl-trimethoxysilane (MPTMS), LPMASQ/Al2O3 composites displaying remarkable thermal conductivity. Additionally, we combined LPMASQ with polybutadiene (PB) to produce hybrid nanocomposites with the addition of functionalized Al2O3 NPs. The materials underwent thermal stability, structural, and morphological evaluations via thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), Fourier transform infrared spectroscopy (FTIR), and solid-state nuclear magnetic resonance (NMR). Both blending PB with LPMASQ and surface functionalization of nanoparticles proved to be effective strategies for incorporating a higher ceramic filler amount in the matrices, resulting in significant increases in thermal conductivity. Specifically, a 113.6% increase in comparison to the bare matrix was achieved at relatively low filler content (11.2 vol%) in the presence of 40 wt% LPMASQ. Results highlight the potential of ladder-like silsesquioxanes in the field of thermally conductive polymers and their applications in heat dissipation for flexible electronic devices.

High Performance Epoxy Composites Containing Nanofiller Modified by Plasma Bubbles

The thermal conductivity of polymer materials is a fundamental parameter in the field of high-voltage electrical insulation. When the operating frequency and power for electrical equipment or electronic devices increase significantly, the internal heat will increase dramatically, and the accumulation of heat will further lead to insulation failure and serious damage of the whole system. The addition of filler with high thermal conductivity into polymer is a common solution. However, the interfacial thermal resistance between filler and bulk materials is the major obstacle to improve thermal conductivity. Herein, in order to reduce the interfacial thermal resistance, nanofillers are modified by plasma technology. The surface modification of nano-Al₂O₃ is carried out using plasma bubbles with three atmospheres (Ar, Ar+O₂, air) as well as coupling agent. The situation of surface grafting before and after the modification is characterized using FTIR, XPS, and SEM. The effect of the mechanism of modification on the thermal conductivity and reaction pathway is investigated. The results showed that the thermal conductivity after plasma modification is increased significantly. Especially, the thermal conductivity is increased by 35% for the sample modified by Ar+O₂ atmosphere. This results because more hydroxyl is introduced on the filler surface by the plasma bubbles, which enhance the interface compatibility between filler and epoxy. In addition, surface insulation performance for the modified samples also is enhanced by 14%. This is associated with the change of surface resistance and trap distribution. These results provide potential support for the development of fabrication for high performance epoxy composites.

One-pot fabrication of an anisotropic thermally conductive boron nitride/polyvinyl alcohol composite film based on salting-out effect

A facile method to accomplish the directional arrangement of thermally conductive lamellar fillers is reported to enhance thermal conductivity of polymer composite.

Improving Thermal Conductivity of Injection Molded Polycarbonate/Boron Nitride Composites by Incorporating Spherical Alumina Particles: The Influence of Alumina Particle Size

In this work, the influences of alumina (Al₂O₃) particle size and loading concentration on the properties of injection molded polycarbonate (PC)/boron nitride (BN)/Al₂O₃ composites were systematically studied. Results indicated that both in-plane and through-plane thermal conductivity of the ternary composites were significantly improved with the addition of spherical Al₂O₃ particles. In addition, the thermal conductivity of polymer composites increased significantly with increasing Al₂O₃ concentration and particle size, which were related to the following factors: (1) the presence of spherical Al₂O₃ particles altered the orientation state of flaky BN fillers that were in close proximity to Al₂O₃ particles (as confirmed by SEM observations and XRD analysis), which was believed crucial to improving the through-plane thermal conductivity of injection molded samples; (2) the presence of Al₂O₃ particles increased the filler packing density by bridging the uniformly distributed BN fillers within PC substrate, thereby leading to a significant enhancement of thermal conductivity. The in-plane and through-plane thermal conductivity of PC/50 μm-Al₂O₃ 40 wt%/BN 20 wt% composites reached as high as 2.95 and 1.78 W/mK, which were 1183% and 710% higher than those of pure PC, respectively. The prepared polymer composites exhibited reasonable mechanical performance, and excellent electrical insulation properties and processability, which showed potential applications in advanced engineering fields that require both thermal conduction and electrical insulation properties.

Tuning the Thermal Conductivity of the Amorphous PAA Polymer via Vapor-Phase Infiltration

The thermal properties of the polymer, together with mechanical stability, have been one of the key engineering factors to be considered for various applications. Here, we engineered the thermal conductivity of the amorphous poly(acrylic acid) (PAA) polymer by vapor-phase infiltration (VPI), which has usually occurred during the atomic layer deposition process. We observed that the VPI causes metal infiltration (e.g., Al and Zn) into the amorphous PAA polymer, which noticeably increases the thermal conductivity of the PAA polymer. From spectroscopy analysis and density functional theory simulations, we found that the carboxyl groups (-COOH) in PAA are notably modified and the bonding states of carbon and oxygen are significantly altered by the infiltrated metal. The newly formed Al-mediated bonds likely provide continuous phonon propagation pathways, thereby enhancing the thermal conductance. We believe that VPI could be a simple and useful way to engineer the thermal properties of various polymeric materials.

Recent Advances in Design and Preparation of Polymer-Based Thermal Management Material

The boosting of consumer electronics and 5G technology cause the continuous increment of the power density of electronic devices and lead to inevitable overheating problems, which reduces the operation efficiency and shortens the service life of electronic devices. Therefore, it is the primary task and a prerequisite to explore innovative material for meeting the requirement of high heat dissipation performance. In comparison with traditional thermal management material (e.g., ceramics and metals), the polymer-based thermal management material exhibit excellent mechanical, electrical insulation, chemical resistance and processing properties, and therefore is considered to be the most promising candidate to solve the heat dissipation problem. In this review, we summarized the recent advances of two typical polymer-based thermal management material including thermal-conduction thermal management material and thermal-storage thermal management material. Furtherly, the structural design, processing strategies and typical applications for two polymer-based thermal management materials were discussed. Finally, we proposed the challenges and prospects of the polymer-based thermal management material. This work presents new perspectives to develop advanced processing approaches and construction high-performance polymer-based thermal management material.

Highly Thermal Conductive Poly(vinyl alcohol) Composites with Oriented Hybrid Networks: Silver Nanowire Bridged Boron Nitride Nanoplatelets

With the increasing demand for thermal management materials in the highly integrated electronics area, building efficient heat-transfer networks to obtain advanced thermally conductive composites is of great significance. In the present work, highly thermally conductive poly(vinyl alcohol) (PVA)/boron nitride nanoplatelets@silver nanowires (BNNS@AgNW) composites were fabricated via the combination of the electrospinning and the spraying technique, followed by a hot-pressing method. BNNS are oriented along the in-plane direction, while AgNWs with a high aspect ratio can help to construct a thermal conductive network effectively by bridging BNNS in the composites. The PVA/BNNS@AgNW composites showed high in-plane thermal conductivity (TC) of 10.9 W/(m·K) at 33 wt % total fillers addition. Meanwhile, the composite shows excellent thermal dispassion capability when it is taken as a thermal interface material of a working light-emitting diode (LED) chip, which is certified by capturing the surface temperature of the LED chip. In addition, the out-of-plane electrical conductivity of the composites is below 10^-12 S/cm. The composites with outstanding thermal conductive and electrical insulating properties hold promise for application in electrical packaging and thermal management.

Tailoring the Thermal Conductivity of Rubber Nanocomposites by Inorganic Systems: Opportunities and Challenges for Their Application in Tires Formulation

The development of effective thermally conductive rubber nanocomposites for heat management represents a tricky point for several modern technologies, ranging from electronic devices to the tire industry. Since rubber materials generally exhibit poor thermal transfer, the addition of high loadings of different carbon-based or inorganic thermally conductive fillers is mandatory to achieve satisfactory heat dissipation performance. However, this dramatically alters the mechanical behavior of the final materials, representing a real limitation to their application. Moreover, upon fillers’ incorporation into the polymer matrix, interfacial thermal resistance arises due to differences between the phonon spectra and scattering at the hybrid interface between the phases. Thus, a suitable filler functionalization is required to avoid discontinuities in the thermal transfer. In this challenging scenario, the present review aims at summarizing the most recent efforts to improve the thermal conductivity of rubber nanocomposites by exploiting, in particular, inorganic and hybrid filler systems, focusing on those that may guarantee a viable transfer of lab-scale formulations to technological applicable solutions. The intrinsic relationship among the filler’s loading, structure, morphology, and interfacial features and the heat transfer in the rubber matrix will be explored in depth, with the ambition of providing some methodological tools for a more profitable design of thermally conductive rubber nanocomposites, especially those for the formulation of tires.