Thermal Conductivity of Polymers and Their Nanocomposites

3D Network of Liquid Metal-Embedded Graphene via Surface Coating for Flexible Thermal Management

The rapid growth of flexible electronics has led to significant demand for relevant accessories, particularly highly efficient flexible heat dissipators. The fluidity of liquid metal (LM) makes it a candidate for realizing flexible thermal interface materials (TIMs). However, it is still challenging to combine LM with a conductive thermal network to achieve the synchronous improvement of thermal conductivity and flexibility. In this work, highly conductive flexible LM@GN/ANF films are made by coating LM nano-droplets with graphene nanosheets (GN) via sonication, and then they are combined with aramid nanofibers (ANF). The LM@GN/ANF film is found to have a thermal conductivity of 5.67 W m-1 K-1 and a 24.5% reduction in Young's modulus, making it suitable for various flexible electronic applications such as wearable devices and biosensors.

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.

2D Materials-Based Thermal Interface Materials: Structure, Properties, and Applications

The challenges associated with heat dissipation in high-power electronic devices used in communication, new energy, and aerospace equipment have spurred an urgent need for high-performance thermal interface materials (TIMs) to establish efficient heat transfer pathways from the heater (chip) to heat sinks. Recently, emerging 2D materials, such as graphene and boron nitride, renowned for their ultrahigh basal-plane thermal conductivity and the capacity to facilitate cross-scale, multi-morphic structural design, have found widespread use as thermal fillers in the production of high-performance TIMs. To deepen the understanding of 2D material-based TIMs, this review focuses primarily on graphene and boron nitride-based TIMs, exploring their structures, properties, and applications. Building on this foundation, the developmental history of these TIMs is emphasized and a detailed analysis of critical challenges and potential solutions is provided. Additionally, the preparation and application of some other novel 2D materials-based TIMs are briefly introduced, aiming to offer constructive guidance for the future development of high-performance TIMs.

Advancing high thermal conductivity: novel theories, innovative materials, and applications in thermal management technologies

Effective thermal management is crucial for the performance and stability of modern electronics, emphasizing the demand for high thermal conductivity (κ). This review summarizes the latest development in highκ, discussing the emerging theories, innovative materials and practical applications for interfacial heat dissipation. Unique phononic thermal transport behaviors are discussed, including four phonon-phonon scattering, hydrodynamic phonons, surface phonon-polaritons, and more. The review also highlights innovative materials with highκ, such as two-dimensional pentagonal structures, boron carbon nitrogen structures, hexagonal boron arsenide andθ-phase tantalum nitride. In addition, the potential of polymer composites reinforced with highκfillers and surface engineering for advanced electronic applications are also discussed. By integrating these theoretical approaches and material innovations, this review offers comprehensive strategies for enhancing thermal management in modern electronic devices.

Mussel-Inspired Polymer-Based Composites for Efficient Thermal Management in Dry and Underwater Environments

To address the escalating power consumption of processors in data centers and the growing emphasis on environmental sustainability, the prospective shift from traditional air-cooling to immersion liquid cooling necessitates multiple functional integrations in polymer-based thermal conductive materials. Here, drawing inspiration from mussels, we showed a copolymer, poly(dimethylsiloxane-co-dopamine methacrylate) (PDMS-DMA), with a variety of reversible molecular interactions and simply combined with liquid metal (EGaIn) can yield a flexible, waterproof, and electrically insulating thermal conductive composite. The obtained PDMS-DMA/EGaIn composites demonstrate a harmonious blend of attributes, including a low modulus (75.8 kPa), high thermal conductivity of 6.9 W m-1 K-1, and rapid room-temperature self-healing capabilities, capable of complete repair within 20 min, even under water. Based on its electrically insulating and water resistance properties, PDMS-DMA/EGaIn emerges as a promising candidate for efficient and stable heat transfer in both air and underwater thermal management. Consequently, this water-resistant polymer-based composite holds significance for application in thermal protective layers for future immersion liquid cooling systems.

Phonon Engineering in Solid Polymer Electrolyte toward High Safety for Solid-State Lithium Batteries

Extensively-used rechargeable lithium-ion batteries (LIBs) face challenges in achieving high safety and long cycle life. To address such challenges, ultrathin solid polymer electrolyte (SPE) is fabricated with reduced phonon scattering by depositing the composites of ionic-liquid (1-ethyl-3-methylimidazolium dicyamide, EMIM:DCA), polyurethane (PU) and lithium salt on the polyethylene separator. The robust and flexible separator matrix not only reduces the electrolyte thickness and improves the mobility of Li+, but more importantly provides a relatively regular thermal diffusion channel for SPE and reduces the external phonon scattering. Moreover, the introduction of EMIM:DCA successfully breaks the random intermolecular attraction of the PU polymer chain and significantly decreases phonon scattering to enhance the internal thermal conductivity of the polymer. Thus, the thermal conductivity of the as-obtained SPE increases by approximately six times, and the thermal runaway (TR) of the battery is effectively inhibited. This work demonstrates that optimizing thermal safety of the battery by phonon engineering sheds a new light on the design principle for high-safety Li-ion batteries.

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.

Principles and Methods for Improving the Thermoelectric Performance of SiC: A Potential High-Temperature Thermoelectric Material

Thermoelectric materials that can convert thermal energy to electrical energy are stable and long-lasting and do not emit greenhouse gases; these properties render them useful in novel power generation devices that can conserve and utilize lost heat. SiC exhibits good mechanical properties, excellent corrosion resistance, high-temperature stability, non-toxicity, and environmental friendliness. It can withstand elevated temperatures and thermal shock and is well suited for thermoelectric conversions in high-temperature and harsh environments, such as supersonic vehicles and rockets. This paper reviews the potential of SiC as a high-temperature thermoelectric and third-generation wide-bandgap semiconductor material. Recent research on SiC thermoelectric materials is reviewed, and the principles and methods for optimizing the thermoelectric properties of SiC are discussed. Thus, this paper may contribute to increasing the application potential of SiC for thermoelectric energy conversion at high temperatures.

Intrinsically thermally conductive polymers

Here, we describe the design features that lead to intrinsically thermally conductive polymers. Though polymers are conventionally assumed to be thermal insulators (<0.3 W m-1 K-1), significant efforts by the thermal transport community have shown that polymers can be intrinsically thermally conductive (>1.0 W m-1 K-1). However, these findings have not yet driven comprehensive synthetic efforts to expose how different macromolecular features impact thermal conductivity. Preliminary theoretical and experimental investigations have revealed that high k polymers can be realized by enhancing the alignment, crystallinity, and intermolecular interactions. While a holistic mechanistic framework does not yet exist for thermal transport in polymeric materials, contemporary literature suggests that phonon-like heat carriers may be operative in macromolecules that meet the abovementioned criteria. In this review, we offer a perspective on how high thermal conductivity polymers can be systematically engineered from this understanding. Reports for several classes of macromolecules, including linear polymers, network polymers, liquid-crystalline polymers, and two-dimensional polymers substantiate the design principles we propose. Throughout this work, we offer opportunities for continued fundamental and technological development of polymers with high thermal conductivity.

SPI-Modified h-BN Nanosheets-Based Thermal Interface Materials for Thermal Management Applications

The rising concern over the usage of electronic devices and the operating environment requires efficient thermal interface materials (TIMs) to take away the excess heat generated from hotspots. TIMs are crucial in dissipating undesired heat by transferring energy from the source to the heat sink. Silicone oil (SO)-based composites are the most used TIMs due to their strong bonding and oxidation resistance. However, thermal grease performance is unreliable due to aging effects, toxic chemicals, and a higher percentage of fillers. In this work, TIMs are prepared using exfoliated hexagonal boron nitride nanosheets (h-BNNS) as a nanofiller, and they were functionalized by ecofriendly natural biopolymer soy protein isolate (SPI). The exfoliated h-BNNS has an average lateral size of ∼266 nm. The functionalized h-BNNS/SPI are used as fillers in the SO matrix, and composites are prepared using solution mixing. Hydrogen bonding is present between the organic chain/oxygen in silicone polymer, and the functionalized h-BNNS are evident from the FTIR measurements. The thermal conductivity of h-BNNS/SPI/SO was measured using the modified transient plane source (MTPS) method. At room temperature, the maximum thermal conductivity is 1.162 Wm-1K-1 (833% enhancement) at 50 wt % of 3:1 ratio of h-BNNS:SPI, and the thermal resistance (TR) of the composite is 5.249 × 106 K/W which is calculated using the Foygel nonlinear model. The heat management application was demonstrated by applying TIM on a 10 W LED bulb. It was found that during heating, the 50 wt % TIM decreases the surface temperature of LED by ∼6 °C compared with the pure SO-based TIM after 10 min of ON condition. During cooling, the modified TIM reduces the surface temperature by ∼8 °C under OFF conditions within 1 min. The results indicate that natural polymers can effectively stabilize and link layered materials, enhancing the efficiency of TIMs for cooling electronics and LEDs.

Easy and Green Method to Fabricate Highly Thermally Conductive Poly(decamethylene terephthalamide)/Graphite Nanoplatelets Nanocomposite with Aligned Structure

With the development of miniaturization and integration of electrical and electronic equipment, the heat accumulation problems caused by the long-term operation of devices have become more and more serious. High thermal-conductivity and high-performance plastic composites have attracted significant interest from both academia and industry. Numerous studies have been recently conducted to enhance the thermal conductivity (TC) of nanofiller-filled polymeric composites. However, the homogeneous dispersion and directional arrangement of nanofillers in the resin matrix are the key factors limiting their effectiveness in enhancing thermal conductivity. Based on the feasibility considerations of mass production and industrial application, this paper reports on a novel preparation method of Poly(decamethylene terephthalamide)/graphite nanoparticle (GNP) nanocomposites with high thermal conductivity. Without borrowing solvents or other reagents, this method can effectively strip the inexpensive scaled graphite into nanoscale for its uniform dispersion and orientation arrangement by relying only on mechanical external forces. The whole technology is simple, green, and easy to industrialize. The fillers were well-dispersed and aligned in the PA10T, which played a role in significantly enhancing the thermal conductivity of the PA10T. In addition, we found that the thermal conductivity of the composites reached 1.20 W/(m·K) at 10 wt% filler content, which was 330% higher than that of the pure matrix. The mechanical properties of the composites were also significantly improved. This work provides guidance for the easy fabrication of thermally conductive composites with aligned structures.

Modulating Thermal Conductivity via Targeted Phonon Excitation

Thermal conductivity is a critical material property in numerous applications, such as those related to thermoelectric devices and heat dissipation. Effectively modulating thermal conductivity has become a great concern in the field of heat conduction. Here, a quantum modulation strategy is proposed to modulate the thermal conductivity/heat flux by exciting targeted phonons. It shows that the thermal conductivity of graphene can be tailored in the range of 1559 W m-1 K-1 (decreased to 49%) to 4093 W m-1 K-1 (increased to 128%), compared with the intrinsic value of 3189 W m-1 K-1. The effects are also observed for graphene nanoribbons and bulk silicon. The results are obtained through both density functional theory calculations and molecular dynamics simulations. This novel modulation strategy may pave the way for quantum heat conduction.

Bioinspired radiative cooling coating with high emittance and robust self-cleaning for sustainably efficient heat dissipation

To overcome the overheating phenomena of electronic devices and energy components, developing advanced energy-free cooling coatings with promising radiative property seem an effective and energy-saving way. However, the further application of these coatings is greatly limited by their sustainability because of their fragile and easy contamination. Herein, it is reported that a bioinspired radiative cooling coating (BRCC) displayed sustainably efficient heat dissipation by the combination of high emittance and robust self-cleaning property. With the hierarchical porous structure constructed by multiwalled carbon nanotubes (MWCNTs), modified SiO2 and fluorosilicone (FSi) resin, the involvement of the BRCC improves the cooling performance by increasing ≈25% total heat transfer coefficient. During the abrasion and soiling tests, the BRCC-coated Al alloy heat sink always displays stable radiative cooling performance. Moreover, the simulation and experimental results both revealed that reducing surface coverage of BRCC (≈80.9%) can still keep highly cooling efficiency, leading to a cost-effective avenue. Therefore, this study may guide the design and fabrication of advanced radiative cooling coating.

3D-Networks Based Polymer Composites for Multifunctional Thermal Management and Electromagnetic Protection: A Mini Review

The rapid development of miniaturized, high-frequency, and highly integrated microelectronic devices has brought about critical issues in electromagnetic compatibility and thermal management. In recent years, there has been significant interest in lightweight polymer-based composites that offer both electromagnetic interference (EMI) shielding and thermal conductivity. One promising approach involves constructing three-dimensional (3D) interconnection networks using functional fillers in the polymer matrix. These networks have been proven effective in enhancing the thermal and electrical conductivity of the composites. This mini-review focuses on the preparation and properties of 3D network-reinforced polymer composites, specifically those incorporating metal, carbon, ceramic, and hybrid networks. By comparing the effects of different filler types and distribution on the composite materials, the advantages of 3D interconnected conductive networks in polymer composites are highlighted. Additionally, this review addresses the challenges faced in the field of multifunctional thermal management and electromagnetic protection materials and provides insights into future development trends and application prospects of 3D structured composites.

Correlating Young's Modulus with High Thermal Conductivity in Organic Conjugated Small Molecules

Attaining elevated thermal conductivity in organic materials stands as a coveted objective, particularly within electronic packaging, thermal interface materials, and organic matrix heat exchangers. These applications have reignited interest in researching thermally conductive organic materials. The understanding of thermal transport mechanisms in these organic materials is currently constrained. This study concentrates on N, N'-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8), an organic conjugated crystal. A correlation between elevated thermal conductivity and augmented Young's modulus is substantiated through meticulous experimentation. Achievement via employing the physical vapor transport method, capitalizing on the robust C═C covalent linkages running through the organic matrix chain, bolstered by π-π stacking and noncovalent affiliations that intertwine the chains. The coexistence of these dynamic interactions, alongside the perpendicular alignment of PTCDI-C8 molecules, is confirmed through structural analysis. PTCDI-C8 thin film exhibits an out-of-plane thermal conductivity of 3.1 ± 0.1 W m-1 K-1, as determined by time-domain thermoreflectance. This outpaces conventional organic materials by an order of magnitude. Nanoindentation tests and molecular dynamics simulations elucidate how molecular orientation and intermolecular forces within PTCDI-C8 molecules drive the film's high Young's modulus, contributing to its elevated thermal conductivity. This study's progress offers theoretical guidance for designing high thermal conductivity organic materials, expanding their applications and performance potential.

Adhesion Energy-Assisted Low Contact Thermal Resistance Epoxy Resin-Based Composite

Although intense efforts have been devoted to the development of thermally conductive epoxy resin composites, most previous works ignore the importance of the contact thermal resistance between epoxy resin composites and mating surfaces. Here, we report on epoxy resin/hexagonal boron nitride (h-BN) composites, which show low contact thermal resistance with the contacting surface by tuning adhesion energy. We found that adhesion energy increases with increasing the ratio of soybean-based epoxy resin/amino silicone oil and h-BN contents. The adhesion energy has a negative correlation with the contact thermal resistance; that is, enhancing the adhesion energy will lead to reduced contact thermal resistance. The contact thermal conductance increases with the h-BN contents and is low to 0.025 mm2·K/W for the epoxy resin/60 wt % h-BN composites, which is consistent with the theoretically calculated value. By investigating the wettability and chain dynamics of the epoxy resin/h-BN composites, we confirm that the low contact thermal resistance stems from the increased intermolecular interaction between the epoxy resin chains. The present study provides a practical approach for the development of epoxy resin composites with enhanced thermal conductivity and reduced contact thermal resistance, aiming for effective thermal management of electronics.

Machine Learning Aided Design and Optimization of Thermal Metamaterials

Artificial Intelligence (AI) has advanced material research that were previously intractable, for example, the machine learning (ML) has been able to predict some unprecedented thermal properties. In this review, we first elucidate the methodologies underpinning discriminative and generative models, as well as the paradigm of optimization approaches. Then, we present a series of case studies showcasing the application of machine learning in thermal metamaterial design. Finally, we give a brief discussion on the challenges and opportunities in this fast developing field. In particular, this review provides: (1) Optimization of thermal metamaterials using optimization algorithms to achieve specific target properties. (2) Integration of discriminative models with optimization algorithms to enhance computational efficiency. (3) Generative models for the structural design and optimization of thermal metamaterials.

Dressing Paraffin Wax/Boron Nitride Phase Change Composite with a Polyethylene "Underwear" for the Reliable Battery Safety Management

Phase change material (PCM) can provide a battery system with a buffer platform to respond to thermal failure problems. However, current PCMs through compositing inorganics still suffer from insufficient thermal-transport behavior and safety reliability against external force. Herein, a best-of-both-worlds method is reported to allow the PCM out of this predicament. It is conducted by combining a traditional PCM (i.e., paraffin wax/boron nitride) with a spirally weaved polyethylene fiber fabric, just like the traditional PCM is wearing functional underwear. On the one hand, the spirally continuous thermal pathways of polyethylene fibers in the fabric collaborate with the boron nitride network in the PCM, enhancing the through-plane and in-plane thermal conductivity to 10.05 and 7.92 W m-1 K, respectively. On the other, strong polyethylene fibers allow the PCM to withstand a high puncture strength of 47.13 N and tensile strength of 18.45 MPa although above the phase transition temperature. After this typical PCM packs a triple Li-ion battery system, the battery can be promised reliable safety management against both thermal and mechanical abuse. An obvious temperature drop of >10 °C is observed in the battery electrode during the cycling charging and discharging process.

Float-stacked graphene-PMMA laminate

Semi-infinite single-atom-thick graphene is an ideal reinforcing material that can simultaneously improve the mechanical, electrical, and thermal properties of matrix. Here, we present a float-stacking strategy to accurately align the monolayer graphene reinforcement in polymer matrix. We float graphene-poly(methylmethacrylate) (PMMA) membrane (GPM) at the water-air interface, and wind-up layer-by-layer by roller. During the stacking process, the inherent water meniscus continuously induces web tension of the GPM, suppressing wrinkle and folding generation. Moreover, rolling-up and hot-rolling mill process above the glass transition temperature of PMMA induces conformal contact between each layer. This allows for pre-tension of the composite, maximizing its reinforcing efficiency. The number and spacing of the embedded graphene fillers are precisely controlled. Notably, we accurately align 100 layers of monolayer graphene in a PMMA matrix with the same intervals to achieve a specific strength of about 118.5 MPa g-1 cm3, which is higher than that of lightweight Al alloy, and a thermal conductivity of about 4.00 W m-1 K-1, which is increased by about 2,000 %, compared to the PMMA film.

Modification of thermal and electrical characteristics of hybrid polymer nanocomposites through gamma irradiation for advanced applications

In this article, we present a straightforward in-situ approach for producing Ag NPs incorporated in graphene oxide (GO) blended with glutaraldehyde (GA) cross-linked polyvinyl alcohol (PVA) matrix. Samples are γ-irradiated by doses of 2, 5, and 10 kGy and in comparison with the pristine films, the thermal conductivity ('k') and effusivity are measured. 'k' decreases with irradiation doses up to 5 kGy and further increase in the dosage results increase in 'k'. We performed FDTD modeling to verify the effect of polarization and periodicity on the absorptivity and emissivity spectra that are correlated to the 'k' and effusivity, empirically. Hence, we can confess that the structural properties of the prepared hybrid nanocomposite are manipulated by γ-irradiation. This attests that the PVA/GO-Ag/GA nanocomposite is radiation-sensitive and could be employed for thermal management systems. Moreover, their strong electrical insulation, as the measured dc conductivity of the γ-irradiated samples is found to be in the range of 2.66 × 10-8-4.319 × 10-7 Sm-1, which is below the percolation threshold of 1.0 × 10-6 Sm-1, demonstrates that they are excellent candidates for the use of thermal management materials. The low 'k' values allow us to use this promising material as thermal insulating substrates in microsensors and microsystems. They are also great choices for usage as wire and cable insulation in nuclear reactors due to their superior electrical insulation.

Fabrication and Characterization of Al2O3-Siloxane Composite Thermal Pads for Thermal Interface Materials

In this study, Al2O3-siloxane composite thermal pads were fabricated using a tape-casting technique, and the thermal conductivity effect of the Al2O3 nanoparticle powder synthesized using a flame fusion process on siloxane composite thermal pads was investigated. Furthermore, various case studies were implemented, wherein the synthesized Al2O3 nanoparticle powder was subjected to different surface treatments, including dehydration, decarbonization, and silylation, to obtain Al2O3-siloxane composite thermal pads with high thermal conductivity. The experimental results confirmed that the thermal conductivity of the Al2O3-siloxane composite pads improved when fabricated using surface-treated Al2O3 nanoparticle powder synthesized with an optimally spheroidized crystal structure compared to that produced using non-treated Al2O3 nanoparticle powder. Therefore, this study provides guidelines for fabricating Al2O3-siloxane composite thermal pads with high thermal conductivity in the field of thermal interface materials.

Application-Driven High-Thermal-Conductivity Polymer Nanocomposites

Polymer nanocomposites combine the merits of polymer matrices and the unusual effects of nanoscale reinforcements and have been recognized as important members of the material family. Being a fundamental material property, thermal conductivity directly affects the molding and processing of materials as well as the design and performance of devices and systems. Polymer nanocomposites have been used in numerous industrial fields; thus, high demands are placed on the thermal conductivity feature of polymer nanocomposites. In this Perspective, we first provide roadmaps for the development of polymer nanocomposites with isotropic, in-plane, and through-plane high thermal conductivities, demonstrating the great effect of nanoscale reinforcements on thermal conductivity enhancement of polymer nanocomposites. Then the significance of the thermal conductivity of polymer nanocomposites in different application fields, including wearable electronics, thermal interface materials, battery thermal management, dielectric capacitors, electrical equipment, solar thermal energy storage, biomedical applications, carbon dioxide capture, and radiative cooling, are highlighted. In future research, we should continue to focus on methods that can further improve the thermal conductivity of polymer nanocomposites. On the other hand, we should pay more attention to the synergistic improvement of the thermal conductivity and other properties of polymer nanocomposites. Emerging polymer nanocomposites with high thermal conductivity should be based on application-oriented research.

Pulse irradiation synthesis of metal chalcogenides on flexible substrates for enhanced photothermoelectric performance

High synthesis temperatures and specific growth substrates are typically required to obtain crystalline or oriented inorganic functional thin films, posing a significant challenge for their utilization in large-scale, low-cost (opto-)electronic applications on conventional flexible substrates. Here, we explore a pulse irradiation synthesis (PIS) to prepare thermoelectric metal chalcogenide (e.g., Bi2Se3, SnSe2, and Bi2Te3) films on multiple polymeric substrates. The self-propagating combustion process enables PIS to achieve a synthesis temperature as low as 150 °C, with an ultrafast reaction completed within one second. Beyond the photothermoelectric (PTE) property, the thermal coupling between polymeric substrates and bismuth selenide films is also examined to enhance the PTE performance, resulting in a responsivity of 71.9 V/W and a response time of less than 50 ms at 1550 nm, surpassing most of its counterparts. This PIS platform offers a promising route for realizing flexible PTE or thermoelectric devices in an energy-, time-, and cost-efficient manner.

Highly Thermoconductive, Strong Graphene-Based Composite Films by Eliminating Nanosheets Wrinkles

Graphene-based thermally conductive composites have been proposed as effective thermal management materials for cooling high-power electronic devices. However, when flexible graphene nanosheets are assembled into macroscopic thermally conductive composites, capillary forces induce shrinkage of graphene nanosheets to form wrinkles during solution-based spontaneous drying, which greatly reduces the thermal conductivity of the composites. Herein, graphene nanosheets/aramid nanofiber (GNS/ANF) composite films with high thermal conductivity were prepared by in-plane stretching of GNS/ANF composite hydrogel networks with hydrogen bonds and π-π interactions. The in-plane mechanical stretching eliminates graphene nanosheets wrinkles by suppressing inward shrinkage due to capillary forces during drying and achieves a high in-plane orientation of graphene nanosheets, thereby creating a fast in-plane heat transfer channel. The composite films (GNS/ANF-60 wt%) with eliminated graphene nanosheets wrinkles showed a significant increase in thermal conductivity (146 W m-1 K-1) and tensile strength (207 MPa). The combination of these excellent properties enables the GNS/ANF composite films to be effectively used for cooling flexible LED chips and smartphones, showing promising applications in the thermal management of high-power electronic devices.

Oriented Three-Dimensional Skeletons Assembled by Si3N4 Nanowires/AlN Particles as Fillers for Improving Thermal Conductivity of Epoxy Composites

With the miniaturization of current electronic products, ceramic/polymer composites with excellent thermal conductivity have become of increasing interest. Traditionally, higher filler fractions are required to obtain a high thermal conductivity, but this leads to a decrease in the mechanical properties of the composites and increases the cost. In this study, silicon nitride nanowires (Si3N4NWs) with high aspect ratios were successfully prepared by a modified carbothermal reduction method, which was further combined with AlN particles to prepare the epoxy-based composites. The results showed that the Si3N4NWs were beneficial for constructing a continuous thermal conductive pathway as a connecting bridge. On this basis, an aligned three-dimensional skeleton was constructed by the ice template method, which further favored improving the thermal conductivity of the composites. When the mass fraction of Si3N4NWs added was 1.5 wt% and the mass fraction of AlN was 65 wt%, the composites prepared by ice templates reached a thermal conductivity of 1.64 W·m-1·K-1, which was ~ 720% of the thermal conductivity of the pure EP (0.2 W·m-1·K-1). The enhancement effect of Si3N4NWs and directional filler skeletons on the composite thermal conductivity were further demonstrated through the actual heat transfer process and finite element simulations. Furthermore, the thermal stability and mechanical properties of the composites were also improved by the introduction of Si3N4NWs, suggesting that prepared composites exhibit broad prospects in the field of thermal management.

Toward Three-Dimensional Printed Thermal Conductive Polymeric Composites Using a Binary-Composite Hybrid Based on Boron Nitride Nanoparticles and Micro-Diamonds

Thermally conductive polymeric composites are promising for heat management in microelectronic devices. This work presents a binary-hybrid composite of boron nitride (BN) nanoparticles and micro-diamond (D) fillers in an elastomeric polyurethane (PU) matrix which can be three- dimensionally printed to produce a highly flexible and self-supporting structure. The research shows that a combination of 16.7 wt% BN and 16.7 wt% D results in a robust network within the polymer matrix to improve the tensile modulus more than nine times with respect to neat PU. Significantly, the hybrid matrix enhances the thermal conductivity by more than two times when compared to neat PU. The enhancement in mechanical, and thermal features make this three-dimensional printable multiscale hybrid composite suitable for flexible and stretchable microelectronic applications.

A Novel Polyester Varnish Nanocomposites for Electrical Machines with Improved Thermal and Dielectric Properties Using Functionalized TiO2 Nanoparticles

Recently, there has been a growing interest in polymer insulating materials that incorporate nanoscale inorganic additives, as they have shown significantly improved dielectric, thermal, and mechanical properties, making them highly suitable for application in high-voltage insulating materials for electrical machines. This study aims to improve the dielectric and thermal properties of a commercial polyester varnish by incorporating different concentrations of titanium dioxide nanoparticles (TiO2) with proper surface functionalization. Permafil 9637 dipping varnish is the varnish used for this investigation, and vinyl silane is the coupling agent used in the surface functionalization of TiO2 nanoparticles. First, nanoparticles are characterized through Fourier transform infrared spectroscopy to validate the success of their surface functionalization. Then, varnish nanocomposites are characterized through field emission scanning electron microscopy to validate the dispersion and morphology of nanoparticles within the varnish matrix. Following characterization, varnish nanocomposites are evaluated for thermal and dielectric properties. Regarding thermal properties, the thermal conductivity of the prepared nanocomposites is assessed. Regarding dielectric properties, both permittivity and dielectric losses are evaluated over a wide frequency range, starting from 20 Hz up to 2 MHz. Moreover, the AC breakdown voltage is measured for varnish nanocomposites, and the obtained data are incorporated into a finite element method to obtain the dielectric breakdown strength. Finally, the physical mechanisms behind the obtained results are discussed, considering the role of nanoparticle loading and surface functionalization.

Nanobrick Wall Multilayer Thin Films with High Dielectric Breakdown Strength

Current thermally conductive and electrically insulating insulation systems are struggling to meet the needs of modern electronics due to increasing heat generation and power densities. Little research has focused on creating insulation systems that excel at both dissipating heat and withstanding high voltages (i.e., have both high thermal conductivity and a high breakdown strength). Herein, a polyelectrolyte-based multilayer nanocomposite is demonstrated to be a thermally conductive high-voltage insulation. Through inclusion of both boehmite and vermiculite clay, the breakdown strength of the nanocomposite was increased by ≈115%. It was also found that this unique nanocomposite has an increase in its breakdown strength, modulus, and hydrophobicity when exposed to elevated temperatures. This readily scalable insulation exhibits a remarkable combination of breakdown strength (250 kV/mm) and thermal conductivity (0.16 W m-1 K-1) for a polyelectrolyte-based nanocomposite. This dual clay insulation is a step toward meeting the needs of the next generation of high-performance insulation systems.

Data-Driven Framework toward Accurate Prediction of Interfacial Thermal Resistance in Particulate-Filled Composites

The interfacial thermal resistance (ITR) inside the particulate-filled polymer composite is a bottleneck for improving the thermal conductivity (TC) of the material. Getting full knowledge of the ITR is crucial to the material design as well as to a faithful prediction of TC of the composite. However, a method fully taking into account the local circumstances inside the composite is yet to be developed to precisely characterize the ITR. Here, we propose a comprehensive framework combining high-throughput numerical simulations, machine learning and optimization algorithms, and experiments, which is demonstrated to be robust for the accurate determination of ITRs inside the particulate-filled composites. The strategy extracts as much information as possible about the structure and heat transfer characteristics of the composite based on simple experiments, which lays the foundation for the method to be effective. We show that the polymer-filler ITRs and the effective filler-filler contact ITRs predicted with the method faithfully represent the true characteristics inside the composite materials; they also provide the exact effective parameters, which cannot be obtained from experiments, for accurate numerical prediction of TCs of composite materials with high efficiency. As a result, the framework not only provides a robust tool for accurate characterization of ITRs inside composites but also paves the way for virtual high-throughput formula screening of thermally conductive composite materials that could be used in industrial product design.

Electrically insulating PBO/MXene film with superior thermal conductivity, mechanical properties, thermal stability, and flame retardancy

Constructing flexible and robust thermally conductive but electrically insulating composite films for efficient and safe thermal management has always been a sought-after research topic. Herein, a nacre-inspired high-performance poly(p-phenylene-2,6-benzobisoxazole) (PBO)/MXene nanocomposite film was prepared by a sol-gel-film conversion method with a homogeneous gelation process. Because of the as-formed optimized brick and mortar structure, and the strong bridging and caging effects of the fine PBO nanofibre network on the MXene nanosheets, the resulting nanocomposite film is electrically insulating (2.5 × 109 Ω cm), and exhibits excellent mechanical properties (tensile strength of 416.7 MPa, Young's modulus of 9.1 GPa and toughness of 97.3 MJ m-3). More importantly, the synergistic orientation of PBO nanofibres and MXene nanosheets endows the film with an in-plane thermal conductivity of 42.2 W m-1 K-1. The film also exhibits excellent thermal stability and flame retardancy. This work broadens the ideas for preparing high-performance thermally conductive but electrically insulating composites.

A Janus membrane doped with carbon nanotubes for wet-thermal management

In a human skin-fibrous fabric-external environment, fibrous materials, as the "second skin" of the human body, provide comfort against the wet and heat effectively. Fibrous materials protect human health and guarantee work efficiency in various outdoor or inner scenes. Personal wet-thermal management based on fibrous materials can regulate comfort in a facile manner with low or zero energy consumption, which has become a potential development area. However, realizing synergistic management of the wet and heat effectively and conveniently is a challenge in the development and production of fibrous materials. We designed and fabricated a Janus fibrous membrane composed of 3-(trimethoxysilyl)propyl methacrylate (TMSPMA)-modified hydrophobic cotton gauze and electrospun carbon nanotubes (CNTs)-doped cellulose acetate (CA) hydrophilic fibrous membrane. Taking advantage of asymmetric wettability along its thickness direction, the Janus fibrous membrane, acting as a "liquid diode", could transport sweat/moisture from human skin to the external environment unidirectionally, which endowed a dry surface on human skin, avoiding "stickiness", and realizing wet management. Doped CNTs had good photothermal-conversion capacity, so the Janus membrane exhibited excellent heating capacity for passive radiation, so excellent synergistic wet-thermal management was obtained. The Janus membrane could be a candidate for diverse applications of fibrous membranes. Our data provide new ideas for the design and fabrication of fibrous membranes with remarkable wet-thermal management.

Preparation of Monotrimethoxylsilylethyl-Terminated Polysiloxane Fluids and Their Application in Thermal Interface Materials

In this study, α-Trimethylsilylmethyl-ω-dimethylsilyl-terminated polydimethylsiloxane, polydiethylsiloxane and poly[2,2,2-trifluoropropyl(methyl)siloxane] are synthesized using an anion catalyzed nonequilibrium polymerization reaction with trimethylsilylmethyl lithium as the initiator; hexamethylcyclotrisiloxane, hexaethylcyclotrisiloxane or 1,3,5-trimethyl-1,3,5-trifluoropropylcyclotrisiloxane as the monomer; and dimethylchlorosilane as an end-capping agent. Three kinds of α-trimethylsilylmethyl-ω-trimethoxylsilylethyl-terminated polysiloxanes are further prepared by hydrosilylation reaction of α-trimethylsilylmethyl-ω-dimethylsilyl-terminated polysiloxanes with vinyltrimethoxysilane using Karstedt's catalyst. These α-trimethylsilylmethyl-ω-trimethoxylsilylethyl-terminated polysiloxanes are functionalized as in situ surface treatment agents for AlN particles. The effects of the structure of these polysiloxanes on the dispersion of AlN in the polysiloxane matrix and on the heat transfer performance of silicone pastes and silicone rubbers are investigated. A possible mechanism of surface treatment of AlN fillers by these novel silicone fluids is also discussed.

Thermal Transport in Poly(p-phenylene): Anomalous Dimensionality Dependence and Role of π-π Stacking

For heat conduction along polymer chains, a decrease in the axial thermal conductivity often occurs when the polymer structure changes from one-dimensional (1D) to three-dimensional (3D). For example, a single extended aliphatic chain (e.g., polyethylene or poly(dimethylsiloxane)) usually has a higher axial thermal conductivity than its double-chain or crystal counterparts because coupling between chains induces strong interchain anharmonic scatterings. Intuitively, for chains with an aromatic backbone, the even stronger π-π stacking, once formed between chains, should enhance thermal transport across chains and suppress the thermal conductivity along the chains. However, we show that this trend is the opposite in poly(p-phenylene) (PPP), a typical chain with an aromatic backbone. Using molecular dynamics simulations, we found that the axial thermal conductivity of PPP chains shows an anomalous dimensionality dependence where the thermal conductivity of double-chain and 3D crystal structures is higher than that of a 1D single chain. We analyzed the probability distribution of dihedral angles and found that π-π stacking between phenyl rings restricts the free rotation of phenyl rings and forms a long-range order along the chain, thus enhancing thermal transport along the chain direction. Though possessing a stronger bonding strength and stabilizing the multiple-chain structure, π-π stacking does not lead to a higher interchain thermal conductance between phenyl rings compared with that between aliphatic chains. Our simulation results on the effects of π-π stacking provide insights to engineer thermal transport in polymers at the molecular level.

Enhancement of Isotropic Heat Dissipation of Polymer Composites by Using Ternary Filler Systems Consisting of Boron Nitride Nanotubes, h-BN, and Al2O3

In this research article, a poly(dimethylsiloxane) (PDMS)-based composite was postulated adapting an interactive ternary filler system consisting of Al₂O₃, hexagonal boron nitride (h-BN), and boron nitride nanotubes (BNNT) to construct a continuous three-dimensional (3D) structure for thermal attenuation. Al₂O₃ was imposed as a main filler, while h-BN and BNNT were assimilated to form interconnected heat conduction pathways for effective thermal dissipation. The structured framework articulates a profound improvement in isotropic thermal conductivity considering both axial and radial heat dissipation. The presence of h-BN entails uniform heat distribution in a planar mode, eliminating the occurrence of hotspots, while BNNT constructed a connecting phonon pathway in various directions, which insinuates effective overall thermal transport. The generated ternary filler composites attained an isotropic ratio of 1.35 and a thermal conductivity of 7.50 W/mK, which is a 36-fold (∼3650%) increase compared to neat PDMS resin and almost 3-fold (∼297%) that of the Al₂O₃ unary filler composite and ∼53% that of its binary counterpart, partaking interfacial thermal gaps of ∼36.15 and ∼62.24% on practical heating performance relative to its counterparts. Moreover, the incorporation of BNNT on a traditional spherical and planar filler offers an advantage not only in thermal conductivity but also in thermal and structural stability. Improvement in thermal stability is stipulated due to a melting point (T_m) shift of ∼11 °C upon the assimilation of BNNT. Mechanical permeance reinforcement was also observed with the presence of BNNT, showcasing a 31.5% increase in tensile strength and a 53% increase in Young's modulus relative to the singular filler composite. This exploration administers a new insight into heat dissipation phenomena in polymeric composites and proposes a simple approach to their design and assembly.

Nonmonotonic dependence of thermal conductivity on surface roughness: A multiparticle Lorentz gas model

Utilizing surface roughness to manipulate thermal transport has aided important developments in thermoelectrics and heat dissipation in microelectronics. In this paper, through a multiparticle Lorentz gas model, it is found that thermal conductivity oscillates with the increase of surface roughness, and the oscillating thermal conductivity gradually disappears with the increase of nonlinearity. The transmittance analyses reveal that the oscillating thermal conductivity is caused by localized particles due to boundary effects. Nonlinearity will gradually break the localization. Thus, localization still exists in the weak nonlinear system, where there exists an interplay between nonlinear interaction and localization. Furthermore, it is also found that boundary shapes have a great influence on the oscillating thermal conductivity. Finally, we have also studied the oscillating thermal rectification effects caused by rough boundaries. This study gains insight into the boundary effect on thermal transport and provides a mechanism to manipulate thermal conductivity.

Recent Progress on Multifunctional Thermally Conductive Epoxy Composite

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

3D-Printed Polyamide 12/Styrene-Acrylic Copolymer-Boron Nitride (PA12/SA-BN) Composite with Macro and Micro Double Anisotropic Thermally Conductive Structures

Anisotropic thermally conductive composites are very critical for precise thermal management of electronic devices. In this work, in order to prepare a composite with significant anisotropic thermal conductivity, polyamide 12/styrene-acrylic copolymer-boron nitride (PA12/SA-BN) composites with macro and micro double anisotropic structures were fabricated successfully using 3D printing and micro-shear methods. The morphologies and thermally conductive properties of composites were systematically characterized via SEM, XRD, and the laser flash method. Experimental results indicate that the through-plane thermal conductivity of the composite is 4.2 W/(m·K) with only 21.4 wt% BN, which is five times higher than that of the composite with randomly oriented BN. Simulation results show that the macro-anisotropic structure of the composite (caused by the selective distribution of BN) as well as the micro-anisotropic structure (caused by the orientation structure of BN) both play critical roles in spreading heat along the specified direction. Therefore, as-obtained composites with double anisotropic structures possess great potential for the application inefficient and controllable thermal management in various fields.

Nanopolyhybrids: Materials, Engineering Designs, and Advances in Thermal Management

The fundamental requirements for thermal comfort along with the unbalanced growth in the energy demand and consumption worldwide have triggered the development and innovation of advanced materials for high thermal-management capabilities. However, continuous development remains a significant challenge in designing thermally robust materials for the efficient thermal management of industrial devices and manufacturing technologies. The notable achievements thus far in nanopolyhybrid design technologies include multiresponsive energy harvesting/conversion (e.g., light, magnetic, and electric), thermoregulation (including microclimate), energy saving in construction, as well as the miniaturization, integration, and intelligentization of electronic systems. These are achieved by integrating nanomaterials and polymers with desired engineering strategies. Herein, fundamental design approaches that consider diverse nanomaterials and the properties of nanopolyhybrids are introduced, and the emerging applications of hybrid composites such as personal and electronic thermal management and advanced medical applications are highlighted. Finally, current challenges and outlook for future trends and prospects are summarized to develop nanopolyhybrid materials.

Self-Stacked 3D Anisotropic BNNS Network Guided by Para-Aramid Nanofibers for Highly Thermal Conductive Dielectric Nanocomposites

The enhancement of the heat-dissipation property of polymer-based composites is of great practical interest in modern electronics. Recently, the construction of a three-dimensional (3D) thermal pathway network structure for composites has become an attractive way. However, for most reported high thermal conductive composites, excellent properties are achieved at a high filler loading and the building of a 3D network structure usually requires complex steps, which greatly restrict the large-scale preparation and application of high thermal conductive polymer-based materials. Herein, utilizing the framework-forming characteristic of polymerization-induced para-aramid nanofibers (PANF) and the high thermal conductivity of hexagonal boron nitride nanosheets (BNNS), a 3D-laminated PANF-supported BNNS aerogel was successfully prepared via a simple vacuum-assisted self-stacking method, which could be used as a thermal conductive skeleton for epoxy resin (EP). The obtained PANF-BNNS/EP nanocomposite exhibits a high thermal conductivity of 3.66 W m^-1 K^-1 at only 13.2 vol % BNNS loading. The effectiveness of the heat conduction path was proved by finite element analysis. The PANF-BNNS/EP nanocomposite shows outstanding practical thermal management capability, excellent thermal stability, low dielectric constant, and dielectric loss, making it a reliable material for electronic packaging applications. This work also offers a potential and promotable strategy for the easy manufacture of 3D anisotropic high-efficiency thermal conductive network structures.

Exploiting Enzyme in the Polymer Synthesis for a Remarkable Increase in Thermal Conductivity

The interest in polymers with high thermal conductivity increased much because of their inherent properties such as low density, low cost, flexibility, and good chemical resistance. However, it is challenging to engineer plastics with good heat transfer characteristics, processability, and required strength. Improving the degree of the chain alignment and forming a continuous thermal conduction network is expected to enhance thermal conductivity. This research aimed to develop polymers with a high thermal conductivity that can be interesting for several applications. Two polymers, namely poly(benzofuran-co-arylacetic acid) and poly(tartronic-co-glycolic acid), with high thermal conductivity containing microscopically ordered structures were prepared by performing enzyme-catalyzed (Novozyme-435) polymerization of the corresponding α-hydroxy acids 4-hydroxymandelic acid and tartronic acid, respectively. A comparison between the polymer's structure and heat transfer obtained by mere thermal polymerization before and enzyme-catalyzed polymerization will now be discussed, revealing a dramatic increase in thermal conductivity in the latter case. The polymer structures were investigated by FTIR spectroscopy, nuclear magnetic resonance (NMR) spectroscopy in liquid- and solid-state (ss-NMR), and powder X-ray diffraction. The thermal conductivity and diffusivity were measured using the transient plane source technique.

Development and Optimization of 3D-Printed Flexible Electronic Coatings: A New Generation of Smart Heating Fabrics for Automobile Applications

Textile-based Joule heaters in combination with multifunctional materials, fabrication tactics, and optimized designs have changed the paradigm of futuristic intelligent clothing systems, particularly in the automobile field. In the design of heating systems integrated into a car seat, conductive coatings via 3D printing are expected to have further benefits over conventional rigid electrical elements such as a tailored shape and increased comfort, feasibility, stretchability, and compactness. In this regard, we report on a novel heating technique for car seat fabrics based on the use of smart conductive coatings. For easier processes and integration, an extrusion 3D printer is employed to achieve multilayered thin films coated on the surface of the fabric substrate. The developed heater device consists of two principal copper electrodes (so-called power buses) and three identical heating resistors made of carbon composites. Connections between the copper power bus and the carbon resistors are made by means of sub-divide the electrodes, which is critical for electrical-thermal coupling. Finite element models (FEM) are developed to predict the heating behavior of the tested substrates under different designs. It is pointed out that the most optimized design solves important drawbacks of the initial design in terms of temperature regularity and overheating. Full characterizations of the electrical and thermal properties, together with morphological analyses via SEM images, are conducted on different coated samples, making it possible to identify the relevant physical parameters of the materials as well as confirm the printing quality. It is discovered through a combination of FEM and experimental evaluations that the printed coating patterns have a crucial impact on the energy conversion and heating performance. Our first prototype, thanks to many design optimizations, entirely meets the specifications required by the automobile industry. Accordingly, multifunctional materials together with printing technology could offer an efficient heating method for the smart textile industry with significantly improved comfort for both the designer and user.

Linking Interfacial Bonding and Thermal Conductivity in Molecularly-Confined Polymer-Glass Nanocomposites with Ultra-High Interfacial Density

Thermal transport in polymer nanocomposites becomes dependent on the interfacial thermal conductance due to the ultra-high density of the internal interfaces when the polymer and filler domains are intimately mixed at the nanoscale. However, there is a lack of experimental measurements that can link the thermal conductance across the interfaces to the chemistry and bonding between the polymer molecules and the glass surface. Characterizing the thermal properties of amorphous composites are a particular challenge as their low intrinsic thermal conductivity leads to poor measurement sensitivity of the interfacial thermal conductance. To address this issue here, polymers are confined in porous organosilicates with high interfacial densities, stable composite structure, and varying surface chemistries. The thermal conductivities and fracture energies of the composites are measured with frequency dependent time-domain thermoreflectance (TDTR) and thin-film fracture testing, respectively. Effective medium theory (EMT) along with finite element analysis (FEA) is then used to uniquely extract the thermal boundary conductance (TBC) from the measured thermal conductivity of the composites. Changes in TBC are then linked to the hydrogen bonding between the polymer and organosilicate as quantified by Fourier-transform infrared (FTIR) and X-ray photoelectron (XPS) spectroscopy. This platform for analysis is a new paradigm in the experimental investigation of heat flow across constituent domains.

Emerging Materials for Interfacial Solar-Driven Water Purification

Solar-driven water purification is considered as an effective and sustainable technology for water treatment using green solar energy. One major goal for practical applications is to improve the solar evaporation performance by the design of novel photothermal materials, with optimized heat localization and water transport pathways to achieve reduced energy consumption for water vaporization. Recently, some emerging materials like polymers, metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and also single molecules were employed to construct novel solar evaporation systems. In this minireview, we present an overview of the recent efforts on materials development for water purification systems. The state-of-the-art applications of these emerging materials for solar-driven water treatment, including desalination, wastewater purification, sterilization and energy production, are also summarized.

Biomimetic Liquid Metal-Elastomer Composited Foam with Adjustable Thermal Conductivity for Heat Control

The application of traditional materials with constant thermal conductivity in time-varying thermal environments poses great challenges due to their inability of adjusting thermal conductivity according to different requirements, for which reason materials with adjustable thermal conductivity have attracted much attention. However, certain limitations induced by those materials' low softness or harsh adjustment conditions restrict them from being applied in heat dissipation and heat transfer scenarios. In this study, we report a biomimetic liquid metal-elastomer composited foam with adjustable thermal conductivity (B-LM-ECF). Inspired by the rationale of homeothermic animals regulating the thermal conductivity of their subcutaneous tissue, the prepared material adjusts its thermal conductivity via adjusting the volume proportion of liquid metal within it. The thermal conductivity of B-LM-ECF can be adjusted within the range of 0.11-8.4 W·m-1K-1. The adjustment factor η of B-LM-ECF is 76, which is defined as the ratio of the highest to the lowest thermal conductivity of the material. The material enabling reversible switching for itself from thermal insulation to heat dissipation. The prepared material exhibits 45 KPa of Young's modulus with the maximum fracture tensile rate of 600%, facilitating better covering for thermal management objects. We selected a power lithium battery and a smartphone as specific thermal management objects to demonstrate its practical application in thermal management experiment.

Synthesis and Properties of a Novel Thermally Conductive Pressure-Sensitive Adhesive with UV-Responsive Peelability

Thermally conductive pressure-sensitive adhesive (PSA) has received a great amount of attention in recent years, but the traditional PSA hardly loses adhesion properties after UV irradiation or heating. Therefore, endowing thermally conductive adhesive with UV-responsive peelability becomes a design strategy. Herein, vinyl-functionalized graphene (AA-GMA-G) is prepared by modifying graphene with acrylic acid and subsequently reacting with glycidyl methacrylate. Then, the UV-curable acrylate copolymer is synthesized by grafting glycidyl methacrylate. Finally, the novel thermally conductivity PSA with UV-responsive peelability is obtained by blending the copolymer with AA-GMA-G and photoinitiator. The results show that the PSA at 2 wt% AA-GMA-G loading exhibits an excellent thermal conductivity (0.74 W m^-1 K^-1 ) and a relatively strong peel strength, increasing by 15% compared with pristine graphene/PSA. Interestingly, the peel strength of AA-GMA-G/PSA can achieve a dramatic drop after UV treatment, and the decrease rate is 96.7%. Therefore, the novel thermally conductive PSA with UV-responsive peelability has potential applications in certain electronic devices.

Connecting the dots for fundamental understanding of structure-photophysics-property relationships of COFs, MOFs, and perovskites using a Multiparticle Holstein Formalism

Photoactive organic and hybrid organic-inorganic materials such as conjugated polymers, covalent organic frameworks (COFs), metal-organic frameworks (MOFs), and layered perovskites, display intriguing photophysical signatures upon interaction with light. Elucidating structure-photophysics-property relationships across a broad range of functional materials is nontrivial and requires our fundamental understanding of the intricate interplay among excitons (electron-hole pair), polarons (charges), bipolarons, phonons (vibrations), inter-layer stacking interactions, and different forms of structural and conformational defects. In parallel with electronic structure modeling and data-driven science that are actively pursued to successfully accelerate materials discovery, an accurate, computationally inexpensive, and physically-motivated theoretical model, which consistently makes quantitative connections with conceptually complicated experimental observations, is equally important. Within this context, the first part of this perspective highlights a unified theoretical framework in which the electronic coupling as well as the local coupling between the electronic and nuclear degrees of freedom can be efficiently described for a broad range of quasiparticles with similarly structured Holstein-style vibronic Hamiltonians. The second part of this perspective discusses excitonic and polaronic photophysical signatures in polymers, COFs, MOFs, and perovskites, and attempts to bridge the gap between different research fields using a common theoretical construct - the Multiparticle Holstein Formalism. We envision that the synergistic integration of state-of-the-art computational approaches with the Multiparticle Holstein Formalism will help identify and establish new, transformative design strategies that will guide the synthesis and characterization of next-generation energy materials optimized for a broad range of optoelectronic, spintronic, and photonic applications.

Analysis of the Structure and the Thermal Conductivity of Semi-Crystalline Polyetheretherketone/Boron Nitride Sheet Composites Using All-Atom Molecular Dynamics Simulation

Thermal transport simulations were performed to investigate the important factors affecting the thermal conductivity based on the structure of semi-crystalline polyetheretherketone (PEEK), and the addition of boron nitride (BN) sheets. The molecular-level structural analysis facilitated the prediction of the thermal conductivity of the optimal structure of PEEK reflecting the best parameter value of the length of amorphous chains, and the ratio of linkage conformations, such as loops, tails, and bridges. It was found that the long heat transfer paths of polymer chains were induced by the addition of BN sheets, which led to the improvement of the thermal conductivities of the PEEK/BN composites. In addition, the convergence of the thermal conductivities of the PEEK/BN composites in relation to BN sheet size was verified by the disconnection of the heat transfer path due to aggregation of the BN sheets.

The Synergistic Effect of Polystyrene/Modified Boron Nitride Composites for Enhanced Mechanical, Thermal and Conductive Properties

Thermal conductivity (TC) and thermal stability are the basic requirements and highly desirable properties in thermal management, heat storage and heat transfer applications. This work is regarding the fabrication of polystyrene/boron nitride composites and melt extruded to produce good thermal stability, increased thermal conductivity and enhanced mechanical properties. Our strategy is potentially applicable to produce thermally conductive composites of low cost over large scale. Boron nitride powder is bath sonicated in 10% NH₃ solution to avoid its agglomeration and tendency toward entanglement in a polymer matrix. An approximately 67.43% increase in thermal conductivity and 69.37% increase in tensile strength as well as 56 multiple increases in thermal stability of the optimum samples were achieved. The developed polymeric composites are potentially applicable in the electronic industry, especially in electronic devices used for 5G, heat sink and several other aviation applications.

Effect of Ambient Plasma Treatments on Thermal Conductivity and Fracture Toughness of Boron Nitride Nanosheets/Epoxy Nanocomposites

With the rapid growth in the miniaturization and integration of modern electronics, the dissipation of heat that would otherwise degrade the device efficiency and lifetime is a continuing challenge. In this respect, boron nitride nanosheets (BNNS) are of significant attraction as fillers for high thermal conductivity nanocomposites due to their high thermal stability, electrical insulation, and relatively high coefficient of thermal conductivity. Herein, the ambient plasma treatment of BNNS (PBNNS) for various treatment times is described for use as a reinforcement in epoxy nanocomposites. The PBNNS-loaded epoxy nanocomposites are successfully manufactured in order to investigate the thermal conductivity and fracture toughness. The results indicate that the PBNNS/epoxy nanocomposites subjected to 7 min plasma treatment exhibit the highest thermal conductivity and fracture toughness, with enhancements of 44 and 110%, respectively, compared to the neat nanocomposites. With these enhancements, the increases in surface free energy and wettability of the PBNNS/epoxy nanocomposites are shown to be attributable to the enhanced interfacial adhesion between the filler and matrix. It is demonstrated that the ambient plasma treatments enable the development of highly dispersed conductive networks in the PBNNS epoxy system.