Thermal stability of polyaniline (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.
Thermal treatment and dynamic mechanical thermal properties of polyaniline
Polymer, 2002
Thermal transitions of polyaniline in the emeraldine base form (Pani-EB) were studied by DMTA using two series of thermally treated samples. In the first series the specimens were annealed at 70 8C for 5, 15 min, 1 and 3.5 h. In the second they were submitted to annealing at 100 8C during the same periods of time plus a 24 h treatment. Two transitions were observed at sub-zero temperatures and were attributed to the motion of solvated water and solvent (NMP). The glass transition and the highest temperature relaxation, assigned to crosslinking depended on the degree of solvation resulting from the thermal treatment. A linear contraction of Pani-EB films with residual water evaporation was reported for the first time. q
Polyaniline Conducting Electroactive Polymers Thermal and Environmental Stability Studies
E-Journal of Chemistry, 2006
In the current studies, polyaniline (PANi) was prepared both chemical and electrochemically in the presence of different bronsted acids from aqueous solutions. The effect of thermal treatment on electrical conductivity, and thermal stability of the PANi conducting polymers were investigated using 4-point probe and TGA techniques respectively. It was found that polymer prepared by CV method is more thermally stable than those prepared by the other electrochemical techniques. In this paper we have also reviewed some fundamental information about synthesis, general properties, diverse applications, thermal and environmental stability of polyaniline conducting polymers.
Experimental procedures for assessing electrical and thermal conductivity of polyaniline
Fundamentals and Emerging Applications of Polyaniline, 2019
Conductive polymers, based on their redox state and dopant strength, exhibit a vast range of conductivity from metallic to insulator, mostly applied as semiconductors. In general, conductive polymers are not thermoformable; they are organic materials like insulatingpolymers. They can offer a high electrical conductivity, but do not necessarily reveal similar mechanical features in comparison with other commercially available materials. The electrical properties of PANI are to a large extent adjusted for specific usage. Since conducting polymers like PANI have backbones of adjacent sp2 hybridized carbon centers, they provide one valence electron on each center in a pz orbital orthogonal to the other three sigma bonds, which are combined with each other to a set of orbitals of wide delocalized molecules. The presence of highly mobile electrons in the delocalized state of a “doped” condition resulting from oxidation causes the removal of some of the delocalized electrons. As a result, the conjugated p-orbitals form a one-dimensional electronic band in assist, with electrons within such band becoming mobile when it is partially emptied. The band structures of a conductive polymer can be easily calculated with a tight-binding model based on the wave function set of isolated atom superposition. In principle, the reduction process is used for doping such materials for which unfilled bands are loaded by electrons. In practice, p-type semiconductors are commonly prepared by oxidative doping.
Thermally processable conducting polyaniline
Synthetic Metals, 1995
Protonation of polyemeraldine base with aryl phosphoric acid diesters have been studied with the main goal to obtain thermally processable conducting polymers. Polyaniline protonated with aryl diesters exhibits excellent thermal properties. Since diesters plasticize polyaniline in addition to its protonation conductive blends of PANI and plasticized PVC with low (ca. 6 wt%) percolation threshold can be prepared by hot pressing.
Effect of Elevated Temperature on the Reactivity and Structure of Polyaniline
Macromolecules, 2002
The structure and oxidation state of emeraldine base polyaniline (PANI) in N-methylpyrrolidinone solutions that have been heated to 120-190°C have been characterized by solid-state NMR, UV/vis, FTIR, and GPC. The spectroscopic studies reveal that the polymer is completely converted to its fully reduced leucoemeraldine form after heating at 175-190°C for only 2 h, and bubbling oxygen gas through the solutions after heating results in partial reoxidation of the polymer. Cross-links, consisting of phenazine structures, have been identified in PANI films cast from heated NMP solutions by 15 N interrupted decoupling solid-state NMR. After heating, the polymer is partially cross-linked with the cross-link density increasing with annealing temperature, and the non-cross-linked regions are the reoxidizable portions of the polymer. A mechanism by which the cross-linking reaction of PANI leads to the polymer reduction is discussed. Scheme 3. Structure of PANI Generated in Heated NMP Solutions 7580 Mathew et al.
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
Journal of Molecular Structure, 2017
Emeraldine-salt polyaniline form (ES-PANI) was chemically synthesized using hydrochloric acid and subjected to heat treatment for 1 h at 50, 100, 200 and 300 °C. X-ray Diffraction (XRD), Le Bail method, Infrared-transform Fourier Spectroscopy (FTIR), Small-angle X-ray Scattering (SAXS), Scanning Electron Microscopy (SEM) and Electrical Conductivity measurements were used to evaluate the influence of heat treatment on the semi-crystalline structure of PANI. The heat treatment has resulted in a progressive decrease of crystallinity from 50 to 22%. A crosslinking process during heat treatment was observed by FTIR at 200 °C, revealing some chemical changes in molecular structure of PANI such as elimination of HCl on the imino groups and the simultaneous chlorination of the aromatic rings. Le Bail method showed that unheated ES-PANI is strongly dependent on the molecular size of the counter ion, so the unit cell volume needed to be increased for their accommodation in polymer structure. The refined parameters suggested decomposition from tetrameric to dimeric-folded chains, accompanied by a decrease in the crystallite anisotropy and average size and shape, which reduced from 36 Å to 16 Å and acquired oblate shape. The pair-distance distribution function (p(r)) curves suggested particles tending from oblate to prolate form over heat treatment. Well-defined nanofibers were observed in unheated ES-PANI, which decreased and lost progressively their initial morphology over heat treatment. Electrical conductivity showed a decreasing of about 90% due to the loss of emeraldine sequences and to the removal of chloride ions.
Thermo-analyses of polyaniline and its derivatives
Thermochimica …, 2010
In this work, is presented the thermal behavior of polyaniline (PANI) and its derivatives poly(oethoxyaniline) (POEA) and poly(o-methoxyaniline) (POMA), which were studied by using differential scanning calorimetry (DSC), modulated DSC (TMDSC), respectively, and thermal gravimetric analysis (TGA). The results from diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and thermal analysis showed the formation of crosslinking isomerization reaction during the heating process. The results showed that the maximum weight loss and the crystallinity degree depend on the type of the aromatic ring substituent group, i.e. hydrogen, ethoxy or methoxy.
Journal of Polymer Research, 2011
Conductive polyaniline has been prepared by solid-solid reaction using ammonium peroxydisulfate as an oxidant. The obtained polymer was examined by X-ray diffraction, UV visible, FTIR spectroscopy, thermogravimetric analysis and impedance spectroscopy. The effect of oxidant/ monomer molar ratio (R) on the structure and electrical properties of polymer has been examined. The analyses of X-ray diffraction patterns demonstrated that polyaniline prepared by this method is more crystalline than that obtained by conventional solution method. The FTIR spectroscopy showed that the emeraldine salt has been formed. The electrical properties were measured at different temperatures in the range of 296-523 K. The ac conduction shows a regime of constant dc conductivity at low frequencies and a crossover to a frequency-dependent regime of the type A ω S at high frequencies.