Preparation,Properties And Mechanism Of Self-healing Polymer-based Conductive Composites

Polymer-based conductive composite is a kind of multiphase composite with regulable electrical conductivity and mechanical performance,which is prepared by adding conductive filler to polymer matrix.Compared with the traditional metal-based conductive material,polymer-based conductive composite has many advantages,such as easy processing,low cost,good flexibility.As a result,it has been widely used in human-computer interface interaction,electronic skin,and human motion monitoring.However,this material is easy to be damaged in the process of processing and use,which seriously affects its service life and safety.Endowing polymer-based conductive composite with self-healing ability can significantly improve its service life,reduce the waste of resource and meet the needs of sustainable development.On the other hand,although the addition of filler can improve its mechanical strength,the motion of the polymer chain is limited,resulting in the harsh self-healing condition and unsatisfactory recovery of conductive performance.Therefore,it is important to study the preparation,property and application of high-performance self-healing polymer-based conductive composite.In this paper,four kinds of self-healing and conductive polymer-based composites were prepared by polymer molecular design,nanoparticles modification and the adjustment of bonding interactions between polymer chains and nanoparticles.These materials included polyurethane elastomer composite,polyurethane sponge composite,polyacrylate hydrogels composite and polyurethane sponge/polyvinyl alcohol hydrogels composite.Besides,the properties and mechanism of the above composites were studied.The main research contents are as follows:(1)A self-healing conductive polyurethane composite was developed based on the synergistic effects of Diels-Alder(DA)chemistry and urea-hydrogen bond.In this material,the carbon nanotubes modified by urea groups and silver nanoparticles were used as conductive fillers and hydrogen bonding reinforcing media,and the polyurethane cross-linked by DA bond was used as polymer matrix.As a result,this material had both high mechanical strength and fast self-healing ability.The self-healing mechanism showed that with the synergistic effect of reversible DA bond and urea-hydrogen bond,the fractured sample could be healed by heating or near-infrared light irradiation,and its tensile strength could be restored to 92.16 %.The results of electrical conductivity and conductive mechanism demonstrated that the bulk resistivity of the composite was as low as 0.134 Ω·cm and it could withstand bending and stretching deformation due to the existence of 3D conductive network.Therefore,it could be applied in flexible electrical interconnection,detachable conductive adhesive and radio frequency identification tag antenna.(2)We proposed a new strategy that could accelerate the disulfide bonds exchange reaction via the phase separation of polyurethane enhanced by multiple hydrogen bonds.The self-healing conductive polyurethane sponge coated with carbon nanotubes and silver nanoparticles was prepared by using 2-ureido-4[1H]-pyrimidinone-based diisocyanate(Upy-HDI-Upy)and 4,4’-diaminodiphenyl disulfide as its hard segment.The self-healing mechanism of the polyurethane sponge showed that Upy-HDI-Upy could significantly enhance the phase separation of polyurethane through multiple hydrogen bonds and accelerate the disulfide exchange reaction between disulfide bonds in its hard segment.The fractured conductive polyurethane sponge could recover 68.3 % of the original tensile strength after contacting for 24 h at room temperature.The piezoresistive effect of the material showed that with the mechanisms of “micro-crack structure” and “contact effect”,the piezoresistive sensor based on this self-healing conductive polyurethane sponge possessed a wide detection range and high detection sensitivity to external stress.The highest gauge factor of the piezoresistive sensor was 15.3 and could be used in human motion monitoring and electronic skin.(3)Inspired by the adhesion mechanism of mussel,a kind of modified cellulose nanocrystal reinforced self-healing conductive hydrogel with unique adhesion was prepared.In particular,cellulose nanocrystal coated with tannic acid and polyaniline was used as functional nanoparticle in the hydrogel,and hydrogen bonding interaction,hydrophobic interaction,metal complexation and reversible borate ester bond were combined in the network.The self-healing property and mechanism showed that the bionics hydrogel possessed fast self-healing ability and could recover 96.1% of its original tensile strength within 30 minutes at room temperature.In addition,the bionic hydrogel had unique adhesion and strain-sensitivity.As a result,it could be used as a flexible strain sensor to directly adhere to the human body surface to monitor human motion,and even pulse beating and water drops.(4)Inspired by the structure of plant tissue,we proposed a new strategy for the preparation of high-performance self-healing conductive hydrogel based on self-healing polyurethane sponge network.First,a self-healing polyurethane sponge was prepared based on the principle that multiple hydrogen bonds could enhance the phase separation of polyurethane and accelerate the exchange reaction of disulfide bonds.Subsequently,the polyurethane sponge was combined with carbon nanotubes/polyvinyl alcohol hydrogel crosslinked by borate ester bonds and hydrogen bonds to prepare the polyurethane sponge reinforced self-healing conductive hydrogel.Due to the reinforcement of polyurethane sponge,the composite hydrogels had excellent mechanical property.Its tensile and compressive strength could reach 1.81 MPa and 1.96 MPa,respectively.The hydrogel-based supercapacitor possessed excellent cycling stability.After 400 times of charge-discharge cycles under bending deformation,the supercapacitor could maintain 90.1 % of the original specific capacitance value.The self-healing property and mechanism of the supercapacitor showed that the hydrogel could be healed at room temperature due to the hydrogen bond and reversible borate bond,as well as the disulfide bond and multiple hydrogen bond in polyurethane sponge.The healed supercapacitor could maintain 75.2 % of the original specific capacitance value after 400 times of charge-discharge cycles.