Research On The Fabrication And Properties Of Fiber Based Stretchable Flexible Devices

With the continuous development of flexible electronics,more and more attention has been paid to flexible strain sensors that can sense environmental information and simulate skin characteristics,It shows important application prospects in intelligent robots,artificial prostheses,wearable devices and physiological health monitoring,etc.,which is of great significance for the development of flexible wearable sensing and natural human-machine interaction.In this dissertation,we discussesed three methods of preparing flexible stretchable sensors and studied their various properties including mechanical properties,electrical conductivity,strain sensing performance,electrothermal performance,and durability.The specific research contents are as follows.The first part of the dissertation is to compound polydopamine on the surface of polyester fiber and then use a knitting machine to weave the polyester fiber and the monofilament into a polydopamine/woven yarn(BYs-PDA).Polypyrrole(PPy)was polymerized in situ on the surface to prepare a woven structure composite yarn(BYs-PDA-PPy)and assembled into a strain sensor.The force-electric properties and strain-sensing properties of woven structure composite yarns were studied.Due to the unique weaving structure of the braided yarn,the braided structure composite yarn strain sensor has excellent strain sensing performance,including a large strain sensing range(up to 105% strain),and high sensitivity(under 0%-40% elongation).,The sensing factor is 51.2;at 40%-105% elongation,the sensing factor is 27.6),good cycle stability and excellent electrical heating performance.In addition,the knitting structure composite yarn sensor can be used to monitor the human body's large deformation movements and fine movements in real time.In addition,the composite structure yarn can be woven into a fabric to achieve the effect of electric heating.These results demonstrate the potential of woven structure composite yarns in wearable electronics.The second part of the dissertation is to soak woven structure yarns(BYs)in a high concentration of carbon nanotube solution and dry them to obtain carbon nanotubes / woven yarns(BYs-CNT),and then electrospinning the carbon nanotubes/woven yarns.A layer of polyurethane(PU)nanofiber membrane was wrapped on the surface to obtain a novel core-sheath nanocomposite yarn.This method is easy to operate and can achieve large-scale production.At the same time,the core-sheath structure nano-composite yarn has a very high sensitivity sensor factor(GF)of up to 980,good cycle stability and excellent durability.The core-sheath structure nano-composite yarn assembled strain sensor can monitor the human body's large deformation movements and fine movements.This work provides a reference for the development of reliable,stable,highly sensitive,flexible and durable wearable electronic products.The third part of the dissertation is to immerse the cotton roving in the carbon nanotube solution,reduce the resistance to a minimum after soaking and drying multiple times,and then use a spinning machine to spin the carbon nanotube/cotton roving into a carbon nanotube/cotton composite yarn Finally,by electrospinning,polyurethane nanofibers containing different colors of temperature-sensitive inks were wrapped on the surface of carbon nanotubes/cotton composite yarns by electrospinning to obtain core-sheath composite yarns(CCY)..The composite yarn has high strength and durable electrothermal discoloration performance.Due to its novel core-sheath structure,the electro-induced thermochromic composite yarn(ECCY)produced has excellent mechanical and electro-thermal properties and electro-chromic properties.Even after 100 heating/cooling cycles,the electrically induced thermochromic composite yarn still has excellent electrical heating performance and stability.In addition,electrically induced thermochromic composite yarns exhibit excellent durability in repeated bending,twisting and stretching,washing and even immersion in acid and alkali solutions.The color of the electrically-induced thermochromic composite yarn was successfully adjusted by changing the applied current,which can be used to design different patterns and form a fabric,thereby producing a color-converted pattern and fabric when current is applied/released.By designing this core-sheath nanofiber composite structure,a new strategy is provided for the development of electrically induced thermochromic composite yarns.