Flexible Electrochromic Fiber Based On PVDF-HFP/TPU Solid Ionic Conductor And Its Properties

Electrochromic fibers can undergo stable and reversible color change under the action of electric field,which has important application value in the field of flexible smart wearable.As an important component of electrochromic fibers,ionic conductor materials not only need to have high ionic conductivity to achieve rapid color change responsiveness of fibers,but also need to maintain the deformability,flexibility and stability of small curvature bending of fibers in the process of taking.Therefore,the development of solid polymer ionic conductors is a key issue to be solved in the development of smart color-changing fibers.Poly（vinylidene fluoride-co-hexafluoropropylene）（PVDF-HFP）has a high dielectric constant that facilitates the dissociation of lithium salts and is often used as an electrolyte matrix material,however,its high rigidity and poor interfacial stability also limit the application in the field of flexible electronic devices.In this thesis,we designed and prepared polyether-type polyurethane molecules with polar soft segments,and used them to reduce the crystallinity of PVDF-HFP by"co-blending"the polymer and optimize the matrix properties to obtain a liquid-free solid polymer ionic conductor,and used it to prepare all-solid electrochromic devices with good environmental stability.Color-changing fiber devices with good environmental stability.Details of the research are as follows:（1）Polyether oligomer polytetrahydrofuran（PTMG）with good lithium salt dissociation ability was selected as the soft segment and polymerized with isophorone diisocyanate（IPDI）and small molecule chain extender 2-amino-2-methyl-1,3-propanediol（AMPD）to prepare polyether-based polyurethane molecules containing polar soft segments.Through the stress-deformation test of the polyurethane elastomer,it is found that the elongation at break can reach129%,the bonding strength can reach 165 N,and shows good comprehensive properties.The polyurethane elastomers constructed based on dynamic hydrogen bonding also showed good repair ability,and the polyurethanes cut with a blade could be repaired quickly（≤1 min）,and the repaired polyurethanes could still reach a 300%elongation at break elongation.（2）Polyether-based polyurethanes were blended with PVDF-HFP and lithium bis（trifluoromethylsulfonyl）imide（LITFSI）,a lithium salt,was introduced to prepare solid-state blended polymer electrolytes.Electrochemical and structural characterization of the blended polyelectrolytes with different ratios revealed that the introduction of polyurethane effectively reduced the crystallinity of PVDF-HFP,formed an amorphous region inside the matrix,and significantly improved its ionic conductivity;in addition,the tensile properties of polyurethane improved the mechanical properties of PVDF-HFP.The elongation at break of the co-blended polyelectrolyte can also reach 800%,which is 1.8 times of the strain at break of polyether-free polyurethane,and is qualified for flexible applications.（3）The TPU:PVDF-HFP:LITFSI=1:1:1 blend system with good ionic conductivity(3.89×10^-5 S/cm)was selected as a polymer ionic conductor material,and electrochromic fibers were prepared by a dry process after the addition of a color-changing dye.The prepared fibers can achieve color change from colorless to blue at-2.9 V.The color change response is rapid with a coloring time of 3 s and a fading time of 4 s.In addition,thanks to the liquid-free property of the solid polymer ionic conductor,the color-changing fibers have good bending stability and environmental stability,and still have stable color-changing behavior at low temperatures of-26℃.