The Study On Preparation And Piezoresistive Sensing Properties Of Polyacrylamidoxime-based Hydrogels With Ultrahigh Ionic Conductivity

The wearable pressure sensor,due to its advantages of small size,simple structure,rapid response to pressure and repetitive compression stability,has a broad application prospect in the field of portable and wearable electronic device sensing.Rencently,polymer conductive hydrogels have been studied as one of the ideal materials for piezoresistive sensors because of its good biocompatibility,certain conductivity and recoverability.Although polymer conductive hydrogels as wearable sensors have made some progress,it is still a challenge to obtain sensors with excellent mechanical properties,high detection sensitivity and wide detection range.With the rapid development of electronic equipment and the increasing demand of people,it is of great significance to develop wearable piezoresistive sensors with ultra-high conductivity,high sensitivity and wide detection range.In this work,polyacrylamidoxime（PAO）with high metal ion coordination capacity,polyethylene imine（PEI）and reduced graphene oxide（r GO）with excellent conductivity,were used as raw materials to prepare PAO/PEI and PAO/PEI/r GO hydrogels with good 3D structure.The LiCl solution was used to firstly develop a PAO-based wearable piezoresistive sensor with ultrahigh ionic conductivity an d good mechanical properties.The formation mechanism,ionic conduction mechanism,mechanical properties and piezoresistive sensing performance of PAO-based hydrogels were investigated.The specific research contents are as follows:（1）Research on PAO/PEI/LiCl₁(1 mol L^-1 LiCl)wearable piezoresistive sensor:The PAO powder was introduced into an alkaline aqueous solution（TBAOH）to fully dissolved,and evenly mixed with a small amount of PEI solution.The PAO/PEI hydrogels were prepared by threamal treatment with ultra-low polymer content（about5 wt%）,excellent compressive resilience（compressive strength almost remained unchanged after 50 cycles of compression under 60%strain）,good transparency,and good tensile strength（maximum recoverable tensile deformation is 60%）.The as-prepared PAO/PEI hydrogels show ultrahigh ionic conductivity of 19.1 S m^-1 in 6mol L^-1 LiCl solution,and higher ionic conductivity of 22.35 S m^-1 and excellent alkali resistance in 6 mol L^-1 KOH solution.This suggests that PAO/PEI hydrogels have great potential in sensing and energy storage fields.In addition,PAO/PEI/LiCl₁hydrogel as a wearable sensor presents excellent pressure sensing performance,with an initial sensitivity of 5.09 k Pa^-1 and detection range of 0.02 to 5.64 k Pa,and the response time and recovery time are only 205 ms and 300 ms,respectively.Moreover,it shows good flexibility and can realize real-time detection of human movement.The effects of PAO concentration and material mass ratio on the compressive mechanical properties and sensing properties of PAO/PEI hydrogels,and the effect of different LiCl concentrations on the piezoresistive sensing performance of PAO/PEI/LiCl sensors were discussed.Based on the molecular structure of the polymer,the ionic conductive mechanism of PAO and PEI promoting the dissociation of lithium salts and the formation of conductive channels with the assist of hydrophilic PEI promoting the migration of lithium ions was proposed.（2）Research on PAO/PEI/r GO/LiCl₁(1 mol L^-1 LiCl)wearable piezoresistive sensor:The PAO/PEI/r GO hydrogels with excellent resilience were prepared by threamal treatment after the GO dispersion is fully mixed with PAO and PEI solutions.The introduced GO formed a three-dimensional network structure in the PAO/PEI/r GO hydrogel,which not only enhanced the compressive strength（8.61 k Pa）of PAO/PEI/r GO hydrogel,but also endowed its electronic conductivity.When PAO/PEI/r GO hydrogels were immersed in KOH and LiCl solutions with different concentrations,it was found that PAO/PEI/r GO hydrogels had ultrahigh ionic conductivity of 12.91 S m^-1 and 15.21 S m^-1 in 4 mol L^-1 LiCl and 6 mol L^-1 KOH solutions,respectively.PAO/PEI/r GO/LiCl₁ sensors with ionic and electron dual conducting networks presented superior pressure sensing performance.The PAO/PEI/r GO/LiCl₁ sensor has an initial sensitivity of 8.55 k Pa^-1,a wide detection range of 0.02 to 7.86 k Pa,a low detection limit of 20 Pa,and fast response times of200 ms and recovery times of 300 ms,respectively.Moreover,the structure remains stable after 1000 times of compression under 10%deformation.The PAO/PEI/r GO/LiCl₁ sensors can provide real-time detection of joint flexion and muscle movement.The efects of r GO and different mass ratio of PAO,PEI and GO on the mechanics and pressure sensing performance of PAO/PEI/r GO/LiCl₁ hydrogel,and a wearable sensor with ionic and electronic dual conduction mode was developed,which has great application potential in touch display and human motion applications.