Heqing Tang

Effects of anions on electrochemical formation and overoxidation of polyaniline

Abstract Electrochemical formation and overoxidation of polyaniline (PAn) were investigated in solutions containing different anions. The anions promoted PAn growth in the order, H2SO4 > HCl > HClO4. The growth rate of PAn in the presence of two different types of anion was governed by the anion with lesser promoting effect. The addition of a small amount of HClO4 into the H2SO4 solution greatly inhibited the initial monomer oxidation and the growth of the polymer. Similar promoting/ depressing effects of anions were observed on electrochemical degradation of PAn films. The effects of anions were possibly related to the stability of complexes between the anion and protonated monomer, and the anion and protonated PAn chains.

Electropolymerization of aniline modified by para-phenylenediamine

Abstract Electropolymerization of aniline in perchloric acid solutions was investigated with presence of para-phenylenediamine (PPDA). Experimental results showed that the presence of PPDA promoted markedly the growth of the polymer. The catalytic effect of PPDA on the polymerization of aniline included its contributions to both the autocatalysis and the external catalysis. Addition of PPDA with an appropriate concentration resulted a polymer with high polymerization degree and higher conductivity, which were closely related to the contribution of PPDA to the autocatalysis in the polymerization of aniline. Memory effects in and else properties of the catalytically electrosynthesized polyaniline were also studied.

Electrosynthesis and properties of self-doped polyaniline

Summary form only given. Self-doped conducting polymers are of considerable interest for recent years. In this study, aminobenzenesulfonic acid (ABS) was polymerized electrochemically to obtain self-doped and water soluble polyaniline. Electrochemical polymerization was performed under controlled current of 0.3 mA cm/sup -2/ in 0.5 M H/sub 2/SO/sub 4/ solution containing 0.125 M monomeric ABS. The polymeric product was precipitated by the addition of methanol after passing the electricity of 2 F mol/sup -1/. The electric conductivity values of polymers derived from three isomers of ABS were in the order of 10/sup -3/ S cm/sup -1/ for as prepared samples, but increased to 10/sup -1/ - 10/sup -2/ S cm/sup -1/ by chemical doping with Fe(III). As is expected for the self-doped polyaniline, the conductivity was unchanged by treating with neutral or alkaline solutions. These polymers were easily soluble in water and showed fairly reversible redox peak around 0.6 V (vs. SCE) in CV diagram.

Electrochemical Formation of Polyaniline in Selenic Acid

The electrochemical formation of polyaniline (PAn) was investigated in selenic acid. The cyclic voltammetry of selenate in the potential window from -0.15 to 0.8 V, indicates that the electropolymerization of aniline is not affected by the oxidizing ability of selenic acid. The growth rate of PAn observed at a potential of 0.8 V in a solution of 0.1 M aniline in 0.2 M H 2 SeO 4 was comparable with that in 0.2 M H 2 SO 4 . However, the PAn growth in H 2 SeO 4 during successive potential cycles between -0.15 and 0.8 V was much lower than that in H 2 SO 4 . In cyclic voltammograms, the first reduction peak for PAn was enhanced by the presence of selenate ions, possibly due to the deposition of elemental selenium catalyzed by the polymer film. The deposition of metallic selenium on the PAn film greatly inhibited the growth of the polymer during successive potential cycling between -0.15 and 0.8 V.

Chronocoulometric determination of doping levels of polythiophenes : influences of overoxidation and capacitive processes

Quasi-stationary determination of doping levels of polythiophenes has been successfully achieved in a wide potential window by using a modified potential-step chronocoulometric measurement of the charges consumed in oxidation and reduction processes of the polymers. Influences of experimental conditions, capacitive current-producing process and overoxidation process are discussed on the estimation of the doping levels of the polymers.

Enhanced hole injection in organic light-emitting diodes consisting of self-assembled monolayer of tripod-shaped π-conjugated thiols

Self-assembled monolayers (SAMs) of two tripod-shaped π-conjugated thiols and a disulfide have been grafted onto Au(111)/mica substrates. These SAMs exhibit oxidation and reduction peaks in the cyclic voltammograms arising from the electrochemical responses of the conjugated oligothiophene parts in the molecules. Organic light-emitting devices have been fabricated by using the SAM-coated Au electrode as the anode. In comparison with the device consisting of Au/TPD/Alq3/Mg–Ag, the electroluminescence performance of the device using the SAM grafted Au electrode is much improved for the SAM of the tripod-shaped thiols and worsened for the SAM of the disulfide. The different influences of the SAMs on the performances are explained by considering structures of the molecules and the SAMs, and the energy level alignment at the related interfaces in the devices.

Electrochemical copolymerization of aniline and aniline-2,5-disulfonic acid

Abstract Electrochemical copolymerization of aniline and aniline-2,5-disulfonic acid (ADSA) was carried out in HCl solutions. The presence of ADSA inhibited significantly the growth of polyaniline (PAn), although the voltammetry of the copolymer was still similar to that of conventional PAn. As the ADSA concentration increased, the deposition rate of the copolymer decreased rapidly and finally no solid film was deposited on the electrode surface. When the ADSA concentration was lower than ~ 5 mM, the depression effect of ADSA on the growth rate of the copolymer is mainly due to its stronger adsorption at the electrode surface. For higher ADSA concentrations, the inhibiting effect of ADSA was dominated by its termination effects, which led to more soluble oligomers and in turn resulted in lower deposition efficiency. Electrolysis of ADSA solution might result in a water-soluble fully sulfonated PAn.

A relationship between driving voltage and the highest occupied molecular orbital level of hole-transporting metallophthalocyanine layer for organic electroluminescence devices

Abstract Effects of metallophthalocyanines (MPcs) are systematically investigated on electroluminescence (EL) characteristics of ITO/MPc/TPD/Alq3/Mg–Ag devices. A linear relationship is found between driving voltages of the devices and energies of the highest occupied molecular orbital (HOMO) level of MPcs, showing that the driving voltage of the device is substantially determined by the energy barrier for hole injection at the ITO/MPc interface. When an MPc having a higher HOMO level, such as CuPc or ZnPc, is selected as a hole transport material, the driving voltage of the device at a luminance of 100 cd m−2 significantly reaches as low as 5.5 V compared with 7.8 V for the device without an MPc layer. The insertion of MPc layer leads to increasing of the EL output, but does not affect the EL efficiency of the devices.

Highly sulfonated polyaniline electrochemically synthesized by polymerizing aniline-2,5-disulfonic acid and copolymerizing it with aniline

Abstract Self-doped polyanilines were electrochemically synthesized in aqueous acid solutions through the copolymerization of aniline (An) and aniline-2,5-disulfonic acid (ADSA) and the polymerization of ADSA alone. The voltammetry of the copolymers shows characteristics similar to those of conventional polyaniline (PAn), and the copolymers exhibit higher electrochemical activity at values of pH higher than about 4. The presence of ADSA inhibits significantly the growth of PAn. When the relative concentration of ADSA approaches unity, no solid film is able to deposit on the electrode surface. However, the polymerization of ADSA results in the formation of water-soluble poly-ADSA. Electric conductivities of poly-ADSA and poly-An—ADSA are in the magnitude of 10−1−10−2 and 10−1 S cm−1, respectively, lower than that of conventional PAn, 100−101 S cm−1. The conductivity of poly-ADSA is found to show little pH dependence up to at least 9.

Cyclic voltammetry of KI at polyaniline-filmed Pt electrodes Part I: Formation of polyaniline-iodine charge transfer complexes

Cyclic voltammetry of KI at high concentrations was studied on Pt and polyaniline-modified Pt electrodes in 0.1 m HClO4 solution. The oxidation of iodide to iodine proceeded at a polyaniline-filmed Pt electrode with a mechanism similar to that at a bare Pt electrode. New peaks appeared in the cyclic voltammograms on the polyaniline-filmed Pt electrodes, depending on the experimental conditions, due to interactions of iodine species with the polyaniline chains. XPS analysis of polyaniline samples doped with iodine during, or after, the synthesis of polyaniline provided further evidence of the existence of polyaniline-iodine charge transfer complexes.