Monoparticulate films of polyaniline

Monoparticulate films were prepared from colloidal polyaniline (PANI) via the Langmuir-Blodgett (LB) technique. An aqueous dispersion of PANI obtained by aniline polymerization in the presence of polyvinyl alcohol was spread at the air-water interface in a LB trough. The floating films were transferred by the vertical lifting method to Si wafer or glass substrates. The films were very stable and could not be removed during immersion in aqueous solutions for at least several months. The color of dry monoparticulate PANI films was violet independently of the color adapted upon immersion in aqueous media at different pH. We suggest that not only the wavelength of the absorbed light, but also that of the scattered light, has an effect on the color of PANI.     

Effect of iodine solutions on polyaniline films

Polyaniline (PANI) emeraldine-base films have been exposed to iodine solutions. The interaction between the films and the iodine solution was studied using the quartz-crystal microbalance (QCM) technique and the UV-visible absorption spectroscopy. The iodine-treated film of emeraldine base was subjected to dedoping process using 0.1 M ammonia solution. The resulting film was exposed again to the previously used iodine solution. Iodine was found to play multiple roles: the ring-iodination of PANI film, the oxidation of PANI to pernigraniline base, and iodine doping to PANI salt. A sensor based on PANI-coated electrode of QCM was developed to monitor the presence of iodine in solution.     

Electrical strength of thin polyaniline films

The electrical strength of in-situ polymerized polyaniline films converted to non-conducting polyaniline base has been compared with the strength of solution-cast polystyrene and poly(methyl methacrylate) films of sub-micrometre thickness. The electrical lifetime of polyaniline film exponentially decreases with the growing electric-field strength. The electric-field strength at breakdown increases with increasing rate of electric field build-up. The breakdown areas in polyaniline films have been characterized by Raman spectroscopy. The possible physical mechanism of the breakdown in thin polymer films is discussed. The proposed concept is based on the steep increase of current density during the transition from the quadratic law at space-limited charge to the regime of complete saturation of traps. As a result, the Joule heat causes the degradation of polyaniline followed by the evaporation of chain fragments in the breakdown area.     

The carbonization of thin polyaniline films

Polyaniline films on silicon and ceramic supports were prepared in situ during the oxidative polymerization of aniline. The films were heated up to 500 °C in an inert nitrogen atmosphere. The changes in molecular structure during the carbonization have been studied by infrared spectroscopy and Raman scattering using 514, 633 and 785 nm laser excitation lines. The transformation from polyaniline salt to the base form has been detected above 100 °C. The conversion to nitrogen-containing carbon-like material followed above 200 °C. The molecular structure of the films produced during heating to 500 °C contains crosslinked phenazine-like and oxidized quinonoid units. The aniline oligomers deposited on the support in the early stages of aniline oxidation are stable during heating as it has been observed by resonance Raman scattering using 785 nm laser excitation line. The water contact angles changed after carbonization, and the films became more hydrophilic as carbonization progressed.     

Thin polyaniline and polyaniline/carbon nanocomposite films for gas sensing

We have studied the gas sensing properties of five polyaniline-based materials—thick and thin PANI films, nanocomposite PANI/MWNT and PANI/SWNT films, and PANI nanogranules embedded in a polyvinylpyrrolidone matrix. The films (except for the latter) were deposited within the induction period of the polymerization process on gold interdigitated micro electrodes. Their sensitivity to NH₃, H₂, ethanol, methanol, and acetone was measured. The thin PANI film (~ 100 nm thick) prepared by a lift-off process had the sensitivity to ammonia below 0.5 ppm, which was higher than that of nanocomposite films. Two materials—thick PANI film and nanocomposite PANI/MWNT film—exhibited a shallow minimum in the temperature dependence of resistance (at 313 K and 319 K), which is a feature exploitable in practical applications, since the gas sensors should be insensitive to small temperature fluctuations at these temperatures.     

Preparation and characterization of doped polyaniline films

Stable monolayer of the polyaniline doped with camphor sulfonic acid at the air-water interface has been obtained, of which multilayers have been successfully deposited by Langmuir–Blodgett technique onto CaF₂ substrate. The limiting mean molecular area and collapse pressure are found to be 0.294 nm² and 41 mN/m, respectively. The multilayers were characterized by IR and UV-Vis-NIR spectroscopies. X-ray small-angle diffraction data show that the multilayer was periodic layer structure with the layer spacing of 1.60 nm. The comparisons are also made with characterization of the casting film.     

Fabrication of self-assembled polyaniline films by doping-induced deposition

The ultrathin films of polyaniline (PAni)/poly (styrenesulfonic acid)(PSSA) were fabricated via a novel self-assembling process by alternately immersing the substrates into dilute PAni solution in N-methylpyrrolidinone (NMP) and the aqueous solution of PSSA. The process was characterized by UV–Vis absorption spectroscopy. It was found that the oxidation state of polyaniline in single monolayers was dependent on the thickness of the film. The self-assembling mechanism was based on the acid-base reaction between PAni and PSSA. The thickness of the films can be easily manipulated at nanometer scale by controlling the solution chemistry and recycling times. The resulting films are uniform and adhere strongly to the substrates.     

Layer-by-layer nanostructured hybrid films of polyaniline and vanadium oxide

Supramolecular structures of polyaniline (PANI) and vanadium oxide (V2O5) have been assembled via the electrostatic layer-by-layer (ELBL) technique. Strong ionic interactions and H-bonding impart unique features to the ELBL films, which are distinct from cast films obtained with the same materials. The interactions were manifested in UV-vis and Fourier transform infrared spectroscopy data. They are enhanced by the intimate contact between the components, as the films are molecularly thin, with 25 A per PANI/V2O5 bilayer.     

Flexible, all-organic ammonia sensor based on dodecylbenzene sulfonic acid-doped polyaniline films

A stable chlorobenzene dispersion of conducting polyaniline (PANI) has been obtained by doping emeraldine base with dodecylbenzene sulfonic acid (DBSA) and studied by spectrophotometric measurements in the UV-vis-IR range. The electrical properties of PANI: DBSA films obtained from the above dispersion have been investigated under different temperature and relative humidity conditions. All-organic chemoresistive devices have been developed by spin-coating the PANI: DBSA dispersion on flexible substrates, and then by depositing electrodes on the top, from a carbon nanotube conducting ink. Sensing tests performed under exposition to calibrated amounts of ammonia reveal that these simple and inexpensive sensors are able to detect ammonia at room temperature in a reliable way, with a sensitivity linearly related to concentration in the range between 5 ppm and 70 ppm.     

Conductive composite films composed of polyaniline thin layers on microporous polyacrylonitrile surfaces

A facile approach for preparing flexible and conductive composite films by chemical polymerization of aniline monomers on the microporous polyacrylonitrile (PAN) surfaces was reported. A good adherence between polyaniline thin layer and PAN substrate was ascribed to the formation of a continuous conductive network in the film thickness along the capillary channel within PAN matrix. The electronic properties of the resulting composite films were tuned easily with the mass fraction of aniline monomer in the PAN solution or through chemical process. It is also found that the thermal stabilities of the composite films were significantly enhanced, while good mechanical properties were maintained.     

Langmuir-Blodgett films of polyaniline for low density lipoprotein detection

Langmuir-Blodgett (LB) films of polyaniline (PANI) were utilized for the fabrication of impedimetric immunosensor for detection of human plasma low density lipoprotein (LDL) by immobilizing anti-apolipoprotein B (AAB) via EDC-NHS coupling. The modified electrodes were characterized by electrochemical impedance spectroscopy (EIS) and scanning electron microscopy. AAB/PANI-SA LB immunoelectrodes studied by EIS spectroscopy revealed detection of LDL in the wide range of 0.018 μM (6 mg/dl) to 0.39 μM (130 mg/dl), covering the physiological range in blood, with a sensitivity of 11.25 kΩ μM^− 1.     

Scanning probe microscopy studies of isocyanide functionalized polyaniline thin films

The technique of scanning probe microscopy was used to study the nanometer-scale morphological changes in isocyanide functionalized polyaniline films due to protonation in aqueous HCl, as well as exposure to Ir⁺ cations in CH₂Cl₂ solution. Electropolymerized isocyanide functionalized aniline films exhibited a highly oriented fibrous structure, with individual strands averaging 25 Å in diameter. Upon protonation, the fibrous structure was lost, with the material reorganizing into oriented, elongated bundles of average diameter 200 Å. Ir⁺ exposed unprotonated films exhibited an oriented, interlocking bundle structure, resulting from Ir⁺ incorporation into the film matrix. The diameter of these bundles averaged 400 Å.     

Photo-assisted electrochromic behavior of polyaniline and polypyrrole films coated on platinized n-type silicon

Photo-assisted electrochromic behavior of the coated polymer films is primarily controlled by intrinsic electrochromic behavior of the polymers, and for this reason polyaniline is superior to polypyrrole on the point of photo-assisted electrochromic response. The presence of a thin Pt layer between the semiconductor substrate and the coated polymer film was found to be effective in improving the durability of photo-assisted electrochromic cycles of the coated polymer film.     

聚苯胺/聚合物透明导电复合膜研究进展

论述了聚苯胺/聚合物透明导电复合膜的制备及性能.原位聚合法、掺杂聚苯胺旋转涂膜法和机械共混浇铸法均可制备透明导电复合膜.所得复合膜具有良好的透明性、导电性、环境稳定性及耐疲劳性能.     

Immobilization of antibodies on polyaniline films and its application in a piezoelectric immunosensor

Conducting polymers, especially polyaniline (PAni), have been extensively used in biosensor applications. A protocol for covalent immobilization of human IgG on polyaniline using glutaraldehyde as the cross-linker is described in this report and utilized in development of a piezoelectric immunosensor. Here, PAni was used as the substrate for immobilization. The electropolymerization parameters were optimized to get suitable thickness and surface morphology of the PAni for obtaining high density and uniformity of immobilized antibodies on the surface of our films. Possible reaction between PAni thin films and glutaraldehyde was explored using FT-IR characterization in grazing angle mode and XPS. The protocol has been characterized with the help of quartz crystal microbalance analysis. An antibody surface density of 4.86 ng/mm2 was obtained. A piezoelectric biosensor developed for detection of IgG with the proposed protocol was capable of differentiating the target analyte concentrations between 500 ng/mL and 25 microg/mL with nonspecific binding of approximately 10%.     

In situ X-ray photoelectron spectroscopy studies of interactions of evaporated metals with electroactive polyaniline films

Transparent conductive aluminum-doped zinc oxide (AZO) films were prepared by an ultrasonic spray pyrolysis method. A vertical type hot wall furnace was used as a reactor in the deposition system Zinc acetate dissolved in methanol was selected as a precursor. The substrate temperature was varied from 180 °C to 240 °C. Aluminum (Al) was doped into ZnO films by incorporating anhydrous aluminum chloride AlCl₃ in the zinc acetate CH₃CO₂)₂Zn solution. The proportion of the Al in the starting solution was varied from 0 wt % to 3.0 wt %. The crystallographic properties and surface morphologies of the films were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The resistivity of the films was measured by the Van der Pauw method, and the mobility and carrier concentration were obtained through Hall effect measurements. Transmittance was measured in the visible region. The effects of substrate temperature and aluminum content in the starting solution on the structural and electrical properties of the AZO films are discussed.     

反应温度对聚苯胺薄膜生长的影响

在不同反应温度条件下采用原位聚合法在石英基片上制备了聚苯胺薄膜．对薄膜样品进行了紫外光谱、SEM、电性能表征。实验结果表明，过高的合成温度会加速聚合反应过程，抑制膜厚的增长，引起薄膜的热降解，进而对样品的导电性产生不良影响。根据生长速率与合成温度的依赖关系，估算了聚合反应的活化能Ea=34.4kJ/mol。