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.

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.

Characterization of natural fiber from manau rattan(Calamus manan)as a potential reinforcement for polymer-based composites

Researches on novel natural fibers in polymer-based composites will help promote the invention of novel reinforcement and expand their possible applications.Herein,in this study,novel cellulosic fibers were extracted from the stem of manau rattan(Calamus manan)by mechanical separation.The chemical,thermal,mechanical and morphological properties of manau rattan fibers were comprehensively analyzed and studied by Fourier transform infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD)analysis,thermogravimetric analysis(TGA),single fiber tensile test and scanning electron microscopy(SEM).Component analysis re-sults showed that the cellulose,hemicellulose and lignin contents of C.manan fibers were 42wt%,20wt%,and 27wt%,respectively.The surface of the rattan fiber was hydrophilic according to the oxygen/carbon ratio of 0.49.The C.manan has a crystalline index of 48.28%,inducing a max-imum degradation temperature of 332.8°C.This reveals that it can be used as a reinforcement for thermoplastic composites whose operating temperature is below 300°C.The average ten-sile strength can reach(273.28±52.88)MPa,which is beneficial to improve the mechanical properties of rattan fiber reinforced composites.The SEM images displayed the rough surface of the fiber,which helped to enhance the interfacial adhesion between the fibers and matrices in composites.These results indicate the great potential of C.manan fibers as the reinforcement in polymer-based composites.