Ivo Křivka

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.

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.

Conductivity of colloidal polyaniline dispersions

Conductivity of polyaniline dispersions stabilized in aqueous medium with poly(N-vinylpyrrolidone) is related to the prediction for the model system composed of conducting spheres dispersed in a continuous medium. The behaviour of as-prepared dispersion, dispersions dialysed against dilute hydrochloric acid and water, and dispersions based on dry particles redispersed in water is reported. An increase in conductivity of the reaction mixture during the polymerization of aniline is discussed in connection with simultaneous changes in acidity and temperature. The use of conductometry in monitoring the aniline polymerization is illustrated on reactions carried out at various temperatures. The course of dispersion and precipitation polymerizations, as reflected by conductivity measurements, is compared.

Enhanced stability of polyaniline/inorganic salt composites during temperature cycling

Abstract The electrical conductivity of polyaniline sulfate was recorded during cycles between room temperature and 85, 105, 125 and 145°C. After each temperature cycle the conductivity decreased. The maxima of the conductivity–temperature heating curves are discussed. Composites of polyaniline sulfate with inorganic salts (ammonium sulfate or potassium bromide) were treated in the same manner. Experimental data and a simple model indicate that the temperature dependence of the composite conductivity changes its character at ca. 80 wt% PANI. Composites containing more than 20 wt% inorganic salt exhibit lower decrease in the conductivity after cycling; i.e. they have a higher thermal stability of electrical properties than polyaniline sulfate alone.

Control of Electrical Properties of Polyaniline

The electrical and material properties of polyaniline can be controlled on the molecular level, e.g. by copolymerization of aniline with p-phenylenediamine. Products having a resistivity from 10° to 10 9 D cm can be obtained. On the supramolecular level, polyaniline dispersions comprising submicrometre particles can be used for the preparation of microstructured composites with water-soluble polymers such as poly(vinyl alcohol) or poly(N-vinylpyrrolidone). On the macroscopic level, the blending of polyaniline with an inorganic salt, ammonium sulphate, produced materials with a percolation threshold at 2.5 vol% polyaniline.

The influence of compression pressure on transport properties of polyaniline

The transport of charge carriers and the thermal diffusivity were studied on a set of polyaniline (emeraldine) samples that were compressed at various pressures, 50–1000 MPa. Marked correlations between the plots of compression pressure dependence of the electrical resistivity, the thermal diffusivity and the sample density were observed. This study has demonstrated that in order to obtain comparable data on samples prepared by compression of polymeric powders it is necessary to use sufficiently high pressure. In the case of polyaniline powder the pressure should be higher than 400 MPa. The values of the thermal diffusivity measured on polyaniline salt and its respective base indicate that charge carriers are not dominant in a heat-transport mechanism; only less than ten per cent of the thermal diffusion in pressed polyaniline samples can be eventually attributed to charge carriers.

AC conductivity in aniline-1,4-phenylenediamine copolymers

Copolymer samples were prepared by joint oxidation of aniline and 1,4-phenyl-enediamine with the possibility of controlling electrical properties by the changing of aniline content in the reaction mixture. Temperature dependence of DC conductivity, frequency dependence of AC conductivity and electric modulus were studied, with the aim to determine mechanisms of charge transport in the material. Due to low molecular weight, polyaniline and phenylenediamine units form amorphous material, similar to typical amorphous semiconductor, where doping leads to creation of electronic states which are localized in sites of dopant counterions. Charge transport takes place via variable range hopping (VRH) in 3 dimensions. The high disorder and broad distribution of relaxation times was found in these materials.