The influence of heat treatment on the semi-crystalline structure of polyaniline Emeraldine-salt form (original) (raw)
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Thermal and conducting behaviour of emeraldine base (EB) form of polyaniline (PANI)
2011
a * Emeraldine base (EB) form of polyaniline (PANI) powder is prepared by chemical oxidative polymerization using different acidic media (HCl or CF 3COOH) at different temperatures (-15 °C to + 5°C). The chemical structure, thermal characterization and conducting behaviour are studied by means of Fourier transform infra-red (FTIR) spectroscopy, differential scanning calorimetery (DSC) and two-probe conductivity method. These polyanilines are soluble in N-methyl-2- pyrrolidone, dimethyl sulfoxide (DMSO) and dimethylpropylene urea (DMPU). The softening temperatures of different EB range from 87.8-116.4 °C, which is believed to be an indication of cross-linking. Conductivity of emeraldine base of PANI is around (0.8-1.5) × 10 -6 S/cm and energy band gap is approximately 0.5 eV, and no detectable crystallinity is observed. Wide-angle XRD technique indicates that PANI- EB base is amorphous in nature.
Science …, 2007
Samples of polyaniline (emeraldine salt) were prepared with different protonic acid dopants, namely, hydrochloric acid (HCl), nitric acid (HNO 3), perchloric acid (HClO 4), sulfuric acid (H 2 SO 4), and hydroiodic acid (HI). Using the two-point probe method, it was found that the samples had ohmic behaviors in which high linear coefficients were found in the range 0.9686-0.9997. On the other hand, the electrical conductivities were measured using the Van der Pauw method. The undoped sample had a conductivity of 5x10-4 S/cm. The highest conductivity of 109.04 S/cm was observed for the HClO 4-doped sample, while the lowest value (0.02 S/cm) was obtained for the HI-doped sample. These conductivities were compared with the computed energy gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) where it was found that they are inversely proportional to each other. Scanning electron microscopy revealed significant differences among the samples in terms of shapes and morphologies.
Journal of Molecular …, 2012
Emeraldine-salt polyaniline form (ES-PANI) was chemically synthesized using hydrochloric acid at time synthesis ranging from 0.5 to 48h and characterized by X-ray Diffraction (XRD), LeBail Fit, Small-angle X-ray Diffraction (SAXD), Small-angle X-ray Scattering (SAXS) and Scanning Electron Microscopy (SEM). Crystallinity and crystal data (a=5.7122, b=17.8393, c=22.8027, α=83.1575, β=84.6971 and γ=88.4419) were obtained by XRD and showed that the crystallinity did not vary with the time synthesis. LeBail fit revealed that the crystallites were very small lamellae with global average size around 39 Å. By SAXS it was obtained the particle Radius of Giration (R g ) of 320 Å. The maximum particle size (D max ) of 650Å was obtained from the Pair-distance distribution Function (p(r)). SEM images showed a fiber morphology formed by interconnected non homogeneous nanospheres. Electrical conductivity of the samples was in ~1.84.10 -4 S/cm.
Synthetic Metals, 2004
The pH sensitivity of polyaniline (PANI) membranes containing potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (KTFPB), potassium tetrakis(4-chlorophenyl)borate (KTpClPB), cesium carborane (Cs-carborane), tetradodecylammonium tetrakis(4-chlorophenyl)borate (TDATpClPB, ETH 500) or tridodecylmethylammonium chloride (TDMACl) as the lipophilic additive have been studied in this work. It is shown with UV-Vis spectroscopy, potentiometry, energy dispersive X-ray analysis (EDXA) and dc conductivity measurements that the PANI membrane containing 30% (w/w) of the anionic additive KTFPB is in the electrically conducting emeraldine salt (ES) form still at pH 9 and that the film is insensitive to pH between 2 and 9. The reason for the unusual pH insensitivity is probably that the TFPB − anions prevent the pH dependent ES-emeraldine base (EB) transition from occurring by hindering the acid anions to leave the polymer chains and in this way locking PANI in the ES form.
Polyaniline Emeraldine Salt (PAni-ES) was synthesized using standard oxidative polymerization. The resulting PAni-ES powder was deprotonized using Ammonium Hydroxide to yield Polyaniline Emeraldine Base (PAni-EB), processible form of PAni. The PAni-EB powder was dissolved using N-methylpyrrolidone and casted into film on a glass substrate. The resulting films were thermally aged near the reported glass transition temperature at 65 0 C. The ageing time was 5 to 60 minutes with a five-minute interval. The unaged sample was used as control. Fourier Transform Infrared Spectroscopy results showed decreasing Quinoid characteristics upon ageing which is consistent with chemical crosslinking. X-ray Photoemission Spectroscopy with Synchrotron Radiation as source showed an increase of CO attributed to sample oxidation. Sample morphologies were characterized using Atomic Force Microscope and Scanning Electron Microscope. It was found out that the surface smoothened and the size of the pinholes decreased with ageing time. These observations are consistent with crosslinking as well. The doped PAni films from the aged samples showed an increase in conductivity up to a maximum value of 2.75 S/cm. This was found from the sample aged at 35 minutes. One of the reasons for this is a better surface morphology induced by ageing that favors electrical conduction. The decrease in conductivity after the optimum value is attributed to a more dominant decrease in conjugation of the chains. The results suggest that thermal treatment of PAni-EB films prior to doping yields to optimizing electrical property of the doped form. ABSTRAK Polyaniline Emeraldine Salt (PAni-ES) was synthesized using standard oxidative polymerization. The resulting PAni-ES powder was deprotonized using Ammonium Hydroxide to yield Polyaniline Emeraldine Base (PAni-EB), processible form of PAni. The PAni-EB powder was dissolved using N-methylpyrrolidone and casted into film on a glass substrate. The resulting films were thermally aged near the reported glass transition temperature at 65 0 C. The ageing time was 5 to 60 minutes with a five-minute interval. The unaged sample was used as control. Fourier Transform Infrared Spectroscopy results showed decreasing Quinoid
Transport studies of emeraldine salts protonated by phosphoric acids
Synthetic Metals, 1996
Electrical transport properties of polyaniline prepared by chemical oxidative polymerization in the presence of phosphoric acid were investigated by low temperature conductivity and thermoelectric power measurements. As the ratio of acid to aniline is optimized (Z= 6) at the stage of polymerization, the freshly prepared emeraldine salt form of the polyaniline shows (i) relatively high electrical conductivity, c-40 S/cm at room temperature, (ii) temperature dependence of the conductivity characteristic of the variable range hopping (VRH), In c a-(To/T)', with exponent x = l/3, and (iii) linear temperature dependence of the thermoelectric power. As the molar ratio Zdecreases from 6 to 1, the VRH exponent n systematically changes from l/3 to l/2 and the thermoelectric power decreases from + 7.6 to + 0.2 uV/ K. The systematic variation of the transport parameters obtained from the temperature dependence was attributed to combined contributions from the metallic transport and VRH process in the disordered polymeric system.
Effect on Poly(C6H5NH2) Emeraldine Salt by FeCl3 and KMnO4 as Secondary Dopants
Polyaniline in its emeraldine salt form was synthesized by chemical method from aniline monomer in the presence of HCl mixed with LiCl and Ammonium-persulphate (APS) as oxidant. Then a portion of samples was de-doped with NH3 solution and another equal portion was separately post doped with secondary dopants such as FeCl3 and KMnO4 respectively. Finally the dried samples of polyaniline prepared in all its three different forms were characterized by ultraviolet – visible (UV-Vis) spectroscopy, Fourier- Transform Infrared (FTIR) spectroscopy and electrical conductivity measurement. FT-IR and UV-Vis spectra confirmed the expected structural modification upon doping, undoping and post doping processes of the polymer. The influences of secondary doping on the electrical conductivity were also investigated from their spectroscopic data and the dramatic rise in conductivity was said to be induced from the secondary doping is attributed by structural rearrangement from a compact-coil form o...