It is a challenge for carbon based conductive polymer composites (CPC) to combine easiness of fabrication, high EMI shielding effectiveness (EMI SE), high absorptivity, high mechanical properties and ...self-healing property in one material. Here, a flexible, self-healing and recyclable EMI shielding material is fabricated based on a bridged micro capacitance structure spontaneously formed in ionomer/carbon fillers nanocomposites. The anionic groups in the ionomer phase-separate into aggregates and moreover drive the carbon fillers to align along the aggregates through the anion-π interaction, thereby forming the bridged micro capacitance structure. This structure leads to outstanding EMI SE of 64 dB and high absorption coefficient of 0.82. Meanwhile, the material is self-healable and recyclable due to the dynamic anion-π interaction and autonomous nature of phase separation. In particular, the healed or recycled material shows nearly 100% recovery of EMI SE. The structural design of bridged micro capacitance can be easily extended to other ionomers, leading to a novel class of CPC with significant promise in electronic fields.
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A modified latex compounding approach was used to prepare graphene/styrene–butadiene rubber (GE/SBR) nanocomposites with multifunctional properties as well as enhanced mechanical property. It is ...found that the method is efficient in achieving a molecular level dispersion of GE nanosheets in the rubber matrix. Moreover, the well dispersed GE nanosheets have strong interfacial interaction with SBR. As a result, the mechanical property of SBR is greatly improved. Nearly 11 folds of increase in the tensile strength is attained upon addition of 7phr of GE, which is comparable to the reinforcement effect of 30phr of carbon black (N330) or 40phr of fumed nanosilica. More intriguingly, the GE/SBR nanocomposites have low heat buildup and gas permeability, as well as high wear resistance, thermal stability and electrical conductivity. Such versatile functional properties promise GE/SBR nanocomposites for many new applications, for example, green tires and electronic skin.
Biological tissues can grow stronger after damage and self-healing. However, artificial self-healing materials usually show decreased mechanical properties after repairing. Here, we develop a ...self-healing strengthening elastomer (SSE) by engineering kinetic stability in an ionomer. Such kinetic stability is enabled by designing large steric hindrance on the cationic groups, which prevents the structural change driven by thermodynamic instability under room temperature. However, once heat or external force is applied to disrupt the kinetic stability, the inherent thermodynamic instability induces the SSEs to form bigger and denser aggregates, thereby the material becomes stronger during the healing process. Consequently, the self-healing efficiency of fractured SSEs is as high as 143%. Unlike conventional ionomers whose mechanical properties change with time uncontrollably due to the thermodynamic instability, the SSEs show tunable self-healing strengthening behavior, thanks to the kinetic stability. This work provides a novel and universal strategy to fabricate biomimetic self-healing strengthening materials.
Cerebral ischemia causes damage to the structure and function of the blood‐brain barrier (BBB) and alleviating BBB destruction will be of great significance for the treatment and prognosis of ...ischemic stroke. Recently, microRNAs have been shown to play a critical role in BBB integrity. However, the potential mechanism by which microRNA‐182 (miR‐182) affects the BBB in ischemic stroke remains unclear. We demonstrated for the first time that cerebral ischemia leads to a significant progressive increase in miR‐182 after pMCAO, and bEnd.3 cells are the primary target cells of miR‐182. In miR‐182 KD transgenic mice, infarct volume, and BBB permeability were attenuated, and tight junction (TJ) proteins increased. Inhibition of miR‐182 with an antagomir reduced OGD‐induced apoptosis of bEnd.3 cells and the loss of ZO‐1 and Occludin. To further explore the mechanism by which miR‐182 regulates BBB integrity, we detected the apoptotic proteins Bcl‐2/Bax and demonstrated that mTOR and FOXO1 were the targets of miR‐182. Inhibition of mTOR/FOXO1 by rapamycin/AS1842856 decreased the ratio of Bcl‐2/Bax and exacerbated TJ protein loss. Taken together, inhibition of miR‐182 protects BBB integrity by reducing endothelial cell apoptosis through the mTOR/FOXO1 pathway. Thus, miR‐182 may be a potential target for the treatment of BBB disruption during cerebral ischemia.
Asphalt mixture is a composite material with a complex multiphase dispersed system, and its macroscopic mechanical behavior is inherently related to the microstructure characteristics. To investigate ...the low-temperature crack resistance degradation law of polyester fiber asphalt mixture under different dry-wet cycling conditions, six polyester fiber contents (0%, 0.3%, 0.35%, 0.4%, 0.45%, and 0.5%) were dry-blended into SMA-13 asphalt mixture to prepare fiber-reinforced SCB specimens with pre-notches. Semi-circular bending tests were conducted to test the crack resistance performance of the fiber asphalt mixture after 0, 2, 4, 6, and 8 dry-wet cycles. The experimental results show that the crack resistance performance of specimens with different fiber contents decreases with the increase of dry-wet cycling times, and the influence of salt-dry-wet coupling is greater than that of water-dry-wet coupling. Under the same conditions, the crack resistance index (CRI) increases first and then decreases with the increase of polyester fiber content, reaching its maximum at a polyester fiber content of 0.4%. When the fiber is added at 0.5%, the agglomeration of polyester fibers restricts the low-temperature performance of the specimen. In addition, the DIC technology is used to analyze the trend of horizontal strain variation of specimens after different dry-wet cycles. The results indicate that with the increase of the cycle period, the strain concentration area becomes more apparent, and in the destruction stage, the full-field horizontal strain Exx in the crack concentration zone gradually increases, while the crack resistance decreases. Finally, addressing the limitations of traditional BP neural networks in solving nonlinear problems, a particle swarm optimization algorithm is proposed to optimize the BP neural network, and a PSO-BP neural network model is constructed. Through the analysis of evaluation indicators, it is found that the PSO-BP neural network has improved generalization ability compared to the traditional BP neural network model, and overfitting is reduced, making it an effective tool for predicting the low-temperature performance of polyester fiber asphalt mixtures.
Abstract
To investigate the low-temperature crack resistance of plant-mixed heated recycled asphalt mixture, we conducted a semi-circular bending (SCB) test to analyze the effects of the reclaimed ...asphalt pavement (RAP) content, salt concentration, and loading rate on the crack resistance at −15 °C. The experimental results show that the fracture energy (
G
f
) of the recycled asphalt mixture decreases with an increase in RAP content and salt concentration but increases with an increase in loading rate. When the RAP content is 0%, the Gf of the specimen reaches its maximum value, while when the RAP content is 50%, Gf reaches its minimum value. When the loading rate is 10 mm s
−1
, the destruction of coarse aggregates in the specimen is much greater than the destruction mode at a loading rate of 2 mm s
−1
. Meanwhile, as the RAP content increases, the influence of chloride salt on the low-temperature crack resistance of the recycled asphalt mixture fluctuates. According to the quadratic fitting of RAP content and
G
f
, it can be concluded that a lower loading rate is more helpful in analyzing the degradation mechanism of reclaimed asphalt mixture by salt, and a loading rate of 5 mm s
−1
ha
−1
s
−1
a significant impact on the degradation trend of the recycled asphalt mixture. Finally, by establishing the relationship between the Mohr-Coulomb expression and the ultimate tensile stress, we obtained the cohesive force (
c
) and further analyzed the degradation mechanism of the recycled asphalt mixture under the loading rate and chloride salt. However, the effect of RAP content on c is influenced by various factors, which should be considered comprehensively. These research results enrich the mechanism analysis of the low-temperature cracking performance of plant-mixed heated asphalt mixture and provide theoretical guidance for enhancing the low-temperature cracking resistance design of asphalt pavement.
Developing degradable and self-healable elastomers composed of reusable resources is of great value but is rarely reported because of the undegradable molecular chains. Herein, we report a class of ...degradable and self-healable vitrimers based on non-isocyanate polyurethane elastomer. Such vitrimers are fabricated by copolymerizing
bis
(6-membered cyclic carbonate) and amino-terminated liquid nitrile rubber. The networks topologies can rearrange by transcarbonation exchange reactions between hydroxyl and carbonate groups at elevated temperatures; as such, vitrimers after reprocessing can recover 82.9–95.6% of initial tensile strength and 59–131% of initial storage modulus. Interestingly, the networks can be hydrolyzed and decarbonated in the strong acid solution to recover 75% of the pure di(trimethylolpropane) monomer. Additionally, the elastomer exhibits excellent self-healing efficiency (~88%) and fracture strain (~1,200%) by tuning the monomer feeding ratio. Therefore, this work provides a novel strategy to fabricate the sustainable elastomers with minimum environmental impact.
Interfacial interaction is of crucial importance for polymer nanocomposites. To improve interfacial interaction between graphene (GE) and isoprene rubber (IR), we grafted a silane coupling reagent, ...(bis-γ-(triethoxysilyl) propyl-etrasulfide), onto graphene oxide (GO). The modified GO was mixed with IR by solution blending and then reduced in situ to prepare IR/surface modified GE nanocomposites (IR/SGE). Raman mapping illustrates that the bound rubber on SGE is much thicker than that on unmodified GE, suggesting a strong interfacial interaction between SGE and IR. As a result, IR/SGE shows slower chain dynamics and lower strain-induced crystallinity than IR/GE. However, on-line Raman measurements show that the G band of IR/SGE shifts more noticeably during uniaxial tensile deformation than that of IR/GE; this suggests more efficient load transfer between SGE and IR. Consequently IR/SGE has better mechanical properties than IR/GE.
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•Interfacial interaction of IR/SGE composite was significantly enhanced by modifying GE with BTESPT.•The thicker bound rubber of IR/SGE composite was observed by Raman mapping.•IR/SGE shows slower chain dynamics and strain-induced crystallization rate than IR/GE.•More efficient load transfer leads to superior mechanical properties of IR/SGE composite.
Abstract
In order to study the influence of different aging conditions on the low-temperature crack resistance and water stability of polyester fiber asphalt mixture. Prepare standard Marshall ...specimens of asphalt mixture with 0.4% polyester fiber doping, and carry out water immersion Marshall test and low temperature splitting test through indoor asphalt mortar aging, asphalt mixture short-term aging and long-term aging. The results show that: under the three aging conditions, when the water immersion and low temperature time are fixed, with the increase of the aging degree, the water stability and low temperature crack resistance of the asphalt mixture decrease. When the immersion time is 2 h, the stability of asphalt mortar aging and short-term aging decreases by 6.0% and 11.8%, respectively, compared with unaging, but the long-term aging is only 3.6% lower than the short-term aging. When the temperature is −5 °C, the split tensile strength of asphalt mortar aged and short-term aged increases by 4.24% and 14.35%, respectively, compared with unaging, while long-term aging only increases 4.18% compared with short-term aging. This indicates that the short-term aging condition has the most significant effect on the water stability and low-temperature crack resistance of polyester fiber asphalt mixes. At the same time, this study established a regression equation between the test temperature and the low temperature evaluation index through quadratic fitting (the correlation coefficient is 0.960–0.998), and the regression relationship can be used to estimate the low temperature evaluation index at different test temperatures.
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