Research On Flexible Stress Sensor For PDMS/CNT Composite Materials Controlled By Electrospinning ECNF

With the development of society,there is an increasing demand for application scenarios of flexible stress sensors.At present,significant progress has been made in the technology of flexible stress sensors.However,there are still many problems that need to be solved in the development of flexible stress sensors,such as how to make resistive flexible stress sensors have better mechanical properties such as tensile and fracture resistance in biological application scenarios,as well as better sensing performance such as sensitivity,stability,and stress response range.Carbon based flexible conductive composite materials are currently a good choice for the sensing layer of resistive flexible stress sensors,and their performance is crucial for improving the performance of resistive flexible stress sensors.However,the dispersion of conductive fillers in carbon based flexible conductive composite materials is poor,and they are prone to agglomeration,which restricts the mechanical and electrical properties of flexible conductive composite materials,thereby affecting the performance of flexible stress sensors.This article prepares electrospun ethyl cellulose fibers(ECNF)with a certain diameter and arrangement,and regulates the dispersion of CNTs in PDMS matrix and the mechanical and electrical properties of PDMS/CNT composites through electrospun ECNF.By utilizing the content,diameter,and arrangement degree of electrospun ECNF to regulate the sensitivity,cyclic stability,and effective stress range of PDMS/CNT/ECNF flexible stress sensors,the sensitivity and stability of monitoring human joint signals using flexible stress sensors can be improved.The main research findings are as follows:1.The effects of EC electrospinning solution concentration,solvent ratio,spinning voltage,electrospinning solution propulsion speed,and receiving roller speed on the surface morphology and diameter of electrospun EC fibers were studied.The results show that: 1)A electrospinning solution with a mass concentration of 10% and a solvent ratio of 5:5 can obtain continuous and smooth electrospinning ECNF;2)When the voltage is 17 kV,the diameter of electrospun ECNF is smaller and the thickness is more uniform,with a diameter of 193.9 ± 5.6nm.The diameter is mainly distributed between 100-300 nm,and the morphology is also smoother;3)By slowing down the electrospinning fluid propulsion speed,a reduced diameter electrospinning ECNF can be obtained.The electrospinning fluid propulsion slows down from 0.3ml/h to 0.2ml/h,and the diameter of the electrospinning ECNF decreases from 193.9 ± 5.6nm to 157.4 ± 4.7nm,with a diameter distribution mainly ranging from 100 to 300nm;4)By accelerating the speed of the receiving roller,an electrospun ECNF with improved directional arrangement can be obtained,and the diameter decreases to a certain extent.When the speed of the receiving roller increases to 1200rpm/min,the directional arrangement of the electrospun EC fibers obtained by electrospinning is high.The diameter of the electrospun EC fibers decreases from 225.1 ± 1.7nm at the receiving roller speed of 400rpm/min to 166.0 ± 3.6nm at the receiving roller speed of 1200rpm/min.2.The effect of electrospun ECNF on the mechanical properties and electrical conductivity of PDMS/CNT flexible conductive composites was studied.The results show that: 1)When the CNT content in PDMS/CNT flexible composite material is 7wt%,the tensile strength is 1.73 MPa,the fracture strain is 86.56%,and the toughness is 0.61MJ/m3;The tensile strength of PDMS/CNT flexible composite material with pre cut notches is 0.34 MPa,fracture strain is 18.85%,toughness is 0.04 MJ/m3,and conductivity resistance is 550 K Ω;2)After introducing 1wt% electrospun ECNF,the tensile strength of PDMS/CNT composite material increased to 2.46 MPa,fracture strain increased to 115.00%,and toughness increased to 1.30 MJ/m3.The tensile strength of PDMS/CNT flexible composite material with pre cut notches increased to 0.78 MPa,fracture strain increased to 19.60%,toughness increased to 0.11 MJ/m3,conductivity decreased to 228 K Ω,and conductivity increased;3)The mechanical properties and electrical conductivity of PDMS/CNT composites prepared by electrospun ECNF with a diameter of about 150 nm were improved,and the tensile strength,fracture strain and toughness were increased to 2.46 MPa,115.00% and 1.30 MJ/m3,respectively.The tensile strength,fracture strain,and toughness of composite materials with pre cut notches were increased to 0.78 MPa,19.60%,and 0.11 MJ/m3,respectively.The conductivity decreases to 228 K Ω and increases;4)When the EDMS/CNT composite material with high arrangement of electrospun ECNF obtained at a receiving roller speed of 1200rpm/min is introduced,the tensile strength is increased to 4.09 MPa,the fracture tensile strength is increased to 1.16 MPa,and the conductivity decreases to 201 K Ω,indicating that the mechanical properties and conductivity of the PDMS/CNT composite material with high arrangement of electrospun ECNF are better.The introduction of electrospinning ECNF effectively improves the mechanical properties and conductivity of PDMS/CNT conductive composites.3.Studied the effects of the content,diameter,and directional arrangement of electrospun ECNF on the sensing performance of electrospun ECNF/PDMS/CNT flexible stress sensors,and selected electrospun EC fiber/PDMS/CNT flexible stress sensors with good sensing performance for evaluation of human joint signal monitoring applications.The results show that: 1)When filled with 1wt% electrospun EC fibers with a diameter of about 150 nm and a high degree of arrangement,the sensitivity of the flexible stress sensor increased from 0.341 k Pa-1 to 11.300 k Pa-1,an increase of about 33 times;2)The repetitive stability of the PDMS/CNT flexible stress sensor prepared by filling 1wt% electrospun EC fibers with a diameter of about 150 nm and a high degree of arrangement has been effectively improved.The change rate of the head and tail resistance of the PDMS/CNT flexible stress sensor during cyclic stretching is basically consistent,demonstrating excellent repetitive stability;3)The PDMS/CNT/ECNF-1,0.21200 flexible stress sensor can effectively monitor joint folding/unfolding motion changes in real-time in human joint signal monitoring applications.