Fabrication Of Janus Graphene Oxide Hybrid Nanosheets For Self-healing Nanocomposite Hydrogels

Self-healing nanocomposite hydrogels can improve the self-healing ability and mechanical strength of nanomaterials through surface modification,and have been widely applied to the human motion and health monitoring fields,such as wearable flexible sensors.Janus nanomaterials are special nanomaterials with asymmetric structures or properties,unique dual functionality,regularity and designability.To improve the performance,a bifunctional nanomaterial can be designed to realize the synergistic enhancement of the electrical/self-healing performance of the hydrogel sensors.In this paper,Pickering emulsion template was utilized to obtain multifunctional Janus nanomaterials,which were then impregnated in hydrogels,and Janus nanocomposite hydrogel sensors with strong application ability and service life were designed.The self-healing mechanism of hydrogels and the synergistic effect of Janus on their mechanical and electrical properties were systematically studied.The simultaneous improvement of the self-healing,electrical and mechanical performances of Janus hydrogels was explored,and wearable flexible sensors with high sensitivity and high stability were prepared.This thesis contains the following three parts:1.Fabrication of Janus graphene oxide hybrid nanosheets by Pickering emulsion template for self-healing nanocomposite hydrogels.Self-healing hydrogels have an extremely hydrophilic three-dimensional network structure,and their self-healing properties similar to human skin are the key to improve durability and prolong service life.However,most self-healing hydrogels have only moderate recoverability.Here,we reported a class of multifunctional Janus graphene oxide（GO）-type nanomaterials,which not only endowed the gel with excellent dual self-healing properties but also enhanced its mechanical strength.Asymmetric functionalization of Janus nanosheets were achieved in typical oil-in-water Pickering emulsion by atom transfer radical polymerization（ATRP）and mussel-inspired chemistry.Poly（2-（acryloyloxy）ethyl ferrocenecarboxylate）（PMAEFc）and polydopamine（PDA）were unsymmetrically grafted on the two sides of GO（Janus GO-PMAEF/PDA（JGNs））,which successfully applied in self-healing nanocomposite hydrogels.At room temperature,the breaking strength is 0.94 MPa and the elongation at break is 508.5%.Based on the collaborative effect of metal-ligand coordination and host-guest interactions,the self-healing efficiency can reach to 93.4%within 1 h.Compared with the same kind of soft material,it can significantly improve the self-healing level,and has an important application prospect in the fields of flexible sensing and human-motion health monitoring.2.Fabrication of Janus nanosheets by Pickering emulsion for self-healing hydrogels and application in strain sensors.Wearable hydrogel sensors have become a popular new device in human health care.In this study,JGNs/polyacrylic acid（JGNs/PAA）hydrogels with dual self-healing properties were prepared and applied to hydrogel flexible sensors.Based on different nanomaterials modification techniques,JGNs nanomaterials were modified by reversible addition-fragmentation transfer（RAFT）polymerization and mussel-inspired chemistry in Pickering emulsion environment,and then firmly bonded to the hydrogel network.Due to the dynamic reversible non-covalent interactions between the cyclodextrin groups of PAA chains and ferrocene groups of JGNs（host-gust interaction）and the metal-ligand coordination among Fe³⁺,H₂O and catechol groups（PDA）,the developed hydrogels have 93.7%self-healing efficiency,0-830%detection range,180 repeated stretching cycles and consistent response/recovery time（～0.5 s）.The hydrogel sensors can detect and monitor various human movements in real time,such as bending,kicking and running of fingers,wrist and elbow,and verifies the rapid self-repair,high sensitivity,sensing stability and strength and toughness of Janus hydrogel sensors.3.Highly conductive,stretchable and mechanical Janus graphene oxide-based self-healing hydrogels for wearable electronic applications.To acquire hydrogels-based sensors for wearable electronic devices,highly conductive self-healing hydrogels substrates with excellent mechanical properties are demanded.Nevertheless,it is a challenge to simultaneously realize the abovementioned characteristics of sensors.Herein,multifunctional Janus GO-type nanoparticles were employed as“hardware”for incorporation in“hard”polyacrylic acid/“soft”polyacrylamide（PAA/PAM）double network hydrogels,for the fabrication of tough nanocomposite hydrogels-based sensors with interconnected double networks.The overall consequences displayed that the polyelectrolyte poly（diallyldimethylammonium）chloride（PDDA）and biocompatible polydopamine（PDA）functionalized GO attributed high sensitivity,toughness and self-healing performance of sensors.The Janus-based wearable sensors thus produced provide outstanding electromechanical properties with mechanical strength of 574.0 KPa,sensing range of 0-1300%and high gauge factor of 6.35.Furthermore,due to the remarkable self-healing efficiency of 95.1%within 40 min,various intense stretching could be monitored steadily in repetitive measurements.This research creates a new opportunity for the convenient fabrication of high-performance nanocomposite hydrogels-based sensors with multifunctional properties.