Structure and stability of thin polyaniline films deposited in situ on silicon and gold during precipitation and dispersion polymerization of aniline hydrochloride

Fresh and one-year-old thin polyaniline films prepared during the in-situ precipitation and dispersion polymerizations of aniline hydrochloride on gold and silicon supports in forms of emeraldine salt and base were characterized by UV-visible, Fourier-transform infrared, and Raman spectroscopies. Raman microscope has been used for the analysis of molecular structure. It has been shown that the films prepared by dispersion polymerization are thinner and more resistant to heating. In all cases, the films prepared on silicon were more stable against aging in air than those prepared on gold, which are, on the other hand, more stable against chemical deprotonation. The role of aniline oligomers adsorbed in the early stages of aniline oxidation on the silicon and gold substrates in the molecular structure and stability of the films has been discussed.     

Polyaniline–CuO hybrid nanocomposites: synthesis, structural, morphological, optical and electrical transport studies

Thin films of semiconducting polyaniline (PANi) nanofibers reinforced with copper oxide (CuO) nanoparticles (NPs) were prepared on glass substrate using spin coating technique. Polyaniline (PANi) have been synthesized by chemical oxidative polymerization method with monomer aniline in presence of (NH₄)₂S₂O₈ as an oxidant at 0 °C. The copper oxide (CuO) nanoparticles were synthesized by sol–gel method. Physical properties of nanocomposite (NCs) films were characterized and analyzed by X-ray diffraction, Scanning electron microscopy, Fourier transform infrared (FTIR) spectroscopy, UV–vis spectroscopy, Two probe resistivity measurement technique and Thermo-emf measurement. Structural analysis showed that the crystal structure of CuO is not disturbed in the PANi–CuO hybrid nanocomposite. Surface morphology study shows the uniform distribution of CuO nanoparticles in PANi matrix. FTIR and UV–Visible studies confirm the presence of polyaniline in emeraldine base form in the composites and suggest incorporation of CuO in polymer. Two probe electrical resistivity measurements of nanocomposites (NCs) film revealed that the resistivity of PANi increases with increasing content of CuO NPs.     

In situ synthesis of gold–polyaniline composite in nanopores of polycarbonate membrane

In situ one-step chemical synthesis route for the preparation of a gold–polyaniline composite in nanopores of polycarbonate (PC) membrane is reported. PC membrane, which was placed in a specially designed two-compartment cell, separated the aqueous solution of aniline from HAuCl₄ solution. Concentration gradient across the membrane caused movement of AuCl₄ ⁻ and anilinium ions in the pores of polycarbonate membrane. Nanopores in PC membrane acted as reaction vessels where aniline and HAuCl₄ were allowed to mix together, and the redox reaction between aniline and HAuCl₄ led to the formation of gold–polyaniline composite. The gold–polyaniline composite in PC membrane was characterised by EDXRF, XRD, UV–Vis spectroscopy, FTIR and TEM. Peak broadening in XRD suggests that Au particles formed in the membrane are nanocrystallites and average crystallite size is (24 ± 4) nm. TEM studies show that gold nanoparticles are randomly dispersed in polyaniline clusters formed in the nanopores of PC membrane. Characterisation results show that the surfaces of the PC membrane exposed to HAuCl₄ and aniline have significantly higher concentrations of Au nanoparticles and polyaniline, respectively.     

Synthesis of H2SO4 doped polyaniline film by potentiometric method

H₂SO₄ doped polyaniline films were synthesized in aqueous acidic media. The polyaniline film deposited on platinum electrode exhibits highest conductivity. The conductivity of each H₂SO₄ doped polyaniline sample was determined by the four-probe technique. The current-voltage curve exhibits that polyaniline sample has an ohmic behaviour. Experiments were conducted to establish the conductivity of the sample from room temperature to 110°C. The current was set constant. It has been observed that at lower current as well as higher current conductivity of the polyaniline sample is due to the electrons transferred to the conduction band. It is observed that the concentration ratio of 0.2:1 of aniline and H₂SO₄ for synthesis of PANI film on platinum electrode shows good conductivity.     

Synthesis and characterization of wormhole-like mesostructured polyaniline

Wormhole-like mesostructured polyaniline (PANi) has been synthesized by using sodium dodecyl benzene sulfonate (SDBS) as a structure directing agent and iron trichloride (FeCl₃ · 6H₂O) or ammonium persulfatee (APS, (NH₄)₂S₂O₈) as an oxidant in an acidic solution. The formation mechanism and structure of polyaniline was studied by powder X-ray diffraction, transmission electron microscopy and FT-IR spectroscopy. It was indicated that aniline (AN)/SDBS would form lamellar structure in an acidic solution, then after introducing oxidant, the wormhole like mesostructures would be formed. The reaction conditions, such as oxidant, oxidant/AN molar ratio, HCl/AN molar ratio, and the reaction temperature had influence on the formation of mesostructures.     

Structural details, electrical properties, and electromagnetic interference shielding response of processable copolymers of aniline

Processable copolymers of aniline with 2-alkylanilines were prepared by in situ chemical oxidative polymerization route. Formation of copolymers was confirmed by X-ray diffractometer (XRD), UV–Vis, and solubility measurements. XRD revealed that copolymerization leads to increase in inter-chain spacing and reduction of doping levels. UV–vis results showed that incorporation of substituted anilines in copolymeric backbone leads to decrease in conjugation, the extent of which is directly related to size of alkyl substituent. The electrical conductivities of these copolymers were slightly less than pure polyaniline, but noticeable improvement in the solution processability was observed. In addition, these copolymers also provided shielding against electromagnetic interference (EMI) with ~99 % attenuation of incident energy. Among various copolymers, 95:5 copolymer of aniline with 2-isopropyl aniline (CP95Ip) gave best performance in terms of electrical conductivity (12.8 S/cm), solubility (4.9 g/L in N-methyl pyrrolidone), and EMI shielding effectiveness (?23.2 dB) values.     

Oxidation of aniline in dopant-free template-free dilute reaction media

The oxidation of aniline with ammonium peroxydisulfate in water without added acid was studied in dilute reaction media. The new nanostructured nonconducting polyaniline sulfate/hydrogen sulfate, synthesized by dilute dopant-free template-free falling-pH method, consists of network of nanorods and nanogranules. The molecular structure of polyaniline, investigated by the elemental analysis, FTIR, Raman, UV–Vis and EPR spectroscopies, was found to be significantly different in comparison with the structure of the nanostructured PANI sulfate/hydrogen sulfate prepared by dopant-free template-free falling-pH method in concentrated aqueous aniline solutions. The mechanism of the formation of nanostructured polyaniline under dopant-free template-free dilute reaction conditions is discussed.     

Polymerization of aniline in the solutions of strong and weak acids: the evolution of infrared spectra and their interpretation using factor analysis

The progress of the oxidative polymerization of aniline with ammonium peroxydisulfate in an aqueous medium has been monitored in situ by attenuated total reflection Fourier transform infrared spectroscopy. The growth of polyaniline film at the crystal surface, as well as the changes proceeding in the surrounding aqueous medium, are reflected in the spectra. The evolution of the spectra during aniline polymerization in the presence of acetic or sulfuric acid was studied with the aim of understanding the influence of acidity on the observed morphology of the final polyaniline films, granular or nanotubes. The changes occurring during polymerization are discussed with the help of differential spectra. Several processes connected with the various stages of aniline oxidation, the evolution of film morphology, or protonation, were distinguished by using factor analysis applied to a large number of spectra obtained in the course of aniline polymerizations on the crystal.     

Poly(N-methyl aniline) thin films on copper: Synthesis, characterization and corrosion protection

Poly(N-methyl aniline) (PNMA) coatings were synthesized on copper by electrochemical polymerization of N-methyl aniline in aqueous oxalic acid solution by using cyclic voltammetry. The optimum electrodeposition conditions (e.g. upper potential limit, scan rate and cycle number) were determined in order to obtain PNMA coatings to have the best corrosion performance. PNMA coatings were characterized by cyclic voltammetry, Fourier Transform Infrared-Attenuated Total Reflectance spectroscopy and scanning electron microscopy. Redox parameters found after electrochemical tests indicate a thin film character and diffusion controlled electroactive behavior of PNMA. Corrosion test results revealed that PNMA coating appears to enhance protection of copper in 0.1 M H₂SO₄ solution.     

Electrosynthesis and analysis of the electrochemical properties of a composite material: Polyaniline + titanium oxide

The analysis of the electrochemical and spectroscopic properties of a composite material obtained starting from the polyaniline and TiO₂ in H₂SO₄ medium, using cyclic voltamperometry, shows three redox couples characteristic of the different oxidation and reduction states of produced polymer. The electroactivity of the composite in acid medium was better than that obtained in basic medium. The impedance spectroscopy study shows that the resistance of the film increases with the aniline concentration, but is not significantly affected by the amount of TiO₂ incorporated in polymer. The increase of pH decreases the resistance of the films and consequently increases its conductivity.     

Synthesis and characterization of polyaniline nanorods/Ce(OH)3-Pr2O3/montmorillonite composites through reverse micelle template

Polyaniline (PANI) nanorods/Ce(OH)₃-Pr₂O₃/montmorillonite (MMT) nanocomposites were synthesized via in situ polymerization of aniline monomer through reverse micelle template (RMT) in the presence of montmorillonite and Ce(OH)₃, Pr₂O₃. In the experiment, sulphosalicylic acid was used as dopant, aniline was designated as oil phase and the aqueous solution comprising Ce³⁺ and Pr³⁺ as water phase. The nanocomposites were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) analysis, Fourier transform infrared (FT-IR) spectroscopy and thermogravimetry-differential thermal analysis (TG-DTA). The results showed that PANI nanorods were synthesized in the interlayer spaces of MMT with uniform spherical rare earth nanoparticles. The thermal stability of the nanocomposites prepared was enhanced drastically compared with pure polyaniline.     

Characterization of polyaniline by cyclic voltammetry and UV-Vis absorption spectroscopy

Characterization of polyaniline (PANI) by electrochemical and spectroscopic techniques are presented. The electrochemical investigation reveals the influence of the dopant acid on the kinetic parameters of polyaniline films: exchange current density (I₀) and the cathodic transfer coefficient (_c). UV-Vis spectra of thin films of polyaniline in N-metil pyrrolidine solutions indicate the increase of the absorbance with the number of deposition cycles, N. The inhibition of polymer degradation in thick films was confirmed by these spectra.     

Electrochemical synthesis and characterization of chloride doped polyaniline

Chloride doped polyaniline conducting polymer films have been prepared in a protic acid medium (HCl) by potentiodynamic method in an electrochemical cell and studied by cyclic voltammetry and FTIR techniques. The FTIR spectra confirmed Cl^- ion doping in the polymers. The polymerization rate was found to increase with increasing concentration of aniline monomer. But the films obtained at high monomer concentration were rough having a nonuniform flaky polyaniline distribution. Results showed that the polymerization rate did not increase beyond a critical HCl concentration. Cyclic voltammetry suggested that, the oxidation-reduction current increased with an increase in scan rate and that the undoped polyaniline films were not hygroscopic whereas chloride doped polyaniline films were found to be highly hygroscopic.     

Synthesis and electrorheological properties of polyaniline/silicon dioxide composites

This study was to synthesize the inherently conductive polymer polyaniline using an optimized process to prepare polyaniline/silicon dioxide (PANI/SiO₂) composites by in situ polymerization and ex situ solution mixing. PANI and PANI/SiO₂ composite films were prepared by drop-by-drop and spin-coating methods. The morphology of particles and films were examined by a scanning electron microscope (SEM). SEM measurements indicated that the SiO₂ were well-dispersed and isolated in composite films. The electrorheological (ER), characteristics of the PANI/SiO₂ composites were investigated. A volume fraction series (φ = 5–25 %) of the PANI/SiO₂/silicone oil dispersions were prepared and sedimentation stabilities were determined. An ER activity was observed from the samples, when subjected to external electric field strength thus, they were classified as smart materials. Some parameters affecting the ER properties of the dispersions such as volume fraction, shear rate, electric field strength, frequency, and temperature were investigated.     

Effect of Pb2+ and Cu2+ as a codopant on the structure,morphology and conductivity of nanostructured polyaniline

Polyaniline (PANI) has been successively synthesized in aqueous diethylene glycol solution medium by chemical oxidative polymerization of aniline using ammonium peroxidisulfate [(NH₄)₂S₂O₈] as an oxidant in an aqueous solution of 0.5 M acetic acid (CH₃COOH) as a dopant. Polyaniline–lead (PANI–Pb) and polyaniline–copper (PANI–Cu) nanocomposites have been chemically prepared for the first time by oxidative polymerization of aniline in aqueous diethylene glycol/acetic acidic medium. The synthesized PANI and nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR). Conductivity measurements of the polymer and nanocomposites were performed using the four-probe technique. Morphology changes of the composites were investigated by scanning electron microscopy (SEM). PANI nanotubes were formed without added codopant, but when Pb(CH₃COO)₂ or Cu(CH₃COO)₂ was added as a codopant, the morphology of PANI obviously changed. The PANI–Cu and PANI–Pb nanocomposites exhibit higher conductivity than the PANI homopolymer, but the conductivity of the composites slightly decreased on increasing the metal concentrations.     

Fabrication of conductive network formed by polyaniline-ZnO composite on fabric surfaces

A conductive network consisting of polyaniline (PANI) and PANI/nm-ZnO immobilized on the surfaces of poly(ethylene terephthalate) (PET) fabrics was synthesized by a route involving a wet-chemical technique and in-situ chemical oxidative polymerization procedures. Morphological, structural, thermal and electrical properties of the PET fabrics modified with PANI-ZnO composites were analyzed. X-ray diffraction (XRD) measurements of the composites revealed that the crystal structure of incorporated ZnO undergone a weak distortion during the polymerization reaction and the XRD pattern of PANI was predominate. Attenuated total reflection Fourier transform infrared spectroscopic studies indicated the presence of interaction between ZnO nanorods and molecular chains of PANI in the ZnO/PANI layers. Field emission scanning electron microscope images implied the thin composite layers showed a submicro-sized rod like network and the homogeneous distribution on the substrates. Thermogravimetric studies exhibited that the PET-ZnO/PANI composite had a higher thermal stability than anyone of PET and PET-PANI. The surface resistance of ZnO/PANI conductive films was found to be smaller than the PANI film, which was declined as aniline concentration in adsorption bath increased and reached a relatively low value when Zn(NO₃)₂ concentration was at 0.03 mol/L in the precursor solution.     

Polyaniline micropattern onto flexible substrate by vapor deposition polymerization-mediated inkjet printing

An approach to pattern a conducting polymer on various flexible substrates using vapor deposition polymerization-mediated inkjet printing method was demonstrated. Complex patterns of doped emeraldine salt polyaniline were obtained via chemical oxidation polymerization of vaporized aniline monomer on inkjet-printed oxidant patterns. The features of pattern were precisely controlled by inkjet printing with a micrometer-scale resolution. Fourier transformed infrared attenuated total reflection analysis was conducted in order to confirm the polymerization of aniline monomer and UV-visible spectroscopy analysis was used to investigate the oxidation state of obtained polyaniline. The minimum width of patterned line was ca. 80 μm. The sheet resistance of patterned polyaniline films was 3.8 × 10³ Ω/□ for an average patterned film thickness of ca. 450 nm.     

Structural and magnetic properties of nanocomposites based on nanostructured polyaniline and titania nanotubes

Nanocomposites consisting of self-assembled polyaniline (PANI) nanostructures and titania nanotubes (TiO₂-NT) were synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate in an aqueous dispersion of TiO₂-NT (outer diameter ~10 nm), without added acid. The influence of initial mole ratio of aniline to TiO₂ (80, 20, and 5) on the morphology, electrical conductivity, molecular structure, crystallinity, and magnetic properties of synthesized PANI/TiO₂ nanocomposites was studied. Transmission electron microscopy, Raman spectroscopy, and X-ray powder diffraction proved that the shape and structure of TiO₂-NT in the final nanocomposites were preserved. The shape of PANI nanostructures formed in the nanocomposites was influenced by the initial aniline/TiO₂-NT mole ratio. Nanotubes and nanorods are predominant PANI nanostructures in the nanocomposite prepared with the highest aniline/TiO₂ mol ratio of 80. The decrease of aniline/TiO₂ molar ratio induced more pronounced formation of nanorod network. The electrical conductivity of PANI/TiO₂ nanocomposites was in the range (1.3–2.4) × 10^?3 S cm^?1. The nanocomposites exhibit weak ferromagnetic behavior. Approximately order of magnitude lower values of coercive field and remanent magnetization were obtained for nanocomposite samples in comparison to pure PANI.     

On the optical and electrical properties of rf and a.c. plasma polymerized aniline thin films

Polyaniline is a widely studied conducting polymer and is a useful material in its bulk and thin film form for many applications, because of its excellent optical and electrical properties. Pristine and iodine doped polyaniline thin films were prepared by a.c. and rf plasma polymerization techniques separately for the comparison of their optical and electrical properties. Doping of iodine was effectedin situ. The structural properties of these films were evaluated by FTIR spectroscopy and the optical band gap was estimated from UV-vis-NIR measurements. Comparative studies on the structural, optical and electrical properties of a.c. and rf polymerization are presented here. It has been found that the optical band gap of the polyaniline thin films prepared by rf and a.c. plasma polymerization techniques differ considerably and the band gap is further reduced byin situ doping of iodine. The electrical conductivity measurements on these films show a higher value of electrical conductivity in the case of rf plasma polymerized thin films when compared to the a.c. plasma polymerized films. Also, it is found that the iodine doping enhanced conductivity of the polymer thin films considerably. The results are compared and correlated and have been explained with respect to the different structures adopted under these two preparation techniques.     

Synthesis, characterization and electrical properties of poly(dibromoaniline-co-aniline)s

The chemical copolymerization of aniline and 2,5-dibromoaniline or 2,6-dibromoaniline by oxidation with K₂Cr₂O₇ in H₂SO₄/acetonitrile media has been carried out. Copolymer composition can be effectively controlled varying the monomer feed ratio. When substituted aniline fraction is increased in the copolymer, the electrical conductivity () decreases; this effect is more important when 2,6-dibromoaniline is used. Thus, the conductivity can be controlled in a broad range, from 1.2 to 10^–6–10^–11 S·cm^–1 depending on the substituted aniline and the feed ratio. The relations between copolymer compositions and comonomer feed molar ratios shows that the aniline is slightly more reactive than dibromoanilines during the copolymerization process. All the copolymers were shown to be more processable than polyaniline.