| Electrically responsive photonic crystals（ERPC）are a new kind of functional material which can control optical signal by electric fields.According to the responsive mechanism of PCs,the materials can be roughly classified into the types of the electrophoresis of charged colloidal particles,electrochemical redox reaction,reorientation of liquid crystal molecules and electroelastic material stretching.Among of them,ERPC based on the electrophoresis of charged colloidal particles is a promising material to construct reflective color displays with the advantages of low-power-consumption,wide tunning range of structure color and simple fabrication process.Although the electrophoretic ERPC has been developed for several years since it was proposed,researchers usually focused on polar colloidal crystal system with large response voltage,which would lead to a series of problems such as a significant decrease in structural color saturation with the increase of applied voltages,deterioration of electrode due to electrochemical side reactions occurred and irreversible response process during the voltage switched on/off.Therefore,people look forward to develop the ERPC materials with low driving voltage and better electric response performance.In this thesis,it will be started with the construction of weak polar liquid colloidal crystal system possessed dynamic reversible and electric response characteristic,exploring key factors such as the assembly and electrophoresis of charged colloidal particles,interactions between colloidal particles and between colloidal particles and electrodes,electrode stability in electric fields and so on,revealing the relationship between the composition of the material and the electric response performance.The specific research content is as follows:In chapter two,Si O2 colloidal particles were firstly modified by silane coupling agent to solve the poor dispersion of them in o-dichlorobenzene（DCB）solvent.Secondly,the charged Si O2 colloidal particles were synthesized by the assistance of aerosols（AOT）and Si O2/DCB-AOT ERPC was successfully fabricated by the assembly of the charged particles in DCB.Compared to the polar ERPCs,the Si O2/DCB-AOT ERPC works at much lower voltages（0.5–1.7 V）and still possesses a wide color tuning range because the weak-polar solvent applies less screening to the coulombic interactions.The low potential further renders the ERPC good capability against color fading in a strong field and long-term reversibility during color switching,which addresses the critical concerns for its application in reflective displays.In the previous chapter,colloidal particles need to undergo hydrophobic modification and self-assemble into liquid colloidal crystals with the assistance of charge control agent.The preparation process is complicated and the amount of charge control agent is not easy to be accurately controlled,which may easily cause the decrease of the electric field response performance of colloidal crystals.So,in chapter three,we successfully prepared weak polar liquid colloidal crystal-Si O2/ANI ERPC through a simple fabrication process without any surfactants,where unmodified Si O2 colloidal particles and aniline were selected as the building blocks and dispersing medium,respectively.As an alkaline weak polar solvent,aniline not only helps to disperse the particles in solution but also renders the particle high surface charge by taking the proton away from the silanol group,both of which favor the formation of ERPC in a weak polar system.Compared to the reported ERPCs,the Si O2/ANI ERPC possessed a broad reflection wavelength tuning range（230 nm）under a low working potential（1.4 V）due to less screening of Coulombic interaction.The low working potential further relieved the decrease of color intensity under large lattice compression and improved the long-term stability and reversibility of reflection signals in electrical tuning.The weak polar liquid colloidal crystals in the above two chapters all show excellent electric field response stability.In order to find out the reason,clarify the relevant influencing factors,and provide certain guidance for the development of highly stable ERPC.So,in chapter four,we firstly prepared Si O2/PCb ERPC and Si O2/DCB-AOT ERPC,where the polar solvent propylene carbonate（PCb）and weak polar solvent DCB were selected as the electrolyte,respectively.Then,both of above ERPCs were applied 3 V DC voltage for different times,and we found that the ITO cathode from Si O2/PCb ERPC turned brown,while there was no color change for corresponding electrode in Si O2/DCB-AOT ERPC device.The conductive layer of ITO cathode was ruined and the main reduction product metal indium（In）was produced on its surface,causing the decrease of conductivity and transmittance of the ITO.So,the degradation of ITO electrodes would damage the electrical tunning ability and response stability of the ERPCs.Over voltage,high content of free H+in electrolyte and ambient humidity are the key factors to induce the reduction of ITO cathode.The purpose of this chapter is to explore the degradation mechanism of ITO electrode in ERPC devices,clarify relevant influencing factors and provide some theoretical guidance for the development of high stability ERPCs. |
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