Modification Mechanism And Infrared Emission Behavior Of Electrochromic Polyaniline Films

With the rapid development of space technology,China’s space infrastructure will usher in a comprehensive update and improvement.Faced with complex and changeable external heat fluxes environment and significant differences in internal heat consumption,spacecraft thermal control system urgently needs to have independent management capability.The new intelligent thermal control technology can give spacecraft the ability of dynamic thermal dissipation.Among various intelligent thermal control technologies,electrochromic intelligent thermal radiation control technology has attracted much attention.This work focused on the construction of intelligent thermal radiation control device based on polyaniline（PANI）film which can work smoothly and efficiently under harsh conditions.Firstly,the infrared electrochromic mechanism of the PANI film was studied deeply.Then the infrared emissivity modulation amplitude of PANI film was improved by the regulation of electrochemical deposition process and the modification of doping acid.Finally,a flexible intelligent thermal control devices was construced basd on the PANI film.The specific research contents and results of this paper are as follows:The HCl O₄ doped-PANI porous film with excellent infrared regulation ability（Δε=0.4）was fabricated via in-situ electrochemical deposition on an Au/microporous substrate.The optimum parameters include the concentration ratio of aniline and HCl O₄ of 1:2（1mol/L）,the current density of 1m A/cm²,and the polymerization charge of 9.0-11.0C.A combination of Raman spectrum,UV-vis spectra,XPS analyses,transmittance curves and emittance curves of PANI porous films at distinct conjugation states and corresponding dedoping states confirm that the most direct and critical factors for realizing the emissivity modulation of PANI film are the formation and the elimination of polarons and bipolarons delocalized on PANI chains.The key factor to achieve large amplitude emissivity modulation of PANI film is fully and effectively regulating the transformation between the various states of PANI.In view of the limited infrared emissivity modulation amplitude of PANI film,the micro-morphology of PANI film was regulated by controlling the polymerization kinetics to explore the effect of micro-morphology on the infrared thermal radiation modulation capability of PANI film.The surface morphology of PANI film was controlled by adjusting the concentration of monomer in the electropolymerization solution.The surface of PANI film prepared at high monomer concentration（PANI2）presents non-directionally distributed nanowire-like structures.Because the IR light propagate into the PANI film and interact with the interface of non-directionally distributed nanowires for many times,it can capture and absorb more infrared light.PANI2 can dynamically adjust the infrared emissivity from 0.712 to 0.321（Δε=0.391）.The PANI film prepared at low monomer concentration（PANI6）presents relatively smooth surface,which can dynamically adjust the infrared emissivity from0.573 to 0.190（Δε=0.383）.In addition,the polymerization current density was used to control the growth rate and aggregation structure of PANI film.It was found that aniline salts could quickly and uniformly oxidize nucleation on the electrode surface with high polymerization current density,and cooperate with the rapid growth of molecular chain.And the PANI film had strong ability to regulate infrared thermal radiation.In order to further improve the infrared emissivity control ability and preparation efficiency of PANI film,the PANI film was modified by the electrostatic interaction between anion and PANI molecular chain.It was found that sulfate ion had a strong proton affinity and could form a strong electrostatic interaction with the protonated amine on the PANI molecular chain.The H₂SO₄ doped-PANI film had a double-layer structure.The electrode surface was a relatively smooth dense layer.The top layer was a loose layer with granular structure adhering together.Due to the high interface resistance of the two layers,the loose layer on the surface could not participate in the redox reaction.The loose layer was removed by surface polishing,which had a good ability to regulate the infrared emissivity.However,this method reduced the utilization rate of PANI.In order to improve the homogeneous film forming efficiency of PANI,polystyrene sulfonate was used as the guiding agent and dopant to regulate the growth and aggregation of PANI molecular chain.And the effects of polymerization charge and the amount of polystyrene sulfonate on the infrared electrochromic properties of the PANI films were investigated.It was found that the PANI film prepared by adding 0.1mol/L polystyrene sulfonate（the concentration of repetitive unit）,the concentration ratio of aniline to H₂SO₄ at 1:2（1mol/L）,current density at 1m A/cm² and polymerization charge at 1.25C had good infrared thermal radiation control ability.The transient thermal analysis of the heat dissipating plate attached with the infrared electrochromic device was carried out by using the Transient Thermal module in the Ansys Workbench simulation platform.It was found that the infrared electrochromic device exhibited an excellent potential for the purposes of efficient thermal management of the satellite.Based on the optimized PANI functional layer,the reflective infrared electrochromic device was constructed by using porous PE film as encapsulation layer and polymer porous film adsorbing ionic liquid as gel electrolyte.After high and low temperature cycle test（1000 cycles）and vacuum environment test,the device showed good thermal radiation modulation capability（Δε=0.38）and low solar absorptivity（α（s）=0.31）,which shown the ability to work smoothly and efficiently under harsh conditions.