A thermally conductive interface material with tremendous and reversible surface adhesion promises durable cross-interface heat conduction

Scalable Compliant Graphene Fiber-Based Thermal Interface Material with Metal-Level Thermal Conductivity via Dual-Field Synergistic Alignment Engineering

High-performance thermal interface materials (TIMs) are highly desired for high-power electronic devices to accelerate heat dissipation. However, the inherent trade-off conflict between achieving high thermal conductivity and excellent compliance of filler-enhanced TIMs results in the unsatisfactory interfacial heat transfer efficiency of existing TIM solutions. Here, we report the graphene fiber (GF)-based elastic TIM with metal-level thermal conductivity via mechanical-electric dual-field synergistic alignment engineering. Compared with state-of-the-art carbon fiber (CF), GF features both superb high thermal conductivity of ∼1200 W m-1 K-1 and outstanding flexibility. Under dual-field synergistic alignment regulation, GFs are vertically aligned with excellent orientation (0.88) and high array density (33.5 mg cm-2), forming continuous thermally conductive pathways. Even at a low filler content of ∼17 wt %, GF-based TIM demonstrates extraordinarily high through-plane thermal conductivity of up to 82.4 W m-1 K-1, exceeding most CF-based TIMs and even comparable to commonly used soft indium foil. Benefiting from the low stiffness of GF, GF-based TIM shows a lower compressive modulus down to 0.57 MPa, an excellent resilience rate of 95% after compressive cycles, and diminished contact thermal resistance as low as 7.4 K mm2 W-1. Our results provide a superb paradigm for the directed assembly of thermally conductive and flexible GFs to achieve scalable and high-performance TIMs, overcoming the long-standing bottleneck of mechanical-thermal mismatch in TIM design.

Recyclable and elastic highly thermally conductive epoxy-based composites with covalent-noncovalent interpenetrating networks

High-power electronic architectures and devices require elastic thermally conductive materials. The use of epoxy resin in thermal management is limited due to its rigidity. Here, based on epoxy vitrimer, flexible polyethylene glycol (PEG) chains are introduced into covalent adaptable networks to construct covalent-noncovalent interpenetrating networks, enabling the elasticity of epoxy resins. Compared to traditional silicone-based thermal interface materials, the newly developed elastic epoxy resin shows the advantages of reprocessability, self-healing, and no small molecule release. Results show that, even after being filled with boron nitride and liquid metal, the material maintains its resilience, reprocessability and self-healing properties. Leveraging these characteristics, the composite can be further processed into thin films through a repeated pressing-rolling technique that facilitates the forced orientation of the fillers. Subsequently, the bulk composites are reconstructed using a film-stacking method. The results indicate that the thermal conductivity of the reconstructed bulk composite reaches 3.66 W m-1 K-1, achieving a 68% increase compared to the composite prepared through blending. Due to the existence of covalent adaptable networks, the inorganic and inorganic components of the composite prepared in this work can be completely separated under mild conditions, realizing closed-loop recycling.

Design of Soft/Hard Interface with High Adhesion Energy and Low Interfacial Thermal Resistance via Regulation of Interfacial Hydrogen Bonding Interaction

Adhesion ability and interfacial thermal transfer capacity at soft/hard interfaces are of critical importance to a wide variety of applications, ranging from electronic packaging and soft electronics to batteries. However, these two properties are difficult to obtain simultaneously due to their conflicting nature at soft/hard interfaces. Herein, we report a polyurethane/silicon interface with both high adhesion energy (13535 J m-2) and low thermal interfacial resistance (0.89 × 10-6 m2 K W-1) by regulating hydrogen interactions at the interface. This is achieved by introducing a soybean-oil-based epoxy cross-linker, which can destroy the hydrogen bonds in polyurethane networks and meanwhile can promote the formation of hydrogen bonds at the polyurethane/silicon interface. This study provides a comprehensive understanding of enhancing adhesion energy and reducing interfacial thermal resistance at soft/hard interfaces, which offers a promising perspective to tailor interfacial properties in various material systems.

Elastomer Composites with High Damping and Low Thermal Resistance via Hierarchical Interactions and Regulating Filler

Modern microelectronics and emerging technologies such as wearable electronics and soft robotics require elastomers to integrate high damping with low thermal resistance to avoid damage caused by vibrations and heat accumulation. However, the strong coupling between storage modulus and loss factor makes it generally challenging to simultaneously increase both thermal conductance and damping. Here, a strategy of introducing hierarchical interaction and regulating fillers in polybutadiene/spherical aluminum elastomer composites is reported to simultaneously achieve extraordinary damping ability of tan δ > 1.0 and low thermal resistance of 0.15 cm2 K W-1, which surpasses state-of-the-art elastomers and their composites. The enhanced damping is attributed to increased energy dissipation via introducing the hierarchical hydrogen bond interactions in polybutadiene networks and the addition of spherical aluminum, which also functions as a thermally conductive filler to achieve low thermal resistance. As a proof of concept, the polybutadiene/spherical aluminum elastomer composites are used as thermal interface materials, showing effective heat dissipation for electronic devices in vibration scenarios. The combination of outstanding damping performance and extraordinary heat dissipation ability of the elastomer composites may create new opportunities for their applications in electronics.

Robust, Self-Healing, and Multi-Use Poly(Urethane-Urea-Imide) Elastomer as a Durable Adhesive for Thermal Interface Materials

Currently, research on thermal interface materials (TIMs) is primarily focused on enhancing thermal conductivity. However, strong adhesion and multifunctionality are also important characteristics for TIMs when pursing more stable interface heat conduction. Herein, a novel poly(urethane-urea-imide) (PUUI) elastomer containing abundant dynamic hydrogen bonds network and reversible disulfide linkages is successfully synthesized for application as a TIM matrix. The PUUI can self-adapt to the metal substrate surface at moderate temperatures (80 °C) and demonstrates a high adhesion strength of up to 7.39 MPa on aluminum substrates attributed its noncovalent interactions and strong intrinsic cohesion. Additionally, the PUUI displays efficient self-healing capability, which can restore 94% of its original mechanical properties after self-healing for 6 h at room temperature. Furthermore, PUUI composited with aluminum nitride and liquid metal hybrid fillers demonstrates a high thermal conductivity of 3.87 W m-1 K-1 while maintaining remarkable self-healing capability and adhesion. When used as an adhesive-type TIM, it achieves a low thermal contact resistance of 22.1 mm2 K W-1 at zero pressure, only 16.7% of that of commercial thermal pads. This study is expected to break the current research paradigm of TIMs and offers new insights for the development of advanced, reliable, and sustainable TIMs.

Alveoli-Mimetic Synergistic Liquid and Solid Thermal Conductive Interface as a Novel Strategy for Designing High-Performance Thermal Interface Materials

Thermal interface materials (TIMs) are in desperate desire with the development of the modern electronic industry. An excellent TIM needs desired comprehensive properties including but not limited to high thermal conductivity, low Yong's modulus, lightweight, as well as low price. However, as is typically the case, those properties are naturally contradictory. To tackle such dilemmas, a strategy of construction high-performance TIM inspired by alveoli is proposed. The material design includes the self-alignment of graphite into 3D interconnected thermally conductive networks by polydimethylsiloxane beads (PBs) -the alveoli; and a small amount of liquid metal (LM) - capillary networks bridging the PBs and graphite network. Through the delicate structural regulation and the synergistic effect of the LM and solid graphite filler, superb thermal conductivity (9.98 ± 0.34 W m-1 K-1) can be achieved. The light emitting diode (LED) application and their performance in the central processing unit (CPU) heat dispersion manifest the TIM developed in the work has stable thermal conductivity for long-term applications. The thermally conductive, soft, and lightweight composites are believed to be high-performance silicone bases TIMs for advanced electronics.

Patterned liquid metal embedded in brush-shaped polymers for dynamic thermal management

Interface thermal resistance has become a crucial barrier to effective thermal management in high-performance electronics and sensors. The growing complexity of operational conditions, such as irregular and dynamic surfaces, demands thermal interface materials (TIMs) to possess high thermal conductivity and soft elasticity. However, developing materials that simultaneously combine soft elasticity and high thermal conductivity remains a challenging task. Herein, we utilize a vertically oriented graphene aerogel (VGA) and rationally design liquid metal (LM) networks to achieve directional and adjustable pathways within the composite. Subsequently, we leverage the advantages of the low elastic modulus and high deformation capabilities of brush-shaped polydimethylsiloxane (BPDMS), together with the bicontinuous thermal conduction path constructed by VGA and LM networks. Ultimately, the designed composite of patterned liquid metal/vertically oriented graphene aerogel/brush-shaped PDMS (LM-VGA/BPDMS) shows a high thermal conductivity (7.11 W m-1 K-1), an ultra-low elastic modulus (10.13 kPa), excellent resilience, and a low interface thermal resistance (14.1 K mm2 W-1). This LM-VGA/BPDMS soft composite showcases a stable heat dissipation capability at dynamically changing interfaces, as well as excellent adaptability to different irregular surfaces. This strategy holds important application prospects in the fields of interface thermal management and thermal sensing in extremely complex environments.

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.

Can Adhesion Energy Optimize Interface Thermal Resistance at a Soft/Hard Material Interface?

Thermal resistance at a soft/hard material interface plays an undisputed role in the development of electronic packaging, sensors, and medicine. Adhesion energy and phonon spectra match are two crucial parameters in determining the interfacial thermal resistance (ITR), but it is difficult to simultaneously achieve these two parameters in one system to reduce the ITR at the soft/hard material interface. Here, we report a design of an elastomer composite consisting of a polyurethane-thioctic acid copolymer and microscale spherical aluminum, which exhibits both high phonon spectra match and high adhesion energy (>1000 J/m²) with hard materials, thus leading to a low ITR of 0.03 mm²·K/W. We further develop a quantitative physically based model connecting the adhesion energy and ITR, revealing the key role the adhesion energy plays. This work serves to engineer the ITR at the soft/hard material interface from the aspect of adhesion energy, which will prompt a paradigm shift in the development of interface science.

Degradation of sulfamethoxazole by super-hydrophilic MoS2 sponge co-catalytic Fenton: Enhancing Fe2+/Fe3+ cycle and mass transfer

To promote the cycle of Fe²⁺/Fe³⁺ in co-catalytic Fenton and enhance mass transfer in an external circulation sequencing batch packed bed reactor (ECSPBR), super-hydrophilicity MoS₂ sponge (TMS) modified by tungstosilicic acid (TA) was prepared for efficiently degrading sulfamethoxazole (SMX) antibiotics in aqueous solution. The influence of hydrophilicity of co-catalyst on co-catalytic Fenton and the advantages of ECSPBR were systematically studied through comparative research methods. The results showed that the super hydrophilicity increased the contact between Fe²⁺ and Fe³⁺ with TMS, then accelerated Fe²⁺/Fe³⁺ cycle. The max Fe²⁺/Fe³⁺ ratio of TMS co-catalytic Fenton (TMS/Fe²⁺/H₂O₂) was 1.7 times that of hydrophobic MoS₂ sponge (CMS) co-catalytic Fenton. SMX degradation efficiency could reach over 90% under suitable conditions. The structure of TMS remained unchanged during the process, and the max dissolved concentration of Mo was lower than 0.06 mg/L. Additionally, the catalytic activity of TMS could be restored by a simple re-impregnation. The external circulation of the reactor was conducive to improving the mass transfer and the utilization rate of Fe²⁺ and H₂O₂ during the process. This study offered new insights to prepare a recyclable and hydrophilic co-catalyst and develop an efficient co-catalytic Fenton reactor for organic wastewater treatment.

Molecular design of a highly matched and bonded interface achieves enhanced thermal boundary conductance

Interfacial binding and phonon mismatch are two crucial parameters in determining thermal boundary conductance. However, it is difficult for polymer/metal interfaces to possess both significant interfacial binding and weak phonon mismatch to achieve enhanced thermal boundary conductance. Herein, we circumvent this inherent trade-off by synthesizing a polyurethane and thioctic acid (PU-TA) copolymer with multiple hydrogen bonds and dynamic disulfide bonds. Using PU-TA/aluminum (Al) as a model interface, we demonstrate that the thermal boundary conductance of the PU-TA/Al interfaces measured by transient thermoreflectance is 2-5 times higher than that of traditional polymer/Al interfaces, which is attributed to the highly matched and bonded interface. Furthermore, a correlation analysis is developed, which demonstrates that interfacial binding has a greater impact than phonon mismatch on thermal boundary conductance at a highly matched interface. This work provides a systematic understanding of the relative contributions of the two dominant mechanisms to thermal boundary conductance by tailoring the polymer structure, which has applications in thermal management materials.

Thermally conductive and compliant polyurethane elastomer composites by constructing a tri-branched polymer network

Most elastomers suffer from poor thermal conductivity, which limits their further applications in various fields, especially for electronic devices. A common method to enhance thermal conductivity is to introduce thermally conductive fillers into elastomers. Unfortunately, thermal conductivity and compliance are often correlated and coupled: large amounts of fillers are required to increase thermal conductivity while damaging the compliance dramatically. In this study, we report thermally conductive and compliant polyurethane elastomer composites by constructing a tri-branched polymer network. The resultant polyurethane elastomer composites exhibit excellent superhigh stretchability (2000%), low Young's modulus (640 kPa), and low thermal resistance (0.11 K cm² W^-1). Experimental rheology and a theoretical tube model are employed to study the nature of the high compliant tri-branched polymer network. Furthermore, the remarkable flexibility of our elastomer composite and heat dissipation act as thermal interface materials in the thermal management of flexible electronics. These findings advance our understanding on the rational design of the polymer frameworks of thermal composites, improving our ability to predict, design, and leverage their unique properties for future applications.

Tailoring Dense, Orientation-Tunable, and Interleavedly Structured Carbon-Based Heat Dissipation Plates

The controllability of the microstructure of a compressed hierarchical building block is essential for optimizing a variety of performance parameters, such as thermal management. However, owing to the strong orientation effect during compression molding, optimizing the alignment of materials perpendicular to the direction of pressure is challenging. Herein, to illustrate the effect of the ordered microstructure on heat dissipation, thermally conductive carbon-based materials are fabricated by tailoring dense, orientation-tunable, and interleaved structures. Vertically aligned carbon nanotube arrays (VACNTs) interconnected with graphene films (GF) are prepared as a 3D core-ordered material to fabricate compressed building blocks of O-VA-GF and S-VA-GF. Leveraging the densified interleaved structure offered by VACNTs, the hierarchical O-VA-GF achieves excellent through-plane (41.7 W m^-1 K^-1 ) and in-plane (397.9 W m^-1 K^-1 ) thermal conductivities, outperforming similar composites of S-VA-GF (through-plane: 10.3 W m^-1 K^-1 and in-plane: 240.9 W m^-1 K^-1 ) with horizontally collapsed carbon nanotubes. As heat dissipation plates, these orderly assembled composites yield a 144% and 44% enhancement in the cooling coefficient compared with conventional Si₃ N₄ for cooling high-power light-emitting diode chips.

Enhanced in-plane thermal conductivity of polyimide-based composites via in situ interfacial modification of graphene

Interfacial thermal resistance is the main barrier restricting the heat dissipation of thermal management materials in electronic equipment. The interface structure formed by covalent bonding is an effective way to promote interfacial heat transfer. Herein, an integrated composite with multi-aspect covalent bonding beneficial for heat transmission is constructed by polyimide (PI) polymerization with maleimide modified graphene nanosheets (M@GNS). The interfacial structure with low thermal resistance built by covalent bonding and oriented graphene arrangement initiated by the coating process makes the in-plane thermal conductivity of the composite as high as 16.10 W m^-1 K^-1. Finite element simulation and 1000 bending tests are carried out to further verify the performance advantages of the integrated structure in the internal thermal diffusion and long-term use of the composite. M@GNS/PI with integrated structure provides extra heat transfer channels for heat dissipation, possibly providing an effective way to address the traditional thermal accumulation issue of electronic devices.

Multifunctional Thermally Conductive Composite Films Based on Fungal Tree-like Heterostructured Silver Nanowires@Boron Nitride Nanosheets and Aramid Nanofibers

Thermal conduction for electronic equipment has grown in importance in light of the burgeoning of 5G communication. It is imperatively desired to design highly thermally conductive fillers and polymer composite films with prominent Joule heating characteristics and extensive mechanical properties. In this work, "solvothermal & in situ growth" method is carried out to prepare "Fungal tree"-like hetero-structured silver nanowires@boron nitride nanosheet (AgNWs@BNNS) thermally conductive fillers. The thermally conductive AgNWs@BNNS/ANF composite films are obtained by the method of "suction filtration self-assembly and hot-pressing". When the mass fraction of AgNWs@BNNS is 50 wt%, AgNWs@BNNS/ANF composite film presents the optimal thermal conductivity coefficient of 9.44 W/(m ⋅ K) and excellent tensile strength of 136.6 MPa, good temperature-voltage response characteristics, superior electrical stability and reliability, which promise a wide application potential in 5G electronic devices.

Thermal Interface Materials with High Thermal Conductivity and Low Young's Modulus Using a Solid-Liquid Metal Codoping Strategy

Thermal interface materials (TIMs), as typical thermal functional materials, are highly required to possess both high thermal conductivity and low Young's modulus. However, the naturally synchronized change in the thermal and mechanical properties seriously hinders the development of high-performance TIMs. To tackle such a dilemma, a strategy of codoping solid fillers and liquid metal fillers into polymer substrates is proposed in this study. This strategy includes a large amount of liquid metals that play the role of thermal paths and a small amount of uniformly dispersed solid fillers that further enhance heat conduction. Through the synergistic effect of the liquid metal and solid fillers, the thermal conductivity can be improved, and Young's modulus can be kept small simultaneously. A typical TIM with a volume of 55% gallium-based liquid metal and 15% copper particles as fillers has a thermal conductivity of 3.94 W/(m·K) and a Young's modulus of 699 kPa, which had the maximum thermomechanical performance coefficient compared with liquid metal TIMs and solid filler-doped TIMs. In addition, the thermal conductivity of the solid-liquid metal codoped TIM increased sharply with an increase of liquid metal content, and Young's modulus increased rapidly with an increase of the volume ratio of copper and polymer. The high-low-temperature cycling test and large-size light-emitting diode (LED) application demonstrated that this TIM had stable physical performance. The synergistic effect of the solid fillers and liquid metal fillers provides a broad space to solve the classic tradeoff issue of the mechanical and thermal properties of composites.

Liquid Metal-Assisted High-Efficiency Exfoliation of Boron Nitride for Electrically Insulating Heat-Spreader Film

Boron nitride nanosheets (BNNSs) are regarded as promising two-dimensional materials in thermally conductive yet electrically insulating applications. Attributed to the strong interlayer "lip-lip" interactions in bulk hexagonal boron nitride (h-BN), high-efficiency exfoliation and scalable fabrication of BNNSs via the top-down strategies remain formidable challenges. Herein, an interesting observation is manifested that gallium-based liquid metal (LM) forming robust coordination interactions with h-BN helps reduce the lip-lip interlayer interactions and thus facilitates successful exfoliation under intense shearing force. For example, employing the ball-milling technique, the BNNS yield can increase to 41.21% with the assistance of LM at only 2 h milling time. Its exfoliation efficiency (yield/time) reaches as high as 26.72%/h, more than 2-fold that of other previously reported methods, including sonication and other ball-milling methods. Moreover, the exfoliated BNNSs are still found to be highly electrically insulating with a band gap of 4.65 eV, showing prospective potential in thermally conductive yet electrical insulating applications. As a proof of concept, a microwave-transparent heat spreader (cellulose nanofiber/BNNSs) is fabricated and verified for applications in high-frequency thermal-management fields.

Bifunctional Liquid Metals Allow Electrical Insulating Phase Change Materials to Dual-Mode Thermal Manage the Li-Ion Batteries

Phase change materials (PCMs) are expected to achieve dual-mode thermal management for heating and cooling Li-ion batteries (LIBs) according to real-time thermal conditions, guaranteeing the reliable operation of LIBs in both cold and hot environments. Herein, we report a liquid metal (LM) modified polyethylene glycol/LM/boron nitride PCM, capable of dual-mode thermal managing the LIBs through photothermal effect and passive thermal conduction. Its geometrical conformation and thermal pathways fabricated through ice-template strategy are conformable to the LIB's structure and heat-conduction characteristic. Typically, soft and deformable LMs are modified on the boron nitride surface, serving as thermal bridges to reduce the contact thermal resistance among adjacent fillers to realize high thermal conductivity of 8.8 and 7.6 W m^-1 K^-1 in the vertical and in-plane directions, respectively. In addition, LM with excellent photothermal performance provides the PCM with efficient battery heating capability if employing a controllable lighting system. As a proof-of-concept, this PCM is manifested to heat battery to an appropriate temperature range in a cold environment and lower the working temperature of the LIBs by more than 10 °C at high charging/discharging rate, opening opportunities for LIBs with durable working performance and evitable risk of thermal runaway.