Polyaniline Salt Research Articles

Protonation and deprotonation behaviour of amine units in polyaniline

The structures of polyaniline salts chemically synthesized in HClO 4 of varying concentrations have been examined by means of X-ray photoelectron spectroscopy. The results indicate that, although the imine units of the as-synthesized salt are preferentially protonated, a large proportion of the amine units are also protonated in the presence of a large excess of HClO 4 on the surface of the salt particles. Protonated amine units are also observed when emeraldine base films cast from N-methylpyrrolidinone solutions are reprotonated by HClO 4. The deprotonation behaviours of the salt synthesized in HClO 4, the reprotonated film and polyaniline from the simultaneous oxidation and polymerization of aniline by Cu(ClO 4) 2.6H 2O in acetonitrile are compared. It is found that the protonated amine units undergo deprotonation in aqueous media more readily than the protonated imine units and that both types of structures are stable when heated to 150°C in air.

Polyaniline salts of toluenesulfonate and sulfonated poly( p-vinylphenol)

Polyaniline salts of toluenesulfonate (TS) and sulfonated poly( p-vinylphenol) (SPVP) have been prepared. The polyaniline salt of TS exhibited a room-temperature electrical conductivity of 10 S cm −1. The activation energy for electrical conduction was 0.02 eV, which was significantly smaller than the value 0.04 eV reported for other salts. The aromatic nature of the organic anion is expected to enhance the interchain diffusion of charge carriers. The electrical conductivity of the polyaniline salt of the polymer anion was of the order of 10 −4 S cm −1. A polyaniline base derived from the SPVP salt was water-soluble in the presence of excess NaSPVP, due to complexation between the two polymers.

EPR study of polyaniline perchlorates: Spin species related to charge transport

The spin susceptibilities χ of polyaniline perchlorates prepared by different methods were determined from electron paramagnetic resonance spectra. The observed χ vs. T curves can be explained by the sum of a Curie term and a thermally activated term. The C-spin species which is responsible for the Curie term is produced upon protonation of polyaniline base, but the concentration is independent of the protonation level. In contrast, the concentration of the TA-spin species that shows the thermally activated susceptibility has a close correlation with macroscopic electrical conductivity. Both spin species are intrinsic of polyaniline salts, and the TA-spin species is expected to be responsible for interchain hopping of charge carriers.

A method to prepare soluble polyaniline salt solutions — in situ doping of PANI base with organic dopants in polar solvents

Soluble PANI salt solutions can be prepared by mixing PANI base solutions with organic doping solutions in select polar solvents such as NMP and DMSO. Dopants containing carboxylate or amino groups, such as sulfosalicylic and m-sulfanic acids, yield soluble salt solutions. Free-standing films prepared from these solutions have a conductivity close to the value obtained in a pressed pellet doped with the identical dopant. UV-Vis spectra demonstrate the co-existence of highly doped and undoped phases in the partially doped solutions indicating that the doping process may not be a homogeneous one.

Physicochemical Properties of Polyaniline Base and Salt Films

Abstract Polyaniline base and perchlorate salt films cast from N-methylpyr-rolidinone (NMP) solutions are studied using thermogravimetric analysis, infrared and ultraviolet-visible absorption spectroscopy, and x-ray photoelectron spectroscopy. Both types of films retain a substantial amount of solvent. Although most of the solvent can be removed by washing the films with deionized water, some C1O− 4 anions are removed from the salt films as well, resulting in a decrease in conductivity. In the salt films, protonation of the amine units in addition to the imine units can be readily achieved using HC1O4. Structural modifications of the base films are apparent after one reprotonation/deprotonation cycle. These result in a decrease in the solubility of the film, the extent of which increases with the protonation level. Although NMP is a useful solvent for casting polyaniline salt and base films, both leucoemeraldine and perchloric acid protonated salt undergo degradation in this solvent.

Electrical conductivities and electron spin resonance spectra of polyaniline salts with different counteranions

Electrical conductivities and ESR spectra were obtained for polyaniline salts that contained different counter anions. The electrical properties were markedly different from one salt to another, although the concentrations of counteranions were almost identical. The ESR spectra showed that different types of unpaired electrons were created upon protonation. There was a close correlation between the charge-transport property and the nature of unpaired electrons created upon protonation.

Synthesis and characterization of FeCl −4-doped polyaniline

A new tetrachloroferrate-doped (FeCl − 4) salt of emeraldine (polyaniline) has been obtained in a non-aqueous medium. From elemental analysis and Mössbauer studies, the salt has been identified to contain iron exclusively in the +3 oxidation state. Data on temperature-dependent d.c. conductivity and dielectric constant measurements on the doped polyaniline salt in the X-band of the microwave region are also discussed.

Three dimensionality of "metallic" states in conducting polymers: Polyaniline.

Anisotropic-conductiity (\ensuremath{\sigma}), thermopower, and dielectric-constant studies show that oriented polyaniline salt is representative of a class of quasi-one-dimensional disordered conductors where coupled parallel chains form ``metallic'' bundles in which electron wave functions are extended three dimensionally. This is in contrast to isolated conducting chains in conventional 1D conductors. The bundles correspond to crystalline regions of the polymer. The results are important for understanding the stabilization of metallic states and achievement of high \ensuremath{\sigma} in conducting polymers.

Preparation of polyanilines doped in mixed protonic acids: Their characterization by X-ray photoelectron spectroscopy and thermogravimetry

A comparative study of polyaniline chemically prepared and simultaneously doped in protonic acid mixtures is presented. As the resultant polyaniline salts (PANI salts) are insoluble, solid-state techniques such as X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG), derivative thermogravimetry (DTG) and elemental analysis have been applied to study the dopant environment as well as the electronic and chemical structure of the polymers. Both XPS and TG/DTG indicate that in the presence of competing acids, the stronger acid component is preferentially incorporated over the others. No advantage can be gained by the use of mixed-acid systems. XPS confirms that ring substitution by the dopant and the degree of protonation can be accurately measured based on the percentage of charged nitrogen in the N 1s envelope. Previous methods based on the total halogen content can lead to serious errors. TG results suggest an upper application temperature limit of about 150°C, at which point elimination of dopant occurs with loss of conductivity.

Sensors based on conducting organic polymers. Polyaniline

The conductivity of a polyaniline salt and base is measured bu ESR, using the two-millimetre range method. Two forms of the polyaniline base having various parameters are found. It is shown that the properties and composition of different media can be determined by means of the sensores developed on the basis of undoped polyaniline films.

Thermopower and conductivity of metallic polyaniline

Abstract The temperature dependences of conductivity and thermopower of the metallic polyaniline salts are presented, along with the dependence of conductivity on chemical potential and doping level. As the degree of protonation increases, the sign of the thermopower changes from positive to negative. Although the structure of the polyaniline is known to be complex, we propose a model which can interpret the thermopower sign-cross-over behavior in a relatively simple way.