Preparation And Wearable Application Of Superelastic Conductive Yarn Based On Helical Three-dimensional Conductive Network

With the rapid development of nanotechnology and electronic information technology,intelligent wearable electronic products have been constantly updated and advanced,rapidly entering every field of human life,and have a wide range of applications in man-machine interaction,sports assistance,health detection and other aspects.Conductive yarn is the key hub of intelligent wearable electronic system.Like the nervous system of human body,it is responsible for uploading and transmitting information.It is an important part of flexible electronic devices.High mechanical elasticity and conductive stability are the basic requirements of wearable electronic products and smart fabrics.However,it is still a great challenge for stretchable conductors to achieve high conductance simultaneously under large mechanical deformation due to the"trade-off"effect between the two properties.Therefore,this paper designs from conductive materials,fiber base materials and structure preparation,studies the structure and performance of the super-elastic conductive yarn,and weaves the successfully prepared elastic conductive yarn into the elastic seamless fabric for the next step of wearable electronic device application research.First,inspired by the adhesion properties of natural mussels,we constructed sandwich structure on the helical elastic core-spun yarn to solve the adhesion problem between conductive material and elastic fiber matrix,and prepared the elastic helical conductive yarn with nonlinear change of strain resistance.In addition,in order to meet the larger wearable application scenario and improve the performance of conductive yarn in all aspects,inspired by the curling structure of climbing plant rattan stem,a layered winding spiral conductive yarn with three-dimensional conductive network was developed on the flexible high-elastic nanofiber substrate.Both spiral conducting yarns of two structures can realize their application research in different directions in the field of intelligent wearable.The main work content of this paper is as follows:（1）Preparation of sandwich helical conductive yarn based on three-dimensional conductive network.Inspired by the adhesion properties of natural mussels,the nonlinear resistance variation spiral conductor of sandwich structure was developed and its mechanical and electrical properties were studied.In order to ensure the high conductivity of flexible conductive yarns,one-dimensional silver nanowires（Ag NWs）and two-dimensional MXene（Ti₃C₂T_x）layers are used to construct a three-dimensional conductive network with synergic effect.At the same time,the spiral core-cored yarn with PU and cotton outer layer was prepared as the conductive material loaded by fiber elastic matrix.The sandwich structure was constructed by the core-absorbing effect of the core-absorbing yarn impregnated with conductive material:the bottom layer was polydopamine（PDA）,the sandwich was composed of three-dimensional conductive network,and the outer layer was poly3,4-ethyldioxthiophene（PEDOT:PSS）.The nonlinear variation of strain resistance presented by the unique structure is used to maintain the conductivity stability of the conducting yarn under a certain strain.The conductive fiber prepared in this work can be stretched to 618%,and the resistance recovery property caused by the unique conductive path is less than 0.06 resistance change at 200%mechanical deformation.At the same time,it has unique photothermal and electrothermal response characteristics,and has the function of human body temperature regulation.Its unique performance has great potential value in the application of flexible wearable intelligent textiles.（2）In order to meet the wider application scenarios of wearable flexible devices and improve the super-stretchability and electrical stability of intelligent conductive yarn,the super-stretchability of spiral structure of climbing plants was studied and a layered interlocking spiral conductive yarn was prepared.At the same time,thermoplastic polyurethane elastomer rubber（TPU）was selected to spin flexible TPU nanofiber films by electrostatic spinning.TPU nanofiber membrane has excellent mechanical properties,the elongation at break can reach 450%,the breaking strength is 20 MPa.The TPU nanofiber film was prepared into spiral structure by the method of motor helix twisting,and the conductive material was atomized and sprayed by the pre-stretched TPU film,and the conductive material was self-assembled in the process of motor helix twisting.With the twist of the spiral,the conductive material is tightly wound into the yarn,ensuring that the spiral stretchable conductive yarn has a good initial conductivity of up to 1.14×10⁵S m^-1.Ag NWs/MXene TPU helical conductive yarn elongation at break is greatly increased to about 2071%,breaking strength up to 42 MPa.The 3D conductive network based stretchable intelligent conductive yarn has excellent strain sensitivity and conductivity exceeding 1.12×10⁵S m^-1（ΔR/R₀<0.03）,whose conductivity under large mechanical deformation is much better than existing stretchable conductive yarns.（3）Based on layered interlocking spiral conductive yarns,in order to realize the application of smart conductive yarns in wearable electronic devices,the Ag NWs/MXene TPU yarns maintain the fiber straight yarn structure and reduce the strain sensitivity by reducing the amount of conductive material adhesion and twist degree of spiral TPU yarns.Nickel-coated conductive fabric is used as the electrode.The stretchable strain sensor is prepared by connecting intelligent conductive yarn with conductive silver adhesive,which can monitor human physiological signal and human movement signal in real time.The experimental results show that the flexible high-elastic conductive yarn has excellent human motion monitoring function.Besides the application of supertensile conductor,spiral conductive yarn has great prospects in human health monitoring.（4）Electrothermal and photothermal performance test shows that the layered interlocking spiral superelastic conductive yarn prepared by using three-dimensional conductive network and spiral structure has good electrothermal and photothermal performance.Under the input voltage of 1.7V,the Joule heating effect of layered interlocking helical conducting yarn can reach 31.5℃.Even if the conductive yarn is stretched to 1400%,it can still reach 31.3℃.When the optical power density is 170 m W/cm²and the light lasts for 20s,the surface temperature of the fiber can reach 45℃.By seamlessly integrating the TPU spiral conductive yarn into the elastic fabric,the excellent electric heating and photothermal effects can be used to prepare intelligent temperature regulating fabric,which can keep the human body at a comfortable temperature in rainy weather and winter by using electric heating and photothermal response.In addition to supertensile conductors,helical conducting yarns show great promise in the personal thermal management of smart fabrics.