Study On Polyaniline Electrochromic Materials And Devices Based On Pre-nucleation Metho

Electrochromism refers to the phenomenon of reversible changes in the optical properties（transmittance,reflectance,absorbance,etc.）of the material under the action of an applied electric field.Electrochromic devices have been widely used in military camouflage,smart display,energy-saving glass,energy storage,etc.In practical applications,the change of color or transparency of the material plays a key role in the electrochromic process.The synthesis of multicolor electrochromic materials and the design of multi-mode electrochromic devices are important development directions in the field of electrochromism.Polyaniline（PANI）electrochromic materials are of great interest because of their easy synthesis,rich color variation,and low redox conversion voltage.The thesis focuses on the preparation of electrochromic conducting polymer PANI and its electrochemical,optical and electrochromic properties.The research work is divided into three parts as follows:（1）Based on the characteristics of aniline polymerization including two stages of nucleation and growth,the traditional direct growth PANI films preparation process is improved and the PANI films are prepared by the pre-nucleation method.PANI films are prepared by constant current,cyclic voltammetry and pre-nucleation methods,and the morphology,structural characteristics and electrochemical properties of PANI films obtained by these methods are compared.The effects of pre-nucleation current,growth current,and pre-nucleation time on the properties of PANI films are investigated.The experimental results show that the pre-nucleation method is able to polymerize high quality PANI films in a simple and efficient way compared to direct growth polymerization.The prepared PANI films exhibit significant multicolor properties,capable of reversible transitions between transparent,yellowish,green,blue and blue-violet colors,and exhibit excellent electrochromic transmittance modulation of 55%at 580 nm.Significant electrochemical properties are also observed,with the films showing a high total active charge of 90.7 m C at a scan rate of 0.05 V s^-1.Compared to the directly grown films,the pre-nucleated PANI films maintain about 91%of the initial active charge retention after 100 cycles,which is a result of the improved uniformity and adhesion of the pre-nucleation method.（2）PANI electrochromic devices are further assembled from PANI films with excellent properties prepared under the optimal parameters of the pre-nucleation method.Based on the mechanism of double ion insertion/removal in the electrochromic process,the conventional voltage-driven electrochromic device is extended and a multi-mode electrochromic device is proposed by combining the double drive to control the three-dimensional movement of ions in the electrochromic device.Then,the electrochromic performance and electrochromic properties of the current-driven device are further investigated.Under current drive,the electrochromic device displays gradient patterned color change with up to 45%transmittance contrast with fast switching time（13.62 s and12.24 s for coloring and fading,respectively）and excellent cycling performance（93%of the maximum transmittance contrast is maintained after 150 cycles）.Finally,a multi-mode electrochromic device capable of additionally displaying different gradient patterns in multiple color states based on a single PANI film is successfully demonstrated.（3）The infrared electrochromic behavior of PANI films and devices is further explored on the basis of visible electrochromism.The infrared emissivity change characteristics of PANI films with different polymerization times under the action of different voltages are investigated in detail,and two operation modes of the infrared emissivity modulation ability of PANI films with the increase of PANI film thickness are analyzed.The PANI infrared electrochromic devices are also assembled to explore the improvement from visible electrochromic devices to infrared electrochromic devices.The infrared emissivity modulation ability of PANI infrared electrochromic devices is tested,and the maximum infrared emissivity modulation of about 0.255 is achieved in the wavelength range of 8-14μm.The results of this thesis may provide some theoretical guidance and technical support for future practical applications of polyaniline-based electrochromic films and devices.