Electrical and structural analysis of conductive polyaniline/polyacrylonitrile composites

Conducting composites of polyacrylonitrile (PAN) copolymer containing 10% mass ratio methylacrylate and dodecylbenzene sulfonic acid doped polyaniline (PANI-DBSA) were prepared by solution blending. Electrical properties of the blends were characterized by means of electrical conductivity measurements and the phase structures were investigated via scanning electron microscopy (SEM), X-ray diffraction (XRD), FT-IR spectroscopy, differential scanning calorimetry (DSC) and dynamical mechanical analysis (DMA). It was found that the electrical conductivity of the composites increased with the increase of PANI-DBSA content and the percolation threshold lay around 3.2 wt%. DSC and DMA measurements showed that there was only one T_g for each blend and the values of T_g varied with the PANI-DBSA content, implying that the PANI-DBSA/PAN blend was at least partially compatible. The formation of the hydrogen bonding between the carbonyl groups in PAN copolymer and the imine groups in PANI-DBSA was identified by the FT-IR spectra. XRD demonstrated that the intrinsic layered arrangement of PANI-DBSA was disaggregated in the blends. Nanosize network structure of PANI-DBSA dispersing in PAN matrix and the so-called phase reverse occurring in the skin layer of the film samples at low PANI-DBSA loading were observed by SEM.     

Thermal degradation of polyaniline films prepared in solutions of strong and weak acids and in water - FTIR and Raman spectroscopic studies

Polyaniline (PANI) films were prepared in situ on silicon windows during the oxidation of aniline with ammonium peroxydisulfate in aqueous solutions of strong (0.1 M sulfuric) or weak (0.4 M acetic) acid or without any acid. In solutions of sulfuric acid, a granular PANI is produced, in solutions of weak acids or without any acid, PANI nanotubes are obtained. The thermal stability and structural variation of the corresponding films produced on silicon windows during treatment at 80 °C for three months were studied by FTIR and Raman spectroscopies. The morphology of the films is preserved during the degradation but the molecular structure changes. The results indicate that the spectral changes correspond to deprotonation, oxidation and chemical crosslinking reactions. The films of PANI salts loose their protonating acid. PANI bases are more stable than the salt forms during thermal ageing. The films obtained in water or in the presence of acetic acid are more stable than those prepared in solutions of sulfuric acid. The protonated structure is more prone to crosslinking reactions than deprotonated one. The molecular structure corresponding to the nanotubular morphology, which contains the crosslinked phenazine- and oxazine-like groups, is more stable than the molecular structure of the granular morphology.     

Conformational transition in polyaniline films - Spectroscopic and conductivity studies of ageing

Polyaniline films were produced in situ at room temperature from aniline hydrochloride oxidized with ammonium peroxydisulfate on glass surfaces immersed in an aqueous reaction mixture. A notable change in the character of the time dependence of resistivity at fixed temperature was observed when the temperature of ageing exceeded 85 °C. The ageing was much faster above this limit. This observation is reflected in the FTIR spectroscopic measurements on the aged protonated, as well as deprotonated, samples. The FTIR spectral variation may be explained by a conformational transition of the polymer chain at about 85 °C. The fact that a similar transition has been found with deprotonated samples indicates that this feature is an inherent property of polyaniline, and is not caused by the acid component of the PANI salt.     

Biofouling resistant polyethylene cage aquaculture nettings: A new approach using polyaniline and nano copper oxide

Biofouling in cage aquaculture netting causes clogging of meshes, increased stress and retards the growth of fishes. This paper describes a new method of protecting polyethylene cage nettings from biofouling using polyaniline and nano-copper oxide. Polyaniline was synthesized in-situ over polyethylene cage netting material and subsequently treated with nano copper oxide. The modified netting material exposed to estuarine environment exhibited excellent fouling resistance. FTIR characterization confirmed the formation of polyaniline and adsorption of nano copper oxide over the netting material. SEM and AFM evaluation showed uniform coating of polyaniline and nano copper oxide on the polyethylene-polyaniline (PE-PANI) matrix. The results highlight the potential application of polyaniline plus nano copper oxide coated polyethylene nettings in controlling biofouling in cage aquaculture.     

Thermal transition of electrochemically synthesized polyaniline

The thermal stability of polyaniline (PAni) is of great importance in commercial applications. PAni and its emeraldine base form (PAni-EB) were electrochemically synthesized and subjected to thermogravimetric analysis (TGA) in inert atmosphere, which illustrated that the dopant HClO₄ could act as the oxidizing agent at elevated temperature and caused serious decomposition of PAni. Combined with differential scanning calorimetry (DSC), in-situ X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) analyses, the crosslinking reaction among PAni-EB molecules at about 250 °C was characterized, and the kinetic parameters were calculated by applying different heating rates in the DSC measurement.     

The effect of a polypyrrole coating on the thermal stability of microporous polyethylene membranes

Microporous polyethylene (PE) membranes were coated on both sides with a polypyrrole (PPy) overlayer. PPy was deposited also on the walls of pores. Thermodeformation measurements indicate that the hard framework produced by rigid-chain PPy controls the mechanical properties of composite membranes. FTIR spectroscopy was used to detect oxidative processes in both polymer components above 200 °C. Elemental analysis showed that the nitrogen content remains at high level, even after the treatment of membranes in air at 300 °C, indicating that the decomposition involved mainly PE while PPy was much more stable. The changes in surface relief after annealing were assessed with electron microscopy. No oxidative processes were identified in the FTIR spectra of composites after annealing in vacuum, even after treatment at 300 °C.     

Synthesis and characterization of red mud/polyaniline composites: Electrical properties and thermal stability

New types of conducting composites using red mud as an inorganic substrate and polyaniline as the conducting phase were prepared. Red mud/polyaniline (RM/PANI) composites were synthesized in acidic aqueous solution by the chemical oxidative polymerization of aniline using ammonium peroxydisulfate as the oxidant. The composites exhibit conductivities in the 0.42-5.2 S cm⁻¹ range, depending on the amount of polyaniline. They were characterized by infrared and UV-vis spectroscopy, scanning electron microscopy and X-ray diffraction. The IR and X-ray results show that PANI is deposited on the RM surface. The composites have a globular structure and the PANI globules synthesized on the surface of RM are smaller than those prepared under the same conditions without the substrate. Thermogravimetric analysis was used for investigation of the thermal stability of the composites. The thermal stability of the conductivity of RM/PANI composites was studied by ageing at 125 °C, the conductivity being measured in situ during this process.     

Thermal stability of plasma deposited polysilanes

A new method for studying thermal stability and concomitant chemical composition changes on thermal treatment of thin polymeric films is presented. It is applied to the study of thermal properties and modification of properties of polysilane-like materials with variable dimensionality prepared by radio frequency plasma enhanced chemical vapour deposition (CVD). Structure and microphysical properties of these materials, modified by progressive annealing, are examined by fluorimetry, FTIR absorption spectroscopy and XPS. In addition, the role, bonding conditions and structural environments of organic moieties as well as their influence on thermal degradation processes are examined. It is found that plasma polysilanes undergo three consecutive thermal degradation processes: Si-Si bond cleavage, elimination of side groups and final carbide formation. Presence of disorder and crosslinking stabilises the plasmatic material in comparison to classically prepared polysilanes. Nanostructural units in low dimensional polysilanes enable the peak of the luminescence to be adjusted in the spectral range from near UV (360 nm) to red (600 nm).     

Spectroscopic characterization of the structural changes of polyaniline nanofibers after heating

The thermal behavior of PANI nanofibers doped with β-naphthalenesulfonic acid (β-NSA) was investigated and their morphological and structural changes after heating were monitored by SEM, XRD and Raman techniques, respectively. By using electron-scanning microscopy it is possible to verify that the nanofiber morphology is stable and no polymer degradation is observed in thermogravimetric (TG) data up to 200 °C. Nevertheless, the heating promotes the formation of cross-linking structures (phenazine and/or oxazine-like rings), that is clearly demonstrated by the presence of bands at ca. 578, 1398, and 1644 cm⁻¹ in resonance Raman spectra of heated PANI-NSA samples. The most important consequence of the formation of cross-linking structures in PANI-NSA samples is that these samples retain their nanofiber morphology upon HCl doping in contrast to PANI-NSA nanofibers without heating.     

Thermal degradation mechanism of dodecylbenzene sulfonic acid- hydrochloric acid co-doped polyaniline

Co-doped polyaniline (PANI) was synthesized in microemulsion by hydrochloric acid (HCl) and dodecylbenzene sulfonate (SDBS) then thermal treated in air at 160 and 200 °C for 0.5 h, respectively. The changes of structure, thermal stability, micromorphology and electrical conductivity after thermal treatment were studied by Fourier transformed infrared (FT-IR), Thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscope (SEM) and four-probe technique. It was found that the conductivity of PANI decreased about 50% after thermal treated at 160 °C, and droped by 2 orders of magnitude at 200 °C. This may be explained by that only a fraction of total mass of HCl losses during thermal treatment at 160 °C, but after heating at 200 °C, the dedoping of dodecylbenzene sulfonic acid (DBSA) along with cross-linking, chain scission and oxygen incorporation in a form of carbonyl groups take place, resulting in destruction of crystal structure, decrease of the emeraldine sequence, lower thermal stability and heterogeneous micromorphology.     

Thermal properties of high density polyethylene composites with natural fibres: Coupling agent effect

High density polyethylene composites with curaua fibres were prepared using an intermeshing co-rotating extruder and two different coupling agents. The thermal stability of the components was studied by thermogravimetric and differential scanning analysis, as well as by the oxidation induction time. Maleic anhydride grafted polyethylene, used as coupling agent, affected the composite stability more markedly than did poly(ethylene-co-vinyl acetate). However, oxidation induction times were analogous for composites with and without coupling agents. Results also indicated that a higher fibre-matrix interaction precludes the crystallinity enhancement caused by the fibre.     

Influence of the preparation procedure on the properties of polyaniline based magnetic composites

A versatile process for the preparation of composite films consisting of magnetite (Fe₃O₄) nanoparticles embedded in a polyaniline (PANI) matrix is reported. Spectroscopic properties of polyaniline matrix (PANI-EB), polyaniline protonated with camphor sulfonic acid (PANI-CSA_0.5) PANI-ES and PANI/Fe₃O₄-CSA_0.5 composites were studied, both in the state of the solutions of m-cresol and in thin films processed from the same solvents. The results of these studies indicate that m-cresol can be used for PANI/Fe₃O₄ composite preparation. Such films show both reasonably high electrical conductivity and magnetic permeability. A controlled application of a magnetic field during the casting process resulted in the formation of the materials with an unusual combination of magnetic and transport properties. The obtained films show the behavior that can be explained by the presence of both ferromagnetic and paramagnetic phases. The superparamagnetic contribution, if any, is very small. Application of the external magnetic field during fabrication of the composites stimulates creation of the aggregates of magnetic particles which, although keeps conductivity at a relatively high level, leads to a small decrease of the conductivity value.     

Preparation,characterization and application of polyaniline/epoxide polysiloxane composite films

Composites of polyaniline(PAn) and epoxide polysiloxane(EPSi) are reported for the first time. EPSi is designed, synthesized and N-grafted onto the PAn backbone through covalent bonds. As-prepared EPSi-g-PAn composites are soluble in organic solvents and the corresponding films can be easily produced via a simple solution-casting procedure. The composite films combine the mechanical characteristics of EPSi and the chemical properties of PAn, enabling the facile introduction of the noble metal particles. The successful fabrication of the composites is confirmed by the investigation of the molecular structure, crystalline structure and microstructure of the materials. The resulting composite films containing noble metal particles are employed as the catalysts for the hydrogenation of phenol to produce cyclohexanone, which exhibit the convenience and recyclability for usage as well as the high catalytic activities, including the conversion ratio of 97%-100% and the selectivity as high as 84%-98%. The present work not only provides a new method to improve the processability of the conducting polymers but also describes a kind of composite materials that may display outstanding preformances in industrial catalysis.     

Thermal degradation of biodegradable edible films based on xanthan and starches from different sources

Films based on xanthan/wheat starch and xanthan/maize starch were prepared in different proportions and analysed in terms of thermal stability in relation to the degradation reaction in an inert atmosphere. The main gaseous decomposition products were identified by infrared spectroscopy. Xanthan was found to be less thermally stable than starch from different sources. The starch addition to xanthan induced an increase in the film thermal stabilities. The thermal degradation mechanism of xanthan starts with scission of the side chain groups with subsequent scission of the main chain. Starches from maize and wheat presented a constant mechanism of thermal degradation. The proportion of xanthan/starch (50/50) presented a synergistic behaviour which may be associated with changes in the mechanism of the thermal degradation process. The FTIR spectra of the gaseous products during thermal degradation of xanthan showed a broad absorption in the 2750–3300 cm⁻¹ region, probably indicating decomposition of β-d-mannopyranosyl groups, present in xanthan side chains. For pure starches, absorptions related to alcohol O–H stretching (3500–3750 cm⁻¹), CO stretching of CO₂, CO and carbonyl compounds (2361, 2177 and 1743 cm⁻¹, respectively) were observed. For xanthan/starch mixtures (50/50) the same compounds as those for the pure polymer degradation were evolved. However, a shift of the CO to higher wavenumber values indicates that new carbonyl compounds are being formed due to changes in the thermal degradation mechanism.     

Thermal oxidation products and kinetics of polyethylene composites

The thermal oxidation behavior of high-density polyethylene (HDPE) composites was investigated at 60 °C, 90 °C and 110 °C, using Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The inorganic fillers do not modify the thermal oxidation mechanisms of HDPE. However, they have great effects on the thermal oxidation kinetics—both the activation energy and the pre-exponential factor increase. That means that although the addition of inorganic fillers retards the onset of thermal oxidation of HDPE, once the oxidation begins, it proceeds much faster than that of HDPE. Stability evaluation of HDPE composites by TGA was not consistent with the result by FTIR. The inorganic fillers influence the oxidation products and their distribution greatly. HDPE/STC and HDPE/mica oxidations were delineated by large amount of carbonyl formation, especially esters and ketones, while HDPE/wollastonite and HDPE/diatomite showed minimum carbonyl formation. In HDPE composites, there is a good relation between the carboxylic formation and the carbonyl index.     

Light scattering of polyaniline films responding to electrochemical switching

When a laser with 543, 668 or 790±50 nm was used to irradiate the reduced polyaniline film on an indium tin oxide electrode in hydrochloric acid, the light was scattered in all directions. The intensity of the scattered light decreased with increase in the detection angle up to the right angle. When the electrode potential was scanned between the insulating and the conducting domain, the intensity varied sigmoidally with hysteresis. The intensity increased with a decrease in the absorbance. The scattering of the light can be ascribed to multiple reflection, luminescence, or Rayleigh scattering. The spectra of the scattered light was identical with that of the incident light, suggesting the absence of luminescence. The intensity increased with an increase in thickness of the film, indicating a negligible contribution of multiple reflection. Since the volume of the oxidized film is larger than that of the reduced one, the film synthesized in the oxidized state is deformed by the electrode reduction. Then, the film density becomes locally inhomogeneous and this may give rise to the Rayleigh scattering. The potential-variation of the light scattering occurred at a more negative potential than that of the absorbance at 310 nm and of the current did.     

Thermal stability study of conductive polyaniline/polyimide blend films on their conductivity and ESR measurement

Conductivity stability at thermal environment of conductive polyaniline‐complexes/polyimide (PANI‐complexes/PI) blends, which were doped by camphorsulfonic acid (CSA) and dodecylbenzenesulfonic acid (DBSA), respectively, were investigated by conductivity measurements, electron spin resonance (ESR) spectra, differential and scanning thermometer (DSC). In the conversion process of PANI/Polyamic acid (PAA) to PANI/PI, the blend endeavored some kinds of alteration such as decomplexation of moisture and solvent, dissociation of dopant, crosslinking of PANI chain, and the imidization of PAA chain. PANI‐DBSA/PI showed higher thermal stability of conductivity than PANI‐CSA/PI, and both samples showed nearly linear decay of conductivity with increasing temperature showing greatly enhancement of conductivity stability. When they were exposed at near or over glass transition temperature, the conductivity decay became faster. The conductivity stability at base environment was also higher for PANI‐DBSA/PI due to difficulty in accessing of hydroxyl ion to PANI, which were resulted from dopant. DBSA‐doped blends showed increased polaron mobility and concentration at relatively high temperature, which led to extremely higher conductivity and its stability at high temperature. Copyright © 2002 John Wiley & Sons, Ltd.     

Thermal and environmental stability of poly(4-ethynyl-p-xylylene-co-p-xylylene) thin films

The aim of this paper was to test the thermal and environmental stability of poly(4-ethynyl-p-xylyleneco-p-xylylene) thin films prepared by chemical vapor deposition(CVD) and to optimize the reaction conditions of the polymer.Fourier transformed infrared spectroscopy(FTIR),thermogravimetric analysis(TGA) and fluorescence microscopy were employed to investigate the stability of the reactive polymer coatings in various environmental conditions.Chemical reactivity of the thin films were then tested by Huisgen 1,3-dipolar cycloaddition reaction(‘‘click' reaction).The alkyne functional groups on poly(4-ethynyl-p-xylylene-co-p-xylylene) thin films were found to be stable under ambient storage conditions and thermally stable up to 100 8C when annealed at 0.08 Torr in argon.We also optimized the click reaction conditions of azide-functionalized molecules with poly(4-ethynyl-p-xylylene-co-p-xylylene).The best reaction result was achieved,when copper concentration was 0.5 mmol/L,sodium ascorbate concentration to copper concentration was 5:1.In contrast,the azide concentration and temperature had no obvious effect on the surface reaction.     

Thermal stability of magnesium-rich primers based on glycidyl carbamate resins

Coatings of outstanding thermal stability were obtained by the combination of two novel technologies, that of a magnesium-rich primer and a silane-modified glycidyl carbamate binder. While conducting a study to evaluate the new binder system with respect to properties of the magnesium-rich primer, during thermogravimetric analysis of samples, previously unobserved and unexpected properties were noted. The samples transformed into an intact solid residue, with the amount of the residual char ranging between 40 and 90% weight depending on the pigment volume concentration (PVC) of the magnesium particles in the composition. It appears that the hitherto unobserved property is essentially a function of the metallic pigment particles in the coating. The discovery of the exceptional thermal stability potentially increases the range of application for these primers and these can be further developed for use as a thermal barrier coating.     

Comparison of the biodegradability of various polyethylene films containing pro-oxidant additives

The biodegradability of high density polyethylene films (HDPE), low density polyethylene films (LDPE) and linear low density polyethylene films (LLDPE) with a balanced content of antioxidants and pro-oxidants (manganese + iron or manganese + iron + cobalt) was studied. Abiotic pre-treatment consisting of photooxidation and thermal oxidation corresponding to about three years of outdoor weathering (including 3-4 months of exposure to daylight) was monitored by FTIR and SEC measurements. The oxidized samples were then inoculated with the strain Rhodococcus rhodochrous in mineral medium, and incubated up to 180 days. The metabolic activity of the bacteria was assessed by measuring adenosine triphosphate content (ATP) and the viability of the cells. Complementary experiments were performed by ¹H NMR spectroscopy to monitor the biodegradation of soluble molecules excreted from the polymer in the incubation medium. Finally SEM was used to visualize the formation of a biofilm at the surface of the polymer. Three samples among the 12 tested were investigated in compost and soil environments. The results show that the main factor controlling the biodegradability of the polyethylene films is the nature of the pro-oxidant additive and to a lesser extent that of the matrix. Except for the samples containing very high content of cobalt additive, the various polymer films were used as substrates by the bacteria.