Variable Infrared Emissivity Properties Of Pani And Its Derivatives Composite Films

Electrochromism is a phenomenon that yields to reversible changes in material's optical properties(transmittance,reflectance,and absorptivity,etc.)under the applied electric field.Electrochromism is under active research due to possibilities of its wide applications such as smart windows for buildings and automobiles,flexible optical display,and anti-glare mirrors.Recently,the properties of electrochromic materials in the mid-to-far IR range have been widely studied due to their pending applications such as IR stealth and aerospace thermal control.Compared to WO3 and other inorganic metal oxide electrochromic materials,conducting polymers,such as polyaniline(PANI)show better perspectives because of the low cost,easy synthesis,fast response time,high IR contrast.PANI has become the most widely studied type of organic infrared electrochromic material.In this paper,the polyaniline films doped with sulfuric acid and dodecyl benzene sulfonic acid(DBSA)and the poly o-toluidine-polyaniline(POT-PANI)composite film were polymerized by electrochemical galvanostatic method.Scanning electron microscopy,Fourier transform infrared spectroscopy,Raman spectroscopy and electrochemical workstations were used to characterize the morphology and property of the prepared films.The influence of the preparation process conditions such as polymerization monomer concentration,polymerization current,and polymerization time on the polymerization curve,cyclic voltammetry characteristics,infrared transmittance,and emissivity performance was investigated.The relationship between the conductivity,the transmittance and the IR emissivity has been investigated in detail for the first time.The results of studies on protonic acid-doped PANI films show that the properties of polyaniline films doped with sulfuric acid and DBSA are different.The sulfuric acid-doped PANI film is denser and more uniform,and the PANI film doped with DBSA acid has a looser and rougher surface.Sulfuric acid-doped PANI has a lower emissivity modulation.The sulfuric acid-doped PANI film with a polymerization time of 4000 s has the highest emissivity modulation,with a maximum of 0.051.The preparation conditions for the DBSA-doped PANI film with the maximum emissivity modulation were: aniline monomer concentration of 0.03 mol/L,polymerization current of 0.4 m A,polymerization time of 1000 s.The maximum emissivitymodulation amplitude is 0.261.After 100 cycles,the emissivity modulation of the PANI film was attenuated by 24.5%,and the electrochromic response time of the PANI film was in second order.The results of PAN-POT double-layer composite films show that the properties of the composite film are different from those of a single-layer film.The microscopic morphology presents a gully-like surface with a gap,and the surface of the double-layer composite film is rougher than that of single-layer film.When the polymerization time of the bottom POT film was 3000 s and the polymerization time of the top PANI film was 1500 s,the emissivity modulation of the obtained double-layer composite film was the largest,and the maximum emissivity modulation was 0.394.The cycling performance of the double-layer composite film is similar to that of single-layer DBSA-doped PANI film.After 100 cycles,the emissivity modulation of the film is reduced by 24.1%,and the electrochromic response time of the double-layer film was twice as slow as that of the single-layer DBSA-doped PANI film.Through the study of conductivity,infrared(IR)transmittance and emissivity of the DBSA-doped PANI films at different polymerization times,the emissivity modulation mechanism of PANI film electrodes was obtained.When the PANI film is thin,the reflection from the double structure ITO/PANI is mainly determined by the high IR reflectance of the ITO substrate,which determines the overall emissivity modulation,and the change of the electrical conductivity of the PANI film causes only the modulation of the ITO reflectivity.When the PANI film is thick enough its IR transmittance decreases remarkably and the incident IR radiation is mainly adsorbed in the PANI film,thus drastically reducing the reflection from the ITO.In the latter case,the entire reflectivity is determined mainly by the PANI film and the substrate IR reflectance has little effect on it.