Electrical Conductivity Of Polyaniline Research Articles

Effect of electron-withdrawing type substituents in the polyaniline ring on the electrical conductivity

Poly(ethyl 3-aminophenyl formate), poly(ethyl 3-aminophenyl acetate) and poly(ethyl 3-aminophenyl propionate) were synthesized in 1 M HCl media from respective monomers using ammonium persulphate as oxidizing. The polymers were characterized by FT-IR, UV-vis and 1H-NMR spectroscopy. The effect of electron-withdrawing on the electrical conductivity of polyaniline, was studied. The electron-withdrawing group (ester) bond to the aniline ring affects the formation of charge carriers and electrical conductivity of polymers, therefore, at various bond lengths of the aniline ring, the electron-withdrawing effect decreases and a polymer with electrical conductivity from the semi-conduction order is obtained.

Fullerene-doped polyaniline

Polyaniline (PANI) doped with [60]fullerene has been prepared by electrochemical method (an aqueous medium at pit ∼1) in a copolymerisation process of aniline and o-, m- and p-aminobenzylamine-C 60 derivatives. The electrical conductivity of PANI with covalently bonded fullerene units is of 10 -2 S/cm and it depends on the temperature with activation energy of 0.002 eV and 0.068 eV, below 200 K and above 275 K, respectively. [60]fullerene units have also been incorporated into polyaniline network by the reaction of PANI macromolecules with hexanitro[60]fullerene. This results in an increase of the electrical conductivity, e.g. from 1 * 10 -3 S/cm to 4.1 * 10 -2 S/cm, while the activation energy does not change so much (0.078 eV above 275 K) except for a low temperature range (0.02 eV below 200 K). Similarly, we have observed a broadening of the EPR signal, changes in FTIR spectra and cyclic-voltammograms. The samples were prepared either as thin layers and a bulk material. In most cases, micro- and nanofiher structures have been observed with SEM.

Intrinsically conducting polymer blends

Polyaniline (PANI) doped with different dopants (HCl, dodecyl benzene sulfonic acid, (+)-Camphor-10 sulfonic acid, dinonyl naphthalene disulfonic acid) was synthesized by chemical oxidation method. The FTIR studies indicated that the back bone structure of doped PANI was similar. Thermal stability was evaluated in nitrogen atmosphere by dynamic thermogravimetry and PANI-HCl sample showed minimum weight loss below 400°C. The electrical conductivity of PANI was not affected by the structure of dopants. The microwave absorption studies of several polymers blends containing PANI-HCl and/or carbon black were also carried out by using wave guide technique.

On the influence of electron energy on iodine‐doped polyaniline formation by plasma polymerization

The influences that both electron energy and density of a plasma bear on thin film formation are examined in the case of iodine-doped polyaniline polymerization. The plasma was produced by means of 13.5-MHz radiofrequency-generated glow discharges in low-pressure (ca. 10 -2 mbar) air between electrodes. Four representative inner regions of the reactor were selected according to the electron incidence. Given the uneven energy distribution found on the inside of this kind of reactors, variations in the polymer structure formed in the presence of iodine were found and studied by elemental analysis, thermogravimetry, infrared spectroscopy, and X-ray diffraction. The results indicate that the electric conductivity of polyaniline by plasma is a function of the iodine content and that such content is a function of the combined conditions of both reactor and plasma.

Thermal degradation of the electrical conductivity in polyaniline and polypyrrole composites

The thermal aging in various conducting polyaniline and polypyrrole composites protonated with hydrochloric acid, containing polymers with sulphonic or phosphoryl groups is investigated. The DC conductivity was measured in the temperature range 300–80 K for aging times from 0 to 300 h at 70°C in room atmosphere. The conductivity decreases with aging time according to the law σ= σ 0exp[−( t/ τ) 1/2], indicating an inhomogeneous structure of the granular metal type. Time τ, which specifies the aging rate, varies with the porosity and the composition of the composites from 40 to 3000 h. The porosity and the presence of sulphonic or phosphoryl groups retards the aging process. The conductivity of the composites with temperature T follows the σ= σ 0exp[− T 1/( T+ T 0)] law predicted by Sheng's model of fluctuation-induced tunneling (FIT), which assumes conductive grains separated by insulating barriers in accordance with the thermal aging law mentioned above. Thermal degradation is attributed to the release of HCl from the samples, which reduces the protonated-conducting phase.

Electronic conductivity of pyrrole and aniline thin films polymerized by plasma

In this article, we present a study of the influence of temperature and humidity on the electric conductivity of polyaniline and polypyrrole thin films doped with iodine and synthesized by plasma (PAn/I and PPy/I, respectively). The polymers presented the characteristic ohmic conduction mechanism via electrons; however, the conductivity was much lower than that presented by the polymers obtained by traditional chemical oxidation. We submitted the polymers to heating–cooling cycles to study the temperature dependence of the conductivity. During the heating stage of the cycles, the electric conductivity of PPy/I showed a strong dependence on the humidity content. However, during the cooling step, the plots of conductivity, as a function of the inverse temperature of PPy/I and PAn/I, showed typical Arrhenius behavior. The activation energy of PPy/I had an average value of 1.1 ± 0.1 eV and was independent of the reaction time, whereas PAn/I presented a more complex behavior with activation energies that depended on the reaction time and the regional crystallinity induced in the heating step of the cycles. All the activation energies were below 2 eV, which places them in the semiconductor regime. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3247–3255, 2000

Radiation Induced Effects on Electrical Properties of Polyaniline

The effect of radiation on the electrical conductivity of polyaniline in the reduced, undoped and doped states has been studied. A model based on the oxidation of the polymeric chain combined with radiolysis of the adsorbed water molecule has been proposed to explain the radiation-induced effects in this polymer. The experimental results show that the film resistance of emeraldine base, and leucoemeraldine salts decrease drastically with exponential decay for the range from 0 to 250 Gy, when exposed to γ radiation, while for emeraldine salt the resistance slightly decreases with exponential decay for low doses of radiation and increases linearly for high doses. Infrared analysis performed in irradiated emeraldine base strongly support a proton doping effect of the polymeric material induced by radiation.

Application of percolation concepts to electrical conductivity of polyaniline–inorganic salt composites

The dependence of the resistivity of protonated polyaniline–inorganic salt composites with the volume fraction of electrically conducting component was analyzed on the basis of percolation theory. A short analysis and a discussion of basic treatment in the evaluation of percolation parameters are included. Microscopical observations showed a non-uniform distribution of polyaniline particles in the composites. The composites of polyaniline sulfate with ammonium sulfate and potassium bromide have a low percolation threshold (<3 vol.% conducting component). This has been explained as a property of the segregated structure of the composites, which is formed because of a large difference in the particle sizes. Basic quantitative characteristics of the morphological structure have been obtained using the percolation model, as proposed by Ewen and Robertson, to explain the properties of thick film resistors.

Transport property of polyaniline and its molecular weight dependence

The electrical conductivity of polyaniline doped with camphor sulfonic acid (PAn-CSA) was studied. The results indicate that there is a critical temperature (Tc) and the temperature dependence of PAn-CSA conductivity shows metallic and semiconductor characteristics above and belowTc, respectively. The higher the molecular weight of PAn, the lower theTc. The conductivity was enhanced remarkably when PAn-CSA film was stretched, its room temperature conductivity is up to 750 S/cm when elogonation is 60%; however,Tc was independent of elongation.

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

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.

Solid-State Protonation and Electrical Conductivity of Polyaniline

Polyaniline base was protonated by blending with camphorsulfonic and picric acids in the solid state. The electrical conductivity of the equimolar mixture was more than 107 times higher compared with the conductivity of components used for blending. The electrical conductivity still increased several times after heating of mixtures to 85 °C. The protonation is reflected by the changes in the infrared spectra. The dependences of the electrical conductivity on the composition of blends differ for the partly protonated polyaniline and mixtures of protonated polyaniline with an excess acid.

Preparation and Properties of Electrically Conductive Polyaniline-Polystyrene Composites by in-situ Polymerization and Blending

Electrically conductive polyaniline (PANI)-polystyrene (PS) composites were prepared by in-situ polymerization and blending. The polymerization was carried out by adding the oxidant and dodecylbenzenesulfonic acid (DBSA) dissolved in xylene to the xylene solution comprising aniline and PS. The electrical conductivity of PANI-PS composites was improved with increasing amount of PANI and reached a high value of 0.1 S cm−1 at content of 12 wt%. The PANI content in PANI-PS composites was calculated by means of elemental analysis and weight measurements. The PANI-PS composites were very soluble in organic solvents such as chloroform, xylene, and N-methylpyrrolidone (NMP). The electrical conductivity of PANI, doped with dodecylbenzenesulfonic acid (DBSA), and thermally treated at 180°C for 3 h was more stable than that of conventional PANI-HCl complex. The structure and morphology of PANI-PS composites were investigated through the measurements of FT-IR and SEM (scanning electron micrograph).

Electrical conductivity of polyaniline as a function of pressure using a diamond anvil cell

We report our results on the electrical resistance of thin films of polyaniline as a function of pressure which was applied to the samples using a diamond anvil cell up to 22 GPa at room temperature. Samples of polyaniline cast from N-methylpyrrolidinone (NMP) and doped with HCl and also those doped with camphor sulfonic acid (CSA) and cast from m-cresol were studied. Resistance versus pressure measurements recorded during the loading and unloading cycle show asymmetry, suggesting irreversible structural changes. Since the primary effect of applying pressure is sample compression, this leads to reduced interchain separation resulting in enhanced interchain charge transport. Such effects are reflected in reduced resistance with increasing pressure as depicted in our results.

Highly conducting polymer blend films of polyaniline and nylon 6 by cosolvation in an organic acid

Polymer blend films of polyaniline and nylon 6 were prepared from homogeneous solutions in formic acid at various weight ratios of polyaniline and nylon 6. Free standing, lustrous and flexible films were obtained by casting. The maximum conductivity of the film was about 0.2 S cm −1, corresponding to a weight ratio of 0.5 wt/wt polyaniline (PAni) and nylon 6. The film exhibits semiconducting behaviour in the range of temperatures between 300 K and 10 K and the data fits in with the VRH model for transport in the range of 150 K to 50 K. Optical absorption spectra reveal absorption bands typical of polyaniline salt. I.r. spectra show a characteristic band at 1145 cm −1 which is associated with electrical conductivity in polyaniline. A simultaneous t.g.a.-d.t.a. scan reveals that the melting temperature of PAni/nylon 6 is slightly reduced. The X-ray diffraction pattern indicates that the crystal structure of nylon 6 in the blend film is retained on modification. The films also exhibit good environmental stability and mechanical strength.

Electro-and thermophysical properties of polyaniline

The electrophysical and thermophysical properties of electrically conducting polyaniline are investigatect in a wide temperature range (77–500 K). Possible mechanisms of polyaniline electrical conductivity depending on the synthesis conditions, doping level, and temperature are analyzed.

Electrical conductivity and magneto-resistance studies on polyaniline-PMMA blends at very low temperature

D.C. electrical conductivity of polyaniline (33%,40%) blended with PMMA was measured from 5K to 300mK. The conductivity behaviour is consistent with fluctuation induced tunneling. Magneto-resistance (MR) was measured between 300K and 2K. From 20K to 2K, a large positive MR was observed. At 2K, for low magnetic fields (<1 Tesla), a deviation from the normal H-2 behaviour was observed.

Effects of ion implantation on the electrical conductivity of polyaniline

Polyaniline with a marked environmental stability was bombarded by beams of hydrogen, boron, fluorine, phosphorus and argon ions. All irradiated surfaces displayed substantial changes in physical properties (e.g. electrical conductivity, colour, etc.). The highest measured conductivity was ∼ 100 S/cm and the irradiated samples have now been shown to be environmentally stable. The conductivity of the irradiated zone depended upon the deposited electronic energy density and also upon the chemical structure and composition. The radicals appeared prior to nitrogen release when the electronic energy deposition density was at the lower threshold in the irradiated layer. The radical concentration, nitrogen release and carbon richness contributed to the conductivity. Shrinkage and colour changes accompanied by nitrogen release and remnant nitrogen reduction or oxidation and also a higher conductivity value were observed.

Radiation Induced Variations of Electrical Conductivity in Polyaniline

Induced variations of electrical conductivity σdc of polyaniline by γ-radiation have been studied, σdc increases from 2.2 to 2.7 S/cm due to radiation with a dose of 30-40 Mrad. EPR results show that spin concentration increases at the same rate as σdc. The characteristics of σdc versus temperature fit to lnσdc∝T-1 before irradiation, but to lnσdc∝T-1/4 after irradiation.

Nature of states in a random-dimer model: Bandwidth-scaling analysis.

The scaling properties of the energy spectra of a random-dimer system are studied to discern the nature of the states at and around the dimer energy (${\mathrm{\ensuremath{\epsilon}}}_{0}$). The system is described by a tight-binding Hamiltonian. The scaling behavior of bandwidths for \ensuremath{\Vert}${\mathrm{\ensuremath{\epsilon}}}_{0}$\ensuremath{\Vert}2 shows that the system contains extended states in the neighborhood of ${\mathrm{\ensuremath{\epsilon}}}_{0}$. This result is further substantiated by the scaling behavior of the total bandwidth. The number of nonscattered states is found to increase with the increase in chain length. The scaling behavior of bandwidths also shows that the width of the nonscattered states depends on the dimer energy and its concentration in the sample. These results are consistent with results obtained from the transmission coefficient analysis. When the dimer energy is at the band edge (${\mathrm{\ensuremath{\epsilon}}}_{0}$=\ifmmode\pm\else\textpm\fi{}2), the bandwidth scaling analysis shows that states around ${\mathrm{\ensuremath{\epsilon}}}_{0}$ are algebraically localized. This result is further substantiated by the behavior of the site Green function. The significance of our results in understanding the anomalous electrical conductivity in polyaniline is discussed.

Electro- and thermophysical properties of polyaniline

The electrophysical and thermophysical properties of electrically conducting polyaniline are investigatect in a wide temperature range (77–500 K). Possible mechanisms of polyaniline electrical conductivity depending on the synthesis conditions, doping level, and temperature are analyzed.