Irina Sapurina

In-situ polymerized polyaniline films

Abstract Polyaniline hydrochloride was prepared by the oxidation of aniline hydrochloride with ammonium peroxodisulfate in dilute hydrochloric acid. The polyaniline films were produced during the polymerization on the glass surfaces immersed in the reaction mixture. The surface composition of the film was characterized by X-ray photoelectron spectroscopy. The thickness of the films d f was determined by the optical interferometry and linked to their optical absorption at the wavelength 400 nm, A 400 =(5.4±0.2)×10 −3 d f (in nm). The effect of the polymerization temperature and concentration of the reactants on the thickness and electrical properties of polyaniline films are reported. The electrical conductivity of the films and of bulk polyaniline produced simultaneously is about the same. A relation between the thickness of the films and the molecular weight of the produced polyaniline was found.

Polyaniline: Thin films and colloidal dispersions (IUPAC Technical Report)

Several workers from various institutions in six countries have prepared thin films and colloidal polyaniline dispersions. The films were produced in situ on glass supports during the oxidation of anilinium chloride with ammonium peroxydisulfate in water. The average thickness of the films, assessed by optical absorption, was 125 ± 9 nm, and the conductivity of films was 2.6 ± 0.7 S cm–1. Films prepared in 1 mol l–1 HCl had a similar thickness, 109 ± 10 nm, but a higher conductivity, 18.8 ± 7.1 S cm–1. Colloidal polyaniline particles stabilized with a water-soluble polymer, poly(N-vinylpyrrolidone) [poly(1-vinylpyrrolidin-2-one)], have been prepared by dispersion polymerization. The average particle size, 241 ± 50 nm, and polydispersity, 0.26 ± 0.12, have been determined by dynamic light scattering. The preparation of these two supramolecular polyaniline forms was found to be well reproducible.

In-situ polymerized polyaniline films: 3. Film formation

Polyaniline films were produced on glass surface immersed in the reaction mixture during the oxidative polymerization of aniline. Glass supports placed in the reaction mixture at the start of the oxidation were gradually removed during the reaction. The thickness of polyaniline films produced on glass, assessed by optical absorption, was followed as a function of reaction time. The progress of polymerization was monitored by temperature changes. In another experiment, glass supports were successively inserted into the polymerization mixture. The formation of polyaniline films on glass, which had been already pre-coated with polyaniline, was also investigated. The proposed model of film formation is based on the concept of the primary and secondary nucleation. Oligoaniline cation radicals adsorbed on the glass surface nucleate the primary growth of polyaniline film, the secondary nucleation occurs on the produced polyaniline layer.

In-situ polymerized polyaniline films: 5. Brush-like chain ordering

The polymerization conditions for preparation of ordered in-situ polymerized polyaniline (PANI) films were established. The thickness of films deposited on glass can be controlled by the time spent in the reaction mixture and varied up to ca. 250 nm. The PANI chains initiated on the glass surface are expected to grow mostly perpendicularly to the support. The concept of brush-like ordering of PANI macromolecules in the films is discussed on the basis of optical anisotropy measurements. The observed linear relation between film thickness and molecular weight of PANI also supports the ordering hypothesis. The differences observed in absorption FTIR spectra of PANI films and powders are discussed.

Polypyrrole nanotubes: mechanism of formation

This article presents a contribution to better understanding of the processes which take place during the synthesis of polypyrrole nanotubes using a structure-guiding agent, methyl orange. Polypyrrole was prepared by oxidation of pyrrole monomer with iron(III) chloride. In the presence of methyl orange, the formation of nanotubes was observed instead of the globular morphology. Two reaction schemes with reversed additions of oxidant and monomer have been tested and they show remarkable influence on the produced morphology. Nanotubes with circular or rectangular profiles and diameters from tens to hundreds of nanometres have been obtained. FTIR and Raman spectra were used to assess the molecular structure of polypyrrole and detect residual methyl orange in the samples. The conductivity of nanotubes compressed into pellets was as high as 68 S cm−1. The mechanism of nanotubular formation starting at the nucleus produced with the participation of organic dye is proposed. The growth of a nanotube, however, proceeds in the absence of a template. An alternative mechanism for the formation of nanotubes, the coating of solid templates with a polypyrrole overlayer, is also discussed.

Polyaniline-coated silica gel

Abstract Silica gel microspheres 7 and 15 μm in diameter were coated with an overlayer of polyaniline camphorsulfonate or hydrochloride during the oxidative polymerization of aniline. Coated silica gel and polyaniline precipitate were separated using a difference in sedimentation rate. In an alternative approach, the microspheres were modified with polyaniline in the presence of 35 nm colloidal silica. This technique prevented the macroscopic precipitation of polyaniline. Coatings of neat, 3-aminopropyl- and octadecyl-modified silica gel with polyaniline hydrochloride were compared. The surface composition of coated microspheres was characterized by X-ray photoelectron spectroscopy. Potential applications of particles in electrorheology, organic catalysis, and in modeling of conductivity behavior in composites are demonstrated.

The role of acidity profile in the nanotubular growth of polyaniline

Conditions of polyaniline (PANI) nanotubes preparation were analyzed. Aniline was oxidized with ammonium peroxydisulfate in 0.4 M acetic acid. There are two subsequent oxidation steps and the products were collected after each of them. At pH > 3, neutral aniline molecules are oxidized to non-conducting aniline oligomers. These produce templates for the subsequent growth of PANI nanotubes, which takes place preferably at pH 2–3. At pH < 2, granular morphology of the conducting PANI is obtained. High final acidity of the medium should be avoided in the preparation of nanotubes, e.g., by reducing the amount of sulfuric acid which is a by-product. Reduction of the peroxydisulfate-to-aniline mole ratio was tested for this purpose in the present study. Lowering of the reaction temperature from 20°C to −4°C had a positive effect on the formation of nanotubes.

Ternary composites of multi-wall carbon nanotubes, polyaniline, and noble-metal nanoparticles for potential applications in electrocatalysis

Multi-wall carbon nanotubes were coated with a conducting polymer, polyaniline phosphotungstate. Such composite structures have mixed electronic and proton conductivity, high surface area and porosity. These materials were decorated with catalytically-active noble metals — Pt, Pd, and Rh. Metal nanoparticles were uniformly distributed in the polymer matrix. Such ternary composites can be considered as electrode materials in sensors, electrolysers, supercapacitors, and especially in low-temperature fuel cells with a proton-conducting polymer membrane.

FTIR spectroscopy of ordered polyaniline films

Polyaniline films were produced on the surface of crystalline silicon wafer during the oxidative polymerization of aniline. Infrared spectroscopy revealed the self-ordering of polyaniline chains via hydrogen bonding. The films were annealed at 120°C. The deprotonation of polyaniline has been observed but the film structure was preserved.

Self-organization of polyaniline during oxidative polymerization: formation of granular structure

The paper is focused on oxidative polymerization of aniline proceeding in an acid medium with a strong oxidant; formation of polyaniline (PANI) granular structures in different steps of the synthesis was studied. The relationship between the processes of self-organization of the growing polymer into supramolecular structures and the steps of molecular synthesis has been revealed. It was shown that during the induction period (the initial synthesis step), insoluble non-conducting products are formed. They are characterized by the absorption band at 430 nm corresponding to the wavelength of the phenazinium cation radical peak. In the second step, the polymer chain growth, conducting PANI granules with the diameter of 50 nm were obtained. These granules consist of spherical particles with the diameter as small as several nanometers. Then, the granule dimensions increased to 200 nm due to the growth of the spheres; the sphere diameter reached 20 nm. The number of spheres in a granule remained constant. Both precipitate and PANI film consist of common structural elements, polymer spheres, organized into granules and larger structures. Suppression of the polymer chain growth leads to the formation of non-conducting aniline oligomers which are self-organized into large particles with fractal structure. To describe the self-organization processes of a growing polymer chain, the diffusion-limited aggregation mechanism was used.