Structural Design And Sensing Performance Investigation Of Fiber-based Flexible Self-Powered Electronic Skin

Biological skin possesses rich sensor networks,which can sensitively sense the changes of external pressure and temperature.Inspired by biological skin,as a new wearable system,electronic skin with tactile sensing function,has broad application prospects in many fields,such as artificial limbs,intelligent robots,wearable devices and health monitoring.In addition to sensing performance,considering the practical application performance of electronic skin,it needs to possess good flexibility,stretchability,lightweight and other basic properties.As the second skin of human body,fiber and fabric materials have good adhesion to skin,and have unique advantages such as softness,air permeability and lightness.It is of great significance to combine them with wearable system to solve the disadvantages of electronic skin sensor such as difficult integration and air tightness.In addition,the battery dependence of wearable sensor system restricts its development to flexibility,miniaturization and lightweight to a certain extent.The self-powered electronic skin based on piezoelectric effect and triboelectric effect can convert mechanical energy into electrical energy,which can realize the function of self-powered and pressure sensing at the same time,so it has become one of the current research hotspots.At present,the sensitivity and stability of the multifunction fiber-based self-powered electronic skin need to be further improved.Further research on fiber based self-powered intelligent electronic skin has laid a foundation for improving the practical application performance of electronic skin and broadening the application field of electronic skin.Aiming at the further improvement of the properties of fiber-based piezoelectric and triboelectric electronic skin,based on the significant advantages of nanofibers in material structure and properties,the sensing properties of piezoelectric fiber and triboelectric layer are further improved through the structural design in the absence of the complex and high-cost preparation processes such as polarization post-treatment and plasma etching.Furthermore,through the structural design of the device and the synthesis and preparation of materials,some smart fiber-based self-powered electronic skin with multi-sensor mode and multi-function was developed.The specific research contents are concluded as follows:(1)Piezoelectric nanofibers with core-shell structure were designed and prepared by coaxial electrospinning technology.The effects of graphene and barium titanate content on?phase content,fiber morphology,piezoelectric properties and mechanical properties of PVDF hybrid fibers were investigated.The fiber-based highly shape adaptive piezoelectric e-skin was prepared by compounding with conductive fabric and ultra-thin polyurethane film.The sensing properties of the fiber-based piezoelectric electronic skin,such as sensitivity and durability,were investigated.The sensing properties of the fiber-based piezoelectric electronic skin for different joint bending degrees and motion frequencies were analyzed.After further extending it into an electronic skin sensor array,the ability of real-time tactile mapping and recognizing the shape and contour of different objects was investigated.(2)Inspired by the micro hierarchical structure of rose petals,a negatively triboelectric sensing layer with more uniform structure was prepared by template sacrifice method.The regulating effect of PVA template on rose petal microstructure was explored.Fiber-based transparent epidermis electrode was prepared by electrospinning technology and filtration deposition method.The effects of the thickness of PVDF fiber membranes and the content of silver nanowires on the transparency and conductivity of the fiber-based flexible electrode were studied.A transparent and antibacterial triboelectric fiber-based electronic skin was obtained by integrating with the prepared sensing layer and antibacterial substrate.The effect of the structure of the triboelectric sensing layer on the output signal was investigated,and its sensitivity,durability,stability,antibacterial properties were also systematically studied.(3)Polydimethylsiloxane triboelectric sensing layer with porous structure was prepared by coating method using lotus leaf as template.The effect of porous structure on the sensing performance of triboelectric sensor was analyzed.A flexible PVDF composite piezoelectric sensing layer with enhanced piezoelectric property was prepared by one-step electrospinning method.The influence of different content of carbon nanotubes(MWCNTs)on the piezoelectric properties of the fiber was systematically studied.The hybrid self-powered electronic skin was fabricated by structural design,and its sensitivity,durability and stability were investigated.The sensing performance of the hybrid electronic skin to different modes of external force was analyzed.The practical applications of the hybrid electronic skin in the fields of respiratory monitoring,head motion sensing,speech recognition,pulse physiological signal monitoring were verified.(4)The electronic skin with high elasticity and air permeability was designed and prepared,in which the negatively triboelectric PVDF nanofiber membrane was used as the sensing layer,the carbon nanofiber membrane doped with SiO₂ nanoparticles was used as the flexible electrode,and the elastic polyurethane(PU)nanofiber membrane was used as the stretchable substrate.The hydrophobic and mechanical properties of PVDF nanofibers and PU nanofiber membranes were investigated.The resistivity and flexibility of flexible carbon nanofiber electrode were studied.The sensitivity,durability,stretchability,thermal and humidity comfort of all fiber structured electronic skin were analyzed,and its electrical output performance and practical application performance in different curved surfaces were studied.(5)The intrinsic self-healing fibers with core-shell structure were prepared by supramolecular interaction between urea group molecules and electrostatic interaction between polyelectrolytes.The effects of different shell layers on the structural stability of the intrinsic self-healing fibers were studied.The stress healing efficiency and strain healing efficiency of the self-healing fiber membrane in the presence of water and without water were investigated,respectively.The self-healing fiber was further compounded by adjusting its surface chemical structure to obtain the all fiber structured temperature visualizaed self-healing electronic skin.The permeability,sensitivity,durability and stability of the self-healing electronic skin were analyzed,and its sensing performance after self-healing and pulling was studied.After further expanding the self-healing fiber into a sensor array,the multi-point synchronous sensing performance and temperature visualization performance were investigated.