Self-Healing High Strength and Thermal Conductivity of 3D Graphene/PDMS Composites by the Optimization of Multiple Molecular Interactions

Imparting Ultrahigh Strength to Polymers via a New Concept Strategy of Construction of up to Duodecuple Hydrogen Bonding among Macromolecular Chains

Interconnecting macromolecules via multiple hydrogen bonds (H-bonds) can simultaneously strengthen and toughen polymers, but material synthesis becomes extremely difficult with increasing number of H-bonding donors and acceptors; therefore, most reports are limited to triple and quadruple H-bonds. Herein, this bottleneck is overcome by adopting a quartet-wise approach of constructing H-bonds instead of the traditional pairwise method. Thus, large multiple hydrogen bonds can be easily established, and the supramolecular interactions are further reinforced. Especially, when such multiple H-bond motifs are embedded in polymers, four macromolecular chains-rather than two as usual-are tied, distributing the applied stress over a larger volume and more significantly improving the overall mechanical properties. Proof-of-concept studies indicate that the proposed intermolecular multiple H-bonds (up to duodecuple) are readily introduced in polyurethane. A record-high tensile strength (105.2 MPa) is achieved alongside outstanding toughness (352.1 MJ m-3), fracture energy (480.7 kJ m-2), and fatigue threshold (2978.4 J m-2). Meantime, the polyurethane has acquired excellent self-healability and recyclability. This strategy is also applicable to nonpolar polymers, such as polydimethylsiloxane, whose strength (15.3 MPa) and toughness (50.3 MJ m-3) are among the highest reported to date for silicones. This new technique has good expandability and can be used to develop even more and stronger polymers.

Pearl-Inspired Intelligent Marine Hetero Nanocomposite Coating Based on "Brick&Mortar" Strategy: Anticorrosion Durability and Switchable Antifouling

Corrosion activities and biofouling pose significant challenges for marine facilities, resulting in substantial economic losses. Inspired by the "brick&mortar" structure of pearls, a novel nanocomposite coating (Pun-HJTx) with long-lasting anticorrosion and intelligent antifouling modes is fabricated by integrating a compatible MoS2/MXene heterostructure as the "brick" into a polyurea-modified PDMS (Pun) acting as "mortar." Notably, the presence of multiple hydrogen bonds within the coating effectively reduces the pinholes resulted from solution volatilizing. In the dark, where fouling adhesion and microbial corrosion activities are weakened, the MoS2/MXene plays a role in contact bactericidal action. Conversely, during daylight when fouling adhesion and microbial corrosion activities intensify, the coating releases reactive oxygen species (such as hydroxyl radicals and superoxide ions) to counteract fouling adhesion. Additionally, the coating exhibits multisource self-healing performance under heated or exposed to light (maximum self-healing rate can reach 99.46%) and proves efficient self-cleaning performance and adhesion strength (>2.0 Mpa), making it highly suitable for various practical marine applications. Furthermore, the outstanding performance of the Pun-HJT1 is maintained for ≈180 days in real-world marine conditions, which proving its practicality and feasibility in real shallow sea environments.

Regulatable Orthotropic 3D Hybrid Continuous Carbon Networks for Efficient Bi-Directional Thermal Conduction

Vertically oriented carbon structures constructed from low-dimensional carbon materials are ideal frameworks for high-performance thermal interface materials (TIMs). However, improving the interfacial heat-transfer efficiency of vertically oriented carbon structures is a challenging task. Herein, an orthotropic three-dimensional (3D) hybrid carbon network (VSCG) is fabricated by depositing vertically aligned carbon nanotubes (VACNTs) on the surface of a horizontally oriented graphene film (HOGF). The interfacial interaction between the VACNTs and HOGF is then optimized through an annealing strategy. After regulating the orientation structure of the VACNTs and filling the VSCG with polydimethylsiloxane (PDMS), VSCG/PDMS composites with excellent 3D thermal conductive properties are obtained. The highest in-plane and through-plane thermal conductivities of the composites are 113.61 and 24.37 W m-1 K-1, respectively. The high contact area of HOGF and good compressibility of VACNTs imbue the VSCG/PDMS composite with low thermal resistance. In addition, the interfacial heat-transfer efficiency of VSCG/PDMS composite in the TIM performance was improved by 71.3% compared to that of a state-of-the-art thermal pad. This new structural design can potentially realize high-performance TIMs that meet the need for high thermal conductivity and low contact thermal resistance in interfacial heat-transfer processes.

Bioinspired H-Bonding Connected Gradient Nanostructure Actuators Based on Cellulose Nanofibrils and Graphene

The construction of flexible actuators with ultra-fast actuation and robust mechanical properties is crucial for soft robotics and smart devices, but still remains a challenge. Inspired by the unique mechanism of pinecones dispersing seeds in nature, a hygroscopic actuator with interlayer network-bonding connected gradient structure is fabricated. Unlike most conventional bilayer actuator designs, the strategy leverages biobased polyphenols to construct strong interfacial H-bonding networks between 1D cellulose nanofibers and 2D graphene oxide, endowing the materials with high tensile strength (172 MPa) and excellent toughness (6.64 MJ m-3). Furthermore, the significant difference in hydrophilicity between GO and rGO, along with the dense interlayer H-bonding, enables ultra-fast water exchange during water absorption and desorption processes. The resulted actuator exhibits ultra-fast driving speed (154° s-1), excellent pressure-resistant and cyclic stability. Taking advantages of these benefits, the actuator can be fabricated into smart devices (such as smart grippers, humidity control switches) with significant potential for practical applications. The presented approach to constructing interlayer H-bonding in gradient structures is instructive for achieving high performance and functionalization of biomass nanomaterials and the complex of 1D/2D nanomaterials.

Epoxy Resins With Controllable "Thermally Conductive-Self-Healing" Synergies: a New Material to Meet the Needs of Flexible Electronic Devices

With the popularization of 5G technology and artificial intelligence, thermally conductive epoxies with self-healing ability will be widely used in flexible electronic materials. Although many compounds containing both performances have been synthesized, there is little systematic theory to explain the coordination mechanism. In this paper, alkyl chains of different lengths were introduced to epoxies to discuss the thermally conductive, the self-healing performance, and the synergistic effect. A series of electronic-grade biphenyl epoxies (4,4'-bis(oxiran-2-ylmethoxy)-1,1'-biphenyl (1), 4,4'-bis(2-(oxiran-2-yl)ethoxy)-1,1'-biphenyl (2), 4,4'-bis(3-(oxiran-2-yl)propoxy)-1,1'-biphenyl (3), and 4,4'-bis(4-(oxiran-2-yl)butoxy)-1,1'-biphenyl (4) were synthesized and characterized. Furthermore, they were cured with decanedioic acid to produce polymers. Results showed that alkyl chains can both affect the two properties, and the epoxies suitable for specific application scenarios can be prepared by adjusting the length of alkyl chains. In terms of thermal conductivity, compound 1 was a most promising material. However, compound 4 was expected to be utilized in flexible electronic devices because of its acceptable thermal conductivity, self-healing ability, transparency, and flexibility.

High-toughness, extensile and self-healing PDMS elastomers constructed by decuple hydrogen bonding

Elastomers are widely used in traditional industries and new intelligent fields. However, they are inevitably damaged by electricity, heat, force, etc. during the working process. With the continuous improvement of reliability and environmental protection requirements in human production and living, it is vital to develop elastomer materials with good mechanical properties that are not easily damaged and can self-heal after being damaged. Nevertheless, there are often contradictions between mechanical properties and self-healing as well as toughness, strength, and ductility. Herein, a strong and dynamic decuple hydrogen bonding based on carbon hydrazide (CHZ) is reported, accompanied with soft polydimethylsiloxane (PDMS) chains to prepare self-healing (efficiency 98.7%), recyclable, and robust elastomers (CHZ-PDMS). The strategy of decuple hydrogen bonding will significantly impact the study of the mechanical properties of elastomers. High stretchability (1731%) and a high toughness of 23.31 MJ m-3 are achieved due to the phase-separated structure and energy dissipation. The recyclability of CHZ-PDMS further supports the concept of environmental protection. The application of CHZ-PDMS as a flexible strain sensor exhibited high sensitivity.

3D Printable Active Hydrogels with Supramolecular Additive-Driven Adaptiveness

Smart hydrogels are a promising candidate for the development of next-generation soft materials due to their stimuli-responsiveness, deformability, and biocompatibility. However, it remains challenging to enable hydrogels to actively adapt to various environmental conditions like living organisms. In this work, supramolecular additives are introduced to the hydrogel matrix to confer environmental adaptiveness. Specifically, their microstructures, swelling behaviors, mechanical properties, and transparency can adapt to external environmental conditions. Moreover, the presence of hydrogen bonding provides the hydrogel with applicable rheological properties for 3D extrusion printing, thus allowing for the facile preparation of thickness-dependent camouflage and multistimuli responsive complex. The environmentally adaptive hydrogel developed in this study offers new approaches for manipulating supramolecular interactions and broadens the capability of smart hydrogels in information security and multifunctional integrated actuation.

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.

Molecular Dynamics Simulation on the Heat Transfer in the Cross-Linked Poly(dimethylsiloxane)

In this work, the effect of cross-linking degree and stretching on the thermal conductivity of poly(dimethylsiloxane) (PDMS) is explored by performing a molecular dynamics simulation. Our results demonstrate that the thermal conductivity of PDMS exhibits a monotonous rise with an increase in the cross-linking degree. By decomposing the total heat flux into three microscopic heat transfer modes, the high cross-linking degree improves the contribution from bonding interactions to the heat transfer more than that from the nonbonding interactions. An analysis of the vibrational density of states shows a blue-shift of the vibrational modes at low frequencies, indicating a large phonon group velocity due to the strong interchain bonding interaction. From the spectral distribution of heat flux, the spectral contributions are shifted toward the higher frequencies with the increasing cross-linking degree, which reflects more contribution from the high-frequency modes to the heat transfer. Stretching can improve the thermal conductivity parallel to the tensile direction with the increase in strain. This is mainly due to the further improved contribution of bonding interactions or high-frequency modes to heat transfer. Interestingly, the anisotropy of the thermal conductivity first decreases and then increases with the increasing cross-linking degree. Our study conducts a detailed investigation of the thermal conductivity of cross-linked PDMS, providing guidance on the application of thermal interface materials.

Exploring Lipoic Acid-Mediated Dynamic Bottlebrush Elastomers as a New Platform for the Design of High-Performance Thermally Conductive Materials

The development of high-performance thermally conductive interface materials is the key to unlocking the serious bottleneck of modern microelectronic technology through enhanced heat dispersion. Existing methods that utilize silicone composites rely either on loading large doses of randomly distributed thermal conductive fillers or on filling prealigned thermal conductive scaffolds with liquid silicone precursors. Both approaches suffer from several limitations in terms of physical traits and processability. We describe an alternative approach in which malleable silicone matrices, based on the dynamic cyclic disulfide nature cross-linker (α-lipoic acid), are readily prepared using ring-opening polymerization. The mechanical properties of the resultant dynamic silicone matrix are readily tunable. Stress-dependent depolymerization of the disulfide network demonstrates the ability to reprocess the silicone elastomer matrix, which allows for the fabrication of highly efficient thermal conductive composites with a 3D interconnecting, thermally conductive network (3D-graphite/MxBy composites) via in situ methods. Applications of the composites as thermal dispersion interface materials are demonstrated by LEDs and CPUs, suggesting great potential in advanced electronics.

Autonomous Healable Elastomers with High Elongation, Stiffness, and Fatigue Resistance

Although self-healing elastomers have been developed in a great breakthrough, it is still a challenge to develop one kind of material that can respond to the fracture instantly even though this characteristic plays an essential role in emergency circumstances. Herein, we adopt free radical polymerization to construct one polymer network equipped with two weak interactions (dipole-dipole interaction and hydrogen bonding). The elastomer we synthesized has a high self-healing efficiency (100%) and a very short healing time (3 min) in an air atmosphere, and it can also self-heal in seawater, showing an ideal healing efficiency of >80%. Additionally, on account of its high elongation (>1000%) and antifatigue capacity (no rupture after loading-unloading 2000 times), the elastomer can be utilized in a wide range of applications, including e-skin and soft robot fields.

Self-Healable Elastomeric Network with Dynamic Disulfide, Imine, and Hydrogen Bonds for Flexible Strain Sensor

Self-healable and stretchable elastomeric material is essential for the development of flexible electronics devices to ensure their stable performance. In this study, a strain sensor (PIH₂ T₁ -tri/CNT-3) composed of self-repairable crosslinked elastomer substrate (PIH₂ T₁ -tri, containing multiple reversible repairing sites such as disulfide, imine, and hydrogen bonds) and conductive layer (carbon nanotube, CNT) was prepared. The PIH₂ T₁ -tri elastomer had excellent self-healing ability (healing efficiency=91 %). It exhibited good mechanical integrity in terms of elongation at break (672 %), tensile strength (1.41 MPa). The Young's modulus (0.39 MPa) was close to that of human skin. The PIH₂ T₁ -tri/CNT-3 sensor also demonstrated an effective self-healing function for electrical conduction and sensing property. Meanwhile, it had high sensitivity (gauge factor (GF)=24.1), short response time (120 ms), and long-term durability (4000 cycles). This study offers a novel self-healable elastomer platform with carbon based conductive components to develop flexible strain sensors towards high performance soft electronics.

Highly Thermally Conductive Adhesion Elastomer Enhanced by Vertically Aligned Folded Graphene

Heat and stress transfer at an interface are crucial for the contact-based tactile sensing to measure the temperature, morphology, and modulus. However, fabricating a smart sensing material that combines high thermal conductivity, elasticity, and good adhesion is challenging. In this study, a composite is fabricated using a directional template of vertically aligned folded graphene (VAFG) and a copolymer matrix of poly-2-[[(butylamino)carbonyl]oxy]ethyl ester and polydimethylsiloxane, vinyl-end-terminated polydimethylsiloxane (poly(PBAx-ran-PDMS)). With optimized chemical cross-linking and supermolecular interactions, the poly(PBA-ran-PDMS)/VAFG exhibits high thermal conductivity (15.49 W m^-1 K^-1 ), an high elastic deformation, and an interfacial adhesion of up to 6500 N m^-1 . Poly(PBA-ran-PDMS)/VAFG is highly sensitive to temperature and pressure and demonstrates a self-learning capacity for manipulator applications. The smart manipulator can distinguish and selectively capture unknown materials in the dark. Thermally conductive, elastic, and adhesive poly(PBA-ran-PDMS)/VAFG can be developed into core materials in intelligent soft robots.

Parallel Structure Enhanced Polysilylaryl-enyne/Ca0.9La0.067TiO3 Composites with Ultra-High Dielectric Constant and Thermal Conductivity

With the rapid development of the microwave communication industry, microwave dielectric materials have been widely studied as the medium of signal transmission. Nowadays, with the increase in communication frequency, devices are miniaturized, and dielectric materials are required to have higher dielectric constants. At the same time, the miniaturization of devices brings about an increase in power density, which puts forward higher requirements for the thermal conductivity of materials. In this work, polysilylaryl-enyne (PSAE) and Ca_0.9La_0.067TiO₃ (CLT) were chosen as the matrix and filler, respectively, to construct a parallel model composite through a freeze casting method and a 0-3 model composite through the direct mixing method, respectively. After comparing the microstructures of the two models, their dielectric properties and thermal conductivity were measured and simulated. The parallel model composites in the stable range possess uniform parallel structures, and the solid content limit for them could be as high as 73.2%, which is much higher than that of the 0-3 model composites. While the 0-3 model composite possesses an optimal dielectric constant of 25.4 (@10 GHz) and a thermal conductivity of 0.965 W·m^-1·K^-1, the parallel model composite possesses a 2 times higher dielectric constant of 76.2 (@10 GHz) and a 1 times higher thermal conductivity of 2.095 W·m^-1·K^-1. Since the parallel model composite possesses much higher dielectric constant and thermal conductivity than traditional 0-3 model composites, it can be an excellent candidate for microwave communication.

Mechano-Regulable and Healable Silk-Based Materials for Adaptive Applications

Mechanically adaptive materials responsive to environmental stimuli through changing mechanical properties are highly attractive in intelligent devices. However, it is hard to regulate the mechanical properties of most mechanically adaptive materials in a facile way. Moreover, it remains a challenge to achieve mechano-regulable materials with mechanical properties ranging from high strength to extreme toughness. Here, inspired by the reversible nanofibril network structure of skeletal muscle to achieve muscle strength regulation, we present a mechano-regulable biopolymeric silk fibroin (SF) composite through regulating dynamic metal-ligand coordination bonds by using water molecules as competitive regulators. Efficient interfacial hydrogen bonds between tannic acid-tungsten disulfide nanohybrids and the SF matrix endow the composite with high mechanical strength and self-healing ability. The resulting composite exhibits 837-fold change in Young's modulus (5.77 ± 0.61 GPa to 6.89 ± 0.64 MPa) after water vapor triggering, high mechanical properties (72.5 ± 6.3 MPa), and excellent self-healing efficiency (nearly 100%). The proof-of-concept ultraconformable iontronic skin and smart actuators are demonstrated, thereby providing a direction for future self-adaptive smart device applications.

Advances and Challenges of Self-Healing Elastomers: A Mini Review

In the last few decades, self-healing polymeric materials have been widely investigated because they can heal the damages spontaneously and thereby prolong their service lifetime. Many ingenious synthetic procedures have been developed for fabricating self-healing polymers with high performance. This mini review provides an impressive summary of the self-healing polymers with fast self-healing speed, which exhibits an irreplaceable role in many intriguing applications, such as flexible electronics. After a brief introduction to the development of self-healing polymers, we divide the development of self-healing polymers into five stages through the perspective of their research priorities at different periods. Subsequently, we elaborated the underlying healing mechanism of polymers, including the self-healing origins, the influencing factors, and direct evidence of healing at nanoscopic level. Following this, recent advance in realizing the fast self-healing speed of polymers through physical and chemical approaches is extensively overviewed. In particular, the methodology for balancing the mechanical strength and healing ability in fast self-healing elastomers is summarized. We hope that it could afford useful information for research people in promoting the further technical development of new strategies and technologies to prepare the high performance self-healing elastomers for advanced applications.

Vertical Alignment of Anisotropic Fillers Assisted by Expansion Flow in Polymer Composites

Orientation control of anisotropic one-dimensional (1D) and two-dimensional (2D) materials in solutions is of great importance in many fields ranging from structural materials design, the thermal management, to energy storage. Achieving fine control of vertical alignment of anisotropic fillers (such as graphene, boron nitride (BN), and carbon fiber) remains challenging. This work presents a universal and scalable method for constructing vertically aligned structures of anisotropic fillers in composites assisted by the expansion flow (using 2D BN platelets as a proof-of-concept). BN platelets in the silicone gel strip are oriented in a curved shape that includes vertical alignment in the central area and horizontal alignment close to strip surfaces. Due to the vertical orientation of BN in the central area of strips, a through-plane thermal conductivity as high as 5.65 W m^-1 K^-1 was obtained, which can be further improved to 6.54 W m^-1 K^-1 by combining BN and pitch-based carbon fibers. The expansion-flow-assisted alignment can be extended to the manufacture of a variety of polymer composites filled with 1D and 2D materials, which can find wide applications in batteries, electronics, and energy storage devices.

Enhanced Thermal Conductivities of Liquid Crystal Polyesters from Controlled Structure of Molecular Chains by Introducing Different Dicarboxylic Acid Monomers

Enhancing thermal conductivity coefficient (λ) of liquid crystal polyesters would further widen their application in electronics and electricals. In this work, a kind of biphenyl-based dihydroxy monomer is synthesized using 4, 4'-biphenyl (BP) and triethylene glycol (TEG) as raw material, which further reacts with three different dicarboxylic acids (succinic acid, p-phenylenediacetic acid, and terephthalic acid, respectively) by melt polycondensation to prepare intrinsically highly thermally conductive poly 4', 4”'-[1, 2-ethanediyl-bis(oxy-2, 1-ethanediyloxy)]-bis(p-hydroxybiphenyl) succinate (PEOS), poly 4', 4”'-[1, 2-ethanediyl-bis(oxy-2, 1-ethanediyloxy)]-bis(p-hydroxybiphenyl) p-phenyldiacetate (PEOP) and poly 4', 4”'-[1, 2-ethanediyl-bis(oxy-2, 1-ethanediyloxy)]-bis(p-hydroxybiphenyl) terephthalate (PEOT), collectively called biphenyl-based liquid crystal polyesters (B-LCPE). The results show that B-LCPE possess the desired molecular structure, exhibit smectic phase in liquid crystal range and semicrystalline polymers at room temperature, and possess excellent intrinsic thermal conductivities, thermal stabilities, and mechanical properties. λ of PEOT is 0.51 W/(m·K), significantly exceeds that of polyethylene terephthalate (0.15 W/(m·K)) which has similar molecular structure with PEOT, and also higher than that of PEOS (0.32 W/(m·K)) and PEOP (0.38 W/(m·K)). The corresponding heat resistance index (T_HRI), elasticity modulus, and hardness of PEOT are 174.6°C, 3.6 GPa, and 154.5 MPa, respectively, and also higher than those of PEOS (162.2°C, 1.8 GPa, and 83.4 MPa) and PEOP (171.8°C, 2.3 GPa, and 149.6 MPa).

Interfacial Coordination Interaction Enables Soft Elastomer Composites High Thermal Conductivity and High Toughness

Soft elastomers have attracted wide applications, such as soft electronic devices and soft robotics, due to their ability to undergo large deformation with a small external force. Most elastomers suffer from poor toughness and thermal conductivity, which limits their use. The addition of inorganic fillers can enhance the thermal conductivity and toughness, but it deteriorates the softness (low Young's modulus and high stretchability). Integrating thermal conductivity, toughness, and softness into one elastomer is still a challenge. Here, we report a strategy of interfacial coordination interaction to achieve soft elastomer composites with high thermal conductivity and high toughness. We demonstrate the strategy by using poly(lipoic acid) elastomer and silver-coated aluminum filler as model, where silver-sulfur coordination cross-links are formed at the interface. The resultant elastomer composite shows high streachability (450%), high thermal conductivity (2.35 W m-1 K-1), low modulus (321 kPa), and high toughness (3496 J m-2), which cannot be achieve in existing elastomers. The time domain thermoreflectance technique demonstrates that the silver-sulfur coordination interaction lowers the interfacial thermal resistance, resulting in enhanced thermal conductivity of the elastomer composites. The excellent softness stems from lower bonding energy of the silver-sulfur coordination cross-links compared with covalent chemical cross-links. The high toughness also benefits from the interfacial silver-sulfur coordination interaction that can dissipate more energy upon deformation. We further demonstrate the potential application of the thermally conductive, tough, and soft elastomer composites for thermal management of chip and soft electronic devices.

Highly Thermally Conductive Polymer/Graphene Composites with Rapid Room-Temperature Self-Healing Capacity

Composites that can rapidly self-healing their structure and function at room temperature have broad application prospects. However, in view of the complexity of composite structure and composition, its self-heal is facing challenges. In this article, supramolecular effect is proposed to repair the multistage structure, mechanical and thermal properties of composite materials. A stiff and tough supramolecular frameworks of 2-[[(butylamino)carbonyl]oxy]ethyl ester (PBA)-polydimethylsiloxane (PDMS) were established using a chain extender with double amide bonds in a side chain to extend prepolymers through copolymerization. Then, by introducing the copolymer into a folded graphene film (FGf), a highly thermally conductive composite of PBA-PDMS/FGf with self-healing capacity was fabricated. The ratio of crosslinking and hydrogen bonding was optimized to ensure that PBA-PDMS could completely self-heal at room temperature in 10 min. Additionally, PBA-PDMS/FGf exhibits a high tensile strength of 2.23 ± 0.15 MPa at break and high thermal conductivity of 13 ± 0.2 W m^-1 K^-1; of which the self-healing efficiencies were 100% and 98.65% at room temperature for tensile strength and thermal conductivity, respectively. The excellent self-healing performance comes from the efficient supramolecular interaction between polymer molecules, as well as polymer molecule and graphene. This kind of thermal conductive self-healing composite has important application prospects in the heat dissipation field of next generation electronic devices in the future.

Flexible thermal conductive Al2O3@siloxane composite with rapid self-healing property based on carboxyl-amine dynamic reversible bonds

Thermal interface materials (TIMs) are one of the efficacious ways to alleviate the heat accumulation problem of microelectronics devices. However, conventional TIMs based on polydimethylsiloxane (PDMS) always suffer from mechanical damage, leading to shortened service life or loss of thermal conductivity. In this work, we fabricated a high-thermal conductivity and fast self-healable Al₂O₃@siloxane composite by hydrosilylation reaction. The siloxane matrix consisted of thermosetting silicone rubber matrix (SR) and heat reversibility matrix (SCNR); the SR was synthesized via hydrosilylation between silicon hydrogen bond and vinyl, the SCNR was fabricated by thermal-curing between amino and carboxyl functionalized PDMS. Different sized spherical Al₂O₃ fillers were introduced into the SR/SCNR matrix system to construct the Al₂O₃@SR/SCNR composites. By adjusting the ratio of SR/SCNR, the obtained composites can achieve flexibility, self-healing and high filling simultaneously. It is notable that the self-healing efficiency of the composite is high, up to 95.6% within 3 minutes with 6.7 wt% mass ratio of SCNR/SR; these fast self-healing behaviors benefit from the assistance of thermal diffusion by 3D heat conduction pathways on the rearrangement of the dynamic cross-linked network. The resultant composites also exhibited the optimal thermal conductivity of 5.85 W mK⁻¹. This work provides a novel approach for constructing longer service life and high thermal conductivity multifunctional TIM based PDMS.

Thermal interface materials (TIMs) are one of the efficacious ways to alleviate the heat accumulation problem of microelectronics devices.

Boronic Acid Esters and Anhydrates as Dynamic Cross-Links in Vitrimers

Growing environmental awareness imposes on polymer scientists the development of novel materials that show a longer lifetime and that can be easily recycled. These challenges were largely met by vitrimers, a new class of polymers that merges properties of thermoplastics and thermosets. This is achieved by the incorporation of dynamic covalent bonds into the polymer structure, which provides high stability at the service temperature, but enables the processing at elevated temperatures. Numerous types of dynamic covalent bonds have been utilized for the synthesis of vitrimers. Amongst them, boronic acid-based linkages, namely boronic acid esters and boroxines, are distinguished by their quick exchange kinetics and the possibility of easy application in various polymer systems, from commercial thermoplastics to low molecular weight thermosetting resins. This review covers the development of dynamic cross-links. This review is aimed at providing the state of the art in the utilization of boronic species for the synthesis of covalent adaptable networks. We mainly focus on the synthetic aspects of boronic linkages-based vitrimers construction. Finally, the challenges and future perspectives are provided.

High-Strength, Large-Deformation, Dual Cross-Linking Network Liquid Crystal Elastomers Based on Quadruple Hydrogen Bonds

Liquid crystal elastomers (LCEs) with large deformation under external stimuli have attracted extensive attention in various applications such as soft robotics, 4D printing, and biomedical devices. However, it is still a great challenge to reduce the damage to collimation and enhance the mechanical and actuation properties of LCEs simultaneously. Here, we construct a new method of a double cross-linking network structure to improve the mechanical properties of LCEs. The ureidopyrimidinone (UPy) group with quadruple hydrogen bonds was used as the physical cross-linking unit, and pentaerythritol tetra(3-mercaptopropionate) was used as the chemical cross-link. The LCEs showed a strong mechanical tensile strength of 8.5 MPa and excellent thermally induced deformation (50%). In addition, the introduction of quadruple hydrogen bonds endows self-healing ability to extend the service life of LCEs. This provides a generic strategy for the fabrication of high-strength LCEs, inspiring the development of actuators and artificial muscles.

Interfacial π-π Interactions Induced Ultralight, 300 °C-Stable, Wideband Graphene/Polyaramid Foam for Electromagnetic Wave Absorption in Both Gigahertz and Terahertz Bands

High-performance electromagnetic wave-absorbing (EMA) materials used in high-temperature environments are of great importance in both civil and military fields. Herein, we have developed the ultralight graphene/polyaramid composite foam for wideband electromagnetic wave absorption in both gigahertz and terahertz bands, with a higher service temperature of 300 °C. It is found that strong interfacial π-π interactions are spontaneously constructed between graphene and polyaramids (PA), during the foam preparation process. This endows the foam with two advantages for its EMA performance. First, the π-π interactions trigger the interfacial polarization for enhanced microwave dissipation, as confirmed by the experimental and simulation results. The composite foam with an ultralow density (0.0038 g/cm³) shows a minimum reflection loss (RL) of -36.5 dB and an effective absorption bandwidth (EAB) of 8.4 GHz between 2 and 18 GHz band. Meanwhile, excellent terahertz (THz) absorption is also achieved, with EAB covering the entire 0.2-1.6 THz range. Second, the interfacial π-π interactions promote PA to present a unique in-plane orientation configuration along the graphene surface, thus making PA the effective antioxidation barrier layer for graphene at high temperatures. The EMA performance of the foam could be completely preserved after 300 °C treatment in air atmosphere. Furthermore, the composite foam exhibits multifunctions, including good compressive, thermal insulating, and flame-retardant properties. We believe that this study could provide useful guidance for the design of next-generation EMA materials used in harsh environments.

Self-Healing Silicone Elastomer with Stable and High Adhesion in Harsh Environments

Adhesive and self-healing elastomers are urgently needed for their convenience and intelligence in biological medicine, flexible electronics, intelligent residential systems, etc. However, their inevitable use in harsh environments results in further enhancement requirements of the structure and performance of adhesive and self-healing elastomers. Herein, a novel self-healing and high-adhesion silicone elastomer was designed by the synergistic effect of multiple dynamic bonds. It revealed excellent stretchability (368%) and self-healing properties at room temperature (98.1%, 5 h) and in a water environment (96.4% for 5 h). Meanwhile, the resultant silicone elastomer exhibited high adhesion to metal and nonmetal and showed stable adhesion in harsh environments, such as under acidic (pH 1) and alkaline (pH 12) environments, salt water, petroleum ether, water, etc. Furthermore, it was applied as a shatter-proof protective layer and a rust-proof coating, proving its significant potential in intelligent residential system applications.

Wood-Derived Composites with High Performance for Thermal Management Applications

Fabricating advanced polymer composites with remarkable mechanical and thermal conductivity performances is desirable for developing advanced devices and equipment. In this study, a novel strategy to prepare anisotropic wood-based scaffolds with a naturally aligned microchannel structure from balsa wood is demonstrated. The wood microchannels were coated with polydopamine-surface-modified small graphene oxide (PGO) nanosheets via assembly. The highly aligned porous microstructures, with thin wood cell walls and large voids along the cellulose microchannels, allow polymers to enter, resulting in the fabrication of the wood-polymer nanocomposite. The tensile stiffness and strength of the resulting nanocomposite reach 8.10 GPa and 90.3 MPa with a toughness of 5.0 MJ m^-3. The thermal conductivity of the nanocomposite is improved significantly by coating a PGO layer onto the wood scaffolds. The nanocomposite exhibits not only ultrahigh thermal conductivity (in-plane about 5.5 W m^-1 K^-1 and through-plane about 2.1 W m^-1 K^-1) but also satisfactory electrical insulation (volume resistivity of about 10¹⁵ Ω·cm). Therefore, the results provide a strategy to fabricate thermal management materials with excellent mechanical properties.

Minireview on Self-Healing Polymers: Versatility, Application, and Prospects

Nature is blessed with self-healing properties. Mimicking nature is a traditional practice to innovate new classes of materials for researchers. In this practice, researchers made a revolutionary approach to innovate self-healing polymer (SHP) that can be used to treat damage-related losses. Different SHPs with various properties have been developed for a wide range of applications. SHPs unlocked the key to the taste of real life through their application and versatility in the sectors close to our day-by-day life of this age and the near future. In this study, we reviewed the scopes and prospects of the application of SHPs owing to different properties. Varieties of amazing properties made SHPs fit in different sectors such as construction, paint and coat, electronics, healthcare, textile, and automotive and aerospace. Similarly, due to having suitable functionality, SHPs can also be used in different industries. Therefore, it is high time to generalize the production of SHPs by suitable research and make sure the easy application for the welfare of human civilization and other living creatures.

Epoxy Composites with High Thermal Conductivity by Constructing Three-Dimensional Carbon Fiber/Carbon/Nickel Networks Using an Electroplating Method

Heat dissipation problem is the primary factor restricting the service life of an electronic component. The thermal conductivity of materials has become a bottleneck that hinders the development of the electronic information industry (such as light-emitting diodes, 5G mobile phones). Therefore, the research on improving the thermal conductivity of materials has a very important theoretical value and a practical application value. Whether the thermally conductive filler in polymer composites can form a highly thermal conductive pathway is a key issue at this stage. The carbon fiber/carbon felt (CF/C felt) prepared in the study has a three-dimensional continuous network structure. The nickel-coated carbon fiber/carbon felt (CF/C/Ni felt) was fabricated by an electroplating deposition method. Three-dimensional CF/C/Ni/epoxy composites were manufactured by vacuum-assisted liquid-phase impregnation. By forming connection points between the adjacent carbon fibers, the thermal conduction path inside the felt can be improved so as to improve the thermal conductivity of the CF/C/Ni/epoxy composite. The thermal conductivity of the CF/C/Ni/epoxy composite (in-plane K∥) is up to 2.13 W/(m K) with 14.0 wt % CF/C and 3.70 wt % Ni particles (60 min electroplating deposition). This paper provides a theoretical basis for the development of high thermal conductivity and high-performance composite materials urgently needed in industrial production and high-tech fields.

MXene Enabling the Long-Term Superior Thermo-Oxidative Resistance for Elastomers

The ability of long-term thermo-oxidative resistance is very important for elastomers in application. However, many conventional antioxidants are difficult to realize the long-term thermo-oxidative resistance. To overcome this limitation, a design strategy is introduced by combing elastomers with MXene and natural rubber (NR) is chosen as a model material. MXene is efficient in absorbing oxygen and the generated free radicals in the NR matrix and can inhibit the diffusion of oxygen toward the interior. Moreover, MXene, like graphene and carbon black, absorbs molecular chains, inhibiting the migration of MXene toward the surface of the sample. Such characteristics of MXene endow NR/MXene with the long-term outstanding thermo-oxidative resistance. For example, after three days of the thermo-oxidative process for NR/MXene, the tensile strength is 19 MPa and the retention of tensile strength is 63%, which far exceeds the effects of conventional antioxidants. This work not only provides a good guide for the universal design of elastomers with long-term thermo-oxidative resistance but also expands the application of MXene.