Construction And Performance Of MXene-Based Textile-Structured Flexible Force Sensors

With the rise of the Internet of Things and artificial intelligence,flexible wearable force sensors composed of flexible substrates and sensitive active materials can convert external stimuli and human physiological information into visualized electrical signals,and show great potential for applications in emerging fields such as smart medicine,human-computer interaction,and virtual reality by their high flexibility,surface conformability,and ease to wear.However,flexible force sensors are still facing many problems,such as high sensitivity and wide sensing range with poor compatibility,single function,and difficulty in effectively identifying and distinguishing different stimuli,which greatly limit their application.Therefore,the development of multifunctional flexible force sensors with excellent sensing performance is of great scientific value and practical significance.With excellent electrical conductivity,rich surface groups,and tunable chemical structure,two-dimensional transition metal carbides or nitrides（MXene）show excellent performance and application advantages in the field of wearable flexible electronics.As the second skin of the human body,textile not only has good wearing comfort,but also the multi-scale textile structure can provide a lot of multi-level deformation space for the design of flexible sensors,which is an ideal flexible substrate material.Therefore,a series of flexible wearable force sensors with excellent sensing performance are constructed by optimizing the design of MXene materials and taking advantage of the textile structure.making it high-performance,multi-functional and multi-modal,which provide new ideas for the development of smart wearable force sensors.The research content is as follows:（1）In view of the effect of MXene kinds and fabric structure on the sensitivity of pressure sensing has not been systematically studied,two series of MXene@fabric composites were prepared by a simple and low-cost dip-coating method,and assembled to obtain two series of flexible pressure sensors.They are Ti₃C₂T_x@fabric flexible pressure sensor with five different structures（plain,3/1twill,weft flat knitted fabric,jersey cross tuck fabric,and non-woven fabric（NWF））as the flexible substrate,and MXene@NWF flexible pressure sensor with six different MXene materials（Ti₃C₂T_x,Ti₂CT_x,Ti₃CNTx,Mo₂CT_x,Nb₂CT_x and Mo₂Ti C₂T_x）as the active material.Benefit from the 3D fluffy fiber network structure of NWF and the superior conductivity of Ti₃C₂T_x,the Ti₃C₂T_x@NWF flexible pressure sensor exhibits good sensitivity(S_max=6.31 k Pa^-1),a wide pressure sensing range（150 k Pa）,fast response/recovery time（300 ms/260 ms）and excellent cycling stability（25k Pa,>2000 cycles）.In addition,it can be used not only for the full range of human activity monitoring from micro-scale activities,but can also be assembled into sensing arrays for finger touch action and spatial pressure distribution.This study provides a reliable theoretical and experimental support for the design of high-performance MXene/textile-based flexible pressure sensors and the on-demand regulation of sensing performance.（2）In view of flexible pressure sensor with low sensitivity and single function,the metal nanoparticles（NPs）/MXene/NWF（Au NPs@MNWF and Ag NPs@MNWF）composite fabrics with multi-scale hierarchical structures were prepared by a self-reduction strategy,and a high-performance,multifunctional fabric pressure sensor with pressure sensing,electric-light dual-energy-driven heating,and antibacterial properties was constructed.The self-reduction strategy is green and introduces metal NPs of uniform size and controlled density on the MNWF without the use of reducing agents and surfactants.Owing to the introduction of metal NPs and the construction of multi-dimensional layer structure,the sensitivity of Au NPs@MNWF flexible pressure sensor is improved by 300%compared to MNWF flexible pressure sensor(exhibiting 24.5 k Pa^-1 sensitivity in 0-100 k Pa).The sensor shows obvious application advantages in high-precision human physiological signal monitoring and disease primary diagnosis.In addition,with the excellent electrical conductivity,unique plasma effect and superior antibacterial properties of metal NPs,Au NPs@MNWF also showed enhanced Joule heating performance（129.9°C at 9V）,photothermal conversion performance（58.6°C under simulated sunlight）and antibacterial performance（The reduction rate of E.coli and S.aureus is 90.6%and 81.4%,respectively）.The self-reduction strategy is also universal,reducing Ag⁺to Ag NPs,and the prepared Ag NPs@MNWF pressure sensors also exhibit enhanced pressure sensing performance and dual photoelectric energy response and antibacterial performance were enhanced.Thus,this study provides a promising general strategy for performance optimization and functional diversification of MXene based flexible pressure sensors.（3）In view of difficulty for remaining high sensitivity in wide range for MXene/fabric based strain sensor,the MXene/PVA/elastic fabric（MPPEF）strain sensor was constructed by depositing Ti₃C₂T_x and polyvinyl alcohol（PVA）in a layer-by-layer self-assembly process to create a micro-nano"brick-mortar"stacked sensing layer and using a highly elastic warp knitting weft insertion fabric as a stretchable substrate.Based on the slip effect between MXene/PVA in the sensing layer of the stacked structure,the microcrack effect and the effective contact-separation mechanism between the conductive yarns,the strain sensing signal is enhanced so that the sensor exhibits a wide strain sensing range（50%）,high sensitivity(GF_max is 288.43),fast response time（50 ms）,ultra-low detection limit（0.067%）,and excellent cycling stability（1000 cylce at 5%strain）.The device can monitor the full range of human activities such as breathing,swallowing,and limb joint movements.This research provides a new approach for developing high-performance MXene based fabric strain sensors.（4）In view of that wearable flexible force sensors have a single sensing mode and are difficult to effectively identify and differentiate mechanical stimuli,a stretchable Carbon/PDMS/MXene composite yarn（CPMY）with a core-sheath coaxial structure was prepared by using Ti₃C₂T_x MXene coated elastic covered yarn as the core stretchable yarn electrode and CB/PDMS conductive elastomer as the sheath piezoresistive sensing material to construct a multi-modal flexible textile mechanical sensor,which can differentiate multiple mechanical stimuli（pressure,stretch and bending）using a single current signal.Thanks to the rich micro-nano multi-stage sensing structure,CPMY shows a pressure sensitivity of up to 16.06 N^-1,a wide sensing range（5 N）and excellent durability.In addition,with the stretchability of the core layer MXene yarn electrode and the good flexibility of the sheath layer CB/PDMS elastomer,CPMY maintains structural integrity under tensile load and shows good tensile sensitivity（GF=12.09）,a wide sensing range of 100%,and excellent cycling stability as a strain sensor.The sensor also has excellent bending sensing performance.In addition,based on the positive and negative response of the current signal,and combined with the multi-electrode signal acquisition mode,the CPMY flexible force sensor can realize the sensing and distinguishing of multiple mechanical stimuli.The CPMY flexible fabric sensor and large-area fabric sensing array（182 pixel）were fabricated by combining it with ordinary fabric using traditional embroidery techniques to verify its feasibility in monitoring human daily activities and spatial pressure distribution.