Multifunctional Thermal Management Materials with Excellent Heat Dissipation and Generation Capability for Future Electronics

Far-Field Radiative Thermal Rectification Based on Asymmetric Emissivity

This experimental study investigates thermal rectification via asymmetric far-field thermal radiation on a fused silica slab. An asymmetrical distribution of surface emissivity is created over the device by partially covering the fused silica with a 100 nm thick aluminum film. The slab is subjected to a thermal bias, and when this bias is reversed, a small temperature difference is observed between the different configurations. This temperature difference arises from the difference in emissivity between the aluminum layer and fused silica, resulting in the transfer of thermal energy to the surrounding environment through radiation. Experimental findings are supported by finite element simulations, which not only confirm the measured values but also provide valuable insights into the rectification efficiency of the system. The rectification efficiency is found to be approximately 50% at room temperature for a thermal bias of 140 K. Simulations, which are performed by considering different environmental conditions experienced by the radiation and free convection processes, provide further insight into the underlying thermal rectification mechanism. These simulations consider an environmental temperature of 4 K for thermal radiation and an ambient temperature of 294 K for free convection and reveal an enhanced rectification effect with a rectification efficiency up to 600% when a thermal bias of 195 K is applied. This result emphasizes the significance of considering both convection and radiation in the thermal management and rectification of asymmetric systems. The outcomes of this study further our understanding of the thermal rectification phenomenon. They also show the importance of system asymmetry, emissivity disparities, environmental conditions, and the interplay between convection and radiation. Furthermore, the findings have implications for heat transfer and rectification in asymmetric systems, offering potential applications in areas such as energy harvesting, thermal management, and heat transfer optimization in electronic devices.

A Novel Thermal Interface Material Composed of Vertically Aligned Boron Nitride and Graphite Films for Ultrahigh Through-Plane Thermal Conductivity

The relentless drive toward miniaturization in microelectronic devices has sparked an urgent need for materials that offer both high thermal conductivity (TC) and excellent electrical insulation. Thermal interface materials (TIMs) possessing these dual attributes are highly sought after for modern electronics, but achieving such a combination has proven to be a formidable challenge. In this study, a cutting-edge solution is presented by developing boron nitride (BN) and graphite films layered silicone rubber composites with exceptional TC and electrical insulation properties. Through a carefully devised stacking-cutting method, the high orientation degree of both BN and graphite films is successfully preserved, resulting in an unprecedented through-plane TC of 23.7 Wm-1 K-1 and a remarkably low compressive modulus of 4.85 MPa. Furthermore, the exceptional properties of composites, including low thermal resistance and high resilience rate, make them a reliable and durable option for various applications. Practical tests demonstrate their outstanding heat dissipation performance, significantly reducing CPU temperatures in a computer cooling system. This research work unveils the possible upper limit of TC in BN-based TIMs and paves the way for their large-scale practical implementation, particularly in the thermal management of next-generation electronic devices.

Thermal Interface Engineering in a 3D-Structured Carbon Framework for a Phase-Change Composite with High Thermal Conductivity

Phase-change materials (PCMs) are promising thermal storage medium for thermal management due to their efficient thermal energy harvesting capabilities. However, the low thermal conductivity (TC) and poor shape stability of PCMs have hindered their practical applications. Construction of an interconnected three-dimensional (3D) heat-conductive structure is an effective way to build phonon conduits and provide PCM confinement. Phonon scattering at the interface is an unavoidable effect that undermines the TC improvement in the PCM composite and necessitates careful engineering. This study focuses on creating a highly thermally conductive 3D carbon-bonded graphite fiber (CBGF) network to enhance the TC of the PCM, with attention especially on thermal interface engineering considering both filler-matrix (F-M) and filler-filler (F-F) interfaces. The composite with an optimized proportion of F-M and F-F interface area achieves the highest TC of 45.48 W·m-1·K-1, which is 188.5 times higher than that of the pure PCM, and a high TC enhancement per volume fraction of the filler (TCEF) of 831% per 1 vol % loading. This also results in an enhanced spatial construction for PCM confinement during the phase change. The results emphasize the significance of interface engineering in creating high-TC and form-stable phase-change composites, providing insightful guidance for rational structural design.

Multifunctional polyimide-based femtosecond laser micro/nanostructured films with triple Janus properties

Flexible multifunctional composite films in which opposing surfaces have two or more distinct physical properties are highly applicable for wearable electronic devices, electrical power systems and biomedical engineering. However, fabrication of such "Janus" films can be time consuming, complex or economically not feasible. In this work, Janus polyimide (PI) films were prepared by femtosecond laser direct writing technology, which generated a honeycomb porous structure (HPS) on one side and a lawn-like structure (LLS) on the other. Deposition of silver nanowires (AGNWs) by drop coating on the LLS side (AGNWs@LLS) resulted in a film in which each face possessed highly distinct triple properties. The HPS side was superhydrophobic with a water contact angle (WCA) of ∼153.3° and electrically non-conductive, while the AGNWs@LLS side was superhydrophilic (WCA ∼7.8°) and highly conductive (∼3.8 Ω). Moreover, the AGNWs@LLS face showed ultra-low thermal radiation performance, almost reaching saturation. On a heating table at ∼100 °C, the temperature of the AGNWs@LLS side remained at ∼44.5 °C, while the HPS side exhibited a temperature of ∼93.9 °C. This "triple Janus film" and lasing techniques developed might be useful for designing new materials for the integration and miniaturization of multifunctional electronic equipment.

Experimental, Theoretical and Numerical Studies on Thermal Properties of Lightweight 3D Printed Graphene-Based Discs with Designed Ad Hoc Air Cavities

The current state of the art on material science emphasizes recent research efforts aimed at designing novel materials characterized by low-density and advanced properties. The present article reports the experimental, theoretical and simulation results on the thermal behavior of 3D printed discs. Filaments of pure poly (lactic acid) PLA and filled with 6 wt% of graphene nanoplatelets (GNPs) are used as feedstocks. Experiments indicate that the introduction of graphene enhances the thermal properties of the resulting materials since the conductivity passes from the value of 0.167 [W/mK] for unfilled PLA to 0.335 [W/mK] for reinforced PLA, which corresponds to a significantly improvement of 101%. Exploiting the potential of 3D printing, different air cavities have been intentionally designed to develop new lightweight and more cost-effective materials without compromising their thermal performances. Furthermore, some cavities are equal in volume but different in the geometry; it is necessary to investigate how this last characteristic and its possible orientations affect the overall thermal behavior compared to that of an air-free specimen. The influence of air volume is also investigated. Experimental results are supported by theoretical analysis and simulation studies based on the finite element method. The results aim to be a valuable reference resource in the field of design and optimization of lightweight advanced materials.

Layer-by-Layer Engineered Flexible Functional Film Fabrication with Spreadability Control in Roll-to-Roll Manufacturing

A roll-to-roll manufacturing system performs printing and coating on webs to mass-produce large-area functional films. The functional film of a multilayered structure is composed of layers with different components for performance improvement. The roll-to-roll system is capable of controlling the geometries of the coating and printing layers using process variables. However, research on geometric control using process variables is limited to single-layer structures only. This study entails the development of a method to proactively control the geometry of the upper coated layer by using the lower-layer coating process variable in the manufacture of a double-coated layer. The correlation between the lower-layer coating process variable and upper coated layer geometry was examined by analyzing the lower-layer surface roughness and spreadability of the upper-layer coating ink. The correlation analysis results demonstrate that tension was the dominant variable in the upper coated layer surface roughness. Additionally, this study found that adjusting the process variable of the lower-layer coating in a double-layered coating process could improve the surface roughness of the upper coating layer by up to 14.9%.

Spatially modulated femtosecond laser direct ablation-based preparation of ultra-flexible multifunctional copper mesh electrodes and its application

Multifunctional electrodes possess superior properties such as high photoelectric properties and high stability. Laser manufacturing process is one of the widely used method for electrode fabrication. However, the current multifunctional electrode laser manufacturing process suffers from low fabrication speed. Here, we report a high-efficiency laser digital patterning process to fabricate copper-based flexible transparent conducting electrodes. By using a spatially modulated, one single laser spot is modulated into an array of spots with equal intensity, and the fabrication speed can be improved by more than 20 times over the traditional single pulse processing. In addition, copper mesh electrodes with a high photoelectric property have been fabricated. A transparent touch screen panel and multifunctional windows are fabricated with transparent electrodes to demonstrate their use in vehicle defogging, portable heating, and wearable devices.

Emerging Flexible Thermally Conductive Films: Mechanism, Fabrication, Application

Effective thermal management is quite urgent for electronics owing to their ever-growing integration degree, operation frequency and power density, and the main strategy of thermal management is to remove excess energy from electronics to outside by thermal conductive materials. Compared to the conventional thermal management materials, flexible thermally conductive films with high in-plane thermal conductivity, as emerging candidates, have aroused greater interest in the last decade, which show great potential in thermal management applications of next-generation devices. However, a comprehensive review of flexible thermally conductive films is rarely reported. Thus, we review recent advances of both intrinsic polymer films and polymer-based composite films with ultrahigh in-plane thermal conductivity, with deep understandings of heat transfer mechanism, processing methods to enhance thermal conductivity, optimization strategies to reduce interface thermal resistance and their potential applications. Lastly, challenges and opportunities for the future development of flexible thermally conductive films are also discussed.

Development and Characterization of a Nonelectronic Versatile Oxygenating Perfusion System for Tissue Preservation

Oxygenated machine perfusion of human organs has been shown to improve both preservation quality and time duration when compared to the current gold standard: static cold storage. However, existing machine perfusion devices designed for preservation and transportation of transplantable organs are too complicated and organ-specific to merit use as a solution for all organs. This work presents a novel, portable, and nonelectronic device potentially capable of delivering oxygenated machine perfusion to a variety of organs. An innovative pneumatic circuit system regulates a compressed oxygen source that cyclically inflates and deflates silicone tubes, which function as both the oxygenator and perfusion pump. Different combinations of silicone tubes in single or parallel configurations, with lengths ranging from 1.5 to 15.2 m, were evaluated at varying oxygen pressures from 27.6 to 110.3 kPa. The silicone tubes in parallel configurations produced higher peak perfusion pressures (70% increase), mean flow rates (102% increase), and oxygenation rates (268% increase) than the single silicone tubes that had equivalent total lengths. While pumping against a vascular resistance element that mimicked a kidney, the device achieved perfusion pressures (8.4-131.6 mmHg), flow rates (2.0-40.2 mL min^-1), and oxygenation rates (up to 388 μmol min^-1) that are consistent with values used in previous kidney preservation studies. The nonelectronic device achieved those perfusion parameters using 4.4 L min^-1 of oxygen to operate. These results demonstrate that oxygenated machine perfusion can be successfully achieved without any electronic components.

Efficient mechanical modulation of the phonon thermal conductivity of Mo6S6 nanowires

Mo₆S₆ nanowires are emerging as key building blocks for flexible devices and are competitive with carbon nanotubes due to easier separation and functionalization. Here, it is reported the phonon thermal conductivity (κ) of Mo₆S₆ nanowires via molecular dynamics simulations. It shows a large tunability of low-frequency phonon thermal conductivity (κ_lf)Amax from 27.2-191 W (m K)^-1, an increase of around 702% via mechanical strain. Below critical tension/torsion strain, their phonon thermal conductivity monotonically reduces/enlarges; whereas above this value, an inverse trend is identified. On the other hand, Mo₆S₆ nanowires show unusual auxetic behavior. The transitions involved in phonon thermal conductivity are molecularly illustrated by a strain-induced crossover in bond configurations and are explained based on a competition mechanism between phonon scattering and group velocity. This study provides insights into the thermal transport and auxetic properties of low-dimensional structures and the thermal management of Mo₆S₆ nanowire-based systems.

Millefeuille-Inspired Thermal Interface Materials based on Double Self-Assembly Technique for Efficient Microelectronic Cooling and Electromagnetic Interference Shielding

Owing to the increasing power density of miniaturized and high-frequency electronic devices, flexible thermal interface materials (TIMs) with the electromagnetic interference (EMI) shielding property are in urgent demand to maintain the system performance and reliability. Recently, carbon-based TIMs receive considerable attention due to the ultrahigh intrinsic thermal conductivity (TC). However, the large-scale production of such TIMs is restricted by some technical difficulties, such as production-induced defects of graphite sheets, poor microstructure architecture within the matrix, and nonnegligible interfacial thermal resistance result from the strong phono scattering. In this work, inspired by the structure and production process of millefeuille cakes, a unique double self-assembly strategy for fabricating ultrahigh thermal conductive TIMs with superior EMI shielding performance is demonstrated. The percolating and oriented multilayered microstructure enables the TIM to exhibit an ultrahigh in-plane TC of 233.67 W m^-1 K^-1 together with an outstanding EMI shielding effectiveness of 79.0 dB (at 12.4 GHz). In the TIM evaluation system, a nearly 45 °C decrease is obtained by this TIM when compared to the commercial material. The obtained TIM achieves the desired balance between thermal conduction and EMI shielding performance, indicating broad prospects in the fields of military applications and next-generation thermal management systems.

Bioinspired Dielectric Film with Superior Mechanical Properties and Ultrahigh Electric Breakdown Strength Made from Aramid Nanofibers and Alumina Nanoplates

Materials with excellent thermal stability, mechanical, and insulating properties are highly desirable for electrical equipment with high voltage and high power. However, simultaneously integrating these performance portfolios into a single material remains a great challenge. Here, we describe a new strategy to prepare composite film by combining one-dimensional (1D) rigid aramid nanofiber (ANF) with 2D alumina (Al₂O₃) nanoplates using the carboxylated chitosan acting as hydrogen bonding donors as well as soft interlocking agent. A biomimetic nacreous ‘brick-and-mortar’ structure with a 3D hydrogen bonding network is constructed in the obtained ANF/chitosan/Al₂O₃ composite films, which provides the composite films with exceptional mechanical and dielectric properties. The ANF/chitosan/Al₂O₃ composite film exhibits an ultrahigh electric breakdown strength of 320.1 kV/mm at 15 wt % Al₂O₃ loading, which is 50.6% higher than that of the neat ANF film. Meanwhile, a large elongation at break of 17.22% is achieved for the composite film, integrated with high tensile strength (~233 MPa), low dielectric loss (<0.02), and remarkable thermal stability. These findings shed new light on the fabrication of multifunctional insulating materials and broaden their practical applications in the field of advanced electrics and electrical devices.

Highly Thermally Conductive Graphene-Based Thermal Interface Materials with a Bilayer Structure for Central Processing Unit Cooling

Innovations of transistors toward miniaturization and integration aggravate heat accumulation of central processing units (CPUs). Thermal interface materials (TIMs) are critical to remove the generated heat and to guarantee the device reliability. Herein, maltose-assisted mechanochemical exfoliation was proposed to prepare maltose-g-graphene as a structural motif of TIMs. Then, maltose-g-graphene/gelatin composite films with a bilayer structure were prepared by two-step vacuum filtration to construct effective thermally conductive pathways consisting of the directionally arranged and tightly packed maltose-g-graphene. The bilayer composite film exhibited a remarkable in-plane thermal conductivity (30.8 W m^-1 K^-1) and strong anisotropic ratio (∼8325%) at 40 wt % maltose-g-graphene addition. More intriguingly, the cooling effect on CPUs was significantly better for the bilayer composite films than commercial thermal pads as TIMs. The outstanding thermally conductive stability in resistance to instantaneous and prolonged thermal shocks as well as fatigue stability was gathered. Our work offers a valuable reference to design and fabricate high-performance TIMs for CPU cooling to surmount harsh application scenarios.

Preparation and mechanism research of bio-inspired dopamine decorated expanded graphite/silicone rubber composite with high thermal conductivity and excellent insulation

This study looked at the process of designing and synthesized expanded graphite (EG) and modifying it with bio-inspired dopamine (DOPA). This is a process used to improve the thermal conductivity and dielectric properties of methyl vinyl silicone rubber (VMQ). The results demonstrated that the EG-DOPA-VMQ composites acquired an exceptional thermal conductivity of 1.015 W mK^-1at the loading of 10 wt%, approximately 480% higher than that of pure silicone rubber (0.175 W mK^-1). This enhancement is mainly attributed to the improved dispersion capability of EG-DOPA and the robust interfacial interaction between EG-DOPA-VMQ interfaces; specifically, this is the result when compared with pristine EG. Moreover, throughout this process, the composites maintained an excellent insulating property with a resistance of ≈10¹²Ω · cm; this particular result was due to the DOPA deposited on EG surfaces because they acted as an insulating layer, inhibiting the electron transfer in composites. Overall, this work demonstrated that it could present a promising strategy for synchronized manufacturing of polymer composites with high thermal conductivity and insulating capability.

Stitching Graphene Sheets with Graphitic Carbon Nitride: Constructing a Highly Thermally Conductive rGO/g-C3N4 Film with Excellent Heating Capability

Driven by the evolution of electronic packaging technology for high-dense integration of high-power, high-frequency, and multi-function devices in modern electronics, thermal management materials have become a crucial component for guaranteeing the stable and reliable operation of devices. Because of its admirable in-plane thermal conductivity, graphene is considered as a desired thermal conductor. However, the promise of graphene films has been greatly weakened as the existence of grain boundaries lead to a high extent of phonon scattering. Here, a stitching strategy is adopted to fabricate an rGO/g-C₃N₄ film, where 2D g-C₃N₄ works as a linker to covalently connect adjacent rGO sheets for expanding the size of graphene and forming an in-plane rGO/g-C₃N₄ heterostructure. The in-plane thermal conductivity of the rGO/g-C₃N₄ film reaches 41.2 W m^-1 K^-1 at a g-C₃N₄ content of only 1 wt %, which increased by 17.3% compared to pristine rGO. The interfaced thermal resistance between rGO and g-C₃N₄ is further examined by non-equilibrium molecular dynamics simulations. Furthermore, owing to the unique light absorption and welding ability of g-C₃N₄, the rGO/g-C₃N₄ film presents superior solar-thermal and electric-thermal responses to controllably regulate the chip temperature against overcooling. This work provides a facile approach to construct a large-sized rGO sheet and combines heat dissipation and heating capability in the same thermal management material for future electronics.

Recent Advances in Preparation, Mechanisms, and Applications of Thermally Conductive Polymer Composites: A Review

At present, the rapid accumulation of heat and the heat dissipation of electronic equipment and related components are important reasons that restrict the miniaturization, high integration, and high power of electronic equipment. It seriously affects the performance and life of electronic devices. Hence, improving the thermal conductivity of polymer composites (TCPCs) is the key to solving this problem. Compared with manufacturing intrinsic thermally conductive polymer composites, the method of filling the polymer matrix with thermally conductive fillers can better-enhance the thermal conductivity (λ) of the composites. This review starts from the thermal conduction mechanism and describes the factors affecting the λ of polymer composites, including filler type, filler morphology and distribution, and the functional surface treatment of fillers. Next, we introduce the preparation methods of filled thermally conductive polymer composites with different filler types. In addition, some commonly used thermal-conductivity theoretical models have been introduced to better-analyze the thermophysical properties of polymer composites. We discuss the simulation of λ and the thermal conduction process of polymer composites based on molecular dynamics and finite element analysis methods. Meanwhile, we briefly introduce the application of polymer composites in thermal management. Finally, we outline the challenges and prospects of TCPCs.

Remarkable Effects of an Electrodeposited Copper Skin on the Strength and the Electrical and Thermal Conductivities of Reduced Graphene Oxide-Printed Scaffolds

Architected Cu/reduced graphene oxide (rGO) heterostructures are achieved by electrodepositing copper on filament-printed rGO scaffolds. The Cu coating perfectly contours the printed rGO structure, but isolated Cu particles also permeate inside the filaments. Although the Cu deposition conveys a certain mass augment, the three-dimensional (3D) structures remain reasonably light (bulk density ≅ 0.42 g·cm^-3). The electrical conductivity (σ_e) of the Cu/rGO structure (∼8 × 10⁴ S·m^-1) shows a notable increment compared to σ_e of the rGO structure (∼2 × 10² S·m^-1). The effect on the scaffold robustness is also notable with an increase of the compressive strength by nearly 10 times (from 20 kPa of the rGO scaffold to 150 kPa of the Cu/rGO structure) and cyclability as well. The improved thermal conductivity of the Cu-coated scaffolds (∼4 times higher), in addition to the σ_e and strength improvements, suggests that 3D Cu/rGO structures could be suitable assemblies for integration into thermal dissipation systems, particularly as thermal interface materials, for compact electronic devices.

Highly Thermal Conductivities, Excellent Mechanical Robustness and Flexibility, and Outstanding Thermal Stabilities of Aramid Nanofiber Composite Papers with Nacre-Mimetic Layered Structures

Aramid nanofiber (ANF) paper has shown potential applications in flexible electronics. However, its inherent low thermal conductivity coefficient (λ) values might threaten the safety of devices under a high-power working condition. In this work, polydopamine-functionalized boron nitride nanosheet (BNNS@PDA)/ANF thermally conductive composite papers with nacre-mimetic layered structures were prepared via highly efficient vacuum-assisted filtration followed by hot pressing. For a given BNNS loading, the surface functionalization of BNNS could further enhance the thermal conductivities and mechanical properties of BNNS@PDA/ANF composite papers. BNNS@PDA/ANF composite papers presented anisotropic thermal conductivities, and the through-plane (λ_⊥) and in-plane (λ_∥) values of the 50 wt % BNNS@PDA/ANF composite papers reached 0.62 and 3.94 W/mK, 181.8 and 196.2% higher than those of original ANF paper, respectively, which were also higher than those of 50 wt % BNNS/ANF composite papers (λ_⊥ = 0.52 W/mK and λ_∥ = 3.33 W/mK). The tensile strength of the 50 wt % BNNS@PDA/ANF composite papers reached 36.8 MPa, 30.5% higher than that of 50 wt % BNNS/ANF composite papers (28.2 MPa). In addition, the heat resistance index (T_HRI) of the 50 wt % BNNS@PDA/ANF composite papers was further increased to 223.1 °C. Overall, our fabricated BNNS@PDA/ANF composite papers possess highly thermal conductivities, excellent mechanical robustness and flexibility, and outstanding thermal stabilities, showing great potential applications in the fields of intelligent wearable equipment, flexible supercapacitors, and flexible electronics.