Polyanilines electrochemically prepared films

Switching properties Chemical properties Mechanical properties of polyaniline Electrochemically Prepared Films Solution Cast Films and Fibers Optical properties of polyanilines Circular dichroism spectra... 

As with polyanilines, polythiophenes can either be prepared directly by electropolymerization, or by casting from solutions (for alkyl-substituted thiophenes). Most interest has focused on the latter because of their improved mechanical properties compared with those of electrochemically prepared films. The factors influencing the mechanical properties of PTh s are reviewed in this section. 

Han et al. [64, 66] reported the synthesis of highly conductive and thermally stable self-doped mercaptopropanesulfonic-acid-substituted polyanilines by the concurrent reduction and substitution reaction between polyaniline and a nucleophile. These reactions were carried out on both electrochemically generated and free standing polyaniline films prepared from emeraldine base dissolved in N-methylpyrrolidinone. The electrochemically prepared films were dedoped with 5 % aqueous NaiCOs to convert them the into the emeraldine base form. The sulfonated polyaniline was prepared by reaction of a polyaniline emeraldine base film with 0.1 M 3-mercapto-l-propanesulfonic acid sodium salt in methanol under nitrogen at room temperature for approximately 14h [66]. A catalytic amount (0.01 M) of acetic acid was reported to accelerate the reaction. The resulting sulfonated polyaniline film was thoroughly rinsed with methanol, followed by 5 % aqueous NaiCOs to remove reactants. 

The polymerisation appears to involve a nucleation process similar to that of the deposition of metals [182], and electrochemically-prepared polyaniline will form dense, non-fibrillar thin films [165, 173], but thicker films ( > 150nm) become less densely packed and more fibrous [176, 182]. This may be due a change in the deposition mechanism when the film becomes sufficiently thick to inhibit direct access to the platinum by unreacted monomer [176],... 

Recent applications of SPM techniques have revealed new details of the electrical properties of conducting polymers. In one example, STM images were taken of the granular structure of electrochemically prepared polyaniline films. Simultane-... 

However, ultra-thin films of unsubstituted polyaniline deposited on ITO glass electrode produced by dip coating, spin coating and the LB technique showed the most informative voltammetric characteristics. The single-layer LB films of polymer showed much better and reversible electrochromic activity on repeated scanning within up to 0,9 V in 1,0 M HCl solution than in electrochemically prepared materials [287],... 

Apart from polyaniline, other condncting polymers that are being studied for electrolytic expansion include polypyrrole [11, 15-17], poly(alkylthiophene) [26] and carbon nanotubes [5]. For example, electrochemically prepared polypyrrole films were used to study the qualitative movement of electrolytic expansion by fabricating a bimorph actuator. The movement of bending and stretching of the actuator was demonstrated in electrolyte solution [15]. Actuators fabricated by electrodeposition on gold-coated polyethylene films were studied [11] for the evaluation of expansion ratio and response time. Also, a microactuator of several tens of microns made from two layers of gold and... 

Several recent reports describe using clay or other inorganic fillers to form CP composites. Polyani-line-polypyrrole composite coatings containing clay or yttria stabilized zirconia were electrodeposited onto AA 2024-T3 [158], with improved corrosion resistance of the substrate. Similarly, particulate-filled polyaniline and polypyrrole films on AA 2024-T3 were prepared electrochemically using a variety of fillers, including clay, carbon black, short carbon fiber, zirconia, and silica [159]. Again, enhanced corrosion performance for these composites was observed. 

Kitani et al. have prepared polyaniline composites using poly(aniline-2-sulfonic acid) [142] and poly(2,5-disulfonic acid) [143] instead of conventional electroinactive sulfonated polymers like polystyrene sulfonic acid. These composites were prepared by electrochemical dopant exchange. Electrochemically prepared polyaniline films were dedoped by treating 1M NaOH solution. Furthermore, these dedoped films were... 

The most important characteristic of monomer molecules for the formation of a conducting polymer is the requirement for the conversion of a closed-shell system to a corresponding cation or anion radical and the stability of the product to form during the process. Polyaniline is prepared by either chemical or electrochemical oxidation of aniline under acidic conditions. An aqueous medium is preferred. The synthesis of polymer by either chemical or electrochemical methods depends upon the intended application of the polymer. Whenever thin films and better-ordered polymers are required an electrochemical method is preferred. 

These metallic features have been reported in conducting versions of both polyaniline and polypyrrole. The ability to process PAN doped with camphorsulfonic acid (CSA) from solution [18,54] has resulted in freestanding films with high conductivity (cTdc 100-400 S/ cm) [39,55,56] that span the insulator-metal transition (IMT) even at low temperature [40,53]. Some samples of electrochemically prepared polypyrrole doped with hexafluorophosphate (Pp6) are metallic to low temperature [23,36,37], However, when PPy is synthesized using different dopants or at high temperatures, the materials are more disordered and show insulating behavior [23-25,57,58]. Similar results are reported in the literature for conducting polyacetylene [36,37]. 

Comparison of chemically and electrochemically prepared PAn films Until recently, it has been generally considered - that PAns prepared by the alternative chemical and electrochemical routes have similar chemical structures, although differences in morphology were noted and there was disagreement in the literature as to which route produces material of the higher molecular weight. From a comparison of the circular dichroism spectra of chemically and electrochemically prepared PAn.(+)-HCSA films (see Chapter 5), we have recently found the first unequivocal evidence that these polyanilines possess different structures/conformations for their polyaniline chains. ... 

The film morphology of electrochemically prepared polyaniline has been shown by many workers to be fibrillar in nature and often quite porous. In... 

Polyaniline (PANI) can be formed by electrochemical oxidation of aniline in aqueous acid, or by polymerization of aniline using an aqueous solution of ammonium thiosulfate and hydrochloric acid. This polymer is finding increasing use as a "transparent electrode" in semiconducting devices. To improve processibiHty, a large number of substituted polyanilines have been prepared. The sulfonated form of PANI is water soluble, and can be prepared by treatment of PANI with fuming sulfuric acid (31). A variety of other soluble substituted AJ-alkylsulfonic acid self-doped derivatives have been synthesized that possess moderate conductivity and allow facile preparation of spincoated thin films (32). 

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