Poly(Ionic Liquid)-Based Electro/Thermochromic Devices

Ionic liquids(ILs)are liquid organic salts at low temperature,with high conductivity,wide electrochemical window,excellent thermal and electric stability.Poly(ionic liquid)s(PILs)combine the functionality of small molecular ILs and the properties of polymer chains,which are widely used in the fields of energy,catalysis,life science,intelligent response materials.Smart materials are a new kind of materials that can respond to external stimuli(temperature,light,electricity,force and pH etc.)and its physicochemical property will be changed,such as electrochromic materials,thermochromic materials,self-healing materials,shape memory materials etc.Electro/thermochromic materials have potential applications in smart windows,biomedical sciences,military and aerospace.However,they have many problems,such as low optical contrast,low optical contrast,and slow response speed.The PIL-based gel electrolytes are widely used in electro/thermochromic devices due to the advantages of non-leakage,high conductivity and strong designability.With the development of smart windows,electronic display and information storage,high/low temperature resistance and good mechanical and electrochemical properties of PIL gels based electro/thermochromic devices are required.In order to solve the problems,a series of PILs and ILs were prepared and were applied to electro/thermochromic devices.The mechanism of action between the polymer network and small molecules,the structure-activity relationship and the operating temperature of the device were explored.The specific research content is as follows:(1)Electrochromic device based on PIL-based gel electrolytesThe high conductivity and non-leakage PIL-based gel electrolytes were prepared by electrostatic crosslinking between pyromellitic tetracarboxylic acid and PILs,and were used as electrochromic electrolytes.Then,the viologens were designed and synthesized,named as[HV][PF6]2,[SHV][PF6],[DMV][PF6]4 and[CNV][PF6]2,which were used as cathode electrochromic material.The color of viologen depends on the electron-withdrawing and electron-donating ability of its substituent group.Finally,the multi-colored,high optical contrast,fast response electrochromic devices were successfully prepared,in which viologen combined with N,N,N’,N’-tetrakis(p-tolyl)benzidine(TPBMe)was used as anodic electrochromic material.Moreover,the photo/electrical properties of viologens and TPBMe and the electrochemical and electrochromic properties(color,voltage,optical contrast,coloring efficiency,response time,etc.)of the corresponding ECDs were studied.(2)Electrochromic device based on high conductivity,self-repairing ionogelsCompared with poly(ionic liquid)-based organogels,ionogels with low volatility and incombustibility,can increase the operating temperature of electrochromic devices.Firstly,by using poly(N,N-dimethylacrylamide)(PDMA)as polymer and IL[1-ethyl3-methylimidazolium bis(trifluoromethylsulfonyl)imide]([EMIM][TFSI])as the solvent,the self-healing ionogels were prepared by UV-curing.Subsequently,the additive lithium bis(trifluoromethanesulfonyl)imide(LiTFSI)was introduced to simultaneously improve the conductivity and mechanical strength of the ionogels.To demonstrate that the ionogels could be used as electrolytes,the ionogels were functionalized by incorporating electrochromic materials(viologen,[HV][TFSI]2,[DMV][TFSI]4)and are applied to ECDs.The devices showed higher optical contrast(>83%),broad operating temperature range(-20～80℃)and good cyclic stability.The ionogels are anticipated to be of advantage in flexible electrochemical applications,such as flexible electronic devices,electrochemical displays and batteries.(3)Shape-color-switchable thermochromic actuators based on metalcontaining ionic liquidsCompared with electrochromic devices,the ionogels with high/low temperature resistance,can be used for thermochromic devices,which get rid of the power supply.We designed and synthesized a metal-based thermochromic ionic liquid([Bmim]2[MCl4](M=Ni,Co))and a thermally induced shape memory triethanolamine cross-linked polyurethane(TEAPU).Subsequently,TEAPU/[Bmim]2[MCl4]thermochromic actuators were prepared by high temperature solvent casting method.Based on the reversible conversion of the Oh-Td configuration of the metal-based ionic liquid and the shape memory function of the TEAPU,the composite films can achieve rapid color and shape change in a narrow temperature range(30～70℃).The water absorption/dehydration and thermodynamic properties of composite films with different metals and different ionic liquid content were explored.The TEAPU/[Bmim]2[NiCl4]material could simulate the blooming of flowers in nature and realize the change of color and shape at the same time by adjusting the temperature.In addition,these thermochromic actuators can lift weight and withstand strains of more than 1100%.The results represent the potential application of artificial muscle actuators and intelligent camouflages.