Preparation Of Multifunctional Hydrogels And Their Application In Sensors And Supercapacitors

With the rapid development of technological society,flexible wearable devices such as sensors and energy storage devices have shown broad application prospects in the fields of personalized electronic products,human-computer interaction,electronic skin,and soft robots.Multifunctional hydrogels are not only widely used in flexible sensors due to their excellent stretchability,self-healing,adhesion,and electrical conductivity,but also are ideal electrolytes for fabricating flexible supercapacitors with high energy density,long cycle life,and environmental protection.However,traditional hydrogels lose mechanical flexibility and ionic conductivity at sub-zero temperatures due to contain a large amount of water,and limiting their practical application as sensors in cold environments.Therefore,it remains a challenge to obtain hydrogels with excellent anti-freezing properties,stretchability,adhesion and ionic conductivity through simple methods.Besides,the reported hydrogels-based supercapacitors still have the disadvantages of poor mechanical properties and low specific capacitance,so it is urgent to develop hydrogels-based supercapacitors with excellent flexibility,self-healing properties and high specific capacitance.Based on the previous research progress,two different hydrogels were prepared for flexible strain sensors and supercapacitors,respectively.The specific research content and results are divided into the following two parts:（1）An organohydrogel with excellent mechanical properties,transparency,adhesion and multi-environmental stability is fabricated via incorporating biological macromoleculeκ-carrageenan,aluminum ion and polymer monomer into DMSO/H₂O binary solvent by a simple UV-initiated polymerization strategy.The existence of aluminum ions andκ-carrageenan endows the organohydrogels with strong toughness and significant anti-swelling behaviors,the strong hydrogen bond interaction between DMSO and water molecules effectively improved the multi-environmental tolerance of the organohydrogel.Consequently,the prepared organohydrogel has excellent mechanical properties（strain 1560%and stress 71 k Pa）,anti-swelling performance,anti-freezing and anti-drying property（80%after 7 days）.Moreover,the as-assembled strain sensor based on this organohydrogel possesses a relatively high strain sensitivity（GF=1.8）and favorable stability,which can also ensure monitor human motions in real time.Furthermore,the sensor can monitor strain and human motion in different solvents and a wide temperature range（-50-50℃）,respectively.Interestingly,the as-prepared organohydrogel displays adjustable optical properties in DMSO and H₂O,and can serve as a dynamic information memory device for recording,erasing and encrypting information.The transparent,stretchable,anti-swelling,anti-freezing and anti-drying property of organohydrogels have great potentiality in the fields of wearable sensing devices and information encryption.（2）A novel multifunctional hydrogel polyelectrolyte is developed comprising the alizarin red S（ARS）redox mediator and the double cross-linked polyacrylic acid（PAA）by the vinyl hybrid silica nanoparticles（VHSNPs）and hydrogen bonds.The PAA is acted as the polyelectrolyte matrix due to its high tenacity,and meanwhile the abundant dynamic hydrogen bonds in the PAA chains endow as-prepared polyelectrolyte with excellent self-healing property.The VHSNPs are used as stress buffer centers when large strain is applied,whereas the dissolved and dispersed protons and ARS redox additive in the polyelectrolyte networks can provide effective ionic conductivity and additional pseudocapacitance.Based on the above synergistic effects,the as-prepared hydrogel exhibits ultrahigh stretchability（～2400%strain）,robust mechanical toughness（lift up the 500 g weights）,favorable self-healability,high ionic conductivity（33 m S/cm）,powerful self-adhesiveness and superior redox activity.The facilely fabricated carbon-based supercapacitor using the obtained hydrogel as the electrolyte can achieve large electrode specific capacitance of 248 F/g and high mass energy density of 16.7 Wh/kg,which are much larger than the recently reported stretchable and self-healing hydrogel electrolytes based flexible supercapacitors.In summary,we preparedκ-CG/p（HEMA-AA-AAm）/Al³⁺organohydrogels with multiple functions such as transparency,stretchability,and anti-freezing property,which can be used as flexible sensors to monitor strain and human motion.In addition,the VHSNPs-PAA/H₂SO₄/ARS hydrogels with ultrahigh stretchability,favorable self-healability,powerful self-adhesiveness and superior redox activity,which can be assembled supercapacitor with activated carbon electrodes to form high mass energy density.