Thermally Conductive Elastomer Composites with High Toughness, Softness, and Resilience Enabled by Regulating Interfacial Structure and Dynamics.

The emerging applications of thermally conductive elastomer composites in modern electronic devices for heat dissipation require them to maintain both high toughness and resilience under thermomechanical stresses. However, such a combination of thermal conductivity and desired mechanical characteristics is extremely challenging to achieve in elastomer composites. Here this long-standing mismatch is resolved via regulating interfacial structure and dynamics response. This regulation is realized both by tuning the molecular weight of the dangling chains in the polymer networks and by silane grafting of the fillers, thereby creating a broad dynamic-gradient interfacial region comprising of entanglements. These entanglements can provide the slipping topological constraint that allows for tension equalization between and along the chains, while also tightening into rigid knots to prevent chain disentanglement upon stretching. Combined with ultrahigh loading of aluminum-fillers (90 wt%), this design provides a low Young's modulus (350.0 kPa), high fracture toughness (831.5 J m-2), excellent resilience (79%) and enhanced thermal conductivity (3.20 W m-1 k-1). This work presents a generalizable preparation strategy toward engineering soft, tough, and resilient high-filled elastomer composites, suitable for complex environments, such as automotive electronics, and wearable devices.

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.

Insight into the fracture energy dissipation mechanism in elastomer composites via sacrificial bonds and fillers.

Most tough elastomer composites are reinforced by introducing sacrificial structures and fillers. Understanding the contribution of fillers and sacrificial bonds in elastomer composites to the energy dissipation is critical for the design of high-toughness materials. However, the energy dissipation mechanism in elastomer composites remains elusive. In this study, using a tearing test and time-temperature superposition, we investigate the effect of fillers and sacrificial bonds on the energy dissipation of elastomer composites consisting of poly(lipoic acid)/silver-coated Al fillers. We found that the fillers and sacrificial bonds mutually enhance both the intrinsic fracture energy and the bulk energy dissipation, and moreover the sacrificial bonds play a more important role in enhancing fracture toughness than the fillers. It is unreasonable to rely solely on the loss factor for bulk energy dissipation. The addition of sacrificial bonds results in a chain segment experiencing greater binding force compared to the addition of fillers. This suggests that the chain segment consumes more energy during its movement. By calculating the length of the Kuhn chain segment and the Kuhn number, it is evident that the addition of sacrificial bonds results in a greater binding force for the chain segment than the addition of fillers, and this enhanced binding force increases the energy consumption during the motion of the chain segment.

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.

Dual Reversible Network Nanoarchitectonics for Ultrafast Light-Controlled Healable and Tough Polydimethylsiloxane-Based Composite Elastomers.

It is highly desirable to develop polydimethylsiloxane (PDMS) elastomers with high self-healing efficiency and excellent mechanical properties. However, most self-healable materials reported to date still take several hours to self-heal and improving the self-healing property often comes at the expense of mechanical properties. Herein, a simple design strategy of dual reversible network nanoarchitectonics is reported for constructing ultrafast light-controlled healable (40 s) and tough (≈7.2 MJ m-3) PDMS-based composite elastomers. The rupture reconstruction of dynamic bonds and the reinforcement effect of carbon nanotubes (10 wt %) endowed our composite elastomer with excellent fracture toughness that originated from a good yield strength (≈1.1 MPa) and stretchability (≈882%). Moreover, carbon nanotubes can quickly and directly heat the damaged area of the composite to achieve its ultrafast repair with the assistance of dynamic polymer/filler interfacial interaction, greatly shortening the self-healing time (12 h). The self-healing performance is superior to that of reported self-healable PDMS-based materials. This novel strategy and the as-prepared supramolecular elastomer can inspire further various practical applications, such as remote anti-icing/deicing materials.

How chemical cross-linking and entanglements in polybutadiene elastomers cope with tearing.

New applications of elastomers, such as flexible electronics and soft robotics, have brought great attention to tear resistance since elastomers are prone to shear failure. Most elastomers contain chemical cross-links and entanglements. The effects of both on their mechanical properties have been intensively studied, while how they cope with tearing remains elusive. Here, in polybutadiene elastomers, we find that the energy release rate of tearing (Gtearing), often employed as a measure of tear resistance, is influenced synergistically by chemical cross-linking and entanglements, while its threshold (G0) is only related to the chemical cross-linking. At a low tear speed, the polybutadiene elastomers with low cross-linking density have Gtearing up to 4 times higher than their G0 compared to highly cross-linked ones. Different from conventional reinforcement due to volume dissipation of a polymer network, enhancement of Gtearing significantly depends on the degree of cross-linking. The enhancement of Gtearing at low cross-linking degrees may be related to a novel mechanism, the friction-strengthening phenomenon, which was possibly caused by the pull-out of the chains at a high degree of orientation.

The Synergy of Hydrogen Bond and Entanglement of Elastomer Captures Unprecedented Flaw Insensitivity Rate.

Elastomers are regarded as one of the best candidates for the matrix material of soft electronics, yet they are susceptible to fracture due to the inevitable flaws generated during applications. Introducing microstructures, sacrificial bonds, and sliding cross-linking has been recognized as an effective way to improve the flaw insensitivity rate (Rinsen ). However, these elastomers still prone to failure under tensile loads with the presence of even small flaws. Here, this work reports a polybutadiene elastomer with unprecedented Rinsen via the synergy of hydrogen bond and entanglement. The resulting polybutadiene elastomer exhibits a Rinsen  ≈1.075, which is much higher than those of reported elastomers. By molecular chain interaction and molecular chain conformation analysis, this work demonstrates that the synergistic effect of hydrogen bond dissociation and entanglement slip in the polybutadiene elastomers during stretching leads to the high Rinsen . Using polybutadiene elastomer as matrix of thermal interface materials, this work demonstrates effective heat transfer for strain sensor and electronic devices. In addition, cytocompatibility of the elastomers is verified by cell proliferation and live/dead viability assays. The combination of outstanding biocompatible and excellent mechanical properties of the elastomers creates new opportunities for their applications in electronic skin.

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.

Zebularine protects against blood-brain-barrier (BBB) disruption through increasing the expression of zona occludens-1 (ZO-1) and vascular endothelial (VE)-cadherin.

Blood-brain-barrier (BBB) disruption is an important pathological characteristic of ischemic stroke (IS) and mainly results from dysfunction of brain vascular endothelial cells and tight junctions. Zebularine is a novel inhibitor of DNA methyltransferase (DNMT). Here, we assessed its effects on BBB disruption in IS. Firstly, we reported that Zebularine maintained BBB integrity in middle cerebral artery occlusion (MCAO) mice by increasing the expressions of zona occludens-1 (ZO-1) and vascular endothelial (VE)-cadherin. Importantly, we found that Zebularine reduced the production of pro-inflammatory cytokines, attenuated brain edema, and improved neurological deficits. In in vitro experiments, the bEnd.3 brain endothelial cells were exposed to oxygen and glucose deprivation/reoxygenation (OGD/R), and the protective effects of Zebularine were assessed. Our findings demonstrated that Zebularine prevented OGD/R-induced cytotoxicity by reducing the release of lactate dehydrogenase (LDH). Additionally, Zebularine protected bEnd.3 cells against OGD/R-induced hyper-permeability and reduction of trans-endothelial electrical resistance (TEER). Notably, we found that treatment with Zebularine activated the Adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) pathway by increasing the phosphorylation of adenosine monophosphate-activated protein kinase α (AMPKα). Blockage of AMPKα using its specific inhibitor compound C abolished the beneficial effects of Zebularine in mitigating endothelial hyper-permeability by reducing the expressions of ZO-1 and VE-cadherin. These findings suggest that the protective effects of Zebularine against OGD/R-induced endothelial hyper-permeability are mediated by the activation of AMPKα. In conclusion, our study sheds light on the potential application of Zebularine in the treatment of IS.

Phoenixin-20 Ameliorates Lipopolysaccharide-Induced Activation of Microglial NLRP3 Inflammasome.

Injury associated with neuroinflammation has been linked with several kinds of neurodegenerative diseases. The activation of the NLRP3 inflammasome plays an important role in microglia-mediated inflammation. Phoenixin (PNX)-20 is a newly discovered neuropeptide with pleiotropic effects involved in the regulation of reproductive and cognitive function, depression, and food uptake. This study investigated whether PNX-20 possesses a protective effect against lipopolysaccharide (LPS)-induced activation of the NLRP3 inflammasome in microglia. Firstly, our results show that the PNX-20 treatment significantly prevented LPS-induced expression of NADPH oxidase 4 (NOX-4) and the generation of reactive oxygen species (ROS). Secondly, PNX-20 mitigated LPS-induced upregulation of TxNIP, an upstream regulator of NLRP3 inflammasome activation. Thirdly, further evaluation of the major components of the NLRP3 inflammasome revealed that PNX-20 inhibited LPS-mediated upregulation of NLRP3, ASC, and cleaved caspase-1 (P10). Notably, based on our results, the inhibitory effect of PNX-20 on the NLRP3 inflammasome results in the inhibition of IL-1ß and IL-18 secretions. Finally, we found that PNX-20 ameliorated the reduction in SIRT1 expression induced by LPS. When microglial SIRT1 was inhibited by nicotine, PNX-20 lost its suppressive effect on the expression of NLRP3, ASC, and caspase-1, as well as the secretion of IL-1ß and IL-18. As a result of these findings, we draw the conclusion that the neuroprotective effect of PNX-20 is dependent on SIRT1. Collectively, the study shows that PNX-20 has a regulatory effect via modulation of neuroinflammation.

Room-Temperature Welding of Silver Telluride Nanowires for High-Performance Thermoelectric Film.

Flexible thermoelectric materials that can harvest waste heat energy have attracted great attention because of the rapid progress of flexible electronics. Ag2Te nanowires (Ag2Te NWs) are considered as promising thermoelectric materials to fabricate flexible thermoelectric film and device because of their high Seebeck coefficient, but poor contact between the Ag2Te NWs results in low electrical conductivity. Generally, hot or cold pressing can increase the electrical conductivity between the Ag2Te NWs. However, these process tend to destroy the initial morphology of the Ag2Te NWs and/or cause only physical contact between the Ag2Te NWs. Herein, we report an approach to the room-temperature welding of Ag2Te NWs to enhance their contacts by facile combination of vacuum filtration and drop-coating methods. The obtained Ag2Te NWs film exhibits excellent Seebeck coefficient of -99.48 µV/K and high electrical conductivity of 15 335.05 S/m at room temperature, which gives the power factor of 151.76 µW m-1 K-2. Surprisingly, an optimal Seebeck coefficient of -154.96 µV/K and electrical conductivity of 14 982.42 S/m can be obtained at 420 K, giving a power factor of 359.76 µW m-1 K-2. Moreover, the electrical resistance of the Ag2Te NWs film was only 1.3 times of the initial electrical resistance after 1000 bending cycles, indicating good flexibility of the film. A finger-touch test is conducted by using the Ag2Te NWs film as thermoelectric power generator, which achieves a stable output voltage of about 0.52 mV, suggesting its great potential applications in self-powered flexible electronic devices.

Highly Compressive Boron Nitride Nanotube Aerogels Reinforced with Reduced Graphene Oxide.

Boron nitride nanotubes (BNNTs), structural analogues of carbon nanotubes, have attracted significant attention due to their superb thermal conductivity, wide bandgap, excellent hydrogen storage capacity, and thermal and chemical stability. Despite considerable progress in the preparation and surface functionalization of BNNTs, it remains a challenge to assemble one-dimensional BNNTs into three-dimensional (3D) architectures (such as aerogels) for practical applications. Here, we report a highly compressive BNNT aerogel reinforced with reduced graphene oxide (rGO) fabricated using a freeze-drying method. The reinforcement effect of rGO and 3D honeycomb-like framework offer the BNNTs/rGO aerogel with a high compression resilience. The BNNTs/rGO aerogels were then infiltrated with polyethylene glycol to prepare a kind of phase change materials. The prepared phase change material composites show zero leakage even at 100 °C and enhanced thermal conductivity, due to the 3D porous structure of the BNNTs/rGO aerogel. This work provides a simple method for the preparation of 3D BNNTs/rGO aerogels for many potential applications, such as high-performance polymer composites.