Synthesis And Properties Of Polyionic Liquid-based New Electrochromic Materials

With the development of society and economy,environmental issues have been repeatedly mentioned and have become a worldwide problem,and the application of smart technology has become increasingly common.As an energy-saving technology,electrochromic technology has been widely studied and applied in the fields of smart windows,anti-corrosion technology,dimming rearview mirrors,micro-displays,memory storage,electrochemical energy storage and conversion,antibacterial drugs and even military camouflage.These superior properties are due to the electrochromic material,such as fast response,low driving energy,low cost,and various colors with structural diversity.Viologen,as the representative of organic small molecule electrochromic materials,is favored by researchers.However,when viologen is colored,free radical cations are easy to form dimers,which leads to poor discoloration performance and the inability of liquid electrolytes to prepare solid or flexible electrochromic devices,which limit its application.To solve the above problems,based on the previous studies,we introduced flexible groups into polyionic liquid,and designed and synthesized a modified flexible polyionic liquid electrolyte material as supporting matrix and ionic conductor,which was used to prepare electrochromic device.A series of studies on its variable performance have been made.The main research contents include:The first part is the synthesis and characterization of polyionic liquid（PIL）and the preparation and performance study of viologen devices with or without crosslinking and different alkyl chain lengths.This topic is divided into two steps to synthesize polyionic liquid.Firstly,vinylimidazole and flexible compound butyl acrylate are used as raw materials,and P（VIM-co-BUA）is formed by free radical copolymerization.After characterization and purification,1,6-Dibromohexane,1-bromoheptane and1-bromobutane are used to synthesize polyionic liquids,and ethyl viologen compound,ferrocene（Fc）and three polyionic liquids are mixed to obtain polyionic liquid gel electrolyte.And assembled into electrochromic devices.The results of comparative color change performance show that the PIL gel electrolyte device with crosslinked structure has a faster response time（t_c=2.49s,t_b=3.44s）,the optical contrast at 606nm is 27%,and the coloring efficiency can reach 54.6%.The retention rate of the device after 2 weeks of continuous circulation in the environment can reach more than 98%,and the optimal conditions for cross-linking PIL devices are obtained when the cross-linked structure of mixed solvents is used in the system 1wt%viologen(EV²⁺),0.8wt%Ferrocene（Fc）,23wt%PIL gel electrolyte electrochromic device has the best comprehensive color change effect.The second part is the preparation and exploration of solid-state and flexible PIL-based viologen devices.In this project,by comparing the performance of PIL devices with different alkyl chain lengths,The result show that the butyl-containing devices have the deepest coloration,and the devices with different degrees of cross-linking are studied.The results show that the 65%cross-linked PIL-based device has a fast coloring response time of 7s,a maximum optical contrast of 68.2%and film-forming performance,mixed with a small amount of UV curing to prepare solid-state electrochromic devices.The device has a transmittance of more than 35%.And has a certain degree of flexibility,this kind of PIL device has good application prospects in the fields of smart wear and flexible display.