O. L. Gribkova

Spectroelectrochemical, EPR and conductivity investigations of thin films of vacuum deposited polyaniline

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.

Electrochromic properties of vacuum-evaporated polyaniline films

Abstract The emeraldine base was deposited on SnO2 glass substrates in vacuum by thermal evaporation in the temperature range 275–325 °C. The as-deposited films differ dramatically from the native polyaniline and are formed by the reduction of oligoanilines with molecular weight about 1500. The cycling acid-base treatment of vacuum thermally deposited films gives rise to formation of polyaniline-like material. The property restoration of sublimed films is apparently determined by the restoration of 3D associates in the film body. Molecular structure defects in vacuum-deposited films are responsible for the lower rates of coloration/decoloration, the lower contribution to imine formation and irreversible injection of anodic charge under the first oxidation/reduction cycle. The lower imine concentration in sublimed polyaniline films results in more coloration/decoloration cycles.

Thin nanocomposite layers based on a complex of polyaniline and graphene

Two techniques of manufacturing a nanocomposite based on a complex of polyaniline with polymer acid and graphene are proposed. The electric conductivity of thin nanocomposite layers is higher than that of a polymer complex of polyaniline and strongly depends on the degree of oxidation of graphene. An explanation of the effect is suggested that takes into account electron interactions between the graphene planes and polyaniline backbone, as well as the possibility of formation of hydrogen bonds between functional groups of semioxidized graphene and polyacid. The results of surface topography analysis for thin layers of polyaniline and nanocomposite agree well with the regularities of the structure of each layer that are due to the above interactions between graphene and the polymer complex.

Fractionating vacuum thermal deposition of polyaniline films. Effect of post-deposition acid-base treatment

Abstract Vacuum thermal evaporation of a single portion of chemically synthesized polyaniline (PAN) base powder was performed step-by-step within four temperature intervals in the 240–450 °C range. The vapour was deposited on quartz and SnO2-glass substrates, each fraction being deposited on a separate substrate. The samples obtained were subjected to cyclic contrast acid-base treatment, and UV-Vis spectra of the fractions after each treatment cycle were registered. The spectra of the as-deposited fractions appear to have little in common with conventional PAN spectra. The appearance of absorption bands essential for conventional PAN spectra is found to occur for some of the fractions only after the above treatment. This is apparently due to recombination of PAN oligomer radical fragments, formed in the course of the evaporation, resulting in restoration of PAN macromolecule structure. The recombination may be intensified by conformational changes during the acid-base treatment. Cyclic voltammetry curves for the most PAN-like fractions resemble the ones for conventional PAN.

Comparative spectroelectrochemical investigation of vacuum evaporated and electrochemically synthesized electrochromic polyaniline films ag

Abstract 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.

The effect of the degree of graphene oxidation on the electric conductivity of nanocomposites based on a polyaniline complex

Experiments show that the electric conductivity of a polyaniline (PANI) complex with polyacid increases upon the introduction of graphene. It is found for the first time that this effect strongly depends on the degree of graphene oxidation: the presence of unoxidized and half-oxidized graphene increases the electric conductivity of the PANI complex by a factor of 3 and 20, respectively. An explanation of this phenomenon is proposed that takes into account the electron interactions between graphene planes and PANI backbone and the formation of hydrogen bonds between the functional groups of half-oxidized graphene and polyacid.

Electrochemical and chemical synthesis of polyaniline on the surface of vacuum deposited polyaniline 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 influence of polyacid nature on poly(3,4-ethylenedioxythiophene) electrosynthesis and its spectroelectrochemical properties

The present study is aimed to elucidate main structural features of polymeric sulfonic acids (the rigidity of main chain, the distance between sulfonic groups on the chain, the hydrophobicity of main chain or side fragments) on the course of 3,4-ethylenedioxythiophene (EDOT) electropolymerization and electronic and chemical structure of the poly(3,4-ethylenedioxythiophene) (PEDOT) films obtained. The films were prepared by electrochemical polymerization in cyclic voltammetry, potentiostatic, and galvanostatic regimes in aqueous solutions of different polyacids in the absence of supporting electrolyte. The effect of the chemical structure of polyacid on the course and rate of PEDOT synthesis was traced by electrochemical and in situ UV-Vis spectroscopic methods. It was shown that the highest rate of EDOT electropolymerization is achieved in the presence of flexible-chain polyacid having hydrophobic fragments (groups) in its structure, followed by hydrophobic rigid-chain polyacids. The lowest rate was observed in the presence of hydrophilic flexible-chain polyacid. The electronic and chemical structure of the PEDOT films obtained was studied by in situ UV-Vis-NIR and Raman spectroelectrochemistry. The films prepared in the presence of rigid-chain polyacids at high anodic potentials demonstrate decreased content of bipolaronic fragments in their structure, while PEDOT complexes with flexible-chain polyacids are very much like conventional polymer prepared in non-aqueous medium. The results are discussed in terms of conformational state (ability to form coils and thus concentrate the monomer) of different polyacids in aqueous solution and hydrophobic interactions between the polyacids and EDOT.

On the nature of influence of polyelectrolyte molecular weight on aniline electropolymerization

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.

PHYSICOCHEMICAL PROPERTIES OF CHEMICALLY AND MECHANOCHEMICALLY PREPARED INTERPOLYMER COMPLEXES OF POLY(3,4-ETHYLENEDIOXYTHIOPHENE) WITH POLYAMIDOSULFONATE DOPANTS

Interpolymer complexes of poly(3,4-ethylenedioxythiophene) (PEDOT) with a series of polyamidosulfonate dopants (PA) characterized by various degree of rigidity in the polymer chain were prepared by chemical and mechanochemical methods. It was shown that the morphology, conductivity, and spectral characteristics of the synthesized PEDOT/PA are determined by the method of preparation of the complexes and by the structure of the PA. It was established that the stability of aqueous dispersions of the interpolymer complexes PEDOT/PA is higher in the case of the chemical method of synthesis. At the same time the conductivity of the films is several orders of magnitude lower in comparison with the mechanochemically obtained analogs.