Conductive Network Construction And Performance Regulation Of Flexible Strain Sensing Sensors

Recently,strain sensing sensors based on flexible polymer（FSSS）have shown a wide range of potential applications in human-machine interaction,electronic skin,and nanogenerators,etc.,which have attracted widespread attention from researchers.However,at present,the preparation method of FSSS is still relatively simple,and its sensing mechanism and theoretical system are not perfect.It is still a huge challenge to take into account of both the wearability and stain sensing performance of FSSS.Hence,in this paper,the structure design and conductive network construction of FSSS are used to realize the regulation of its strain sensing performance and wearability,and provide a theoretical basis for the development,research and application of high-performance flexible wearable materials.The specific research content and main results are as follows:1.The high stretchability and high sensitivity of the FSSS are achieved by designing the“wrinkle-assisted crack”microstructure,which overcomes the interrelationship between sensitivity and working strain range of FSSS to a certain extent.The carbon nanotube（CNTs）ink/polyurethane（PU）yarn conductive polymer composite was prepared by swelling-ultrasonic method.The yarn was pre-stretched,and the wrinkle-assisted crack microstructure is constructed on the surface of the yarn.The design of this structure is attributed to the mismatch of Young’s modulus between the CNTs ink and the PU yarn during the stretching process and the Poisson effect of the elastic matrix.The microstructure endows the FSSS high strain sensing sensitivity（gauge factor（GF=1344.1）at 200%strain）and a wide working strain response range（0-200%）,In addition,this FSSS also has an ultra-low detection limit（<0.1%strain）,excellent durability（>10,000 cycles）,and excellent bending strain response sensitivity and stability.This high-performance FSSS can achieve a full range of human motion monitoring.2.The wearability of FSSS is improved by designing the modulus-adjustable polyacrylamide（PAM）hydrogel as the flexible polymer matrix.Highly stretchable,and biocompatible PAM/calcium alginate（CA）（PAC）hydrogel was prepared by the ionic cross-linking with calcium chloride/ethyl alcohol and the construction of ion conductive network.Under large deformation conditions,the dynamic ionic bond between sodium alginate and Ca²⁺serves as the“sacrifcial bond”,which can effectively dissipate energy,while the PAM chain bridges the crack and stabilizes the network,endowing PAC hydrogel with outstanding mechanical performances,compressibility and good self-recovery performance.The ionic hydrogel FSSS has satisfactory sensing range（0-1700%）and can precisely detect dynamic strains（20-800%strain）.Meanwhile,it also exhibits fast response time（800 ms）and long-time stability（200stretch-recovery cycles）.The low-modulus PAC hydrogel posses good skin adaptability,which can improve wearability.The assembled FSSS can monitor and distinguish complex human movements.3.The sensitivity of the conductive hydrogel FSSS is further improved by designing a more complete conductive network.Gelatin is a promising material for improving the dispersion of intrinsically conductive polymers inside the hydrogel because of its favorable affinity to the intrinsically conductive polymers.A stretchable,flexible and conductive PAM/gelatin/PEDOT:PSS composite hydrogel was prepared by in-situ polymerization,which was used the intrinsic conductive polymer PEDOT:PSS as conductive components to construct the conductive network.The physical entanglement between polymer chains and rich dynamic hydrogen bonding endows the composite hydrogel excellent mechanical properties and self-healing ability.The conductive hydrogel FSSS possess good sensitivity（GF=1.58）,ultra-wide sensing range（0-2850%strain）,short response time（200 ms）,and excellent stability（1200cycles）.This excellent strain sensing ability endows FSSS effective discernibility for detecting intricate human motions.Importantly,the hydrogel device can also act as a stretchable（300%strain）triboelectric nanogenerator（STENG）to achieve efficient energy harvesting.Working in single-electrode mode,STENG can generate a short-circuit current of 26.9μA,an open-circuit voltage of 383.8 V and short-circuit transfer charge of 92 n C.The integrated abilities of strains sensing and energy harvesting promise the hydrogels for high performance self-powered wearable devices and stretchable power sources.4.The ultra-high stretchable and modulus-adjustable FSSS is designed through the synergistic effect of the nano effect of inorganic nano-materials and the cross-linking of the hydrogel itself.Montmorillonite（MMT）-dispersed CNTs were incorporated into PAM hydrogel to successfully prepare ultahighly stretchable and strain-sensitive PAM/MMT/CNTs（PAMMC）conductive nanocomposite hydrogel,which used CNTs as conductive fillers and MMT as the dispersant for CNTs.It has been found that MMT could not only assist the homogeneous dispersion of MWCNTs but also effectively enhance the mechanical property of the resultant hydrogels.Uniaxial tensile tests show that the nanocomposite hydrogel exhibits excellent flexibility and can be stretched to a strain of 4210%.In addition,PAMMC hydrogel strain sensing material exhibits good sensitivity（GF=1.39）and a very wide response range（0-4210%strain）,and can accurately detect ultra wide dynamic strain（5-2500%）.It also exhibits fast response time（300 ms）and excellent durability and reproducibility（500 stretch-recovery cycles）.The FSSS can also detect various complex human movements.5.The conductive hydrogel requires to maintain good stability when it is used as a wearable electronic device.Especially,when the temperature is below zero and long-term storage,the moisture in the material is extremely volatile,which often leads to unstable sensing signals.Taking advantage of the lower vapor pressure and hygroscopicity of glycerol,an antifreeze and anti-drying organohydrogel was prepared through partially replacing the water molecules in the above PAMMC nanocomposite conductive hydrogel by a simple solvent replacement method.The organohydrogel exhibits long-lasting moisturizing ability（8 days）,excellent freeze resistance（-30°C）,and outstanding mechanical flexibility.Thanks to the inherent stretchability and stability of the organohydrogel,the assembled FSSS exhibits an extremely wide strain sensing range（>4196%strain）and high sensitivity（GF=8.5）.More importantly,the FSSS can withstand more than 2000 loading-unloading cycles at ambient temperature,exhibiting high stability and excellent durability.Furthermore,the antifreeze organohydrogel possesses high sensitivity（GF=3.37）in a relatively wide strain response range（0-1000%strain）at extremely low temperatures（-30°C）.The FSSS can be used for human motion monitoring under different environments.This design shows the great potential applications for the development of artificial skin,intelligent communication and human-machine interaction at extremely low temperatures...