Preparation And Performance Study Of Flexible Strain Sensors Based On Porous Conductive Polymer Composites

In recent years,flexible strain sensors have shown promising applications in the fields of wearable.Among them,flexible piezoresistive strain sensors have been widely studied due to their simple composition and easy signal processing.Flexible conductive polymer composites(CPCs),as a new type of functional material,have gradually become a popular material to enhance the performance of piezoresistive strain sensors.Currently,flexible piezoresistive strain sensing still suffers from narrow compressive strain response range,poor stability and durability.Porous CPCs materials naturally attract the attention of researchers because of their large compressive strain range.The selection of suitable materials and simple processes to realize porous CPCs with large compressive strain,high mechanical strength,and good stability are important to improve the sensing performance of piezoresistive strain sensors.In this paper,the preparation of high-performance flexible porous CPCs-based piezoresistive strain sensors was realized by designing and constructing different three-dimensional porous conductive network morphologies,exploring the intrinsic connection between the structure of porous CPCs and sensing performance,optimizing the mechanical properties of porous CPC-based sensors,solving the problem of unbalanced sensing performance such as sensitivity and response range,and further investigating the application of flexible porous CPC-based piezoresistive sensors.The practical applications of flexible porous CPC-based piezoresistive sensors in human motion monitoring,physiological health detection,and coping with complex external environmental changes are further investigated.The specific research results are as follows:(1)The CCS/KH560/PEI/CNT-COOH(CKPC)porous aerogel was prepared by freeze-drying technique using silane coupling agent(KH560)with carboxymethyl chitosan(CCS)and polyethyleneimine(PEI),respectively,introducing carboxylic carbon nanotube(CNT-COOH)with excellent electrical conductivity as conductive filler.In this study,the problem of poor mechanical properties and low resilience of CKPC aerogel was solved,the porous aerogel exhibited 86.3%mechanical compressive strain and retained the intact structure after unloading.In addition,the problem of unbalanced sensitivity and sensing range was solved,the porous CKPC composite aerogel-based sensor has a high sensitivity of 42.9 in the large strain range of 60%～76.3%.It also shows stable and repetitive electrical signal response under different strains.This porous structure of CKPC conductive aerogel-based sensor has very broad applications in the fields of human motion and flexible electronics.(2)The TPU/GNS/AgNWs@textile(TAG@textile)composite textile was prepared by coating graphene(GNS),silver nanowire(AgNWs)and polyurethane(TPU)layer by layer on a porous weft flat knitted textile substrate through a simple dip coating process,respectively.Since a small amount of conductive filler is adsorbed on the textile fiber surface,the mesh-like macropore structure of the textile is retained.TAG@textile-based flexible piezoresistive strain sensors have excellent breathability and are more comfortable to wear than composites such as aerogel.TAG@textile-based composite textile sensors also exhibit a wide strain response range of 90%,fast response time(40 ms)and reliable cycling stability(1000 strain cycles).Based on these excellent sensing properties,the TAG@textile sensor successfully achieved the detection of electrical signals such as such as pulse,limb activity,foot pressure distribution magnitude and position.In addition,it was shown that the introduction of AgNWs greatly improved the electrical conductivity of the textile(conductivity reached 115.73 S/m).The total electromagnetic shielding performance SET improved 10 times comparing to GNS@textile(6.75 dB increased to 61.68 dB).And the textile sensor also conferred excellent electro-thermal conversion performance under low voltage drive(at a low voltage of 2 V,the textile surface temperature rises from room temperature to 45.7℃ after 30 s),providing an effective strategy for wearable multifunctional applications of TAG@textile-based piezoresistive strain sensors.