Preparation And Properties Of Electrospun Nanofiber Membrane Strain Sensor

With the developing of 5G technology,smart wearable products,such as smart bracelets,smart glasses or smart wristbands,have gradually become the important parts in people's lives because of their outstanding contributions in human health monitoring,motion detection and even human-computer interaction.Strain sensors,which play the core component in smart wearable products,possesse the functions of sensing external stimuli and acquiring data and information,whose research is mainly focused on the improvement of performance such as working range,sensitivity,response time and working stability.Owing to the large specific surface area,good flexibility,good stretchability,lightness and air permeability,fiber-based flexible strain sensors have attracted widespread concern of researchers.In this work,electrospinning technology was utilized to prepare flexible polyurethane(TPU)fiber substrates,and multi-walled carbon nanotubes(CNTs)with good electrical conductivity and mechanical properties were employed as conductive media to fabricate fiber-based flexible strain sensors.Aiming to enhance the number of CNTs coated on TPU fiber substrate and improve the fastness of adsorption,dopamine(DA)was used to modify the TPU fiber substrate(DATPU)firstly and then CNTs were used to coat on the DATPU substrate by ultrasonication(DATPU/CNTs).In this paper,two kinds of strain sensors were prepared using isotropic and anisotropic electrospun fiber films as the substrate and CNTs as the conductive medium,firstly.The results indicated that isotropic fiber film substrate is more conducive for developing strain sensors with good performance.Then,in order to further improve the properties of the strain sensors,carboxylated CNTs(CNTs-COOH)with good dispersion were deposited on the isotropic fiber film substrate,and finally a strain sensor with excellent performance was obtained.(1)The modification of TPU nanofiber membranes were modified by using rapid dopamine self-polymerization method.The resultant TPU nanofiber membrane was successfully modified by dopamine certified from the results of the surface morphology,contact angle test,XPS test and so on.Comparing to the TPU/CNTs,DATPU/CNTs exhibited larger working range of 422%,higher sensitivity(GF=116)and better washing fastness.In addition,with excellent working stability,DATPU/CNTs can withstand 5000 cycles of stretching-releasing tests,indicating good repeatability and durability.(2)For fabricating oriented DATPU/CNTs conductive fiber membrane,TPU fiber membrane with oriented arrangement was prepared by using high-speed drum collector.Then the electromechanical properties of oriented DATPU/CNTs were tested,from which it can be found that when stretched parallel to the fiber direction(P-DATPU/CNTs),the relative resistance changed linearly with strain,and the linearity of r~2 could reach 0.997.In addition,the working range of the P-DATPU/CNTs conductive fiber membrane could reach 370%,the sensitivity of GF was 22 with excellent working stability.After 5000 cycles of stretching-releasing tests,the P-DATPU/CNTs conductive fiber membrane still exhibited excellent durability and repeatability.(3)The DATPU/CNTs-COOH conductive fiber membrane was prepared by using dopamine modified TPU fiber membrane with non-oriented structure as substrate,CNTs-COOH as conductive filler.Owing to the remarkable dispersity and firm adsorption on DATPU fiber resulted from the hydrogen bonds with the amino and hydroxyl groups of dopamine,the DATPU/CNTs-COOH conductive fiber membrane had simultaneously larger working range of 710%,higher sensitivity of gague factor(GF)>1126 and excellent working stability.During 15000 cycles of stretching-releasing tests,the conductive fiber membrane exhibited excellent repeatability and durability.Finally,a good response can be acquired when applyed DATPU/CNTs to detect human movement,such as:swallowing and joint bending.Integrating the DATPU/CNTs-COOH strain sensor,Bluetooth signal acquisition device and battery into a kneecap,an intelligent motion detection kneecap was produced,which can accurately respond to different types of leg movements.