Controllable Preparations And Flexible Mechanical Sensing/Supercapacitor Performances Of Stretchable Ionic Conductive Gel Composites

Ionic conductive gels are made of polymers mixed with salt electrolytes that can be electrolyzed into ions,showing wide applications in wearable electronics,human-machine interactions and soft robotics due to their simple preparation method,good biocompatibility,adjustable mechanical properties and high ionic conductivity.However,ionic conductive gel composites are still faced with the following urgent problems.Firstly,ionic conductive gel composites are prone to structural rupture when damaged by external forces,which greatly reduces the service life of the material.Secondly,the low mechanical strength of ionic conductive gel composites limits their matching degree with the mechanical modulus of human skin as a wearable electronic device.Thirdly,ionic conductive gel composites exhibit poor fatigue resistance,which results in poor recovery ability for multiple deformations.Finally,in the practical application,ionic conductive gel composites inevitably lose water at high temperatures and freeze at low temperatures,limiting their application in extreme environments.In view of this,this paper focuses on the precise design of gel network compositions,regulation of network interaction mechanisms,choice of electrolyte solvents and construction of gel network structures to develop a new type of stretchable multi-function integrated ionic conductive gel composites with good self-healing performance,high mechanical strength,excellent fatigue resistance and a wide temperature tolerance range.The applications in flexible electronic devices,such as wearable strain sensors and stretchable supercapacitors are explored.The main research work is as follows:（1）A dual-dynamic-network ionic conductive hydrogel（DICH）with both a hydrophobic association network and a metal coordination network was prepared by the one-pot method.Benefiting from the dual dynamic networks and its high-density hydrogen-bonded interactions,the prepared DICH showed a high fracture strength,a large tensile strain,and excellent fracture toughness.The dual dynamic networks in DICH have high-density dynamic reversible interactions,which could dissipate a lot of energy through fracture and recombination during the deformation process of materials,resulting in excellent notch insensitivity,self-healing properties at room temperature and good secondary processing ability.Due to the high tensile properties and high ionic conductivity,DICH could be directly used as a stretchable ionic conductor for assembling wearable strain sensors,displaying high sensitivity,fast response time and wide strain range,and still maintaining excellent mechanical and sensing properties even after cutting and self-healing or reprocessing.As a demonstration of device performance,the wearable resistive strain sensor assembled from DICH could monitor and recognize subtle and large human movements at joints in real time.（2）A densified hydrogen-bonded Fe³⁺/chitosan/polyacrylic acid（DHB-Fe/CS/PAA）with high tensile and compressible properties was obtained by a hydrogen-bonded network densification strategy,during which a dense hydrogen bond network between chitosan and polyacrylic acid networks activated by salt impregnation.By introducing the densified hydrogen bond networks,the prepared DHB-Fe/CS/PAA exhibited high tensile strength,large tensile strain and excellent fatigue resistance.The dynamic reversibility of metal coordination and hydrogen bonding gave DHB-Fe/CS/PAA good thermal accelerated self-healability.In addition,due to the high concentration of inorganic salts and charged functional groups in the polymer network of the gel,the DHB-Fe/CS/PAA still maintained high ionic conductivity and mechanical flexibility at-25 ^oC.The DHB-Fe/CS/PAA was directly used as a stretchable ionic conductor to assemble a wearable strain sensor,which not only had the advantages of a wide strain range and high sensitivity but also showed a fast response time and excellent cycle durability.As a demonstration of device performance,the wearable strain sensor assembled from DHB-Fe/CS/PAA detected and identified complex human movements rapidly and in real time.（3）A poly（zwitterion-acrylic acid）polyelectrolyte ionogel（PPIG）was prepared by one-step photoinitiated polymerization,among which ionic liquid was tightly locked in the random copolymer network of zwitterions and acrylic acids.Ascribing to the highly dynamic and adjustable electrostatic and hydrogen bond interactions,the PPIG showed high tensile strength,large tensile strain,high fracture toughness,excellent fatigue resistance,and self-healing performance.The PPIG used the water-free ionic liquid as the solvent,giving it a wide temperature operating range.Ascribing to the strong non-covalent interaction and good interface compatibility between the polymer chains and the ionic liquid,the PPIG showed high transparency and excellent self-adhesion with various substrates.Due to extraordinary mechanical resilience and high ionic conductivity,the resistive-type strain sensor assembled by PPIG exhibited a linear dependence of sensitivity on strain over a wide strain range and still showed excellent mechanical sensing performance after fracture/self-healing and peeling/self-adhesion.As a demonstration of device performance,a wearable strain sensor assembled by PPIG as a stretchable conductor could detect small and large human physiological activities in real time.（4）A novel pre-stretching/cryopolymerization/stress-releasing strategy was developed to prepare a self-wrinkled polyaniline hydrogel composite（SPHC）with a unique core-sheath structure.Due to the wrinkled structure as well as abundant hydrogen bonds and electrostatic interactions,the prepared SPHC material possessed high tensile strength,large tensile strain,and excellent fatigue resistance.The formation of the 3D interconnected polyaniline skeleton structure of the sheath in SPHC provided abundant active sites for its electrochemical storage.The good interfacial interaction of sheath and core enabled solid/liquid contact at the molecular level between the polyaniline electrode materials and the ionic conductive electrolyte interface,which optimized the ion diffusion dynamics in the electrochemical reactions.Upon cutting off the edge connections,the prepared SPHC could be directly used as an integrated stretchable all-in-one supercapacitor with outstanding capacitance,a high energy density and long cycle stability.The prepared stretchable all-in-one supercapacitor effectively avoided the delamination or slippage of electrodes and electrolytes of traditional flexible supercapacitors during deformation.The supercapacitor also maintained excellent electrochemical stability under large deformations of 500%strain and 180°bending.