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The redox transformations in a conducting polymer film on a platinum electrode were studied by Raman spectroelectrochemistry at fixed potentials depending on the incidence angle of the laser beam. Raman scattering was excited with a laser at a wavelength of 532 nm. Polyaniline (PANI) and its complex with poly-2-acrylamido-2-methyl-1-propanesulfonic acid (PAMPSA) were used as a conducting polymer. The polymer films were deposited by potentiostatic electropolymerization. By varying the incidence angle of the beam it is possible to obtain a Raman spectrum without the bands of the substrate overlapping with the characteristic bands of the polymer to minimize the substrate effect on the interpretation of the results. A comparative study of the electrochemical oxidation/reduction of the PANI films taking into account the detected angular dependence showed that, unlike the PANI films obtained in the presence of hydrochloric acid, the films of the PANI-PAMPSA complex retained the radical cation state of PANI in the range of the cathodic potentials. The reason for this is the presence of a nonconductive polymer acid phase in the PANI-PAMPSA film, as a result of which the percolation threshold of the conducting domains of PANI appears at less cathodic potentials, hindering further extraction of the positive charge during the film reduction. In addition, the use of this approach can significantly improve the accuracy of determination of the threshold potential of the leucoemeraldine-emeraldine transition.

Electrodeposition of polyaniline (PANI) complexes with a polymeric sulfonic acid of variable molecular weight has been studied with the purpose to explain specific features of aniline electropolymerization in the presence of polyelectrolytes. Poly-(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA) was taken as a model polyelectrolyte due to the ease of varying its molecular weight during polymerization of the monomer. Depending on the polyacid molecular weight, crucial changes in the shape of charge– and potential–time dependences and cyclic voltammograms have been observed during potentiostatic, galvanostatic, and cyclic voltammetry syntheses of PANI, respectively. The results are considered in terms of the influence of molecular weight on proton condensation ability of the polyacid and, therefore, on the degree of aniline protonation and its local concentration in the vicinity of polyacid macromolecule. The PANI films obtained are characterized by cyclic voltammetry and UV–vis and Raman spectroelectrochemistry, and the influence of the polyacid molecular weight on these properties is discussed.

The nucleation of the solid phase of interpolymer complexes of polyaniline (PAn) during electropolymerization of aniline on highly orientated pyrolytic graphite in aqueous solutions of hydrochloric acid and polymer sulfoacids, which differ in the rigidity of the polymer framework, was studied in situ by atomic force microscopy. The rigidity of the polyacid chain, which determines possible changes in its conformation in solution and its ability to adapt its conformation to that of the rigid conjugated PAn macromolecule, directly affects the shape and growth rate of the nuclei of solid phase of PAn and the film morphology at the early stages of electropolymerization. The rigid-chain and semirigid-chain polymer acids, which have the conformation of an elongated or slightly bent rod in solution, determine the conformation of the interpolymer complex nuclei. In contrast, in the presence of flexible-chain polyacids, the process is mainly controlled by the conformation of PAn macromolecules.

The electrodeposition of polyaniline (PANI) was carried out in potentiostatic, galvanostatic and potential sweep regimes in the presence of water-soluble polymeric sulfonic acids with different structure. The course of polymerization was traced by chronoamperometry, chronopotentiometry, cyclic voltammetry and in situ AFM measurements. The rigidity of the polyacid backbone, the distance between sulfonic groups on the backbone, the length and rigidity of the side chains containing sulfonic groups were shown to affect the onset potential of aniline oxidation, the character and the rate of the initial stages of PANI/polyacid film growth. AFM data indicated that the structure of the polyacids has a direct influence on the shape of PANI “nuclei” and the morphology of the film in the early stages of the electropolymerization. The obtained films were characterized by UV-Vis-NIR spectroscopy and cyclic voltammetry.

We demonstrate that the solvent-free mechanochemical method, previously used for the synthesis of polyaniline (PANI) protonated with low molecular weight inorganic acids, can be extended to the preparation of conductive, all-polymeric PANI/polyacid molecular composites. Two polymeric sulfonic acids differing in their chain rigidity were selected as PANI protonating agents, namely: poly-(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA, flexible backbone polyacid) and poly(p,p′-(2,2′-disulfonic acid)-diphenylene- tere -phthalamide) ( t -PASA, rigid backbone polyacid). Spectroscopic (UV–vis–NIR, FTIR, EPR), morphological, structural (TEM), electrochemical and spectroelectrochemical properties of the mechanochemically prepared molecular composites were compared with those determined for their analogs synthesized by oxidative polymerization in aqueous solution. The mechanochemically synthesized molecular composites show a characteristic layer-type morphology, distinctly different from that observed for the composites prepared chemically in aqueous solutions. UV–vis–NIR and FTIR spectroscopy clearly indicate better polaron delocalization in the mechanochemically prepared samples. These results are in line with those obtained in ESR, electrochemical and spectroelectrochemical investigations unequivocally showing better charge carrier delocalization in the mechanochemically prepared composites. The measured dc-conductivity of the mechanochemically prepared samples is 24 mS/cm and 31 mS/cm for PANI/PAMPSA and PANI/ t -PASA, respectively.

In this work, we carry out spectroelectrochemical studies of films of interpolymer complexes of polyaniline (PANI) prepared via the chemical and electrochemical template polymerization of aniline in the presence of polyamide sulfonic acids with different structures. It is shown that their spectroelectrochemical behavior in the near infrared region depends on the rigidity of the chain of the polymer sulfonic acid matrix. Electrodeposited films of PANI complexes with a rigid-chain polyacid exhibit a more intense absorption in the near infrared region (1000–2200 nm) and a less intense absorption in the absorption region of localized polarons (around 750 nm) in comparison with complexes with a flexible-chain polyacid. The comparison of the dependence of absorption in the near infrared region on potential with the cyclic voltammetry curves suggests that the chromophores responsible for this absorption are radical cations in nature. In the spectra of the films of chemically synthesized PANI complexes with a flexible-chain polyacid, during a long-term cycling in the region of potentials of the first redox stage of PANI, the absorption in the near infrared region which corresponds to delocalized polarons is also formed. This is apparently attributed to the intensification of the intermolecular interactions under the conformational fluctuations that accompany the change in the degree of oxidation of the film during cyclic voltammetry.

Films of polyaniline (PANI) interpolymer complexes were electrodeposited from aqueous solutions of aniline containing: (1) poly-(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA, flexible-backbone), (2) poly-(p,p′-(2,2′-disulfoacid)-diphenylen-tere-phthalamid) (t-PASA, rigid-backbone), (3) mixtures of the former two polyacids in different ratios (6:1, 3:1, 1:1, 1:3, 1:6). The obtained polymer films were characterized by UV–vis–NIR spectroscopy, CV, spectroelectrochemical and AFM measurements. An abnormally intensive influence of the rigid-chain polyacid on the process of matrix electropolymerization of aniline in the presence of the polyacid mixtures was at first demonstrated. Spectroelectrochemical properties of the obtained PANI complexes with the mixtures of flexible-backbone and rigid-backbone polyacids in different ratios (up to 6:1) are very similar to those ones for the complex with rigid-backbone t-PASA. The films prepared in the presence of polyacid mixtures (up to 6:1) have high absorbance in the NIR region similarly to the complexes with rigid-backbone t-PASA.

With the purpose of determining prospects of possible applications of interpolymer complexes of polyaniline (PANI) with poly(amidosulfonic acid)s, we have performed a comparative study of polyaniline films prepared by electrochemical polymerization of aniline in the presence of the polyacids distinguished by different rigidities of the polymer backbone: (1) poly(2-acrylamido-2-methyl-1-propanosulfonic acid) (flexible backbone); (2) poly-p,p′-(2,2′-disulfoacid)-diphenylen-iso-phthalamid (semi-rigid backbone); (3) poly-p,p′-(2,2′-disulfoacid)-diphelylen-tere-phthalamid (rigid backbone); and (4) a copolymer of the latter two acids with monomer feed ratio 1:1 (co-PASA). Spectroelectrochemical studies in the UV–vis–NIR range showed that PANI complexes with rigid-chain polyacids far more effectively modulate absorbance in the Vis–NIR range and can be considered as promising candidates for “smart windows” development. Due to the presence of bulky unmovable polyacid anion, PANI interpolymer complexes (particularly those with the semi-rigid-chain polyacids) possess much wider pH range of electroactivity than common PANI, which is of great importance for biosensor applications. The interpolymer complexes with flexible-chain and semi-rigid-chain polyacids exhibit good optical response to ammonia vapors at conditions of high humidity, which make them promising materials for the development of ammonia optical sensors.

Electrochemical matrix polymerization of nanostructured polyaniline layers in the presence of polyamidosulfonic acids differing in the rigidity of the polymer framework was studied in a wide concentration range. The spectroscopic, electrochemical, and morphological properties of the resulting layers were examined. It was found that the accelerated electropolymerization is due to (1) preliminary association of aniline with the sulfo groups of the polyacids and (2) a high local concentration of the protons near its macromolecule. The use of a polyacid with a rigid polymer framework afforded an interpolymer complex with polyaniline in side chains. With a semirigid matrix, both a two-strand complex (characteristic of an acid matrix with a flexible chain) and a branched complex were obtained.

We have studied electrochemical matrix polymerization of aniline in the presence of poly(amidosulfonic acid)s of different nature: poly(2-acrylamido-2-methyl-1-propanosulfonic acid) (PAMPSA, flexible backbone); poly(p,p′-(2,2′-disulfoacid)-diphenylene-iso-phthalamid) (i-PASA, semi-rigid backbone); poly(p,p′-(2,2′-disulfoacid)-diphelylene-tere-phthalamid) (t-PASA, rigid backbone). Also, we have investigated spectral and electrochemical properties of the films obtained, as well as their surface morphology. The matrix polymerization results in the formation of interpolymer complexes of polyaniline (PANI) and the above-cited polyacids. The acceleration of aniline electropolymerization in the presence of poly(amidosulfonic acid)s was observed due to association of aniline molecules to sulfonic groups of the polyacid and higher local concentration of protons near the polyacid backbone. The rigid-chain polyacids interfere with the normal course of the electropolymerization, which manifests itself in the changes of the shape of time dependences of absorbance and charge. Cyclic voltammetry and spectroelectrochemical experiments showed that the formation of interpolymer complex with rigid-chain polyacids distorts spectroelectrochemical characteristics of PANI. This evidently results from steric hindrances in the formation of quinoid units.

The electrochemical matrix polymerization of aniline in the presence of poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA) is performed in conditions that lead to the formation of an interpolymer complex comprising polyaniline and PAMPSA of the 1: 2 composition. The acceleration of the process of polymerization of aniline in the presence of PAMPSA as compared with traditional electropolymerization of aniline in hydrochloric acid is caused by the association of aniline molecules with the sulfo groups of PAMPSA and by a high concentration of hydrogen ions in the vicinity of a molecule of PAMPSA. It is established for the first time ever that, in the initial stages of synthesis for both polymeric and low-molecular-weight acids, the rate of polymerization is substantially greater at a smaller concentration of the acid. The distinguishing feature of the initial stage of electropolymerization of aniline at a low acidity of the environment is a non-autocatalytic character of the process, which may exert a discernible influence on a complex of physicochemical properties of polyaniline, including electric conduction. Studying spectroelectrochemical properties of the obtained films shows practical identity of their spectra with the spectra of standard polyaniline.

The not-sufficient-enough conductance of semioxidized protonated polyaniline (PANI) is usually attributed to the presence of ordered quasi-metallic domains surrounded by a poorly conducting amorphous phase. The paper presents experimental results testifying to the existence, in semioxidized PANI, of multilevel redox heterogeneity that crucially effects the conductance magnitude in view of specific topology at which higher-oxidized (conducting) domains are surrounded by less oxidized (poorly conducting) domains and because the PANI conduction is extremely sensitive to the oxidation degree. It is shown experimentally that the interphase doping with metals and degenerate semiconductors of a semioxidized salt of PANI and poly(2-acrylamide-2-methyl-1-propanesulfonic acid) (PAMPSA) with a 1: 2 ratio between PANI and PAMPSA raises the PANI-PAMPSA conductivity by 3–8 orders of magnitude due to the formation near the interface of thin layers whose conductance depends on the work function of the material in contact with PANI-PAMPSA and in extreme cases substantially exceeds the conductance of gold and copper at room temperature.

Heterogeneity relates to the principal features of polyaniline (PAn). For the most part the heterogeneity in PAn belongs to redox type. Our detailed investigation of the vacuum deposited PAn and the study of the luminescence of PAn base (by Shimano and MacDiarmid) reveal the existence of a block structure of PAn molecules formed of quinoid and amine units. There are also direct evidences of existence of the redox heterogeneity in PAn in nano scale (Kelvin scanning microscopy). We have observed by optical and Kelvin the microscopy the formation of various types of the redox heterogeneous structures in microscopic scale in the course of the chemical or electrochemical treatment of the vacuum thermally deposited or electrochemically produced PAn films. Macroscopic scale redox heterogeneity was observed also under chemical oxidation of the vacuum deposited PAn and in the course of PAn matrix synthesis. Hence, multilevel redox heterogeneity from molecular to macroscopic scale takes place in PAn. The fundamental reason for the redox heterogeneity formation is the autocatalytic, non-equilibrium character of the oxidation processes in PAn coupled with non-linear mass transfer processes. Evidently this type of heterogeneity influences markedly the whole range of PAn properties including conductivity.

This study is aimed at clarifying the role of the counter anions used in the electrochemical synthesis of polyaniline (PAn) on the spectroelectrochemical properties of the resulting film (so-called “structural memory” effect). Polyaniline films were synthesized in aqueous solutions of different acids: HCl, HClO 4 and H 2 SO 4 (‘parent’ acids). Further spectroelectrochemical studies were performed in aqueous solutions of the above-mentioned acids for each of the films synthesized in the above ‘parent’ acids. Differential voltabsorptometric curves (d A /d t versus potential (DCVA)) were measured at certain characteristic wavelengths corresponding to the individual absorption bands separated from the spectra using Alentsev–Fock method. These are the bands of the radical cations (435 nm), quinoid fragments (570 nm), dimers of radical cations (presumably 665 nm) and ‘localized polarons’ (755 nm). Particular attention has been paid to the formation of the dimers of radical cations and their role in the redox transitions in the film. Comparing our results with the literature data, we suppose that such dimers may facilitate electron exchange between adjacent polymer chains contributing to the conductivity increase. Complex nature of the first voltammetric peak was discovered, which is probably due to the heterogeneous structure of PAn. Results of molecular modeling of the interchain dimers of the radical cations using semi-empirical PM3 calculations are reported and their electronic spectrum was simulated.

The electrochemical oxidation–reduction of films of polyaniline is studied in the presence of various counteranions. The differential cyclic voltabsorptometric (DCVA) curves (dA/dt relative to potential, where A is the optical absorption) are recorded at characteristic wavelengths corresponding to individual spectrum components previously isolated with the Alentsev–Fok method. The DCVA curves for aqueous solutions of HCl, HClO4, and H2SO4 at different potential scan rates are compared to traditional cyclic voltammograms. For the DCVA curves obtained at 665 nm discovered is one broad peak of dA/dt in the region of potentials between the first and second stages of polyaniline oxidation ( 0.6 V vs. Ag/AgCl). An assumption is made about a chemical nature of the process of generation of absorption in this spectral region, which, more likely than not, is connected with the emergence of dimers of radical cations of polyaniline. It is discovered that the electrochemical processes in the region of potentials that correspond to the first stage of oxidation give rise to variations in the absorption inside several regions of spectrum: 435 nm (radical cations) and 755 nm (localized polarons). An assumption is made that the first peak of the current corresponds to several successive processes that occur in a polyaniline molecule in the course of oxidation as well as to the existence of heterogeneous regions where the generation of localized polarons proceeds at different rates.

This paper presents the results of the investigation of the effect of pH of highly acidic medium (pH 0 and 1) on the structure of the electronic spectra of polyaniline films in the spectral range 300–900 nm. The analysis was carried out using the Alentsev–Fock method, which requires no preliminarily notion about the possible shape and/or number of the individual absorption bands and extensive statistical calculations. Along with the six absorption maximums described earlier by other authors three new individual bands were separated. On the basis of the comparison of our results with the literature data, we are inclined to assign the new band near 530–570 nm (depending on the pH) to the donor–acceptor interaction between the quinoid fragments and the counter anions and the new band at λmax>900 nm to the ‘free carriers’ absorption. We also suppose that the new band near 810–830 nm may be associated with the second absorption band of the cation-radical dimers. The effect of an increase in pH on the structure of polyaniline absorption spectra manifests itself in the increase of the portions of the bands corresponding to different electron transitions in the quinoid fragments, as well as in the decrease of the portions of the bands related to the conductivity of the film (i.e. the bands of the cation-radical dimers (or polarons) and free charge carriers).

A comparative cyclic voltabsorptometric study was carried out for polyaniline (PAn) films prepared by electrochemical polymerization and vacuum thermal evaporation. The absorption values were measured at different characteristic wavelengths (895, 755, 665, 435, and 325 nm) corresponding to the individual absorption bands separated by us earlier from the spectra using the Alentsev–Fock method. Differential voltabsorptometric curves (dA/dt vs. potential (DCVA)) measured in aqueous HCl were compared with ordinary cyclic voltammetry (CVA). The experiments for different sweep rates were also compared. It was found that the DCVA peak at 895 nm corresponds perfectly to the CVA peak both in the electrosynthesized and the vacuum deposited PAn. The DCVA peak at 435 nm (cation-radicals) precedes the CVA peak (similar to the maximum of the EPR signal), while that at 755 nm (polarons or cation-radical dimers) lags behind the CVA peak. For the vacuum deposited films an intense intermediate DCVA and current peaks (at about 0.6 V vs. Ag/AgCl) are observed. The results are discussed in terms of the heterogeneous structure of PAn; particularly, its specific features in the films prepared using different methods.

The absorption spectra of polyaniline (PAN) films obtained by electrochemical polymerization on transparent SnO2-glass electrodes are analyzed. The spectra are recorded at steady-state potentials of 0.0 to 0.8 V (Ag/AgCl) in an aqueous HC1 solution. Individual absorption bands, isolated by the Alentsev-Fok method, include both earlier known bands and some new absorption bands. The former correspond to π-π* transitions in the benzenoid rings (300-320 nm), radical cations (∼435 nm), localized polarons (∼755 nm), and quinoid structures (∼655 nm). By comparing these results with the spectroelectrochemical data obtained earlier for electrochemically synthesized PAN in solutions of various acids and for vacuum-deposited PAN, the newly found bands are assigned to different intermolecular interactions, specifically, a donor-acceptor coupling of the quinoid moieties with counter anions (at 570 nm) and an electron exchange between highly conducting domains of the film (∼900 nm)

Using the results of spectroelectrochemical experiments (absorption spectra measured at different stationary potentials from 0.0 to 0.8 V versus Ag | AgCl) performed in aqueous acidic medium for polyaniline (PAN) films electrochemically deposited onto SnO2-glass substrates, individual absorption bands composing the spectra were analyzed. The key point of the method used for separation of the individual bands (Alentsev–Fock method) is that one need not have a preliminary notion about real shape, number and positions of individual components of the spectrum. The necessary conditions are the following: (1) in the most common case, the number of spectra used for separation should be equal to or exceed the number of possible components; (2) the spectra should contain different proportions of the individual bands. Both well-known (cation-radicals (near 435 nm), localized polarons (near 755 nm), quinoid structures (near 665 nm)) and some new absorption bands were found. Comparing these results with our earlier data for electrochemically deposited and vacuum evaporated PAN films in different acidic media, the newly revealed band near 570 nm may be attributed to donor–acceptor interaction of quinoid fragments of the polymer chain with counter anions. The band in the NIR region (>900 nm), which is often referred to as that of ‘free carriers’, apparently characterizes electron exchange between highly conductive areas of the film.

Thin polyaniline (PAN) films were prepared by evaporation of emeraldine base in vacuum at 275–325°C, followed by deposition of the vapors onto SnO 2 –glass transparent electrodes. With the purpose to restore the original structure of the polymer, the films were subjected to a postdeposition oxidative treatment in HNO 3 according to the following three different procedures: (1) treatment in vapors of 10 M acid, (2) treatment in 2 M HNO 3 aqueous solution, (3) cyclic treatment: in 2 M aqueous HNO 3 , then in 2 M aqueous NH 3 and so on. Electrochemical and spectroelectrochemical characteristics, namely cyclic voltammetry curves at different sweep rates and optical spectra at stationary potentials, were investigated for these films. It was found that the above characteristics of the films oxidized according to the cyclic procedure are most close to those of conventional PAN. However, in the optical spectra recorded at 0.0 V (vs. Ag/AgCl) for all the vacuum deposited films no absorption band in the area longer than 800 nm was observed. The results are discussed in terms of correlation of changes in the spectroelectrochemical characteristics with formation of heterogeneous structure of PAN by means of arising of intermolecular interactions, as well as, with specific features of vacuum the deposited PAN films.

Electrochemical and chemical synthesis of polyaniline (PAN) was performed in an aqueous acidic solution of aniline on the surface of vacuum deposited thin polyaniline films applied on an SnO2 glass electrode. The composite films obtained have a high homogeneity and uniform thickness, essential for vacuum deposited layers. Spectroelectrochemical characteristics of the composite layers prepared by electrochemical synthesis are similar to those of electrodeposited PAN. Composite layers prepared by chemical synthesis have different Spectroelectrochemical characteristics, probably due to the presence of by-products of chemical synthesis. High selectivity of the synthesis was observed on the covered areas of partly sputtered substrates, evidently due to the autocatalytic character of PAN synthesis.

The fractionating vacuum thermal deposition of emeraldine base produces the oligomers of polyaniline dispersed in the polymer organic matrix. The cyclic acid-base treatment of the low temperature fractions results in restoration of their polyaniline-like spectral, electrochemical, electric and paramagnetic properties. This is not the case for the high temperature fractions possibly as a consequence of their more defective structure and higher content of the thermal destruction products.

A spectroelectrochemical study of thin electrochromic polyaniline (PAN) films deposited on SnO 2 glass substrates by a vacuum thermal evaporation method has been carried out. The films obtained were studied by means of spectral, spectroelectrochemical and electrochemical methods, and the results were compared with those obtained for PAN films prepared by electrochemical polymerization. Spectroelectrochemical data (obtained under a potential step) and cyclic voltammetry data showed that the evaporated PAN films did not undergo a second oxidation stage resulting in formation of a quinoid structure. Current vs. time dependences processed according to the Cottrell equation showed that the diffusion coefficient for the evaporated PAN layers was almost a factor of 3 lower than that for the electrochemically deposited films. During cyclic tests in a real electrochromic optical filter the evaporated PAN layers exhibited a stability more than 2.5 times higher than that of the electrochemically deposited films.

A template oxidative polymerization of aniline in aqueous solutions containing poly-(2-acrylamido-2-methyl-1-propanesulfonic acid) and ammonium persulfate yields a polyaniline complex with the polyacid soluble in water. According to the data of spectral measurements, the process of polymerization is of a pronounced autocatalytic nature. The consequences of this are both the formation of a nonuniform distribution of oxidized and nonoxidized fragments of the polymer chain and the formation of a macroscopic scale of redox nonuniformities in the reaction volume during the process of polymerization. The spectra of absorption of the polyaniline/polyacid films on transparent glass electrodes with a conductive layer of SnO2 and the data of potentiodynamic measurements in the potential region 0–1.0 V (Ag/AgCl) are typical for polyaniline with moderate electroconduction.

By using formal estimation methods, it is shown that heterogeneous redox structures, which are formed in the course of oxidation of vacuum evaporated thin polyaniline layers in the temperature range of 0–30°C, become more ordered with the increase in the oxidation temperature.