ESR of protonated “emeraldine”: Insulator to metal transition

doi:10.1016/0379-6779(89)90330-5

Synthetic Metals

Volume 29, Issue 1, 7 March 1989, Pages 439-444

https://doi.org/10.1016/0379-6779(89)90330-5 Get rights and content

Abstract

The temperature dependence of the X-band electron spin resonance for the emeraldine oxidation state of polyaniline is investigated under different protonation levels ranging from the unprotonated insulating emeraldine base to the metallic emeraldine hydrochloride. For all the samples studied, the signal is composed of two lines, one Lorentzian and the other Gaussian and broader. The different temperature dependences of the intensity of the Lorentzian and Gaussian signals for each sample allows one to distinguish between localized and mobile spins. Moreover the study of the linewidth of the Lorentzian signal as a function of the temperature and of the protonation level leads to a discussion on the nature of the conduction mechanism in polyaniline.

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It is well known that in conducting polymers (CP) there are no permanent dipoles. However, the charge carriers of these CPs are strongly trapped and their brief localized motion under the application of ac field may act as dipole, which is termed as 'effective electric dipole' [45–47]. The increase in real dielectric permittivity with increase in temperature indicates the increase in mobility of the effective electric dipoles in these polymers.
Present work is primarily emphasized on the study of dielectric properties of sulphonic acids (SA) incorporated polyaniline (PANI). SA's function as dopants as well as surfactants for PANI. The PANI and PANI-SA samples are prepared by interfacial technique. The three composites prepared with three SA's (camphor sulphonic acid (CSA), dodecylbenzene sulphonic acid (DBSA) and polystyrene sulfonic acid (PSSA)) are characterized by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), field effect scanning electron microscopy (FESEM) and thermogravimetric analysis (TGA) and differential thermogram (DTG) prior to dielectric studies. The results of PANI not incorporated with SA are also shown for comparison. XRD shows enhancement of crystallinity on SA doping. FTIR confirms the molecular structure with enhanced oxidation states on SA doping. FESEM shows fibrillar morphology with reduced fiber diameter from 86 nm in pure PANI to minimum of 50 nm in one of the composites. TGA and DTG results show better thermal stability on SA doping. The dielectric and AC conductivity measurements of the undoped and dopedPANI are studied inthe frequency range of 42 kHz - 2 MHz and in the temperature range of 300 K–330 K. The dielectric constant for all the PANI composites increases with increase in temperature which indicates increase in mobility of the electric dipoles in the polymers. The dielectric constant for DBSA doped PANI is nearly 5000 which is much higher in context to interfacially polymerized nanofibres compared to that of undoped PANI where this value is about 800. Electric modulus studies show relaxation peaks in imaginary modulus spectra which ascertains about the type of relaxation process. The AC conductivity of the composites is found to be much higher than that of undoped PANI. The electrical conductivity increases with increase of temperature. This is suggested to be caused due to the activated trapped charge carriers.
Conducting and magnetic mango fibers
2015, Industrial Crops and Products
Citation Excerpt :
Among possible oxidation states, due to the higher electrical conductivity of the protonated form, the emeraldine one is the most important. Emeraldine can be isolated in the insulating or conducting forms, named emeraldine base and emeraldine salt (Dimitriev, 2001; Jamadade et al., 2010; Javadi et al., 1989; Lee et al., 2009; Wang, 2002), respectively (Duboriz and Pud, 2014; MacDiarmid and Epstein, 1995), which can be identified by their characteristic bluish and greenish colors (Duboriz and Pud, 2014; Souza and Soares, 2006). Polyaniline is frequently a good choice for manufacture of sensitive devices (Rahaman et al., 2013; Souza et al., 2008b, 2009, 2010b, 2011), because of its low cost, very good electrical and electronic properties and easy preparation (Alizadeh et al., 2011; Kar et al., 2011; Ram and Palaniappan, 2004; Souza et al., 2006, 2008a,c, 2010b).
This paper presents a new magnetic material, obtained from the modification of mango (Mangifera indica L.) fibers with polyaniline (PAni). The obtained materials were characterized through wide-angle X-ray scattering, scanning electron microscopy, Fourier transform infrared spectroscopy, and ultraviolet–visible spectroscopy. Additionally, the electrical resistivity and magnetic behavior of the obtained samples were evaluated with the help of volume resistivity measurements assisted by probability density function analysis and magnetic force tests. The materials presented good electrical and magnetic properties. For instance, in the best case, fibers modified with PAni are approximately 120,000 times more conductive than raw mango fibers. In addition, mango fibers modified with PAni were increasingly attracted by the magnetic field, presenting magnetic force and magnetic susceptibility equal to 6.69 ± 0.05 mN/g (at 872 ± 4 Gauss) and (2.48 ± 0.04) × 10⁻⁴ m³ kg⁻¹, respectively. As a consequence, modification of mango fibers with PAni constitutes a very promising way for the preparation of green magnetic devices.
Effects of tungsten carbide on electrochemical properties and microstructural features of Al/Pb-PANI-WC composite inert anodes used in zinc electrowinning
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PANI doped with inorganic acid possesses higher electrical conductivity owing that the extension of molecular chain structure leads to high conjugate degree and close chain packing those are favorable to the transmission of charge in the chain and between the chains (Javadi et al., 1998). The conductive mechanism of doped PANI differs from metal and semiconductor, in which the carriers are composed of “delocalization” π electrons and solitons, polarons or bipolarons formed by doping (Li and Zhao, 2000), which has been described by PEACE Model (Nechtschein et al., 1987; Wang and Wang, 1990), Granular Metal Island Model (Javadi et al., 1989; Lundberg and Salaneck, 1987; Nechtschein et al., 1989) and Monopole and Bipolar Sub-transformation Model (Wang et al., 1991). Meanwhile, PANI has activity surface that exceeds geometric surface and can play a role in selective catalysis to some certain surfaces when used as the electrode materials, for example, the electrocatalytic oxidation of ascorbic acid at polyaniline film modified glassy carbon electrodes (Dong and Song, 1992), the electrocatalysis of polyaniline film on Fe [II] and Sb [II], the synergistic effects of electrocatalytic oxidation of polyaniline on small organic molecules (DuIć and Griglć, 2001; Mikhaylova et al., 2001; Rajendraprasad and Munichandraiah, 2002) and the same electrocatalytic activity for Pb/PANI and Pt/PANI in acid solutions (Cheraghia et al., 2009).
In order to search for a suitable anode material in place of Pb–Ag alloy in zinc electrowinning, Al/Pb-PANI(polyaniline)-WC(tungsten carbide) composite inert anodes on aluminum substrates were prepared by double pulse electrodeposition (DPE) of WC and PANI particles with Pb²⁺ from an original plating bath, in which solid particles were suspended by mechanical stirring. Thereafter, the anodic polarization curves, cyclic voltammetry curves and tafel polarization curves for the composite inert anodes obtained under different WC concentrations in the original plating bath, were measured in a synthetic zinc electrowinning electrolyte of 50 g·L^− 1 Zn²⁺, 150 g·L^− 1 H₂SO₄ and 35 °C, and the microstructural features were also observed by scanning electron microscope (SEM). The results show that the co-deposition of WC and PANI particles with Pb²⁺ in the original plating bath, changes the electrocrystallization morphologies for matrix metal Pb on aluminum substrates. Al/Pb-PANI-WC composite inert anode obtained under WC concentration of 30 g·L^− 1 and PANI concentration of 20 g·L^− 1 in the original plating bath, possesses uniform surface and cross sectional microstructures, higher electrocatalytic activity, lower overpotential of oxygen evolution, better reversibility of electrode reaction, better corrosion resistance and longer service times in a synthetic zinc electrowinning electrolyte of 50 g·L^− 1 Zn²⁺, 150 g·L^− 1 H₂SO₄ and 35 °C.
Effects of polyaniline on electrochemical properties of composite inert anodes used in zinc electrowinning
2012, Transactions of Nonferrous Metals Society of China (English Edition)
In order to search for a suitable anode material used in zinc electrowinning in place of Pb–Ag alloy, Al/Pb–PANI (polyaniline)–WC (tungsten carbide) composite inert anodes were prepared on aluminum alloy substrate by double pulse electrodeposition (DPE) of PANI and WC particles with Pb²⁺ from an original plating bath. Thereafter, anodic polarization curves, cyclic voltammetry curves and Tafel polarization curves for the composite inert anodes obtained under different PANI concentrations in the original plating bath were measured, and the microstructural features were also investigated by scanning electron microscopy (SEM). The results show that Al/Pb–PANI–WC composite inert anode obtained under PANI concentration of 20 g/L in the original plating bath possesses uniform microstructures and composition distributions, higher electrocatalytic activity, better reversibility of electrode reaction and corrosion resistance in a synthetic zinc electrowinning electrolyte of 50 g/L Zn²⁺, 150 g/L H₂SO₄ at 35 °C. Compared with Pb–1%Ag alloy, the overpotential of oxygen evolutions for the composite inert anode are decreased by 185 mV and 166 mV, respectively, under 500 A/m² and 1000 A/m².
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2009, Reactive and Functional Polymers
4,4′-Bipyridinium salts (PAS-BPy(R)s) of poly(2-methoxyaniline-5-sulfonic acid) (PAS) were synthesized by the reaction of PAS with N-4-halophenyl-4-(4-pyridyl)pyridinium chlorides (BPy(X)s) or N-2,4-dinitrophenyl-4-(4-pyridyl)pyridinium chloride (BPy(NO₂)). The UV–vis, ESR and X-ray photoelectron spectroscopy (XPS) data suggested the occurrence of the self-doping in PAS-BPy(R)s that was based on the electron transfer from the nitrogen atom in the polymer backbone to the 4,4′-bipyridinium unit. PAS-BPy(R)s behaved as polymeric electrolytes in the dilute solutions. Electric conductivity of PAS-BPy(R)s was almost constant when it was measured in the range of 1 ⩽ pH ⩽ 10. Cyclic voltammetry suggested that PAS-BPy(R)s received two-step electrochemical reduction in film, and the electrochemical reaction was accompanied with electrochromism.
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Polyanilines doped with (HCl + KCl) and (HCl + CoCl₂) were prepared by co-doping method, respectively. For comparison, polyaniline emeraldine salt (ES) by doping with HCl and its emeraldine base (EB) form were also synthesized. The co-doped polyanilines, ES and EB samples were all characterized by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy aiming to understand the transformations in the different doping status. The results show that the doping degree of K⁺ ions is considerably higher than that of Co²⁺ ions under the same co-doping conditions possibly due to different pseudoprotonation constants of EB with K⁺ ions and Co²⁺ ions. Moreover, morphology difference of polyaniline co-doped with alkaline metal ions or transition meal ions may arise from different coordination geometry of metal ions. Nevertheless, there are similar chemical transformations of quinoid units to benzenoid ones on polyaniline backbones for the ES and both co-doped samples. And the polyaniline backbones co-doped with H⁺ and metal cations are found to attain weaker charge delocalization than the ES which is doped solely with H⁺.

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ESR of protonated “emeraldine”: Insulator to metal transition

Abstract

J. Electroanal. Chem.

Synth. Met.

Synth. Met.

Phys. Rev. B

Phys. Rev. B