Preparation Of Multifunctional Conductive Hydrogels And Its Application In Flexible Electronic Devices

With the rise of the era of big data,internet of things and human-machine interaction,flexible strain sensors and supercapacitors have attracted continuous research from academia for their potential applications in next-generation environmentally friendly electronics.However,conventional hydrogel-based flexible electronic devices often face the problem of low-temperature freezing and water loss due to long-term storage,which greatly reduces the device performance.In addition,the e-waste generated after device damage will also greatly increase the pressure on environmental governance.Therefore,the preparation of multifunctional conductive hydrogels that tolerate extreme conditions and its appliation in flexible electronic devices is still a direction to be broken through.This thesis focuses on how to design and prepare hydrogels with high conductivity,anti-freezing,anti-drying and recyclable properties,and investigates its application potential in flexible strain sensors and supercapacitors.The main work is as follows:（1）PVA/SS/Gly/Li Cl（PSGL）hydrogels with excellent anti-freezing,anti-drying and recyclable properties have been prepared by using a dual-solvent system of Gly/H₂O,Li Cl as the conductive material,and polyhydroxy SS and PVA to form a hydrogel network framework by physical cross-linking.The results show that PSG₂L₂hydrogels can be repeatedly remolded into various shapes and the ionic conductivity maintains at 80.00%after recycling.DSC result shows that the freezing temperature of PSG₂L₂ hydrogel is as low as-63.38°C.The weight of PSG₂L₂ hydrogel is maintained at 78.3%of the initial after drying at room temperature for 20 days.In addition,PSG₂L₂hydrogel-based strain sensors achieve a sensitivity of 1.68 and a fast response time of0.2 s,which can accurately monitor complex human motion.After being frozen at-40℃for 24 h or stored at room temperature for 7 days,the GF reaches 1.61 and 1.60,respectively,and the sensor can still output stable signals.The supercapacitor achieves a specific capacitance of 107.1 m F cm^-2 at a current density of 0.2 m Acm^-2and a capacitance retention of 98.16%after 10000 charge/discharge cycles.In addition,the device has 91.9%specific capacitance retention at 90°bending and 56.5%specific capacitance retention after storage at-40℃for 24h.（2）Multifunctional SF/PVA/Gly/Li Cl（SPGL）conductive hydrogels have been prepared by using silk fibroin（SF）and PVA as gel skeleton and introducing Gly and Li Cl.Due to the abundant reactive groups（-COO-/-NH₂/-OH）and the specialβconformation of natural silk protein（SF）,which can greatly improve the ionic conductivity,anti-freezing,anti-drying and recyclable properties.The ionic conductivity of SPG₃L₂ hydrogel is as high as 52.63 m S cm^-1,and the ionic conductivity remains 84.71%after recycling.The DSC demonstrates that SPG₃L₂ hydrogels can be frozen at temperatures as low as-70℃,and retain 69.33%ionic conductivity after storage at-40℃for 24h.The weight retention rate of SPG₃L₂ hydrogels is also 82.6%after drying at room temperature for 30 days.In addition,the SPG₃L₂ hydrogel-based strain sensor has relatively higher sensitivity（GF=2.18）and response time（0.2 s）.After freezing at-40°C for 24 h or storing at room temperature for 7 days,the GF reaches2.00 and 1.87.The specific capacitance of the SPG₃L₂ hydrogel-based supercapacitor is 110.8 m F cm^-2 at a current density of 0.2 m A cm^-2,and the capacitance retention reaches 89.1%after 10000 charge/discharge cycles.In addition,the device exhibits 93%capacitance retention at 90°bending and 66.5%capacitance retention after storage at-40℃for 24h,with higher anti-freezing properties than the PSGL hydrogel-based supercapacitor.（3）Multifunctional GEL/PVA/Gly/CNT（GPGC）hydrogels have been successfully prepared by adding gelatin（GEL）and PVA into the mixed suspension of Gly/CNTs.Benefiting from the good conductivity of CNTs,the GPGC₃ hydrogels show high conductivity of 148.74 m S m^-1,189.57%breaking strain and 88.80%conductivity retention after 5 recycling cycles.The Gly/H₂O solvent system endows GPGC₃hydrogels excellent anti-freezing and anti-drying properties.The results of DSC show that the freezing temperature of GPGC₃ hydrogel is-45.67℃,and the conductivity remained 90.11%after storage at-40℃for 24h.GPGC₃ hydrogel maintains 68.75%weight and 85.73%conductivity after 30 days.In addition,the sensitivity of GPGC₃hydrogel-based strain sensor is as high as 3.98,which is much higher than that of PSGL and SPGL hydrogel-based sensors.The sensor has a response time as low as 0.2 s,allowing accurate monitoring of complex human motion.After freezing at-40℃for24 h or storing at room temperature for 7 days,the GF reaches 3.88 and 3.94 and the sensor still outputs stable and repeatable signals.Notably,the GPGC₃ hydrogel-based writing sensor also exhibited high reproducibility.