Regulation Of PEDOT:PSS Fiber Surface Structure By Coagulation Bath Toward Multifarious Applications

Conductive polymers are a class of photoelectronic materials with highly π-π conjugated structures,which have many potential applications in the manufacture of flexible,wearable electronic devices.Among them,poly（3,4-ethylenedioxythiophene）:poly（styrene sulfonate）（PEDOT:PSS）has high conductivity at room temperature and is considered to be the most promising conductive polymer materials.Compared with 2D thin films,1D fiber materials have natural advantages in terms of flexibility and integration.As the main technique for macroscopically preparing conductive fibers,wet-spinning for PEDOT:PSS fibers has aroused great interest among researchers.Although PEDOT:PSS can be prepared into continuous fibers,the rigid PEDOT molecular backbone makes the resulting fibers generally poor in stretchability,which greatly limits the large-scale application of PEDOT:PSS fibers in the field of flexible wearable electronics.In addition,the conductivity and electrical stability of PEDOT:PSS fibers are also poor,which not only has a large gap compared with metal,but also decreases sharply with the passing of time.Therefore,the way to prepare highperformance PEDOT:PSS fibers with excellent electrical conductivity,stretchability and sensitive electrical signal detection and stability is still a hot and difficult research topic in this field.Meanwhile,fibers will inevitably suffer some mechanical effects and environmental changes.Therefore,mechanical stability and environmental stability are also an important index of fiber.In this paper,the preparation of PEDOT:PSS fiber with high conductivity and high elongation was realized by coagulation bath regulation.Besides,continuous preparation of PEDOT:PSS fibers with different structures as well as special properties and applications is realized through the design of the coagulation bath.Firstly,a continuous preparation of PEDOT with high elongation at break and conductivity was proposed by using copper chloride as precipitator and urea as auxiliary forming agent to conduct electrostatic complex with PSS and copper ions in a coagulation bath system composed of water and ethanol:Wet-spun PEDOT:PSS/UREA（PPU）fibers revealed a maximum elongation at break to exceed 100%and the maximum conductivity to exceed 100 S·cm^-1,an improvement of about 1.5 orders of magnitude compared to the fibers without urea.It is worth mentioning that the conductivity of fiber can remain stable for a long time due to the protection of urea.The characterization tests verified that urea molecules could effectively change the conformation and arrangement of PEDOT and PSS molecules in the fiber,and expounded the mechanism that urea could improve the stretchability and conductivity of the fiber at the same time by changing the internal structure.In addition,the influence of urea molecules on the surface microstructure of the fiber was also investigated.Urea can effectively regulate the morphology and growth density of the surface array structure,which provides a new idea for improving the morphology and properties of fiber from the molecular level.Secondly,inspired by the skin structure,a strategy of self-assembly induced by chemical reduction method was proposed and realized,and the fibers with multi-layer core-shell structure were constructed while the PEDOT:PSS fibers were continuously prepared on a large scale.That is based on the PEDOT:PSS fibers with surface array structure.The special silver mirror reaction is excited by hydroxy-urea to achieve the displacement of elements in the surface array structure（from copper to silver）,and the array structure is used as the connecting layer to further form the outer layer of silver nanoparticles,which realizes the stable binding of metal and polymer and the spontaneous growth of metal nanoparticles on the outer surface of the fiber.The final Ag/AgCl/PEDOT:PSS（AAP）composite fiber is formed.It is worth mentioning that this reaction process can be realized continuously with the fiber preparation process without complex post-processing.Due to the existence of silver nanoparticles,AAP fibers have extremely high electrical conductivity(up to more than 50,000 S·cm^-1),ultra-low detection limit（～82 Pa）and fast response time（47 ms）.In addition,thanks to the three-layer core-shell structure,AAP fibers have the characteristics similar to human skin structure,that is,they have completely different signal responses to high pressure（>20000 Pa）and low pressure（＜20000 Pa）.On this basis,its performance in the field of pressure（gravity）sensing and temperature sensing is further explored,and the potential application of auxiliary touch is proposed.More importantly,based on the study of the influence of urea on the surface structure of PEDOT:PSS fibers,the formation mechanism of the hierarchical structure of fibers by chemical reduction method and the in-situ growth mechanism of silver nanoparticles were revealed,which provided a new idea for improving the comprehensive properties of fibers from the perspective of fiber structure design.Finally,inspired by the vein structure,a method for the preparation of PEDOT:PSS fibers with textured core-shell structure was proposed and realized by a spinning process with the surface structure controlled by polymeric coagulation bath.The PEDOT:PSS/PEG（PPP）fibers with a thin core-shell structure can be prepared by a single needle by adding polyethylene glycol in a coagulation bath.The formation of thin core-shell structure and fiber molding is accomplished synchronously by double diffusion without any additional postprocessing.Due to the thin core-shell structure of the fiber,PPP fiber has higher tensile strength and elongation at break（>100%）,and the shell structure can significantly improve the hydrophilicity of the fiber and protect the inner fiber from the damage of external mechanical action and temperature change.In addition,by reasonably controlling temperature and humidity,the smooth core-shell structure can also be transformed into textured core-shell mechanism,so that PPP fiber has a huge specific surface area（184.2 m²/g）,which enables the fiber to have a high evaporation rate,so as to achieve the effect of evaporative cooling as a fabric.At the same time,as a conductive fiber,its conductive characteristics can realize the low voltage heating function,combined with rapid sweat absorption and evaporative cooling function,can realize the comprehensive personal thermal management effect of "warm in winter and cool in summer",greatly broaden the application range of PEDOT:PSS fiber,to meet the requirements of the new generation of intelligent fabric functional integration.