Jan Prokeš

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.

The effect of polymerization temperature on molecular weight, crystallinity, and electrical conductivity of polyaniline

Abstract The influence of the polymerization temperature (from −50 to +50°C) on molecular weight, crystallinity, and electrical conductivity of polyaniline has been investigated. Aniline was oxidized in aqueous medium with ammonium peroxodisulfate at equimolar and excess concentrations of hydrochloric acid. The reaction mixture freezes below −10°C and the polymerization of aniline then proceeds in the solid state. As the reaction temperature decreases, both the molecular weight of polyaniline (determined by gel permeation chromatography) and its crystallinity (observed by X-ray diffraction) increase. The morphology of polyaniline changes from granular (reaction in a liquid medium) to macroporous (polymerization in the frozen state). Electrical conductivity of polyaniline is higher for samples prepared under more acidic conditions. It was found to be independent of the polymerization temperature and, consequently, of the molecular weight.

Polyaniline dispersions 8. The control of particle morphology

Abstract Polyaniline dispersions are obtained when aniline is oxidized in an acidic aqueous medium with ammonium peroxodisulfate in the presence of hydroxypropylcellulose. The progress of aniline polymerization has been monitored by the acidity changes and the formation of colloidal particles by dynamic light scattering. Submicrometre spherical polyaniline particles of good uniformity in size are produced at 0°C, while at 40°C the resulting objects have coral-like cylindrical morphology. A similar change of particle shape has been achieved at 0°C by the acceleration of polyaniline formation by addition of a mediator, p -phenylenediamine. The concept of the formation of spherical and non-spherical morphologies and the role of the autoacceleration effect in the dispersion polymerization of aniline are proposed. Polymerization in the frozen reaction mixture at −25°C yielded a macroporous composite.

Infrared spectroscopic study of solid-state protonation and oxidation of polyaniline

Infrared spectrum of the polyaniline sulfate was compared with the spectrum of the polyaniline base after solid-state protonation with an equimolar amount of camphorsulfonic acid and with the spectrum of the polyaniline base after solid-state oxidation with ammonium peroxodisulfate. In both cases electrically conducting product was obtained. The bands characteristic of conducting protonated or oxidized form were identified in the spectra of the blends.

Aniline-phenylenediamine copolymers

The electrical conductivity of materials based on polyaniline can be controlled on submolecular level by the copolymerization of aniline with various phenylenediamines. The joint chemical oxidation of aniline with phenylenediamines yields products with the dc conductivity spanning over more than eleven orders of magnitude. The dependence of the conductivity on the composition of reaction mixture was investigated for all three comonomers, o-, m-, and p-phenylenediamine. The electrical properties of copolymers and mixtures of corresponding homopolymers are compared.

Conductivity ageing in temperature-cycled polyaniline

The conductivity of polyaniline (PANI) hydrochloride was measured in situ during successive temperature cycles from room temperature to 85, 115, 146 and 179 °C. FTIR spectroscopy, gel-permeation chromatography and X-ray diffraction assessed the changes in polymer structure after each run. The conductivity ageing of PANI in terms of deprotonation, degradation and crystallinity reduction is discussed. The behaviour of PANI in compressed pellets and as powders is compared.

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 cellulose fibers decorated with silver nanoparticles

Cellulose fibers of 20 μm in diameter and aspect ratio of 2 or 10 were coated with protonated polyaniline (PANI) during the oxidation of aniline hydrochloride with ammonium peroxydisulfate in an aqueous medium. The presence of PANI has been proved by FTIR spectroscopy. The conductivity increased from 4.0 × 10−14 S cm−1 to 0.41 S cm−1 after coating the fibers with PANI. The percolation threshold in the mixture of original uncoated and PANI-coated fibers was reduced from 10 mass % PANI to 6 mass % PANI, as the aspect ratio changed from 2 to 10. The subsequent reaction with silver nitrate results in the decoration of PANI-coated cellulose fibers with silver nanoparticles of about 50 nm average size. The content of silver of up to 10.6 mass % was determined as a residue in thermogravimetric analysis. FTIR spectra suggest that the protonated emeraldine coating changed to the pernigraniline form during the latter process and, consequently, the conductivity of the composite was reduced to 4.1 × 10−4 S cm−1, despite the presence of silver.

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.

Reduction of silver nitrate by polyaniline nanotubes to produce silver-polyaniline composites

Polyaniline (PANI) nanotubes were prepared by oxidation of aniline in 0.4 M acetic acid. They were subsequently used as a reductant of silver nitrate in 1 M nitric acid, water or 1 M ammonium hydroxide at various molar ratios of silver nitrate to PANI. The resulting PANI-silver composites contained silver nanoparticles of 40–60 nm size along with macroscopic silver flakes. Under these experimental conditions, silver was always produced outside the PANI nanotubes. Changes in the molecular structure of PANI were analyzed by FTIR spectroscopy. Silver content in the composites was determined as a residue by thermogravimetric analysis, and confirmed by density measurements. The highest conductivity of a composite, 68.5 S cm−1, was obtained at the nitrate to PANI molar ratio of 0.67 in water. Also, the best reaction yield was obtained in water. Reductions performed in an acidic medium gave products with conductivity of 10−4–10−2 S cm−1, whereas the reaction in alkaline solution yielded non-conducting products.