Preparation Of Nucleotide-regulated Adhesive And Tough Hydrogels And Their Application In Flexible Electronics

With the development of science and technology and the continuous progress of artificial intelligence technology,stretchable and bendable flexible wearable electronic devices have attracted great attention.Wearable sensors and supercapacitors,as popular electronic devices,are gradually becoming flexible,which will adapt to the deformation of integrated devices and meet the needs of practical applications.Recently,due to their high flexibility,stretchability,and tunable conductivity,hydrogels have been widely used in flexible sensors and supercapacitors.Although hydrogel electronic devices have made great progress,they still suffer from somes problems,such as poor mechanical properties,unsatisfying self-adhesiveness,low transparency,and inferior environmental stability,limiting their further development.As for the above problems,this work developed a series of conductive hydrogels with adhesion,toughness,rapid self-recovery capacibility,skin-like mechanoresponse,anti-freezing and anti-drying ability via the introduction of functional nucleotide molecule based on the design of network structure.The hydrogels were applied in flexible wearable sensors and supercapacitors,which greatly improves the comprehensive performances of hydrogel-based wearable sensors and supercapacitors.The detial contents and results are as follows:(1)To solve the problem of poor durability of hydrogel sensors,adenylic acid was used as a dynamic crosslinked agent to strengthen the hydrophobically associated polyacrylamide network,thus the hydrogels with high toughness,rapid self-recovery and fatigue resistance were successfully constructed.Adenylic acid could form ionic bonds and hydrogen bonds with cationic hydrophobically associated micelles and polymer chains,which significantly improved the mechanical properties of hydrogels.The optimum tensile strength and toughness of the hydrogels were 620 k Pa and 3.63 MJ/m³,respectively.Meanwhile,based on the dynamic reversibility of non-covalent bonds,the hydrogels exhibited good self-recovery property at room temperature without external stimulation.In addition,the presence of Na⁺and Cl^-endowed the hydrogels with good conductivity.The hydrogel sensor exhibited excellent durability and high sensitivity as a pressure and strain sensor in detecting various mechanical deformations.The hydrogel sensors could be used to continuously monitor and differentiate large range human activities and subtle physiological signals,such as movements of various human joints,making a fist,coughing,breathing,and speaking.(2)To prepare hydrogel sensors with excellent signal synchronization and biocompatibility,the adenylic acid cross-linked chitosan quaternary ammonium salt physical crosslinked network and covalent crosslinked polyacrylamide network are composited to construct a hydrogel with skin-like sensing ability and nonlinear mechanical response via imitating the structural composition of the dermal layer of skin.The two networks with distinct crosslinked strength underwent sequential rupture under tensile strain,thus the hydrogels exhibited low modulus,high resilience,strain-stiffening.Moreover,the hydrogels also possessed good biocompatibility,which can be safely used in wearable devices.The hydrogel sensors exhibited high strain sensitivity(GF=3.38),pressure sensitivity(GF=0.013 k Pa^-1),short response time(0.21 s)and negligible signal hysteresis.The output signals of the hydrogel sensors were almost synchronized with the input strain signals even at 500%strain.The hydrogel acted as a tactile sensor could detect differences in the weight of objects.Furthermore,the hydrogel wearable sensors could be used to detect limb bending,facial emotion changes,breathing,and speech signals.(3)In order to improve the accuracy of the hydrogel wearable sensor for human motion monitoring and achieve a clear observation of the detection site,in the further study,an adhesive and tough conductive hydrogel with high transparency was prepared via introducing adenylic acid into the poly(acrylamide-co-2-(dimethylamino)ethyl methacrylate)hydrogels.Since adenylic acid could form physical adhesion interactions with the surface of the materials via hydrogen bonds,metal coordination,hydrophobic interaction,cation-?and?-?stacking interactions,the hydrogels not only exhibited excellent adhesive property to various solid materials,but also possessed strong adhesion on skin.The hydrogel sensors could conformally adhere to the skin even during human motion and deform as the skin dynamically deformed.Therefore,the hydrogel sensors could accurately monitor large joint movements and small strains caused by speaking.In addition,due to the high transparency of the hydrogel sensor,the sensing sites could be clearly observed.More importantly,the human activities could be monitored wirelessly via combining the the hydrogel sensors with the wireless sensing devices and the smart phones.(4)Recently,hydrogel-based supercapacitors have attracted much attention,however,due to the weak interaction between traditional hydrogel electrolytes and electrodes,supercapacitors are prone to delamination when deformed.Moreover,traditional hydrogel-based supercapacitors trend to exhibit poor environmental stability,which greatly limits the development of traditional hydrogel-based supercapacitors.As for above problems,in this part of the thesis,the organohydrogel electrolytes with excellent adhesiveness,antifreezing ability,and water retention were successfully prepared by using water/glycerol binary solvent system,based on the nucleotide tackified strategy.The excellent adhesion of the organohydrogel electrolytes guaranteed the strong bonding between the electrolytes and the electrodes,thus an integrated supercapacitor with low interfacial contact resistance was designed,which effectively prevented its interlayer separation.The maximum area specific capacitance of the supercapacitor was 163.6m F/cm².In addition,the introduction of glycerol and Li Cl significantly promoted the anti-freezing and anti-drying abilities of the organohydrogel electrolytes,thus the capacitance of the supercapacitors still could keep 90.6%after 5000 charge-discharge cycles under-20°C.Meanwile,only 13.9%decay in specific capacitance was found after5 days of storage in an open environment.In addition,the supercapacitors presented excellent electrochemical stability based on the integrated structural design,and there was no dislocation occurs between the electrolytes and the electrodes even under severe deformations such as bending and twisting.The capacitance retention rate of the supercapacitors still reached 86.8%after 500 bending cycles.