| Conductive aerogel has attracted wide attention in flexible piezoresistive sensors due to its good conductivity,excellent compressibility,high specific surface area,and strong designability.However,conductive aerogel is currently plagued by its complex preparation process,low mechanical strength,and poor structural stability.It is of great significance for the development of flexible pressure sensors to develop high-performance conductive aerogel based active materials with simple preparation process,clarify the relationship between the internal structure and performance regulation of conductive aerogel,and study the methods to improve the piezoresistive sensing performance.Aiming at the problems of the traditional piezoresistive sensors with limited sensitivity,narrow detect pressure range,poor long-term stability,and complex preparation process,this paper designs and prepares a series of novel nanofiber composite conductive aerogels based active material.Starting from simple and readily available electrospun CA nanofiber,and focusing on the influence of nanofiber on the microstructure,performance optimization,and interaction mechanism of conductive aerogel.Meanwhile,the preparation process,structure design,performance optimization,sensing mechanism,and wearable application of nanofiber composite conductive aerogel based active material for flexible piezoresistive sensors were studied.This high-efficiency electrospun nanofiber synergistic reinforcement strategy is expected to provide a new idea for the development of next-generation high-performance conductive aerogel based flexible piezoresistive sensing active materials.（1）Based on the 3D reconstruction of electrospun nanofiber,with CA nanofiber as skeleton and PPy as chemical crosslinker,the conductive PPy/CA nanofiber aerogel was prepared by the ice template assisted pore-forming and freeze-drying technology.The hydroxy-rich CA nanofiber and the in-situ polymerized PPy were remodeled under the hydrogen bond to construct a continuous 3D nanofiber network.The prepared PPy/CA nanofiber aerogel has the advantages of low density,high porosity,good flexibility,and designability.The PPy effectively prevents the slippage of nanofiber during deformation,and the internal nanofiber network also effectively dissipates the compression energy,making the compression strength of PPy/CA aerogel up to 14.7 k Pa.Moreover,the multilevel conductive structure of PPy/CA aerogel,from centimeter block,to micrometer pore,and to nanometer surface protrusion gives the flexible piezoresistive sensor assembled by PPy/CA-4:1 aerogel has a high sensitivity up to 60.28 k Pa-1 in a wide pressure range of 24 k Pa.It has a fast response time as low as 90 ms and can withstand more than 13000compression cycles.In addition,it can accurately recognition of many daily human movements signals as a wearable pressure sensor,such as joint bending,gesture change,pulse beating,and Adam’s apple movement.（2）Using MXene as conductive framework,CA nanofiber as supporting skeleton,and water-soluble SA as physical crosslinker,the CA/SA/MXene conductive aerogel was constructed via the liquid nitrogen-assisted directional freezing and freeze-drying technology.The mechanical property of MXene aerogel was significantly improved（18.6 k Pa）based on the double strengthening of two hydroxy-rich materials on MXene nanosheets to build a leaf-like structure,which was much higher than the one or two components MXene composite aerogels.The internal pore structure of CA/SA/MXene aerogel was macro-disorder but micro-order,and the nanofiber had a support and reinforcement effect on the pore wall from point to line and then to surface.The unique microstructure and controllable conductivity make CA/SA/MXene-0.3 aerogel assembled piezoresistive sensor achieve a high sensitivity of 114.55 k Pa-1 and a wide pressure range up to 21.78 k Pa.It has a fast response time of 150 ms and can withstand more than 24000 compression cycles.In addition,the wearable pressure sensor assembled by CA/SA/MXene aerogel can not only realize the real-time monitoring of various human motion signals but also realize the wireless signal transmission to the smartphone terminal after combining it with the Bluetooth module.（3）3D highly conductive graphene aerogel was constructed by 1D nanofiber and 2D pyrrole-reduced GO.The in-situ polymerized PPy enhanced the interaction and conductivity between each r GO nanosheet.And the CA nanofiber was used to synergistically build a"brick-mortar-rebar"reinforced structure of CA/PPy/r GO conductive aerogel.The presence of nanofiber can effectively dissipate the compression energy and provide strong support to the internal structure of aerogel.The mechanical performance of aerogel can be directly improved by regulating the content of nanofiber,and the strength of CA/PPy/r GO aerogel can reach 57.7 k Pa when the nanofiber content is 2 wt%.Meanwhile,its compression strength is further improved with the mass ratio of pyrrole:GO increase,and its conductivity reaches the highest（0.13 S/m）when the ratio is 5:1.The piezoresistive sensor based on CA/PPy/r GO-5:1aerogel has a high sensitivity up to 32.39 k Pa-1 in the pressure range of 30.5k Pa,and can withstand more than 10000 compression cycles.It can be used as a wearable pressure sensor to achieve real-time monitoring of pulse beating,finger bending,and foot pressure distribution of the human body.（4）Nanofiber-reinforced MXene/r GO conductive aerogel was prepared via the reduction of GO by pyrrole and in-situ composite with MXene.Combined with low-content 2D conductive nanosheets（MXene and r GO）as"brick",conductive polymer PPy as"mortar",and 1D nanofiber as"rebar"to build a"brick-mortar-rebar"reinforced structure.And a strong interfacial crosslinking of r GO and MXene nanosheets was realized based on the interactions of covalent and non-covalent bonds.It effectively overcomes the defects that 2D nanosheets which are prone to break and slip during compression deformation.Compared with the compression strength of r GO aerogel for 0.2 k Pa,the strength of MXene/r GO-0:2 aerogel increased sharply to 9.9 k Pa,and the mechanical property of aerogel was further improved with the increase of MXene.The sensitivity of the piezoresistive sensor assembled by MXene/r GO-1:2 aerogel is up to 20.80 k Pa-1 in a wide pressure range of15.6 k Pa.It has a fast response time of 100 ms and can withstand more than5000 compression cycles.Meanwhile,this wearable piezoresistive sensor can be applied to real-time monitoring of various human motion signals. |
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