Study On The Construction And Properties Of Cellulose Based Multifunctional Conductive Gel Materials

Conductive gels,a class of hybrid materials that consists of conductive materials and polymer networks,are mainly divided into ionogels and conductive hydrogels.Conductive gels show great market prospects in artificial intelligence,brain-machine interfaces,implantable medical,advanced energy and wearable devices due to their combination of ultra-high flexibility,electrical properties,easy processing and epidermal compliance.However,the fabrication of high-performance conductive gel materials still faces challenges,for instance,ionogels suffer from poor mechanical properties and environmental stability;electronically conductive hydrogels face difficulties in balancing mechanical strength and high ductility as well as low electrical conductivity.Cellulose is an abundant biomass material with good biocompatibility and mechanical properties.In this dissertation,a series of cellulose-based gels with flexible,conductive and multiple functional features are prepared by utilizing cellulose as functional building blocks,combined with a composite construction strategy of in-situ rapid polymerization and dynamic physical cross-linking.The structure-property relationship between the gel network structure and target properties as well as their regulatory mechanisms are revealed by investigating the gelation and dynamic cross-linking processes.Finally,the feasibility of cellulose-based conductive gels in flexible wearable strain sensors,flexible display devices and other applications is explored.The main research content is described as follows:（1）Water-free ionogels suffer from poor mechanical properties.Inspired by the anisotropy and high strength of human tendon tissue,a novel wood-based ionogel（TCW）is prepared from macroscale delignified wood（DW）by vacuum-assisted infiltration and subsequent in-situ photoinitiated polymerization of polymerizable deep eutectic solvent（PDES）.The TCW is characterized in detail by 3D laser scanning confocal microscopy,2D X-ray diffraction,mechanical and electrical test systems.The composite of DW results in anisotropy and high mechanical strength of TCW like human tendon tissue（1.34 MPa,35 MPa）.TCW also possesses high transparency（90%）,stretchability（80%）,tunable high ionic conductivity（0.16S/m）.Due to the unique composite structure,TCW-based strain/touch sensors exhibit high sensing sensitivity（GF=1.13）,fast respondability and long-term signal stability to external stimuli.It can be used as flexible sensor components for attaching to human joints to detect subtle human movements.（2）Water-free ionogels suffer from poor humidity stability.The micro/nano scale natural bacterial cellulose（BC）3D network with improved flexibility is used as a reinforcing template.A double-network（DN）ionogel（BC-PDES）is constructed by multiple solvent substitution and in-situ polymerization.BC-PDES exhibits significantly enhanced tensile properties,compressive resistance and an order of magnitude higher toughness（1.86 MJ/m²）than PDES.Furthermore,compared to deliquescent PDES,BC–PDES shows moisture stability.The ionogel is demonstrated to be sensitive to external stimuli such as strain,pressure,bending and temperature.BC-PDES-based strain/pressure sensors exhibit high sensitivity（GF=1.29）and fast response features（response time is 14 ms）,enabling real-time discrimination and monitoring of human motion,physiological signals and different handwriting as wearable/touch sensors.In addition,BC-PDES possesses high transmission（90%）and high ionic conductivity（0.18 S/m）,the assembled electroluminescent devices exhibit high luminescence intensity,flexibility and patternability.（3）It is difficult for ionogels to obtain self-healing properties in anhydrous systems,and the conventional synthesis process is time-consuming.Nanoscale anionic bacterial nanocellulose（SBNC）acts as a dispersant for liquid metal（LM）to form stable core-shell structured LM nanoparticles（LMNPs）by a sonication process,avoiding the aggregation and poor compatibility of LMNPs.The mixing of LMNPs with DES can directly induce its rapid gelation（6 min）and form a solid water-free ionogel（LM-PDES）.The release of free radicals and Ga³⁺during sonication was demonstrated by electron paramagnetic resonance（EPR）,dye fading,UV-Vis spectroscopy and XPS,and a rapid gelation strategy of"LM initiation and cross-linking"is proposed.The rheological properties,viscosity,molecular mass and gelation time of the polymers are investigated.The modulation of the polymer network microstructure and crosslinking density is achieved by regulating the content of LMNPs,resulting in LM-PDES ionogel with printability,high transparency（94.1%）,ultra-stretchability（2600%）,autonomous self-healing,self-adhesion and high ionic conductivity（0.13 S/m）.In addition,LM-PDES exhibits good stability with less than 5%weight loss until 200°C and still shows high flexibility at-40°C.LM-PDES features multiple sensing properties and successfully demonstrates the application in wearable devices,3D forces mapping and flexible electroluminescent devices.（4）Inorganic conductive materials exhibit poor dispersion in gels and their contribution to gelation is often neglected.Surface microstructure design is critical for smart hydrogels.Upon one-step sonication,the hydrogel（LMBP）is rapidly gelated and cross-linked by using the"LM and MXene dual initiation and dual cross-linking"strategy,where nanoscale SBNC is the dispersant and support material.Meanwhile,upon ultrasonic cavitation,SBNC assists peeling of multilayer MXene and wrapping of LMNPs to avoid macro-phase separation.The mechanism of gelation initiated by dual initiation of LM/MXene and the formation of polymeric double network structure are investigated by various spectral characterization,EPR,and IR thermography systems.The hydrogels spontaneously undergo surface wrinkling due to the unique gelation mechanism and anchoring by LM/Mxene.LMBP hydrogels further display printability,shape adaptivity,superelasticity（800-3200%）,compressibility,self-healing,notch insensitivity and ionic/electronic complex conductivity.Finally,LMBP hydrogel-based strain sensors provide accurate and fast responsiveness to strain,and the wrinkled surface structure improves the sensitivity（GF=8.09）.LMBP-based flexible wearable strain sensors,electronic fabric sensing arrays and flexible electroluminescent devices are developed and successfully demonstrated.（5）Considering the structural flexibility,interfacial compatibility and high conductivity of conductive polymers,PEDOT:SBNC conductive polymers are prepared using SBNC as a persulfate template at the molecular scale.After the introduction of persulfate（APS）and AA monomers,a rapid gelation（only 14-27 s）of PEDOT:SBNC is achieved via the"LM initiation and crosslinking"strategy.A fully polymeric conductive hydrogel（LPBP）is constructed with electrostatic interactions,non-covalent hydrogen bonds and ionic ligand bonds mediated synergistically.The gel kinetics and self-heating rates of two"LM-initiated"strategies in the presence and absence of APS are analyzed using an IR thermography system.LPBP hydrogels are printable,shape-adaptive,self-adhesive,highly ductile（≈2850%）,compressible,self-healing,highly conductive（≈5 S/m）and antibacterial activity As a strain sensor,the LBPB hydrogel allows sensing of a wide strain range（>500%）and possesses a high strain sensitivity（GF=4.12）.Other physical stimuli,such as temperature,humidity and solvents,also can be sensed effectively.LPBP-based electronic fabrics and flexible electroluminescent devices are designed,and both demonstrate that LPBP hydrogels have potential for development in the fields of touch sensors and flexible displays.