Maria C. Miras

Redox coupled ion exchange in cobalt oxide films

Ion exchange coupled to oxidation–reduction cycling of electrochromic cobalt oxide films was studied using Probe Beam Deflection (PBD) techniques. The films were deposited by potentiodynamic cycling of glassy carbon electrodes in aqueous Co+2 solution. The cyclic voltammograms of cobalt oxide films present three peaks in basic (pH=13) solution. The PBD signal is positive during oxidation indicating insertion of hydroxide ions. The results are confirmed by monitoring the PBD signal during pulse potential experiments at varying distances of the beam from the electrode. Using the theory of PBD behaviour for discontinuous reactions, a diffusion coefficient for the mobile ion of 1.68×10−5 cm2/s was measured, which agreed with that observed for NaOH diffusion in similar systems. The results are explained on the basis of a scheme of solid state oxidations from CoII to CoIV in three redox steps, coupled to hydroxide ion insertion.

Sulfonated polyaniline films as cation insertion electrodes for battery applications. Part 1.—Structural and electrochemical characterization

Sulfonated polyaniline (SPAN) was synthesized by sulfonation of polyaniline (PANI) base with fuming sulfuric acid. Thin films were cast from polymer solutions in basic media. The polymer films were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible–near-infrared spectroscopy, scanning electron microscopy (SEM) and cyclic voltammetry. XPS in combination with FTIR showed that the preparation procedure led to ca. 47% sulfonation of an otherwise unchanged polyaniline backbone. The NIR spectra of SPAN films showed a polaron band at higher energies than with polyaniline. This is in agreement with the lower conductivity of SPAN as compared with polyaniline. SEM micrographs of the SPAN films showed a compact globular morphology. Electrodes modified with thin SPAN films exhibited two redox steps, both in aqueous and in non-aqueous electrolytes. The specific charge stored in SPAN films was found to be ca. 37 A h kg–1 in aqueous solution (only the first redox step) and ca. 68 A h kg–1 in non-aqueous media (both redox steps). A practical SPAN–Li battery could have 50% more specific energy than a PANI–Li battery. The optical spectra of SPAN films exhibited bands at 310, 450 and 750 nm, the intensities of which changed during the redox process. The absorption coefficients of SPAN (emeraldine base state) solutions had values of a= 410 at 313 nm and a= 239 at 563 nm. The suitability of SPAN for use as a cation-insertion material for battery and electrochromic applications is discussed.

Effects of high hydrochloric acid concentration on aniline chemical polymerization

The rate of aniline polymerization, measured by calorimetry, decreases when the hydrochloric acid concentration in the polymerization solution is increased from 2 to 6 M. The amount of chloride covalently bonded to the aromatic rings of the polymer backbone, estimated from the presence of new vibrational bands in the i.r. spectra, increases with an increment of hydrochloric acid concentration. The enlarged substitution on the polymer backbone is correlated with a decrease of the extension of the electronic conjugation, as shown by the shift towards higher energy of the broad band due to extended conjugation. The trend is related with a simultaneous decrease of the polymer d.c. conductivity.

Functionalised conjugated materials as building blocks of electronic nanostructures

Two different approaches towards conjugated material (carbon nanotubes, conjugated polymers) functionalisation are presented: covalent bonding of functional groups and covalent interaction with soluble polymers. Covalent functionalisation of carbon nanotubes is made by reaction of the aromatic ring with aryl radicals, produced by reduction of diazonium ions. In the case of conducting polymers, covalent functionalisation is brought about by reaction of polyanilines with diazotized aromatic amines (including amino terminated azo dyes). The non covalent functionalisation of carbon nanotubes is made by wrapping the nanotubes with soluble conducting polyanilines. The functionalised materials are characterised by FTIR spectroscopy, X-ray diffraction, dynamic light scattering, ultraviolet-visible absorption and emission spectroscopy, transmission electron microscopy, cyclic voltammetry, differential electrochemical mass spectroscopy and conductivity measurements. The materials are to build ionic self assembled multilayers using a layer-by-layer deposition process. The charge transport and electrocatalytic behaviour of the assemblies, relevant to the application of the assemblies in nanostructured electrochemical biosensors, are evaluated using different redox molecules and/or its intrinsic electroactivity as probes.

A soluble and electroactive polyaniline obtained by coupling of 4-sulfobenzenediazonium ion and poly(N-methylaniline)

Abstract A modified polyaniline was obtained by coupling of the 4-sulfobenzenediazonium ion with poly ( N -methylaniline) (PNMANI) at temperatures below 5°C and in basic or neutral pH conditions. The FT-IR spectra of the product show all bands due to the poly( N -methylaniline). Additional bands at 1007, 1003 and 623 cm −1 are assigned to the vibrations of the sulfonate group, incorporated in the polymer matrix. A new band at 1485 cm −1 is also present, assigned to the stretching of the azo bond. The polymer is soluble in aqueous base. The results suggest the formation of an azo-substituted poly ( N -methylaniline): poly(4-sulfobenzenazo-( N -methylaniline)) (p(4SBA-NMANI)). The solution spectra show absorption bands at 242, 310 and 595 nm. Thin films deposited on glassy carbon show clear electroactivity. The method could be used to produce electroactive films with bonded functionalities.

Synthesis, properties and aplications of functionalized polyanilines

Novos polimeros condutores funcionalizados foram sintetizados a partir de modificacoes das reacoes de acoplamento polianilina-diazonio, adicao nucleofilica e N-nitrosacao. O acoplamento de diazonio fornece polimeros modificados que sao eletroativos e soluveis em solventes comuns. Adicao nucleofilica tambem pode ser usada para modificacoes da polianilina. Polimeros modificados pela adicao de tiois, carbânions e acidos arilsulfinicos sao apresentados. A adicao nucleofilica de acidos arilsulfinicos a polianilina oxidada mostrou ser controlada pelos estados de oxidacao e/ou protonacao do polimero. A N-nitrosacao de polianilina tambem e possivel, produzindo material soluvel em solventes comuns. Esta reacao pode ser revertida por tratamento acido. A reacao de nitrosacao reversivel foi usada para controlar processos litograficos e fotolitograficos de deposicao de padroes de PANI.

Anion effects on aniline polymerisation

The polymerisation of aniline by oxidation with ammonium persulfate was studied, by potentiometry and calorimetry, in presence of different anions. It was observed that the nature of the anion affects clearly the polymerisation rate. Possible reaction mechanisms are proposed.

Double layer properties of carbon aerogel electrodes measured by probe beam deflection and AC impedance techniques.

Probe beam deflection (PBD) and AC impedance are used to quantitatively evaluate the double layer properties of carbon aerogel electrodes in aqueous media (NaF). The measurements allow determination of the potential of minimum charge of the material.

New methods of polyaniline functionalization

Abstract Novel synthetic methods of PANI functiooalization are described. We investigated coupling of diazonium salt and electrophilic nitration of the aromatic ring, amine group protection by amide formation, nucleophilic reaction with activated aromatic moieties and nucleophilic addition of sulfite ions to the ring. The structure of the products and their properties were studied by FTIR, UV-vis spectroscopy and electrochemistry.

Organic Chemistry of Polyanilines: Tailoring Properties to Technological Applications~!2008-08-19~!2008-09-11~!2008-11-28~!

The use of organic chemistry reactions to introduce additional functional groups on polyanilines is described. Among the reactions discussed are: electrophilic aromatic substitution, nucleophilic addition to the aromatic rings, nu- cleophilic substitution on the amine groups and reactions on pendant groups. The use of combinatorial chemistry tech- niques, by coupling of combinatorially synthesised diazonium salts with polyaniline, to produce a functionalized polyani- lines library is also reviewed. The modification of polyaniline introduces or alters different properties of the materials: solubility, self-doping and redox coupled ion exchange. The tailoring of those properties to technical applications is there- fore examined.