Electrochromic features of hybrid films composed of polyaniline and metal hexacyanoferrate

Hybrid organic/inorganic films, composed of polyaniline (PANI) matrix and Prussian blue-like nickel hexacyanoferrate redox centers, showed reversible electrochromic behavior in acidic potassium salt electrolytes. The system's coloration properties were assessed from various spectroelectrochemical measurements including voltabsorptometry that involved monitoring of the time-derivative signal of absorbance at 700 and 410 nm as a function of linearly scanned potential. Gold-covered foil was used as a conductive, optically transparent, substrate onto which the composite film was electrodeposited by potential cycling in the mixture for modification consisting of aniline monomer, Ni²⁺, Fe(CN)₆³⁻ and electrolyte containing K⁺ and H⁺ ions. An important feature of hybrid (composite) material was that its electrochromic properties were dominated by color changes occurring in the PANI component. Coloration originating from nickel hexacyanoferrate barely affected the system's electrochromic characteristics. But the cyanometallate redox centers distributed in the PANI matrix behaved reversibly as expected for a system capable of fast charge transport.     

Thermal stability studies of transparent conducting polyaniline composite films on their conductivity and optical spectra

The thermal stability of highly transparent and conducting polyaniline–Nylon 6 (PAn-N) composites films doped with various protonic acids such as hydrochloric acid (HCI), benzenesulfonic acid (BSA), sulfosalicylic acid (SSA), and p-toluenesulfonic acid (TSA) was investigated at different elevated temperatures under air atmosphere. Two different degradation kinetic processes of electrical conductivity were found depending on the species of protonic acids. The conductivity degradation of PAn-N composite films doped with SSA and TSA were found to obey first-order reaction kinetics, while that of the other dopants was found to follow multiorder kinetics. Spectroscopic studies revealed that the thermal de-doping process of doped composite films, which reversed the doping process, took place without major structural modifications of the polyaniline in the composite system but was not completely reversible. From the differential scanning calorimetry (DSC) study, the crystal structure of the composite films was found to be affected by the formation of polyaniline in matrix polymer and depended on the types of dopant species. © 1995 John Wiley & Sons, Inc.     

Fabrication of honeycomb‐patterned polyaniline composite films containing cellulose triacetate with high conductivity and mechanical stability

Polyaniline (PANI) biocomposites were prepared via in situ polymerization of aniline monomer with cellulose triacetate (CTA) and by using ammonium persulfate as an initiator in an aqueous solvent. The composites exhibited high solubility in organic solvents due to the incorporated CTA component, and enabled the fabrication of honeycomb‐patterned thin films by casting the PANI composite solutions under humid conditions. The honeycomb‐patterned PANI–CTA composite films showed a high conductivity corresponding to about 1.5 S/cm, good mechanical stability, and high flexibility. The composites have a potential advantage comparing to pure PANI because of biodegradability and high solubility due to included CTA. These composite films can usefully be applied in the field of bio‐nanotechnology and medicine including micro‐structured electrode surfaces, filters for cell sorting, and bio‐interfaces and so on. POLYM. COMPOS., 37:2649–2656, 2016. © 2015 Society of Plastics Engineers     

Fabrication of honeycomb-patterned polyaniline composite films using chemically modified polyaniline nanoparticles

A novel polyaniline composite was prepared by in situ ring-opening polymerization of ε-caprolactone in the presence of chemically modified polyaniline nanoparticles (PANI-NPs) using Sn(Oct)₂ as an initiator, which exhibited a high solubility in organic solvent to enable the fabrication of stable honeycomb-patterned thin films by casting the PANI composite solutions under humid conditions. The chemically modified PANI-NPs were produced from the polymerization of aniline in the cationic surfactant of cetyl trimethyl ammonium bromide (CTAB). The polyaniline composites were characterized via Fourier transform infrared, ultraviolet–visible spectroscopy, X-ray diffraction, transmission electron microscopy, and thermogravimetry. The analyses indicated that the PANI-NPs were well incorporated in the poly(ε-caprolactone) (PCL) backbone. The patterned PANI composite films showed high DC conductivity up to 10⁻² S/cm, which can be useful in applications such as bio-sensing, bio-nanotechnology, biological science, and medicine.     

Chronoamperometry of prussian blue films on ITO electrodes: ohmic drop and film thickness effect

The chronoamperograms associated with the reduction of prussian blue films deposited onto indium tin oxide (ITO) electrodes to the Everitt’s salt form, are influenced by the ohmic drop effect. These chronoamperometric curves have been simulated by means of a numerical finite difference model which is able to explain their shape and their dependence on the thickness of the film and on the uncompensated resistance. An analytical expression which describes the dependence of current against time at initial times considering the ohmic drop effect has also been proved when applied to these chronoamperometric curves at short times.     

Electrochromic properties of chemically prepared polyaniline

The electrochromic properties in non-aqueous medium of chemically prepared polyaniline films proved not to depend on the oxidizing agent used for the synthesis and were very similar to the properties of electrochemically prepared films. These properties were studied by measuring the optical contrast changes at fixed wavelengths in the uv/visible region during cyclic voltammetric scans and by applying 7 × 10³–8 × 10³ redox potential steps.     

Well-dispersed single-walled carbon nanotube/polyaniline composite films

Single-walled carbon nanotube (SWNT)/polyaniline (PANI) composite films with good uniformity and dispersion were prepared by electrochemical polymerization of aniline containing well-dissolved SWNTs. The results of atomic force microscopy (AFM) and UV-Vis adsorption spectroscopy show that aniline can be used to solubilize SWNTs via formation of donor-acceptor complexes. The electrochemical deposition of SWNT-aniline solutions have been investigated by cyclic voltammetry. The results show that SWNT-based aniline solutions exhibit a drastic increase in peak current within the potential scanning region. The doping effect of SWNTs on PANI films was investigated by electrochemistry and FTIR spectroscopy. The results indicate that the enhanced electroactivity and conductivity of the SWNT/PANI composite films may be due to the strong interaction between SWNTs and PANI, which facilitates the effective degree of electron delocalization.     

Growth mechanism of transparent and conducting composite films of polyaniline

Composites of polyaniline (PANI) with various polymeric matrices as substrates were synthesized by means of diffusion–oxidation of aniline swollen polymeric matrices with FeCl₃ as oxidizer. The conductivity at room temperature, transmittance at 400–800 nm, stability in air, and morphology of PANI composite films depend on the polymerization time, concentration of FeCl₃, and substrate used. A maximum conductivity at room temperature and the highest transmittance at 500–800 nm can be achieved of 10^?1 S/cm and 70–80%, respectively. The growth mechanism of PANI composite films has been discussed. © 1993 John Wiley & Sons, Inc.     

Improved charging/discharging behavior of electropolymerized nanostructured composite films of polyaniline and electrochemically reduced graphene oxide

In this work, a simple electrochemical reduction procedure has been applied to nanostructured composite films of polyaniline (PANI) and graphene oxide (GO) having a globular surface morphology with the grain size of 50 nm. The reduction converts GO to reduced GO (rGO) which improves the electroactivity of the PANI composite films with 30%. Cyclic voltammetry confirmed the reduction of GO to rGO whereas electrochemical impedance spectroscopy showed that the rGO network increases the redox capacitance of the composite films with 15% to 77 mF cm⁻². In a three-electrode cell, the anodic charge of the PANI film containing GO increased with 18.7% during the potential cycling stability test for 10,000 cycles between −0.2 and 0.5 V, indicating that the film had a good stability against degradation. This composite film type still maintained a high capacitance of 15 mF cm⁻² in a symmetric two-electrode cell after 10,000 potential cycles between 0 and 0.4 V. The electrochemically prepared PANI composite films reported here are aimed to be used in capacitor applications where it is crucial to deposit thin PANI layers on well-defined small surfaces where other polymerization or deposition techniques cannot be used and in solid-state chemical sensors as ion-to-electron transducer interfaces.     

Preparation and electroanalytical characterization of polyaniline: Polyacrylonitrile composite films

Electrically conducting composite films of polyaniline:polyacyrlonitrile (PANI:PAN) prepared with varying composition ratios of aniline mixed with a fixed amount PAN. The films of optimum thicknesses (0.10 mm) were obtained using an electrically operated automatic pressure machine. The films polymerized by oxidative polymerization using 0.1M potassium persulphate (K₂S₂O₈), undoped in 1M aqueous ammonia (NH₄OH) and doped in 1M hydrochloric acid (HCl). The conductivity of composite films was studied by keeping it in 1M HCl for different time period using 4-in-line probe DC electrical conductivity measuring instrument and the temperature dependence of DC electrical conductivity was studied using isothermal technique. The PANI:PAN composite film is used as a working electrode in an electrochemical cell. Chemically doped composite film is used as cathode (working electrode), aluminum metal foil as anode (counter electrode) and platinum foil as reference electrode. The electrolyte is of 0.05M aluminum chloride (AlCl₃) in dimethyl sulfoxide (DMSO). The voltage of the working electrode is stabilized with respect to the reference electrode and current applied between the working and counter electrode through a 9-V battery. The change in voltage versus time is plotted as the discharge curve and reversing the cell processes results in the doping of the composite films. The diffusion coefficient of the dopant ion (Cl⁻) present in the fully doped films were estimated by the galvanostatic pulse technique and found to bedifferent in different samples in the range of 10⁻¹⁶ to 10⁻¹² cm² s⁻¹. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Electrochemical formation of Ir oxide/polyaniline composite films

The primary goal of this work has been to electrochemically form and then characterize a composite polyaniline (PANI)/hydrous Ir oxide (IrOx) film. Efforts to electrochemically form IrOx and PANI simultaneously in acidic aniline-containing solutions failed, likely as aniline adsorption on Ir prevents IrOx formation. Successful composite films were therefore made by first forming an anodic IrOx film on bulk Ir and then depositing PANI into its pores. Based on the characteristics of the PANI redox peaks, it is seen that all of the PANI film that is electrochemically active is in direct electrical contact with the Ir surface at the base of the IrOx film pores. This is consistent with the cross-sectional SEM and EDX analyses, showing the formation of films of uniform thickness and composition. Thin films of Ir nanoparticles, subsequently converted to IrOx, were also used as a template for PANI formation within the porous structure. These hybrid films exhibit an enhanced internal porosity, ease of multiple coating formation (up to 20 μm in thickness), high charge densities, unusual electrochromic behavior, and very rapid charge transfer kinetics. The formation of composite IrOx/PANI films also resulted in a widening (by 0.3-0.4 V) of the potential window over which a pseudocapacitive and electrochromic response is seen.     

Structure and gas separation properties of composite films based on polyaniline

Composite films based on the polyvinyltrimethylsilane (PVTMS) with polyaniline (PANI) coating were obtained by borderline polymerization of aniline. The obtained coating was shown to differ from the polymer forming in the reaction mixture bulk both in chemical structure and morphology. Ratio and concentration of the reagents, mixing rate, reaction time, and condition of support surface were among the investigated factors affecting the growth and quality of PANI coating. The gas separation characteristics of composite membranes, as affected by the process conditions and the type of PANI, were investigated. It is shown that the proposed method provides a means for obtaining composite membranes that combine high selectivity, especially in O₂/N₂, He/CH₄, and CO₂/CH₄ separation, with permeability higher than that of known composite materials. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1379–1384, 2003     

Characterization of viscoelastic properties of composite films involving polyaniline and carbon nanotubes

The deposition and properties under electrochemical potential control of composite films of polyaniline and single walled carbon nanotubes were studied using high frequency acoustic wave measurements at quartz crystal resonators. Acoustic admittance spectra were used to provide shear moduli for the growing films as functions of thickness and dopant anion (sulfate, nitrate or perchlorate). The electrochemical and viscoelastic data were compared with those obtained in a parallel set of experiments in the absence of carbon nanotubes. The presence of carbon nanotubes in the deposition solution enhances the rate of polyaniline deposition by a factor of 3-5, according to the dopant. In all media, the shear modulus components increased with film thickness and in any given medium both the storage and the loss moduli were greater in the presence of carbon nanotubes. Since SEM images do not reveal the presence of the carbon nanotubes directly, they are deduced to interact sufficiently strongly with the polymer as to become fully encapsulated. A mean field model is adapted to provide predictive capability at a simplistic level for composite film viscoelastic properties in terms of the mechanical properties of the constituents. When applied to the experimental data, it suggests that the level of carbon nanotube incorporation is modest, despite its significant effect on film deposition and properties.     

Electroanalytical studies on electrically conducting polyaniline:polyethyleneterephthalate composite films

Polyaniline (PANI):polyethyleneterephthalate (PET) composite was prepared by chemical polymerization of aniline diffused in the PET matrix. Thus prepared composite films were characterized by fourier‐transform infrared spectroscopy and scanning electron microscopy and their electrical properties and the thermo‐oxidative stability was studied by thermogravimetry and differential thermal analysis. The stability in terms of DC electrical conductivity retention was studied in an oxidative environment by two slightly different techniques viz. isothermal and cyclic techniques. DC electrical conductivity of composite films was found to be stable up to 90°C for most of the composites under ambient conditions. The composite films were employed as cathode material in secondary cells containing 1M ZnCl₂ solution. The studies were carried out on the charge/discharge cycles under a constant current load 140 mA. The composite films showed similar behavior in electrolyte solution and cell response is reversible. To determine the diffusion coefficient for the chloride ions diffusion into the composite films electrochemically, galvanostatic pulse method was used. The diffusion coefficient was estimated to be ～ 3.28 × 10^?12 cm² s^?1. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Thermal behavior of polyaniline films and polyaniline–polystyrene blends

In this article, a study of the thermal behavior of polyaniline films and polyaniline–polystyrene blends is presented. Transport measurements (electrical conductivity and thermoelectric power) at high temperature and thermogravimetric analysis show that an irreversible degradation is observed near 450 K for films doped with DiOHP and near 500 K for films doped with CSA. In both cases, the thermoelectric power is the most sensitive parameter to electrical degradation during the heating of conducting films. Electrical conductivity measurements during heating–cooling cycles show a diminution of the room temperature conductivity after evaporation of the solvent (water, m‐cresol). A model of cluster with a variable diameter allows interpreting this phenomenon by assuming the existence of a sensitive frontier to the solvent at the periphery of conducting clusters. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1848–1855, 2002; DOI 10.1002/app.10468     

A tungsten-trioxide/prussian blue complementary electrochromic cell with a polymer electrolyte

Optically variable windows (smart windows), which control the transmission of light into buildings and vehicles, are of interest both for the control of solar heat load and for privacy applications. Such windows are likely to utilize electrochromic technology to achieve optical control. An electrochromic device consisting of a cathodically colouring tungsten trioxide (WO₃) film, an anodically colouring Prussian blue (PB) film, and a polymer electrolyte was made. The polymer electrolyte was prepared from polyvinyl alcohol doped with H₃PO₄ and KH₂PO₄ to accommodate the conduction of both H⁺ and K⁺ ions. The electrochromic WO₃ and PB films functioned in a complementary way such that the device was coloured or bleached by the application of –0.5 V or +0.5 V (WO₃ films vs PB film), respectively. The spectral characteristics of the coloured device confirmed the complementary colouration of WO₃ and PB in the device.     

Well-aligned polyaniline/carbon-nanotube composite films grown by in-situ aniline polymerization

Multiwalled carbon nanotubes (MWNTs) encapsulated by polyaniline (PANI) of nanometer size have been synthesized by in-situ polymerization, and are found to be orientationally ordered by the aligned MWNTs. Procedures are demonstrated for the preparation of nanocomposite-tube (NCT) films with controlled organization. Changes in the dimensions of the nanocomposites were measured using SEM and TEM techniques. The interaction between PANI and MWNTs and the nature of chain growth have been investigated and explained according to the results of FT-IR analysis. The improvement of thermal stability and crystallinity of the nanocomposites have been evaluated by using TGA and XRD. The mechanism of charge transport in these composites has also been studied by measuring the DC conductivity of all samples and examining the temperature-conductivity relations. MWNT alignment should be possible with other nanometer-sized building composites films, offering a general route for controlled assembly of organized nanomaterials and devices.     

Thermal ageing of electrical conductivity in carbon nanotube/polyaniline composite films

The influence of carbon nanotubes on the thermal ageing effect of the electrical conductivity of composite thin films is presented. The composite thin films comprise carbon nanotube/polyaniline nanofibers. When subject to thermal treatment, the presence of nanotubes retards the loss of dopants from the polyaniline and enhances the thermal stability in electrical conductivity of the composite thin films. Specifically, an increase in temperature for the conductivity degradation and a significant reduction in the rate of the conductivity degradation of the composite thin films are observed. Upon prolonged heating, the composite thin films exhibit relative large conductivity at high nanotube content, while the polyaniline thin films become insulating.     

Flexible single-walled carbon nanotubes/polyaniline composite films and their enhanced thermoelectric properties

Flexible single-walled carbon nanotubes/polyaniline (SWNT/PANi) composite films with enhanced thermoelectric properties were prepared via a simple method. Furthermore, these paper-like composite films show good flexibility, which makes them possible to be widely applied in various flexible energy converter devices.     

Nano-Al doped-MoO3 high-energy composite films with excellent hydrophobicity and thermal stability

Developing the thermal stability of metal-based ceramic composites or their films has always been challenging and bottlenecks for the utilization of energy. In this paper, the novel mesh-like functional Al doped-MoO₃ nanocomposite film with even distribution and high purity was firstly fabricated by the high-efficiency electrophoretic deposition and surface modification. The optimal suspension turned out to be the mixture of isopropanol and the additives of polyethyleneimine and benzoic acid. The microtopography, crystalline structure, environmental resistance and thermal stability were analyzed by field emission scanning electron microscope (FESEM), energy dispersive X-ray (EDX), X-ray diffractometer (XRD), exposure and droplet-impacting test, DSC analysis and ignition test, respectively. The water contact angle and sliding angle of product can reach ~170° and <1°, indicating the excellent anti-wetting property. In addition, the high heat-release (~3180 J/g) of product all kept almost unchangeable after six months exposure experiments, demonstrating the outstanding thermostability. The exquisite design idea here can perfectly match microelectromechanical system (MEMS), providing the valuable reference for fabricating other metal-based high-energy composites with long lifespan for real industrial applications.