Polyaniline prepared in ethylene glycol or glycerol

Oxidations of aniline or aniline hydrochloride have been carried out in ethylene glycol or glycerol and in their mixtures with water. Ammonium peroxydisulfate was used as oxidant. The oxidation of aniline is exothermic and changes in temperature were monitored to follow its progress. The effect of the solvents on the course of oxidation, morphology, and properties of final products has been studied by scanning electron microscopy, FTIR spectroscopy, and conductivity measurements. It is proposed that the reduction of dielectric constant of the reaction medium results in the reduced dissociation of ionic species that take a part in oxidative polymerization. Consequently, the addition of an organic solvent has a similar effect as a decrease in the acidity of the reaction mixture. Conductivity and morphology depend on the mole ratio of oxidant and monomer, and the type and volume fractions of organic solvents, viz. ethylene glycol and glycerol, which were used in reactions.     

Polyaniline and polypyrrole prepared in the presence of surfactants: a comparative conductivity study

Polyaniline and polypyrrole have been prepared by chemical oxidative polymerization of the corresponding monomers in an aqueous medium containing an anionic surfactant—sodium bis(2-ethylhexyl) sulfosuccinate, dodecylbenzenesulfonic acid and its sodium salt, and sodium dodecyl sulfate. Determination of the yield, elemental composition and density proved, and FTIR spectroscopy confirmed, that the anionic surfactants become incorporated in the conducting polymers. The polymerizations in the presence of a cationic surfactant, tetradecyltrimethylammonium bromide, were carried out for comparison. While the conductivity of polypyrrole became enhanced after the introduction of an anionic surfactant, the changes in the conductivity of polyaniline were marginal. The conductivity changes in both polymers during thermal ageing were measured at 175 °C. The electrical stability of polyaniline was better than that of polypyrrole. The presence of a surfactant improved the stability of conductivity of polypyrrole but reduced the electrical stability of polyaniline.     

Polyaniline as corrosion inhibitor for iron in acid solutions

In recent years, polymer amines have been studied as an efficient corrosion inhibitor for iron in acid media. In this article, the performance of water soluble polyaniline as corrosion inhibitor for iron in 0.5M H₂SO₄ has been evaluated by potentiodynamic polarization, linear polarization, and electrochemical impedance spectroscopy and compared with the performance of the aniline monomer. It has been found that polyaniline is an efficient inhibitor, since the maximum efficiency of 84% has been observed at a concentration of 100 ppm, whereas the monomer has accelerated the corrosion. FTIR studies have shown that the polyaniline is strongly adsorbed on the iron surface and inhibits the corrosion effectively. However, aniline has been found to improve the passivation tendency of iron at higher concentrations. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2144–2153, 2006     

Photoluminescence emission of nanoporous anodic aluminum oxide films prepared in phosphoric acid

The photoluminescence emission of nanoporous anodic aluminum oxide films formed in phosphoric acid is studied in order to explore their defect-based subband electronic structure. Different excitation wavelengths are used to identify most of the details of the subband states. The films are produced under different anodizing conditions to optimize their emission in the visible range. Scanning electron microscopy investigations confirm pore formation in the produced layers. Gaussian analysis of the emission data indicates that subband states change with anodizing parameters, and various point defects can be formed both in the bulk and on the surface of these nanoporous layers during anodizing.     

Synthesis and Characterization of a Conducting Composite of Polyaniline,Poly(o-Anisidine), and Poly(Aniline-co-o-Anisidine)

A conducting composite of polyaniline, poly(o-anisidine), and poly(aniline-co-o-anisidine) using incorporation of TiO₂ and SiO₂ was prepared by electrochemical polymerization. The films were electropolymerized in a solution containing 0.1 M monomer(s), 1 M sulfuric acid as supporting electrolyte, and 10^?5 M TiO₂ and SiO₂ by applying a sequential linear potential scan rate of 50 mV/s between ? 0.2 and 1.0 V versus an Ag/AgCl electrode. The composites were characterized by cyclic voltametry, UV-visible spectroscopy, electrical conductivity, and thermogravimetric analysis. It was observed that the UV-visible peaks appeared in the region of the conducting emerladine salt phase. In an overall study, the polymers prepared using TiO₂ had a higher conductivity than those prepared with SiO₂; however, higher conductivity was observed for the polyaniline-TiO₂ conducting composite than for the other polymers. The composites did not lose their color at higher temperature and hence can be utilized as the conductive pigments required for antielectrostatic applications.     

Polyaniline-silver composites prepared by the oxidation of aniline with mixed oxidants, silver nitrate and ammonium peroxydisulfate: The control of silver content

Aniline was oxidized with mixtures of two oxidants, ammonium peroxydisulfate and silver nitrate, to give polyaniline-silver composites with variable content of silver in the composites. The presence of peroxydisulfate has a marked accelerating effect on the oxidation of aniline with silver nitrate. Oxidations in 1 M methanesulfonic acid produced composites in high yield. The molecular structure of the polyaniline was confirmed by UV-visible and FTIR spectra, and the polymeric character was established by gel-permeation chromatography. The content of silver varied between 0 and 70 wt.%. The silver nanoparticles were smaller than 100 nm. The conductivity of the composites was of the order of units S cm⁻¹. Only at high silver nitrate contents in the reaction mixture, the conductivity of products exceeded 100 S cm⁻¹. The conductivity of the composites sometimes increased after deprotonation of the polyaniline salt to a non-conducting base. Such conductivity behaviour is discussed in terms of the percolation model.     

Electrophoretic deposition of BaTiO3 thin films from stable colloidal aqueous solutions

Polycrystalline BaTiO₃ (BTO) thin films were electrodeposited on titanium foils from colloidal aqueous solutions of BTO nanoparticles which were synthesized by a hydrothermal process, under autogenous conditions. Two kinds of reactants have been studied: one involves an aqueous solution of titanium tetrachloride and barium hydroxide octahydrate without any added solvent, whereas the second was obtained by dispersing amorphous titanium oxide in different volumes of barium hydroxide aqueous solutions. The nanoparticles were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The particle size distribution (PSD) and the zeta potential measurements indicate that the colloids in the solution are polydisperse when using the first synthesis method, and they tend to be quasi monodisperse in the case of the second synthesis route. A porous microstructure of the electrodeposited films was detected by SEM. Finally, the dielectric properties of the BTO thin films were investigated.     

Supramolecular hydrogels of polyaniline-poly(styrene sulfonate) prepared in concentrated solutions

Polyaniline-poly(styrene sulfonate) (PAn-PSS) hydrogels have been synthesized via supramolecular self-assembly between positively-charged PAn chains and negatively-charged PSS chains. Phase diagram is plotted to systematically investigate the gelation conditions for the PAn-PSS system. A hierarchical porous microstructure consisting of oriented 1D nanofibers is observed in the hydrogels, and the phase structure, molecular structure and crystal structure are also characterized. Based on the investigation of a unique transformation of the hydrogels to colloidal particles in alkaline solutions, the electrostatic interaction is proposed to be the origin force for the gelation of the materials. Additionally, in comparison with conventional PAn-PSS colloids, as-prepared PAn-PSS hydrogels are demonstrated to possess improved capacitance performance, such as higher energy density, higher power density and better electrochemical stability. The present study gives valuable hints for achieving controlled fabrication of supramolecular materials with designed structures and outstanding properties.     

Polyaniline prepared in the presence of various acids: a conductivity study

Polyaniline (PANI) was prepared by the oxidation of aniline in the presence of various inorganic and organic acids at 20 °C and ?50 °C. When strong acids were used, the conductivity of the protonated PANI was typically 1–10 S cm^?1. The results indicate that the protonation of PANI in media containing carboxylic acids was achieved with the help of sulfuric acid produced during the reaction with ammonium peroxydisulfate. The conductivity of PANI prepared under such conditions was reduced. Partial benzene‐ring sulfonation has been proposed to explain the wide range in conductivity of PANI bases, 10^?11–10^?7 S cm^?1. The densities of the samples reflect the nature of the acid used. The densities of the corresponding PANI bases exhibit much less variation. Molecular weight and degree of crystallinity of PANI are higher when the polymerization is carried out at ?50 °C. The conductivity of the PANI is determined mainly by way of protonation. The effects of molecular weight and of crystallinity on PANI conductivity are marginal. Copyright © 2004 Society of Chemical Industry     

Adsorption efficiency of poly(malachite green) films towards oxidation of ascorbic acid

Thickness of poly(malachite green) films electropolymerized on a glassy carbon electrode surface, the concentration of ascorbic acid, pH value of the solution, and accumulation time were found to affect the adsorption-controlled anodic peak current of ascorbic acid on this polymer film coated electrode. Adsorption efficiency, defined as the ratio of the active sites in polymer films to the amount of adsorbed ascorbic acid molecules, was then proposed and estimated from the comparison of mathematically simulated cyclic voltammograms with experimental ones. The concentration of ascorbic acid is the greatest parameter affected the adsorption efficiency. Poly(malachite green) film electropolymerized on the glassy carbon electrode was found to be not totally active towards oxidation of ascorbic acid when the concentration of ascorbic acid is too high or when the poly(malachite green) film is too thick. The potential shift of ascorbic acid on the modified electrodes was also discussed.     

Poly(malachite green) film: Electrosynthesis, characterization, and sensor application

Poly(malachite green) films were synthesized electrochemically on the glassy carbon electrode in the potentiodynamic mode. The characterization and growth mechanism of as-prepared films were studied with FT-IR spectroscopy, UV-vis spectroscopy, cyclic voltammetry, chronocoulometry, and electrochemical impedance spectroscopy. Charge transfer and ion transport of poly(malachite green) films were investigated in the aqueous solutions with different types of supporting electrolytes. The poly(malachite green) film coated glassy carbon electrode showed catalytic ability towards ascorbic acid and dopamine. The difference of the anodic peak potential of ascorbic acid on the poly(malachite green) film modified electrode from that of dopamine was 180 mV. Based on their voltammetric responses, the poly(malachite green) film coated glassy carbon electrode was utilized as an electrochemical sensor for the content determination of ascorbic acid and dopamine simultaneously and separately in pharmaceutical and injections.     

Compressive thermal stress and microstructure-driven charge carrier transport in silicon oxycarbide thin films

This work correlates the charge carrier transport mechanism of silicon oxycarbide-based thin films with their morphology and thermal stress. Segregation of highly-graphitized carbon-rich, oxygen-depleted C/SiC areas homogeneously dispersed within an oxygen-rich C/SiOC matrix was seen on the 500 nm-SiOC thin films. Compressive biaxial stress induced by the mismatch with the Si-substrate thermal expansion coefficient was calculated at 109 MPa. Through Hall measurements, p-type carriers were shown dominating the SiOC film similar to monolithic samples. Thin films and monoliths have comparable carrier concentrations while the carrier mobility in SiOC thin films was 2 magnitudes higher than that of monolithic samples and is considered a consequence of the compressive thermal stress acting on the film. Improved conductivity of 16 S cm -1 is measured for the SiOC thin film sample which is assumed considering the enhanced carrier mobility alongside the reduced percolation threshold ascribed to the phase-separated morphology of the thin film.     

Polyaniline/PVAc blends: Variation with time of structure and conductivity of films cast from aqueous dispersions

Recently, a polymerization process of Anilinium‐Dodecyl Benzene Sulfonic Acid (DBSA) complex in an aqueous dispersion was developed in our laboratories. Simple mechanical mixing of the aqueous PANI–DBSA dispersion with a PVAc aqueous latex leads to highly conductive blends at low PANI–DBSA contents. The percolation threshold of the dried films is extremely low (∼0.5 wt %). The combined aqueous PVAc/PANI–DBSA dispersions exhibit a gradually decreasing electrical conductivity accompanied by a gradually increasing viscosity, with the storage time. However, an aged cast film from these blends maintains its electrical conductivity with time. These phenomena are associated with acidic hydrolytic reactions of the ester group, resulting in the formation of vinyl acetate–vinyl alcohol copolymer and evolution of acetic acid, and also the interaction of the DBSA surfactant with the PVAc, causing swelling and disintegration of PVAc particles. A chemical structural model describing these changes with storage time is suggested. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 760–766, 2001     

Polymer hollow particles: Encapsulation of phosphoric acid partial esters and morphology manipulation

The present work demonstrates the possible use of emulsion polymerization for fabricating structured-polymer particles which can store active materials. The hollow polymer particles were synthesized by multi-stage emulsion polymerization consisting of four main stages, (1) the preparation of alkali-swellable core latexes containing active materials, (2) first core-shell polymerization of a monomer mixture of methyl methacrylate (MMA), butyl acrylate (BA) and methacrylic acid (MAA), (3) second core-shell polymerization of styrene and (4) a neutralization stage. The morphology of synthesized capsules was observed by transmission electron microscopy (TEM). The size of the capsule prepared by standard recipe was around 300 nm and the polydispersity index was 0.024 representing that size distribution was highly monodisperse. The specific target material of encapsulation was the phosphoric acid partial ester. The amount of phosphoric acid partial ester encapsulated was determined by thermogravimetric analysis (TGA). From studies of encapsulation behaviors, it was found that the encapsulation efficiency and location of phosphoric acid partial ester in the interior of the particles were mainly dependant on its partition coefficient. In addition, the morphology of polymer capsule was manipulated by varying process parameters. The morphology changes, such as those of pore size and roughness of polymer shell, were characterized by scanning electron microscopy (SEM) and analysis of nitrogen adsorption and desorption isotherm. When neutralized with N,N′-dimethylethanolamine simultaneously during the styrene polymerization, the surface area of polymer capsule was increased drastically by about 5 times due to the formation of mesopores and the roughening of the surface on the hollow polymer shell.     

Electrosyntheses of free-standing and highly conducting polyselenophene films in an ionic liquid

The electrochemical polymerization of selenophene in a room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF₆) led to the formation of free-standing and highly conducting polyselenophene (PSe) films with an electrical conductivity as high as 2.3 S/cm, higher than PSe electrodeposited in conventional media. The polymerization rate was significantly improved as BmimPF₆ served as both the growth medium and an electrolyte. PSe showed good electroactivity and stability even in concentrated sulfuric acid. Infrared (IR) spectra confirmed the polymerization mainly through α-α′ coupling. Scanning electron microscopy results indicated the formation of smooth and compact PSe films.     

Crystallization of calcium sulphate hemihydrate in concentrated phosphoric acid solutions

We aim to show the existence of agglomeration by measuring and modelling secondary nucleation and crystal growth rates of calcium sulphate hemihydrate, CaSO₄-0.5 H₂O, in concentrated phosphoric acid solutions. Using a batch crystallizer we measured the evolution of the population density as a function of supersaturation, H₂SO₄ excess and stirring rates. All experiments were carried out at 90 °C in solutions at 40 wt.% of P₂O₅, simulating the usual conditions for crystallizing hemihydrate in the industrial processes of phosphoric acid production. Nucleation and growth rates were calculated from the population number densities, using the moments analysis method. A model is presented for describing the crystallization process of hemihydrate. It is shown that secondary nucleation and growth rates are quadratic functions of supersaturation. H₂SO₄ concentrations affect supersaturation but at the same supersaturation the growth rates are not significantly different. Nucleation is independent of the stirring rate, whereas growth rates are slightly affected for stirring rates up to 500 rpm. Taking agglomeration into account, the moments method fits very well the experimental data.     

Synthesis,characterization and nonlinear optical properties of plasma‐prepared poly(4‐biphenylcarbonitrile) thin films

A novel conjugated polymer, poly(4‐biphenylcarbonitrile) (PBPCN), was prepared using a plasma polymerization technique. The effect of the discharge power on the chemical structure and surface compositions of PBPCN thin films was investigated using Fourier transform infrared, UV‐visible absorption and X‐ray photoelectron spectroscopies. A femtosecond time‐resolved optical Kerr effect technique was applied to investigate the third‐order nonlinearity of the obtained plasma PBPCN thin films. For the first time, a non‐resonant optical Kerr effect and ultrafast response for the PBPCN thin films were observed. Copyright © 2006 Society of Chemical Industry     

Multilayer thin films of colloidal gold and silica nanoparticles: Effect of polyelectrolyte coating

The use of oppositely charged colloidal nanoparticles to build multilayered structures is an approach in thin film science. In this work, uniform spherical nano‐dispersions of gold (ca. 20 nm) and silica (ca. 30 nm) were synthesised with specific volume concentration to achieve colloidal stability. Exploiting the use of self‐assembly, multilayers of these oppositely charged nanoparticles were built using alternate coating with chitosan. Gold nanoparticles have strong optical absorption in visible region of electromagnetic spectrum resulting from its surface plasmon resonance. Silica nanoparticles have low refractive index and absorb light mostly in the ultraviolet (UV) region. The optical absorption band of the fabricated thin films extends from UV to visible region of the electromagnetic spectrum. The spectral characteristics of these thin‐film assemblies are a combination of thickness and the order of the layers in a stack. These films have potential applications as optical elements and in optoelectronics. © 2011 Canadian Society for Chemical Engineering     

Dopant macroinitiator for electropolymerisation and functionalisation of conducting polymer thin films

Grafting of polymer brushes from conducting polymer (CP) thin films by controlled radical polymerisation provides a versatile route for the synthesis of functional, electroactive surfaces, with applications in diverse fields. However, one of the drawbacks of this approach is the difficulty of upscaling the synthesis due to the need for specialised CP precursor monomers functionalised with initiation sites. We herein describe an alternative approach to the synthesis of CP‐based polymer brushes whereby atom transfer radical polymerisation initiation sites are attached to a macrodopant incorporated into CP films during electropolymerisation. The facile electropolymerisation of commonly studied CPs with an initiator‐functionalised macrodopant – poly[(styrene sulfonate)‐co‐(2‐bromopropionyloxyethyl methacrylate)] – is demonstrated. The composite polymer films thus synthesised were used as substrates for grafting of hydrophilic polymer brushes. Although poly(styrene sulfonate) is commonly used as a macrodopant in CP films, its initiator‐functionalised derivatives have not previously been utilised in this manner. Despite the elegance of this approach, to the authors' knowledge, there have been no previous examples reported of utilising macromolecular dopants as initiators for subsequent grafting of polymer brushes. © 2017 Society of Chemical Industry