Effect Of The New Polymer Crosslinking Method And The Branching On The Electrochromic Properties Of The Material

With the continuous development of the economy,the environmental crisis and shortage of resources is currently the most pressing challenges for the world.So,it is critical to develop green energy,small emissions,low energy-consuming materials.Electrochromic materials,as of the novel functional material,have attracted significant attention owing to its potential application in buildings and vehicles.Electrochromic(EC)material refers to material which can reversibly change their color via readox reaction under external electric field.At present,the full-color display property and stability improvement have important practical significances for the application of the polymer electrochromic devices.Our thesis focuses on how to improve the electrochromic stability of the film and explored the relationships between the polymer structure,film morphology and electrochromic properties.The detailed works are listed as follows:1)At first,we have synthesized the donor-acceptor polymer material P(CZ-BT-CZ)based on carbazole and benzothiadiazole with the terminal of alkyl side chain functionalized with carbazole groups.PP(CZ-BT-CZ)was then obtained by further electrochemical crosslinking of the polymer P(CZ-BT-CZ).The results indicated that the electrochemical stability of the electrochemical polymer film was significantly enhanced compared to polymer P(CZ-BT-CZ)with alkyl side chain.The main reason for the property difference can be ascribed to be that the electrochemical crosslinking film PP(CZ-BT-CZ)showed a loose structure and large surface roughness,which can provide sufficient surface area to contact with the electrolyte and increase the rate of ion insertion/extraction of the film.However,due to the nonuniformity of film thickness,the inferior aggregation property and decreased conductivity lead to reduced response time and coloring efficiency.2)A novel PP(CZ-BT-CZ)/WO3 composite has been designed and synthesized.The WO3 nanorods have been synthesized by simple one-step hydrothermal method and incorporated to function with PP(CZ-BT-CZ)to yield the PP(CZ-BT-CZ)/WO3 composites.The electrochromic PP(CZ-BT-CZ)/WO3 film was obtained by depositing P(CZ-BT-CZ)on the surface of WO3 nanorod and followed by electro-polymerization.Compared with PP(CZ-BT-CZ)film,the PP(CZ-BT-CZ)/WO3 composite film showed superior electrochemical stability,retaining 75.9%of electrical property after being recycled 500 times.Besides,the response time is also significantly improved,with the coloring and bleading time are determined as 0.67s and 0.33s,respectively.Compared with the electrodeposition film,the high conductivity of WO3 and more ordered structure of the nanorod can promote the electrolyte solution and charge penetrate through the film as well as increase the ion insertion/extraction rate.3)A series of carbazole and benzodithiophene(BDT)based polymers P(CZ-BDT-CZ)-C8,P(CZ-BDT-CZ)-2C8,P(CZ-BDT-CZ)-C12 and P(CZ-BDT-CZ)-C4C6 with different alkyl side chains.The results indicated that the side chains gave rise to significant influence on the electrochemical stability.P(CZ-BDT-CZ)-C8,P(CZ-BDT-CZ)-C12 and P(CZ-BDT-CZ)-C4C6 could retain 95.2%,76.3%and 79.2%of electrical property after being recycled 1000 times,respectively.However,the electrical property of P(CZ-BDT-CZ)-2C8 film degraded to 53.5%after being recycled only 100 times.The main reason for the difference in stability is the length and amount of branches in the polymer side-chain,which will influence the aggregation property and film morphology.The long and abundant branches of alkyl side chain could hinder the polymer molecule pack orderly,leading to a limited charge-transfer ability and loose contact with the substrate,consequently resulted in the poor electrochromic performance and stability.