Study On Infrared Radiation Regulation Mechanism And Stability Of Electrochromic Camouflage Device

With the continuous development of infrared detection technology,the continuous popularity of infrared imaging equipment and the further improvement of recognition accuracy,coupled with the rapid transformation of the time and space background of the battlefield,the infrared camouflage technology based on emissivity regulation has put forward higher and newer requirements.However,the traditional infrared camouflage technology mostly uses camouflage coating with fixed emissivity,and its radiation characteristics are not adjustable,which can not be adjusted adaptively according to the changes of the target’s heat and the temperature and solar radiation in the background environment,and can not fully meet the needs of the target’s infrared camouflage.The infrared radiation control device based on electrochromic technology can realize the active control of the surface infrared radiation characteristics by changing the value and direction of the voltage according to the heat of the target and the radiation change of the background environment,thus realizing the adaptive infrared camouflage of the target in different background environments.Therefore,it is of great significance to study the infrared radiation control mechanism and stability of electrochromic camouflage devices for improving the infrared camouflage ability of military targets and enhancing the battlefield survival probability of targets.This paper mainly takes polyaniline as the research object,explains the emissivity control mechanism of polyaniline electrochromic materials,analyzes the influencing factors of the emissivity control of electrochromic devices,studies the degradation mechanism and improvement strategy of the cyclic stability of electrochromic devices,and verifies and evaluates the infrared radiation control effect of electrochromic devices.In view of the shortcomings of polyaniline electrochromic devices,a new type of electrochromic device based on two-dimensional material MXene is developed,which is of great significance to promote the development of adaptive infrared camouflage technology.This paper is mainly carried out from the following aspects:(1)Study on emissivity regulation mechanism of polyaniline electrochromic materialsThe molecular doping model of polyaniline is established.Based on the density functional theory,the structural characteristics and photoelectric characteristics of polyaniline under different camphor sulfonic acid doping levels are analyzed.The simulation results show that the doping of camphor sulfonic acid occurs at the imine site in the polyaniline chain,and the deepening of the doping level will lead to changes in the alternating bond length,dihedral angle and electrostatic potential in the polyaniline molecular chain,making the molecular chain structure more planar and the electrostatic potential distribution more uneven,resulting in an increase in the conductivity and infrared spectrum absorption of polyaniline.Furthermore,the electrochromic film of polyaniline was prepared by ultrasonic spraying.According to the simulation calculation model,the polyaniline doping experiment was designed to change the concentration of camphor sulfonic acid during the doping process,so as to achieve the change of doping level.The morphology,structure and properties of polyaniline films with different doping levels were characterized by atomic force microscopy,Raman spectroscopy,X-ray photoelectron spectroscopy,four-probe resistivity tester and Fourier transform infrared spectroscopy.The experimental results show that the change of the emissivity of polyaniline under different doping concentrations is due to the change of its molecular structure,but not its surface morphology.With the increase of camphor sulfonic acid doping concentration,the content of protonated amine and protonated imine in the molecular chain increases continuously,and the doping degree deepens,as well as the increase of the conductivity.With the increase of doping concentration and conductivity,the optical penetration depth of polyaniline layer will decrease and the reflectivity will increase.Under the joint action of the two factors,the infrared emissivity of polyaniline will increase first and then decrease with the increase of doping concentration.(2)Influence factors on emissivity regulation of electrochromic devicesIn order to improve the regulation range of infrared emissivity of the device,the factors of polyaniline layer thickness,surface morphology,and electrochemical polymerization conditions on the emissivity variation was studied.When studying the factor of thickness,the electromagnetic field simulation calculation model of the infrared radiation control layer of the device is established,and the electromagnetic field equation is solved by using the finite-difference time-domain(FDTD)method to obtain the change rule of the device emissivity control amplitude with the thickness of the polyaniline layer.According to the simulation calculation model,further design experiments,change the power-on time in the process of electropolymerization to achieve the thickness control,and analyze the change rule of the emissivity variation range of electrochromic devices under different thickness of polyaniline layer.The results show that the emissivity variation range of the device increases first and then decreases with the change of thickness,and there is an optimal thickness to maximize the emissivity of the device.The influence of electrode substrates type on the emissivity variations of polyaniline was analyzed.The results show that the pore size distribution of the electrode substrate will affect the growth orientation of polyaniline chain in the process of electropolymerization,resulting in the difference of surface morphology.With macroporous substrate,the morphology of polyaniline becomes rougher and the infrared absorption of polyaniline increases;at the same time,the large hole will also reduce the reflectivity of the gold electrode layer.Under the joint action of the two factors,the range of emission control of polyaniline is reduced.In the study of the influence of polymerization conditions,the change rule of the emissivity variation of polyaniline under the condition of constant current polymerization with different current values and different kinds of doped acid was analyzed.The results show that the polymerization current will affect the nucleation and growth process of polyaniline,and the larger current will cause the rapid growth of polyaniline,which will lead to the reduction of the binding force with the substrate and the difficulty to form an effective thickness,and finally lead to the reduction of the emissivity variation range of polyaniline.Different doping acids will affect the spatial growth state of polyaniline chain,resulting in the difference of film morphology.Compared with the flat and uniform polyaniline-hydrochloric acid surface,using camphor sulfonic acid as doping acid will lead to the accumulation of polyaniline particles to form clusters,thus enhancing the infrared absorption of doped state,thus showing a higher emissivity regulation range.(3)Study on cyclic stability of electrochromic deviceIn order to improve the stability of electrochromic device in the electrification cycle,the cyclic voltammetric curves of polyaniline film and the UV-Visible-NIR spectra of the electrolyte under different cycles were tested to explain the degradation of polyaniline.At the same time,the morphology,molecular structure,electrochemical performance and ion transport characteristics of polyaniline film after degradation under different cycles were analyzed,and the stability decline mechanism of electrochromic devices was elucidated.The results show that polyaniline will produce irreversible degradation products in the process of electrification,and some of them will dissolve into the electrolyte,resulting in the falling off of polyaniline layer and the reduction of electrochromic area;The other part will accumulate on the surface of the substrate,resulting in the blockage of the ion transport channel,which leads to the reduction of the emissivity control performance.Furthermore,polyaniline/carbon nanotube composite structure is constructed by introducing carbon nanotubes to improve cycle stability.Compared with the rapid decay of pure polyaniline material after 30 cycles,the composite structure only decayed 11.6% after 800 cycles,and the stability was greatly improved.(4)Infrared camouflage applications of electrochromic devicesIn order to verify the infrared camouflage effect of polyaniline electrochromic devices,polyaniline electrochromic devices were prepared in batches.It is assembled into an adaptive infrared camouflage array of electrochromic devices(4×4),and the generation scheme of adaptive infrared camouflage is designed.Compared with the camouflage coating with fixed emissivity and the aluminum sheet with single emissivity,the adaptive camouflage effect of the adaptive camouflage array in the typical background(bare soil-grass)was tested at different times.By introducing temperature index and image index,the camouflage effect of materials is evaluated,and the camouflage performance of adaptive infrared camouflage array at different times is quantitatively analyzed.The results show that the adaptive camouflage array shows the best infrared camouflage performance compared with aluminum sheet or fixed emissivity camouflage coating at the time of low ambient temperature in the morning and evening,or at the time of high solar radiation and ambient temperature at noon.In addition,a monolithic and large-area polyaniline electrochromic array was prepared by ultrasonic spraying,and its application in the field of infrared display was explored.The results show that the array can realize the dynamic change of infrared characters,which will have application prospects in infrared projection,infrared decoy and other camouflage fields.(5)Exploration of new infrared electrochromic materials based on MXeneIn view of the disadvantage that polyaniline electrochromic devices rely on noble metal electrodes,a new two-dimensional material MXene is explored in this paper.Combined with the electrical characteristics and pseudo-capacitance characteristics of MXene,the infrared electrochromic devices without metal electrodes are prepared for the first time.The morphology,structure,electrochemical characteristics and emissivity control performance of MXene were analyzed,revealing the emissivity control mechanism of MXene.The results show that MXene will undergo ion intercalation and deinterlation reaction under the action of electric field,which will cause the change of O-terminal group content,and finally lead to the change of emissivity.This research expands the material system of infrared electrochromic devices,and provides a new choice for the application of adaptive infrared camouflage materials and devices.