Development Of Carbon-reinforced Self-healing Materials For Flexible Sensors Based On Hydrogen Bonding

Polymer materials suitable for flexible sensors have been widely used in military,medical,and manufacturing fields.But these materials are prone to microcrack during deformation,which affects the service life of the materials.The "self-healing technology" was introduced into polymer materials to extend the life of the material by making the cracks self-heal.The polymers could be divided into different types through their different self-healing mechanisms.Among them,intrinsic hydrogen self-healing polymers based on dynamic hydrogen bonding present excellent properties of rapid and repeated self-healing.These excellent properties provide us a simple and widely applicable guideline.With the continuous development of flexible intelligent technology,flexible strain sensors have been arousing great interests of people around the world.However,the repeated use of these materials must cause failure of the electrical performance of the devices.Therefore,it is of great significance to self-heal the electrical properties of materials after the cracks and fractures forming.Therefore,the main research content of this paper is to prepare hydrogen-bonded self-healing polymers with excellent mechanical properties that is suitable for flexible sensor devices.To solve the problems above,in this paper,carbon fibers(CFs),carbon nanotubes(CNTs),and graphene oxide(GO)were introduced into the condensed oligomers of fatty acid and polyamine.Six types of self-healing carbon composite materials were prepared in this method,and they exhibit improved mechanical properties and are suitable for different application fields.Two of these self-healing materials were screened out to prepare self-healing flexible strain sensors which process high tensile strength and high elongation.The main research content is as follows:(1)Development of carbon fibers reinforced self-healing materialsThe carbon fibers self-healing polymer composite materials(HD-CF for short)were prepared by adding CFs and urea into the oligomers.The optimal addition of CFs was obtained by the measurements of mechanical property,self-healing property,thermogravimetric test,etc.The optimal addition of CFs is 9%.The tensile strength of the material at this addition ratio is 10.21±0.26 MPa.The optimal healing condition was chosen to be 60? for 3 h after exploring 20 different healing conditions.The HD-CF could be recovery by continuous damage-healing cycle 10 times.Amidated carbon fibers(referred to as Am-CFs)were prepared by the acidification and graft of CFs through one-step amidation,with a graft rate of 23.88%.Am-CFs were directly cross-linked with oligomers to obtain amidated carbon fiber self-healing polymer composites(referred to as AD-CF).After a series of characterizations,the optimal addition ratio of Am-CFs is 7%.The tensile strength and elongation at break of AD-CF are 0.231±0.011 MPa and 103.33±2.08%,respectively.By exploring 12 healing conditions,the healing efficiency of 60 minutes healing at room temperature could reach 100%,and the healing efficiency could reach 100%after continuous damage-healing 10 times.(2)Development of carbon nanotubes reinforced self-healing materialsCarbon nanotube self-healing polymer composites(HD-CNT)were prepared by adding CNTs and urea into the oligomers.The optimal addition ratio of CNTs was 9%,through a series of tests.The tensile strength of the material at this addition ratio is 4.27±0.11 MPa.The optimal healing condition is at 60? for 6 h,and 93%healing efficiency could still be achieved by continuous damage-healing cycle for 10 times.The amidated carbon nanotubes(Am-CNTs for short)with a grafting ratio.of 32.16%could be prepared by one-step amidation of CNTs.Am-CNTs were directly cross-linked with oligomers to obtain amidated carbon nanotubes self-healing polymer composites(referred to as AD-CNT).A series of characterization of the materials proved that 3%addition ratio of Am-CNTs was the optimal ratio.The tensile strength and elongation at break of the material at this ratio are 0.0124±0.0006 MPa and 72.6023±1.1649%,respectively.The healing efficiency of the materials could reach 100%after healing for 40 min at room temperature,and it could reach 100%after continuous 10 damage-healing cycles.(3)Development of graphene oxide reinforced self-healing materialsThe graphene oxide(GO)was prepared by the improved Hummers method.The GO and urea were added into the oligomers to prepare graphene oxide self-healing polymer composites(HD-GO for short).The optimal GO addition ratio of HD-GO is at 3%.The tensile strength of the material at this addition ratio is 2.99±0.07 MPa.The optimal healing condition of HD-GO is at 60? for 1 h,and 100%healing efficiency could still be achieved by continuous damage-healing cycle for 10 times.The amidated graphene oxide(Am-GO for short)with a graft ratio of 26.54%could be prepared by the one-step amidation of GO.Am-GO was directly cross-linked with oligomers to obtain amidated graphene oxide self-healing polymer composites(referred to as AD-GO).The Am-GO was detected by a series of characterization to know that 5%is the best addition ratio of GO.The tensile strength and elongation at break of AD-GO at this addition ratio are 0.1401±0.0090 MPa and 696.7858±3.6176%,respectively.The healing efficiency could reach 100%after 40 minutes healing at room temperature,and 100%healing efficiency could be reached after 10 continuous damage-healing cycles.(4)Carbon-reinforced self-healing materials for flexible strain sensorsThe HD-CF and AD-CNT which exhibits high tensile strength and elongation,were selected as carriers to load the conductive medium of silver nanowires prepared by a one-step polyol reduction method,to prepare two kinds of self-healing flexible strain sensors.The resistance of the sensors based on HD-CF and AD-CNT are about 3.1 ? and 9.9 ?,respectively,and both exhibit excellent conductivity and sensitivity.Different movement states,movement amplitudes and even changes in human facial expressions could be detected by the two types of self-healing flexible strain sensors which are adhered to human hand joints,elbow joints,knee joints,etc.The self-healing flexible strain sensors have provided a solid technical foundation for the development and application of human health monitoring and information sensing equipment,which has broad application value and good promotion prospects.