Electrostatic Self-Assembly of Ti_(3)C_(2)T_(x) MXene/Cellulose Nanofiber Composite Films for Wearable Supercapacitor and Joule Heater

The titanium carbide nanosheets(MXene)hold great potential for fabricating high-performance electronics due to their two-dimensional layered structure,high electrical conductivity,and versatile surface chemistry.However,assembling the small MXene nanosheets into flexible macroscopic films for wearable electronics still remains a challenge.Herein,we report the hierarchical assembling of MXene nanosheets and cellulose nanofibers into high-performance composite films via an electrostatic self-assembly strategy induced by polyethyleneimine.Benefited from the nacre-like microstructure of MXene"bricks"and cellulose nanofibers"mortars"interlocked by polyethyleneimine via hydrogen bonding and electrostatic interaction,composite films possess integrated superior flexibility,high tensile strength,and stable electrical conductivity,which are advantageous for wearable electronic applications.To provide a proof-of-concept design,a symmetric quasi-solid-state supercapacitor with the as-prepared composite film as electrode is fabricated,which exhibits a specific capacitance of 93.9 mF cm^(-2)at a current density of 0.1 mA cm^(-2)and almost constant capacitive behavior under different bending states.In addition,the composite film possesses capacities of electrothermal conversion and complete degradation in a hydrogen peroxide solution.These results demonstrate that the electrostatically self-assembled composite films hold great promise in the development of highly flexible,mechanically robust,and environmentally friendly energy storage and conversion devices.

Study of the Single Shear Performance of a Joint with a New Beech and Self-Tapping Screw Composite Dowel

A new beech and self-tapping screw composite dowel is proposed and studied,its performance being compared with that of beech dowels and self-tapping screws alone.The single shear performance of components connected by composite dowels was tested.Results show that the dowels are a good choice for components requiring high stiffness.Screws remain a good choice for components requiring excellent seismic performance.Combination group presents similar maximum load stiffness to those of composite dowels,but other ductility parameters are superior for composite dowels.The best connection mode was provided by two composite dowels.Based on connecting two points,structural elements with two composite dowels showed much better load bearing ability than when joined by two beech dowels or by two self-tapping screws separately.The structural element with two composite dowels not only presented better initial stiffness,but also exhibited a better ductility coeffi-cient and less energy consumption.So,the composite dowels can be used for beam column connection,dowel laminated timber,and restoration or enhancement of ancient buildings.

Energy Release Rate Measurement of Welded Bamboo Joints

Double cantilever beam tests were used to measure the energy release rates of linear vibrational welded moso bamboo joints.The influence of the length of the preserved cracks,the different combinations of the inner and outer bamboo surfaces and the moisture content is studied herein.The experimental compliance method,which is based on linear elastic fracture mechanics and has been shown to be an ideal method,was used to analyze data with the power equation.The results show that the preserved initial crack length does not have a significant effect on the final measured energy release rate,while the moso bamboo combination does affect the properties dramatically.The welded moso bamboo joints with inner-inner surfaces have the highest energy release rate of 122 J/m^2.The average energy release of the outer-outer combination was only 102 J/m^2.The expansion of the cracks also became easier when the moisture content of the welded joints was 18.5%compared to 4.5% and 10.1%.So the moisture resistance of the welded joints should be duly improved.

Environment-tolerant ionic hydrogel-elastomer hybrids with robust interfaces,high transparence,and biocompatibility for a mechanical-thermal multimode sensor

The human skin,an important sensory organ,responds sensitively to external stimuli under various harsh conditions.However,the simultaneous achievement of mechanical/thermal sensitivity and extreme environmental tolerance remains an enormous challenge for skin-like hydrogel-based sensors.In this study,a novel skin-inspired hydrogel–elastomer hybrid with a sandwich structure and strong interfacial bonding for mechanical–thermal multimode sensing applications is developed.An inner-layered ionic hydrogel with a semiinterpenetrating network is prepared using sodium carboxymethyl cellulose(CMC)as a nanofiller,lithium chloride(LiCl)as an ionic transport conductor,and polyacrylamide(PAM)as a polymer matrix.The outer-layered polydimethylsiloxane(PDMS)elastomers fully encapsulating the hydrogel endow the hybrids with improved mechanical properties,intrinsic waterproofness,and long-term water retention(>98%).The silane modification of the hydrogels and elastomers imparts the hybrids with enhanced interfacial bonding strength and integrity.The hybrids exhibit a high transmittance(~91.2%),fatigue resistance,and biocompatibility.The multifunctional sensors assembled from the hybrids realize real-time temperature(temperature coefficient of resistance,approximately1.1%℃^(-1))responsiveness,wide-range strain sensing capability(gauge factor,~3.8)over a wide temperature range(from-20℃ to 60℃),and underwater information transmission.Notably,the dualparameter sensor can recognize the superimposed signals of temperature and strain.The designed prototype sensor arrays can detect the magnitude and spatial distribution of forces and temperatures.The comprehensive performance of the sensor prepared via a facile method is superior to that of most similar sensors previously reported.Finally,this study develops a new material platform for monitoring human health in extreme environments.

湿法改性石墨烯在制备橡胶复合材料中的应用

橡胶由于其高弹性、良好的生物相容性、耐化学腐蚀及长期使用的稳定性等优点,在众多领域已有一百多年的应用历史。一般来说,在生胶硫化之前需要加入增强填料、润滑剂、偶联剂和促进剂等各类添加剂,以达到使用要求的性能。其中增强填料起到提高橡胶强度、提高橡胶耐磨耐热性、延长橡胶使用寿命的作用。相比于炭黑或者二氧化硅这些传统增强填料,新兴纳米材料石墨烯由于其优异的性能,只需极少量便可使橡胶的性能显著增强。然而,石墨烯片层之间的范德华力严重的阻碍了其在高分子机体内的分散,其在橡胶基体的分散性直接决定了石墨烯对于橡胶材料的增强效果。近年来,越来越多的研究开始关注通过在溶液中的湿法改性,包括物理或化学的方法来改性石墨烯,促进它与橡胶二者界面的相互作用,提高石墨烯在橡胶基体中的分散效果。本文总结了近几年湿法改性石墨烯在制备石墨烯/橡胶复合材料方面的研究进展。

Spectroscopic/Microscopic Elucid

The Arundo donax is a typical fast-growing species from the family Gramineae,which is widely cultivated in China.With a huge yield of A.donax in China,this plant offers great potential for biofuels production.The different types of organization of cell and the tissue in the A.donax could influence the efficiency of enzymatic hydrolysis.In this study,A.donax was subjected to 0.5%(w/w)sulfuric acid(H2SO4)for pretreatment at 140℃for 10 min,20 min,40 min,and 60 min,respectively.The changes in microstructure,chemical composition,topochemical properties were comprehensively analyzed.Using a series of spectroscopic and microscopic techniques including Fourier transform infrared spectroscopy(FT-IR),X-Ray diffraction(XRD),polarized light microscopy(PLM),and confocal Raman microscopy(CRM)to obtain the correlative structural and chemical information.Analysis results of chemical composition,FT-IR spectra and XRD indicated that with increasing reaction time,more hemicellulose and lignin would be removed.Correspondingly,there was an obvious increase of the cellulose relative crystallinity via extending reaction time.Results of the PLM observations showed that the birefringence gradually dimmed due to the diminishing of the cellulose component.Furthermore,the CRM mapping images showed the lignin component in compound middle lamellar(CML)was difficult to remove relatively as compared with that in secondary walls.These results indicated that the combination of spectroscopic and microscopic elucidation could give an insightful understanding of chemical changes in cellular level during pretreatment.