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

Application of Aramid Nanofibers in Nanocomposites: A Brief Review

The diameter of fibers is a critical factor in determining their final applications. When the diameter of aramid fibers changes from microns to nanoscale, its range of applications will be greatly extended. In this short review, the preparation of aramid nanofibers (ANFs) with diameters from ten nanometers to more than one hundred nanometers is introduced. Due to their excellent mechanical properties and their chemical and thermal stability, ANFs have been widely used as novel nanomaterials and composited with other materials, mainly for use in reinforced composites, energy storage, filtration and adsorption, biomedicine and electromagnetic fields. In this short review, the application of ANFs and their composites during the last 10 years is concisely summarized and a brief perspective on ANFs and their composites is also presented.

Hyaluronic Acid/Collagen Nanofiber Tubular Scaffolds Support Endothelial Cell Proliferation, Phenotypic Shape and Endothelialization

In this study, we designed and synthetized artificial vascular scaffolds based on nanofibers of collagen functionalized with hyaluronic acid (HA) in order to direct the phenotypic shape, proliferation, and complete endothelization of mouse primary aortic endothelial cells (PAECs). Layered tubular HA/collagen nanofibers were prepared using electrospinning and crosslinking process. The obtained scaffold is composed of a thin inner layer and a thick outer layer that structurally mimic the layer the intima and media layers of the native blood vessels, respectively. Compared with the pure tubular collagen nanofibers, the surface of HA functionalized collagen nanofibers has higher anisotropic wettability and mechanical flexibility. HA/collagen nanofibers can significantly promote the elongation, proliferation and phenotypic shape expression of PAECs. In vitro co-culture of mouse PAECs and their corresponding smooth muscle cells (SMCs) showed that the luminal endothelialization governs the biophysical integrity of the newly formed extracellular matrix (e.g., collagen and elastin fibers) and structural remodeling of SMCs. Furthermore, in vitro hemocompatibility assays indicated that HA/collagen nanofibers have no detectable degree of hemolysis and coagulation, suggesting their promise as engineered vascular implants.

Synergetic integration of thermal conductivity and flame resistance in nacre-like nanocellulose composites

Highly thermally conductive and flame resistant nanocellulose-based composites can synchronously achieve efficient thermal dissipation and low fire hazards of electronic devices, which shows great promise in next-generation green and flexible electronics. However, it has long been intractable to optimize the high thermal conductivity (TC) and flame resistance simultaneously. Herein, synergetic integration of high TC and flame resistance in nacre-like nanocellulose composites has been successfully achieved by the vacuum-assisted filtration of cellulose nanofibers (CNFs) and functionalized boron nitride nanosheets (BNNS-p-APP). Benefiting from the highly oriented hierarchical microstructure, strong hydrogen-bonding interaction, and successful immobilization of ammonium polyphosphate (APP), the as-obtained CNFs/BNNS-p-APP composite film achieves a high in-plane TC of 9.1 W m^-1 K^-1 and outstanding flame resistance. Meantime, this eco-friendly nanocellulose-based composite also exhibits remarkable flexibility, folding endurance, and mechanical robustness, robustness, which may open up a new opportunity for the thermal management of flexible electronics.

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

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

Ultra-Robust Thermoconductive Films Made from Aramid Nanofiber and Boron Nitride Nanosheet for Thermal Management Application

The development of highly thermally conductive composites with excellent electrical insulation has attracted extensive attention, which is of great significance to solve the increasingly severe heat concentration issue of electronic equipment. Herein, we report a new strategy to prepare boron nitride nanosheets (BNNSs) via an ion-assisted liquid-phase exfoliation method. Then, silver nanoparticle (AgNP) modified BNNS (BNNS@Ag) was obtained by in situ reduction properties. The exfoliation yield of BNNS was approximately 50% via the ion-assisted liquid-phase exfoliation method. Subsequently, aramid nanofiber (ANF)/BNNS@Ag composites were prepared by vacuum filtration. Owing to the "brick-and-mortar" structure formed inside the composite and the adhesion of AgNP, the interfacial thermal resistance was effectively reduced. Therefore, the in-plane thermal conductivity of ANF/BNNS@Ag composites was as high as 11.51 W m-1 K-1, which was 233.27% higher than that of pure ANF (3.45 W m-1 K-1). The addition of BNNS@Ag maintained tensile properties (tensile strength of 129.14 MPa). Moreover, the ANF/BNNS@Ag films also had good dielectric properties and the dielectric constant was below 2.5 (103 Hz). Hence, the ANF/BNNS@Ag composite shows excellent thermal management performance, and the electrical insulation and mechanical properties of the matrix are retained, indicating its potential application prospects in high pressure and high temperature application environments.

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.

Surface Modification Using Polydopamine-Coated Liquid Metal Nanocapsules for Improving Performance of Graphene Paper-Based Thermal Interface Materials

Given the thermal management problem aroused by increasing power densities of electronic components in the system, graphene-based papers have raised considerable interest for applications as thermal interface materials (TIMs) to solve interfacial heat transfer issues. Significant research efforts have focused on enhancing the through-plane thermal conductivity of graphene paper; however, for practical thermal management applications, reducing the thermal contact resistance between graphene paper and the mating surface is also a challenge to be addressed. Here, a strategy aimed at reducing the thermal contact resistance between graphene paper and the mating surface to realize enhanced heat dissipation was demonstrated. For this, graphene paper was decorated with polydopamine EGaIn nanocapsules using a facile dip-coating process. In practical TIM application, there was a decrease in the thermal contact resistance between the TIMs and mating surface after decoration (from 46 to 15 K mm2 W-1), which enabled the decorated paper to realize a 26% enhancement of cooling efficiency compared with the case without decoration. This demonstrated that this method is a promising route to enhance the heat dissipation capacity of graphene-based TIMs for practical electronic cooling applications.

Highly thermally conductive and eco-friendly OH-h-BN/chitosan nanocomposites by constructing a honeycomb thermal network

More than 110,000,000 tons of mismanaged plastics were to be produced in 2020. Polymers are favored in the preparation of thermally conductive materials due to their excellent comprehensive properties. However, most polymers fabricated for thermally conductive materials are difficult to degrade in the natural environment. To alleviate the increasingly severe environmental problems, we reported a novel eco-friendly material with high thermal conductivity, which was composited of chitosan microspheres (CSM) and hydroxyl-functionalized hexagonal boron nitride (OH-h-BN) nanoplatelets. Utilizing their significant difference in scales, the OH-h-BN nanoplatelets were arranged between each CSM. Their overall structure was similar to the honeycomb: CSM were honeycomb cores, and OH-h-BN nanoplatelets were honeycomb network. The routine-structure OH-h-BN/CS nanocomposites were only 0.94 ± 0.02 W·m^-1·K^-1 at 50 wt% in thermal conductivity. However, the OH-h-BN/CSM nanocomposites with honeycomb structure can reach 5.66 ± 0.32 W·m^-1·K^-1 in the same loading, for enhancement of 502% and 1914% than OH-h-BN/CS nanocomposites and pure CS, respectively.

Breaking Through Bottlenecks for Thermally Conductive Polymer Composites: A Perspective for Intrinsic Thermal Conductivity, Interfacial Thermal Resistance and Theoretics

Rapid development of energy, electrical and electronic technologies has put forward higher requirements for the thermal conductivities of polymers and their composites. However, the thermal conductivity coefficient (λ) values of prepared thermally conductive polymer composites are still difficult to achieve expectations, which has become the bottleneck in the fields of thermally conductive polymer composites. Aimed at that, based on the accumulation of the previous research works by related researchers and our research group, this paper proposes three possible directions for breaking through the bottlenecks: (1) preparing and synthesizing intrinsically thermally conductive polymers, (2) reducing the interfacial thermal resistance in thermally conductive polymer composites, and (3) establishing suitable thermal conduction models and studying inner thermal conduction mechanism to guide experimental optimization. Also, the future development trends of the three above-mentioned directions are foreseen, hoping to provide certain basis and guidance for the preparation, researches and development of thermally conductive polymers and their composites.

Thermal interface materials with graphene fillers: review of the state of the art and outlook for future applications

We review the current state-of-the-art graphene-enhanced thermal interface materials for the management of heat in the next generation of electronics. Increased integration densities, speed and power of electronic and optoelectronic devices require thermal interface materials with substantially higher thermal conductivity, improved reliability, and lower cost. Graphene has emerged as a promising filler material that can meet the demands of future high-speed and high-powered electronics. This review describes the use of graphene as a filler in curing and non-curing polymer matrices. Special attention is given to strategies for achieving the thermal percolation threshold with its corresponding characteristic increase in the overall thermal conductivity. Many applications require high thermal conductivity of composites, while simultaneously preserving electrical insulation. A hybrid filler approach, using graphene and boron nitride, is presented as a possible technology providing for the independent control of electrical and thermal conduction. The reliability and lifespan performance of thermal interface materials is an important consideration towards the determination of appropriate practical applications. The present review addresses these issues in detail, demonstrating the promise of graphene-enhanced thermal interface materials compared to alternative technologies.

Lightweight, Flexible Cellulose-Derived Carbon Aerogel@Reduced Graphene Oxide/PDMS Composites with Outstanding EMI Shielding Performances and Excellent Thermal Conductivities

In order to ensure the operational reliability and information security of sophisticated electronic components and to protect human health, efficient electromagnetic interference (EMI) shielding materials are required to attenuate electromagnetic wave energy. In this work, the cellulose solution is obtained by dissolving cotton through hydrogen bond driving self-assembly using sodium hydroxide (NaOH)/urea solution, and cellulose aerogels (CA) are prepared by gelation and freeze-drying. Then, the cellulose carbon aerogel@reduced graphene oxide aerogels (CCA@rGO) are prepared by vacuum impregnation, freeze-drying followed by thermal annealing, and finally, the CCA@rGO/polydimethylsiloxane (PDMS) EMI shielding composites are prepared by backfilling with PDMS. Owing to skin-core structure of CCA@rGO, the complete three-dimensional (3D) double-layer conductive network can be successfully constructed. When the loading of CCA@rGO is 3.05 wt%, CCA@rGO/PDMS EMI shielding composites have an excellent EMI shielding effectiveness (EMI SE) of 51 dB, which is 3.9 times higher than that of the co-blended CCA/rGO/PDMS EMI shielding composites (13 dB) with the same loading of fillers. At this time, the CCA@rGO/PDMS EMI shielding composites have excellent thermal stability (T_HRI of 178.3 °C) and good thermal conductivity coefficient (λ of 0.65 W m^-1 K^-1). Excellent comprehensive performance makes CCA@rGO/PDMS EMI shielding composites great prospect for applications in lightweight, flexible EMI shielding composites.

Wall Density-Controlled Thermal Conductive and Mechanical Properties of Three-Dimensional Vertically Aligned Boron Nitride Network-Based Polymeric Composites

Polymeric composites with good thermal conductive and improved mechanical properties are in high demand in the thermal management materials. Construction of a three-dimensional (3D) structure has been proved to be an effective method to obtain polymeric composites with improved through-plane thermal conductivity (TC) for efficient thermal management of electronics. However, the TC enhancement of the obtained polymeric composites is limited, mainly due to poor control of the 3D thermal conductive network. Additionally, achieving high thermal conductive properties and enhanced mechanical properties simultaneously is of great challenge for polymeric composites. In this work, a 3D boron nitride framework (BNF) with a well-defined vertically aligned open structure and designed wall density fabricated by a unidirectional freezing technique was applied. The as-prepared BNF/polyethylene glycol (PBNF) composites exhibit enhanced through-plane TC, excellent thermal transfer capability (ΔT_max = 34 °C), and improved mechanical properties (Young's modulus enhancement up to 356%) simultaneously, making it attractive to thermal management applications. Strong correlation between the TC and mechanical properties of the PBNF composites and the wall density of the BNF scaffolds was found, providing opportunities to tune the TC and mechanical properties through the controlling of wall density. Furthermore, the models between TC and Young's modulus of PBNF composites were established by using the data-driven method "sure independence screening and sparsifying operator", which enables us to predict TC and Young's modulus of the polymeric composites for designing promising composite materials. The design principles and fabrication strategies proposed in this work could be important for developing advanced composite materials.

Biomimetic electrospun tubular PLLA/gelatin nanofiber scaffold promoting regeneration of sciatic nerve transection in SD rat

The micro- or nanoscale surface morphology of the tissue engineering nerve guidance scaffold (NGS) will affect different cell behaviors, such as their growth rate, migration, and matrix secretion. Although different technologies for manufacturing scaffolds with biomimetic topography have been established, most of them tend to be high cost and long preparation time. Here we have prepared a biomimetic NGS with physical properties to simulate native nerve tissue more accurately. We used poly(l-lactic acid) (PLLA) nanofibers doped with gelatin to prepare a biomimetic NGS whose structure mimics the native epineurium layer. By adjusting the doping ratio of gelatin and PLLA in the tubular scaffold, the bionic scaffold's surface morphology and mechanical properties are closer to native tissues. In vitro cell scaffold interaction experiments demonstrated that the PLLA/gelatin nanofibers could significantly promote the elongation, proliferation, and the secretion of glial cell-derived neurotrophic factor (GDNF) of RSC96 Schwann cells (SCs), as well as the diffusion of GDNF. In vivo scaffold replacement of SD rat, sciatic nerves showed that the nerve guide scaffold composed of PLLA/gelatin nanofibers was helpful to the myelination of SCs and the remolding of epineurium in the injured area, which could effectively rehabilitate the motor and sensory functions of the injured nerve and prevent the atrophy of the target muscle tissue. This study showed that the synergistic impact of nano topographical and biochemical clues on designing biomimetic scaffolds could efficiently promote regenerating nerve tissue.

Significant Reduction of Interfacial Thermal Resistance and Phonon Scattering in Graphene/Polyimide Thermally Conductive Composite Films for Thermal Management

The developing flexible electronic equipment are greatly affected by the rapid accumulation of heat, which is urgent to be solved by thermally conductive polymer composite films. However, the interfacial thermal resistance (ITR) and the phonon scattering at the interfaces are the main bottlenecks limiting the rapid and efficient improvement of thermal conductivity coefficients (λ) of the polymer composite films. Moreover, few researches were focused on characterizing ITR and phonon scattering in thermally conductive polymer composite films. In this paper, graphene oxide (GO) was aminated (NH₂-GO) and reduced (NH₂-rGO), then NH₂-rGO/polyimide (NH₂-rGO/PI) thermally conductive composite films were fabricated. Raman spectroscopy was utilized to innovatively characterize phonon scattering and ITR at the interfaces in NH₂-rGO/PI thermally conductive composite films, revealing the interfacial thermal conduction mechanism, proving that the amination optimized the interfaces between NH₂-rGO and PI, reduced phonon scattering and ITR, and ultimately improved the interfacial thermal conduction. The in-plane λ (λ _||) and through-plane λ (λ _⊥) of 15 wt% NH₂-rGO/PI thermally conductive composite films at room temperature were, respectively, 7.13 W/mK and 0.74 W/mK, 8.2 times λ _|| (0.87 W/mK) and 3.5 times λ _⊥ (0.21 W/mK) of pure PI film, also significantly higher than λ _|| (5.50 W/mK) and λ _⊥ (0.62 W/mK) of 15 wt% rGO/PI thermally conductive composite films. Calculation based on the effective medium theory model proved that ITR was reduced via the amination of rGO. Infrared thermal imaging and finite element simulation showed that NH₂-rGO/PI thermally conductive composite films obtained excellent heat dissipation and efficient thermal management capabilities on the light-emitting diodes bulbs, 5G high-power chips, and other electronic equipment, which are easy to generate heat severely.

A biodegradable block polyurethane nerve-guidance scaffold enhancing rapid vascularization and promoting reconstruction of transected sciatic nerve in Sprague-Dawley rats

Reconstruction of peripheral nerve defects with tissue engineered nerve scaffolds is an exciting field of biomedical research and holds potential for clinical application. However, due to poor neovascularization after the implantation, nerve regeneration is still not satisfactory, especially for large nerve defects. These obstacles hinder the investigation of basic neurobiological principles and development of a wide range of treatments for peripheral nerve diseases. Herein, we designed an amphiphilic alternating block polyurethane (abbreviated as PU) copolymer-based nerve guidance scaffold, which has good Schwann cell compatibility, and more importantly, a rapid vascularization of the scaffold in vivo. In the sciatic nerve transection model of SD rats, vascularized PU nerve guidance scaffolds induced rapid regeneration of nerve fibers and axons along the scaffold. Through the analysis of nerve electrophysiology, sciatic nerve functional index, histology, and immunofluorescence related to angiogenesis, we determined that PU with rapid vascularization function enhances recovery and re-obtains nerve conduction function. Our study points out a new strategy of using nerve tissue engineering scaffolds to treat large nerve defects.

A Dual-Crosslinked and Anisotropic Regenerated Cellulose/Boron Nitride Nanosheets Film With High Thermal Conductivity, Mechanical Strength, and Toughness

The highly thermo-conductive but electrically insulating film, with desirable mechanical performances, is extremely demanded for thermal management of portable and wearable electronics. The integration of boron nitride nanosheets (BNNSs) with regenerated cellulose (RC) is a sustainable strategy to satisfy these requirements, while its practical application is still restricted by the brittle fracture and loss of toughness of the composite films especially at the high BNNS addition. Herein, a dual-crosslinked strategy accompanied with uniaxial pre-stretching treatment was introduced to engineer the artificial RC/BNNS film, in which partial chemical bonding interactions enable the effective interfiber slippage and prevent any mechanical fracture, while non-covalent hydrogen bonding interactions serve as the sacrifice bonds to dissipate the stress energy, resulting in a simultaneous high mechanical strength (103.4 MPa) and toughness (10.2 MJ/m³) at the BNNS content of 45 wt%. More importantly, attributed to the highly anisotropic configuration of BNNS, the RC/BNNS composite film also behaves as an extraordinary in-plane thermal conductivity of 15.2 W/m·K. Along with additional favorable water resistance and bending tolerance, this tactfully engineered film ensures promised applications for heat dissipation in powerful electronic devices.

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.

Novel bio-inspired three-dimensional nanocomposites based on montmorillonite and chitosan

In this study, inspired by nacre-like structural natural shells, novel three-dimensional (3D) nanocomposites based on natural nanoplatelets of montmorillonite (MMT) and polysaccharide of chitosan (CS) were prepared with solution intercalation and self-assembly process. The CS-intercalated-MMT nanoplatelets units acted as "bricks" and CS molecules acted as "mortar", arranging in fairly well-ordered layered structure. With addition of glutaraldehyde (GA) and Pd²⁺ cations, synergistic toughening and strengthening effects of covalent and ionic bonds could be achieved. The best mechanical properties of the prepared 3D nanocomposites were observed as 5.6 KJ/m² (impact strength), 3.3 GPa (flexural modulus), and 65.8 MPa (flexural strength), respectively, which showed higher toughness but lower flexural properties than natural pearl mussel shells. Nevertheless, both the impact and flexural properties of the prepared 3D nanocomposite were much higher than the other natural shell, i.e. green grab shell. Besides conventional methods characterizations, the nacre-like structure of the artificial 3D nanocomposite was further evidenced with positron annihilation lifetime spectroscopy characterizations. This work might facilitate a versatile platform for developing green 3D bionanocomposites with fairly good mechanical properties.

Improving the thermal conductivity of epoxy composites using a combustion-synthesized aggregated β-Si3N4 filler with randomly oriented grains

Electrically insulating and thermally conductive polymer matrix composites are desirable for industry applications as they improve the reliability of high-performance electronic devices, particularly via heat dissipation in devices loaded with several electronic components. In this study, an aggregated β-Si₃N₄ filler with randomly oriented grains was produced via combustion synthesis to improve the thermal conductivity of epoxy composites. The thermal conductivities of the prepared composites were investigated as a function of the filler content, and the values were compared to those of composites loaded with commercial β-Si₃N₄ (non-aggregated)_. Negligible difference was observed in the thermal conductivities of both types of composites when the Si₃N₄ content was below 40 vol%; however, above 40 vol%, the aggregated β-Si₃N₄ filler-loaded composites showed higher thermal conductivities than the commercial β-Si₃N₄-loaded composites. The aggregated β-Si₃N₄ filler-loaded composites exhibited isotropic thermal conductivities with a maximum value of 4.7 W m⁻¹ K⁻¹ at 53 vol% filler content, which is approximately 2.4 times higher than that of the commercial β-Si₃N₄-loaded composites, thereby suggesting that the morphology of the aggregated filler would be more efficient than that of the commonly used non-aggregated filler in enhancing the thermal conductivity of a polymer matrix composite.

Reactive amphiphilic hollow SiO2 Janus nanoparticles for durable superhydrophobic coating

Durable superhydrophobic coating is attractive due to its long-term superhydrophobicity, anti-fouling and self-cleaning properties. However, the fabrication of durable superhydrophobic coatings on a fragile surface, including leather and paper, is still a challenge due to its bad resistance to harsh environments such as high temperature, high pressure and strong acid or strong base. Herein, we developed a universal way to fabricate long-lasting superhydrophobic coating on leather via amphiphilic Janus particles, which have one of the semispheres functionalized with hydrophobic 1-dodecanethiol and the other semisphere functionalized with hydrophilic β-mercaptoethylamine. Polyurethane with isocyanate end groups was sprayed on the leather surface as an intermediate layer to strongly link Janus particles with leather via cross-linking. Moreover, amphiphilic Janus particles were fabricated from hollow SiO₂ particles via a thiol-ene click reaction due to its low density. The superhydrophobic coating on leather possessed a high water contact angle of 162.2°. Furthermore, it still retained excellent hydrophobicity with a water contact angle of 154° after 140 cycles of abrasion using sandpaper. This study not only provides a novel method for the fabrication of amphiphilic hollow SiO₂ Janus nanoparticles, but also resolves the difficulties in constructing long-lived superhydrophobic coatings on fragile surfaces by existing methods. Meanwhile, the present study also suggests a potential way to translocate functional Janus microcapsules, which may give some significant suggestions on the future nanoparticle design for drug delivery and energy storage.

Ultraflexible and Mechanically Strong Double-Layered Aramid Nanofiber-Ti3C2Tx MXene/Silver Nanowire Nanocomposite Papers for High-Performance Electromagnetic Interference Shielding

High-performance electromagnetic interference (EMI) shielding materials with ultraflexibility, outstanding mechanical properties, and superior EMI shielding performances are highly desirable for modern integrated electronic and telecommunication systems in areas such as aerospace, military, artificial intelligence, and smart and wearable electronics. Herein, ultraflexible and mechanically strong aramid nanofiber-Ti₃C₂T_x MXene/silver nanowire (ANF-MXene/AgNW) nanocomposite papers with double-layered structures are fabricated via the facile two-step vacuum-assisted filtration followed by hot-pressing approach. The resultant double-layered nanocomposite papers with a low MXene/AgNW content of 20 wt % exhibit an excellent electrical conductivity of 922.0 S·cm^-1, outstanding mechanical properties with a tensile strength of 235.9 MPa and fracture strain of 24.8%, superior EMI shielding effectiveness (EMI SE) of 48.1 dB, and high EMI SE/t of 10 688.9 dB·cm^-1, benefiting from the highly efficient double-layered structures, high-performance ANF substrate, and extensive hydrogen-bonding interactions. Particularly, the nanocomposite papers show a maximum electrical conductivity of 3725.6 S·cm^-1 and EMI SE of ∼80 dB at a MXene/AgNW content of 80 wt % with an absorption-dominant shielding mechanism owing to the massive ohmic losses in the highly conductive MXene/AgNW layer, multiple internal reflections between Ti₃C₂T_x MXene nanosheets and polarization relaxation of localized defects, and abundant terminal groups. Compared with the homogeneously blended ones, the double-layered nanocomposite papers possess greater advantages in electrical, mechanical, and EMI shielding performances. Moreover, the multifunctional double-layered nanocomposite papers exhibit excellent thermal management performances such as high Joule heating temperature at low supplied voltages, rapid response time, sufficient heating stability, and reliability. The results indicate that the double-layered nanocomposite papers have excellent potential for high-performance EMI shielding and thermal management applications in aerospace, military, artificial intelligence, and smart and wearable electronics.

In situ molten phase-assisted self-healing for maintaining fiber morphology during conversion from melamine diborate to boron nitride

C₃N₆H₆·2H₃BO₃ (M·2B) is a highly promising precursor of boron nitride (BN) fibers due to its eco-friendly and low-cost fabrication. However, it is still unclear why the fibers can maintain their morphology in spite of drastic weight loss (nearly 80 wt%) during M·2B-to-BN pyrolysis. Herein, an interesting cracking and self-healing behavior of the heated M·2B fibers was observed at initial pyrolysis. In situ formed molten boron oxide (B₂O₃) was figured out to be the healing agent for the cracks and subsequently merged into the continuous matrix enclosing melamine/melem molecules, which subsequently acted as a nitrogen source. The B₂O₃ matrix helped to keep the fiber morphology undamaged under the second weight-loss stage in the pyrolysis process. This strategy of taking advantage of the in situ formed molten phase for healing cracks offers detailed guidance to prepare defect-free M·2B-derived BN fibers and would be significant in defect repair for other ceramics.

Morphology evolution and the corresponding structure transformation from C₃N₆H₆·2H₃BO₃ supramolecule to BN fiber.

3D Shapeable, Superior Electrically Conductive Cellulose Nanofibers/Ti3C2Tx MXene Aerogels/Epoxy Nanocomposites for Promising EMI Shielding

In this work, 3D highly electrically conductive cellulose nanofibers (CNF)/Ti₃C₂T_x MXene aerogels (CTA) with aligned porous structures are fabricated by directional freezing followed by freeze-drying technique, and the thermally annealed CTA (TCTA)/epoxy nanocomposites are then fabricated by thermal annealing of CTA, subsequent vacuum-assisted impregnation and curing method. Results show that TCTA/epoxy nanocomposites possess 3D highly conductive networks with ultralow percolation threshold of 0.20 vol% Ti₃C₂T_x. When the volume fraction of Ti₃C₂T_x is 1.38 vol%, the electrical conductivity (σ), electromagnetic interference shielding effectiveness (EMI SE), and SE divided by thickness (SE/d) values of the TCTA/epoxy nanocomposites reach 1672 S m^-1, 74 dB, and 37 dB mm^-1, respectively, which are almost the highest values compared to those of polymer nanocomposites reported previously at the same filler content. In addition, compared to those of the samples without Ti₃C₂T_x, the storage modulus and heat-resistance index of TCTA/epoxy nanocomposites are enhanced to 9792.5 MPa and 310.7°C, increased by 62% and 6.9°C, respectively, presenting outstanding mechanical properties and thermal stabilities. The fabricated lightweight, easy-to-process, and shapeable TCTA/epoxy nanocomposites with superior EMI SE values, excellent mechanical properties, and thermal stabilities greatly broaden the applications of MXene-based polymer composites in the field of EMI shielding.

Urethral reconstruction using an amphiphilic tissue-engineered autologous polyurethane nanofiber scaffold with rapid vascularization function

We report the efficient application of a well-layered tubular amphiphilic nanofiber of a polyurethane copolymer (PU-ran) for the regulation the phenotypic expression of epithelial cells (ECs) and smooth muscle cells (SMCs) for vascularized urethral reconstruction.