Preparation And Properties Of Oligoaniline/Nano-carbon Electrochromic Composites

Electrochromism refers to the optical properties of materials,such as transmittance,absorption,and reflectance,that undergo a stable and reversible change under the action of the electric field,usually manifested as color changes.The electrochromic materials can be used as anti-vertigo rear-view mirrors,energy-saving windows for smart buildings,photoelectric information storage,displays,etc..Among various electrochromic polymers,polyaniline?PANI?has multiple colored forms depending on the oxidation states,including leucoemeraldine?bright yellow?,emeraldine?green?,and pernigraniline?dark blue?.However,PANI prepared by chemical and/or electrochemical means usually exhibits structural defects and limited solubility in many solvents.Recently,extensive efforts have been made in synthesizing oligoaniline-containing polymers incorporated with other functional groups to achieve high electrochromic performance and enhanced processability.However,it still has the problems of small optical contrast,poor stability,and easily peeled off from the substrate.In this thesis,we have prepared three types of oligoaniline/nano-carbon composites by modifying oligoaniline with two-dimensional,one-dimensional,and zero-dimensional nano-carbon materials.Moreover,the microstructure,electrochemical activity and electrochromic properties of the three composites were studied in detail,and the experimental data were analyzed and discussed.The thesis could mainly be divided into the following three parts:First,graphene oxide?two-dimensional nano-carbon material?and oligoaniline were chemically modified to prepare two hydrolyzable and crosslinkable siloxane precursors,which were coated on the surface of hydrophilic Indium-Tin Oxide?ITO?glass substrate.The resulting oligoaniline/graphene oxide ITO electrode was used as a working eletrode to contract a three-electrode system.Cyclic voltammetry?CV?was carried out on this three-electrode system and brought out a three-dimensional network porous structure.This unique hydrolytic cross-linking method was defined as electrochemistry-assisted hydrolytic crosslinking reaction and the porous structure inside the thin film reduce the film peeling in an acid electrolyte and improve the electrochemical stability.The effects of the addition of graphene oxide on the electrochromic properties of materials were investigated through comparative experiments.Compared with the oligoaniline/SiO₂ films,the composite films with graphene oxide show significantly improved electrochromic properties,such as stability,coloring efficiency,and response time.In conclusion,the graphene oxide exhibits a positive effect on the electrochromic properties of aniline.Subsequently,we report a new tetraaniline/carbon nanotubes composite film prepared through an electrochemistry-assisted hydrolytic crosslinking reaction.The resultant samples were characterized through scanning electron microscope,Fourier transform infrared spectroscopy,CV and electrochemical impedance spectrum.Compared to the silica/tetraaniline binary film,this silica/tetraaniline/carbon nanotubes ternary composite film displays enhanced electrochromic performance with large optical contrast values??=67%at 700 nm?,high coloration efficiency?85.6cm²/C?,and fast switching speed?t_c=1.5 s and t_b=5.2 s?.This improvement could be attributed to its interpenetrating network architecture,resulting in porous structure and good conductivity of the carbon nanotubes.Furthermore,the electrochromic electrode exhibits outstanding cycling stability,due to its robust crosslinking molecular structure and good adhesion to the conductive substrateFinally,we report a new electro-optical composite film based on oligoaniline and carbon dots,which prepared by a hydrolytic crosslinking reaction under electrokinetic potentials.The electroactive oligoaniline and fluorescent carbon dots are covalently linked through hydrolysis of siloxane,resulting in multifunctional composite films.The resultant crosslinked architecture endows the films with high flexibility and robust durability.These films display good electrochromic behavior with obvious color contrast,quick switching rate,and acceptable cycling stability.Moreover,these films reveal an interesting electrofluorochromic performance in continuous potential ranges,attributed to the interaction between oligoaniline and carbon dots,and the change in structure that occurs with changing redox potentials.Further,an enhanced photocurrent response is observed in these materials,as a result of the organic-inorganic interfaces.