Construction And Strain Response Performance Of Flexible Conductive Composite Fiber Based On Skin-core And Porous Structure

Conductive polymer composites(CPCs)are made by combining polymer with various conductive materials in a certain way,which possess good electrical conductivity,stretchability,and easy processing.CPCs can convert mechanical deformation into electrical signals through changes in conductive paths,and are widely used in flexible strain sensors.In this paper,in order to obtain a strain sensing material with broad scope of working strain and ultrahigh sensitivity,we use carbon black(CB),carbon nanotubes(CNT)as conductive fillers and thermoplastic polyurethane(TPU),poly(styrenebutadiene-styrene)(SBS)were chosen as flexible substrate.Then,the flexible fibers with sheath-core and porous structure were prepared via coaxial wet spinning method.The internal structure and strain response performance of the fibers were explored in depth.The details were as follows:1?The fabrication and properties research of TPU-CB/TPU fiber(1)TPU was chosen as the elastic matrix for the materials.Low-dimensional CB was served as conductive filler.The flexible composite fiber with a porous and skincore structure were prepared by simple coaxial wet spinning.Morphological manifestation displayed that the fiber has a two-layer structure consisting of an insulating inner layer(elastic zone)composed of pure TPU and a conductive outer layer(sensitive zone)composed of CB/TPU.In the conductive outer layer of the fiber,CB is distributed evenly,forming a favorable conductive path of CB.The evolved mechanism of multihole structure and the pore size in fiber were explored.By adjusting the experimental parameters(mainly the content of conductive filler),the sensing performance of porous fibers was regulated.(2)The strain response performance test showed that TPU-20CB/TPU conductive composite fiber(20 wt% CB in outer layer)successfully achieved ultra-high sensitivity(Gauge factor,GF=28084),wide strain response range(0-204%)and rapid response time(200 ms).In the cyclic response process,the TPU-20CB/TPU conductive composite fiber is not affected by the tensile rate.The conductive composite fiber exhibits excellent ohmic properties under different strains,and presents remarkable reliability in 11,000 stretch-release cycles.(3)We adopted the tunnel theory to analyze the strain sensing behavior of the TPU-20CB/TPU fiber,and the sensitive mechanism of the fiber under different strain was investigated according to the morphology observation of the fiber under different tensile conditions.(4)The practical application of the fiber was studied,and the strain sensor based on the composite material are insensitivity to the variation of the outside humidity and temperature,can be used for a variety human motion detection.The TPU-20CB/TPU strain sensor has rapid and reversible response to the circular motion of joints,and has a broad application prospect in the field of flexible wearable devices.2?Preparation and performance study of SBS-CNT/SBS and SBS-CB/SBS fiber(1)SBS was chosen as the flexible matrix for the mterials,zero-dimensional CB and one-dimensional CNT were used as conductive fillers.SBS-CNT/SBS and SBSCB/SBS conductive composite fibers were fabricated by coaxial wet spinning.Microstructure morphology revealed that the cross-sectional morphologies of fibers were irregular and the porous structure of different sizes existed in the sheath layer and the core layer.It was observed that CNT and CB were evenly distributed in SBS matrix,forming a complete conductive network.(2)The influence of diverse dimensional fillers on the strain sensitivity of conductive composite fibers under tensile action were studied.The resistance response mechanism of SBS-CNT/SBS and SBS-CB/SBS conductive composite fibers under tension was analyzed on the basis of the conductive theory of different dimensional conductive fillers.Due to the higher freedom of zero-dimensional CB particle and the larger aspect ratio of one-dimensional CNT,the sensitivity range of SBS-CNT/SBS fiber(0%?900%)was higher than that of SBS-CB/SBS fiber(0%?394%)due to the difference in fillers dimension and structure,while the sensitivity(GF=346.6)was lower than that of SBS-CB/SBS fiber(GF=81958.3).(3)The cyclic responses of SBS-CNT/SBS and SBS-CB/SBS conductive composite fibers under various tensile conditions were explored and compared.It was cleared that the composite fibers exhibited different resistance response signals to different strains.The stretching rate had no effect on the output signal of resistance responses of the two conductive composites fibers,and it have high stability and excellent reliability.(4)The practical application of fibers were studied.The strain sensor assembled with SBS-CNT/SBS and SBS-CB/SBS conductive composite fibers can be used for the detection of large strain range,and can reflect the change of strain in the circuit through the brightness of the small bulb,indicating that the conductive composite materials have a good application prospect as a flexible strain sensor.