Design,Synthesis And Characterization Of High-performance Polythiophene Composites

Polythiophene(PTh)exhibit fantastic optical and electrochemical properties because of their ?-conjugated molecular structure.Poly(3,4-ethylenedioxythiophene)(PEDOT),a derivative of polythiophene,is the most widely employed commercial conducting polymer for its excellent conductivity and stability.However,because of the rigid ?-conjugated chain structure of polythiophene,PTh-based materials suffer from poor mechanical performance,and is often deposited onto a proper substrate and employed as a coating.In order to improve the mechanical performance of PTh without sacrificing its electrochemical permance,we firstly synthesized two kinds of flexible PEDOT-based composite materials with mechanical robustness and electrochemical activity by the assembly of rigid PEDOT s and flexible polymer chains at molecular level,which are the highly capacitive PEDOT-PVA(polyvinyl alcohol)hydrogel and the humidity-responsive PEDOT/PAA-AMPS(2-acrylic acid-2-acrylanmido-2-methylpropanesulfonic acid)film,and we fabricate a high-performance flexible supercapacitor and a bio-inspired helical-locomotive actuator based on these two composite materials.Then we electropolymerized polythiophene with different kinds of plasticizers and anionic surfactants as dopants.PEG2000-SPTS-PTh(polyethylene glycol-sodium p-toluene sulfonate-PTh)exhibits the best tensile strength,elongation rate,toughness and electrical conductivity,which was used for fabrication of PTh supercapacitors with excellent capacitive behavior and cycling stability.Our work would be instructive for the design and synthesis of flexible conductive polymer composite materials and flexible functional devices.This thesis is devided into the following parts:1.Flexible PEDOT-PVA supercapacitor:Many PEDOT-based hydrogels have been developed for fabricating flexible supercapacitors.However,most of these flexible supercapacitors are limited by potential safety hazards brought by low energy density ang low operating potential windows.We designed of PEDOT-based robust hydrogels by supramolecular assembly of EDOTs and PVA through dynamic boronate bonds.Moreover,we synthesized PVA-Na2SO4 film as neutral-pH electrolyte and separator,and assembled a flexible solid-state supercapacitor(SSC)by sandwiching the neutral electrolyte with two PEDOT-PVA hydrogel electrodes.This SSC can operate at a high voltage of 1.4 V,which provides a high energy density of 15.2 Wh kg-1,superior to other PEDOT-based SSCs.The robustness of this SSC is demonstrated by the 100%capacitance retention after 1000 mechanical folding cycles,and the 89%capacitance retention after 1000 charge-discharge cycles.The combination of high energy density,chemical and mechanical robustness,and safety enable the PEDOT-PVA hydrogel based SSCs promising high-voltage and safe power device for flexible electronics.2.Humidity-responsive PEDOT/PAA-AMPS film:Although a great effort is devoted to the synthesis of humidity-responsive materials,recently developed humidity-respnsible actuators suffer from low actuation speed,low strength output and difficulty in controlling moving direction.Humidity-responsive PEDOT/PAA-AMPS(PPA)film was prepared by in situ chemical synthesis and immersing-drying method.The obtained PPA film undergoes fast and reversible expansion and contraction in response to moisture gradient by breaking and reforming hydrogen bonds with water molecules,generating continuous locomotion when placed onto a moist substrate.The film could generate a contractile stress of 45 MPa during swelling and shrinking,and lift up objects 240 times heavier than itself to a height of 2 mm.By simply varying the cutting angle between the strip's long axis and the same film's symmetric axis,we obtained two PPA strips that undergo either left-handed or right-handed helical motion.When a cargo with the same weight as itself was loaded,PPA strips transported the cargo in a preprogrammed helical-locomoted way.This is the first report of predefined chiral motion from a polymer actuator that doesn't contain chiral molecules,fribrous polymer chains or bilayered structures.Thus the PPA film holds great potential for applications in artificial muscles,robotic hands,and electromagnetic-free generators.3.Strong and tough PTh composite for flexible electronics:We have electrosynthesized a series of polythiophene films using chronoamperometry in boron trifluoride diethyl etherate(BFEE)electrolyte with different types of plasticizers and anionic surfactants as dopants to improve the electrical and mechanical properties of polythiophene.Meanwhile,we have studied the impacts of molecular weight of PEG,polymerization potential and temperature on mechanical properties of polythiophene and found that when PEG2000 and SPTS were added,the greatest strength(130 MPa)and elongation rate(140%)were simultaneously obtained.Moreover,we have demonstrated the good conductivity(9.5 S cm-1)and flexibility of PEG2000-SPTS-PTh film,which can be used as a conductor to light up a LED when powered by a 3 V battery.In addition,we have fabricated PEG2000-SPTS-PTh supercapacitor with a specific capacitance of 65 F g-1(0.6 A g-1)and cycling stability of 83%(0.6 A g-1 1000 cycles),comparable to current electro-polymerized PTh-based supercapacitors,demonstrating its potential in application of flexible electronic devices.Finally,we have proposed the doping mechanism of PEG2000-SPTS-PTh and established the relationship between the structural,electrical and mechanical properties of polyol-PTh.