W.M. de Azevedo

Photo-induced polymerization of polyaniline

A straightforward route to prepare polyaniline is presented in which photons and metallic ions replace conventional oxidants to promote polymerization of aniline monomer. The photopolymerization methods yield a composite material that has been characterized by its UV, visible and Raman spectroscopic analysis and by scanning electron microscopy and X-ray microanalysis as well. Intriguing forms of silver wires embedded in polyaniline are observed, typically of 1 μm wide and up to 100 μm long. It is shown that the morphology of the resulting conducting polymer strongly depends on the excitation wavelength, while a globular morphology is found for the UV synthesis and a fibrillar one is found for visible light excitation.

Semi-interpenetrating polymer networks based on polyaniline and polyvinyl alcohol-glutaraldehyde

Abstract A new semi-Interpenetrating Polymer Network (semi-IPN) based on polyvinyl alcohol–glutaraldehyde/polyaniline was synthesized and characterized by spectroscopic analysis in the UV–Visible–Infrared region and by scanning electron microscopy (SEM). The semi-IPNs exhibit good mechanical properties, characteristic of polyvinyl alcohol–glutaraldehyde polymer network, and excellent optical properties. The UV–Visible results show that the optical properties of the semi-IPNs are characteristic only of polyaniline polymer, and that the semi-IPNs are able to preserve the reduced or oxidized state of polyaniline for several months. The scanning electron microscopy of the semi-IPNs shown that phase separation occurs and the domains formed probably are due to polyaniline particle covered with an adsorbed layer of electrically insulating PVA stabilizer. The domains have a rice-grain morphology with average length of 1 μm, and average width of 0.5 μm for less cross-linked samples. The morphology of the phase domains change from rice-grain to spherical shape, as the cross-linking degree increases.

Growth of sub-micron fibres of pure polyaniline using the electrospinning technique

In this work we report on the formation of pure polyaniline fibres by the electrospinning method. The fibres present diameters ranging from hundreds of nanometres to a few micrometres and have lengths of hundreds of micrometres. The fibres were collected on SiO2/Si and Si wafer pieces in the form of isolated fibres. Morphological characterization by scanning electron microscopy shows smooth fibre surfaces and lack of failure effects such as necking and fibrillation. The current?voltage characteristics are linear and the conductivity values vary in the range usually observed for partially doped polyaniline.

Doped polymers with Ln(III) complexes: simulation and control of light colors

Complexes of Eu(III) and Tb(III) were dispersed in polystyrene for the purpose of generating the primary red and green light colors, and simulating of the secondary yellow color. The polymer was doped with one or both complexes. Under ultraviolet excitation, the Eu(III) and Tb(III) complex-doped polymers, both solid state light emitters, generate the red and green colors, respectively. The Eu(III) and Tb(III) mixed complexes in the polymer present the characteristic emissions of the lanthanide ions, simulating the secondary yellow light color.

The effect of glutaraldehyde on the electrochemical behavior of polyaniline

Polyaniline was exposed to glutaraldehyde under different experimental conditions and in all cases reduction of the polymer was observed. The reduction of polyaniline by glutaraldehyde in non-electrolytic, aqueous medium under reflux, caused the polymer to become completely undoped and with high impermeability to anions as evidenced by the displacement of the first anodic voltammetric wave of polyaniline in acidic medium and by its dependence on the kind of acid employed. The permeability and the normal electrochemical behavior of the polymer could be restored after the first voltammetric cycle. Under simple exposure to glutaraldehyde in buffered solution (pH 8) the reduction is not so extensive and changes in voltammetric behavior from cycle to cycle are related to the high pH of the medium. Some glutaraldehyde polymerizes inside the polyaniline matrix, causing the first voltammetric wave of polyaniline to be slightly displaced to more anodic potentials. Enzyme immobilization on polyaniline with glutaraldehyde seems to be related to this polyglutaraldehyde produced in buffered solutions.

Formic acid an efficient solvent to prepare polyaniline/silicate glass composite using sol–gel technique

Abstract In this work an efficient method to prepare silicate glass and hybrid inorganic–organic material composed of polyaniline (PANi) and silica gel network has been developed using the sol–gel technique. The method consists in mixing tetraethoxysilane (TEOS) and PANi in formic acid, which acts as solvent and catalyst simultaneously. This process is based on the facts that PANi is souble in formic acid and the acid is an efficient catalyst to form polysilicate network. Transparent and monolithic hybird glass doped with PANi has been obtained. The extent of the polysilicate network development was investigated by 29 Si nuclear magnetic resonance spectroscopy. Spectroscopic analysis in the ultraviolet–visible (UV–Vis) region as a function of the pH shows that this composite can be used as an efficient pH sensor, since PANi remains optically active.

Nonlinear-optical properties of a poly(vinyl alcohol)- polyaniline interpenetrating polymer network

The nonlinear-optical properties of a semi-interpenetrating polymer network of poly(vinyl alcohol) glutaralde-hyde-polyaniline were studied. Large (>/=10(-12) cm(2)/W) and fast (<50 ps) refractive optical nonlinearites were observed. The potential of this novel material for photonic applications is evaluated.

An example of concentration sensitive electron-phonon coupling in {(C4H9)4N}3 EuxY1−x(NCS)6 and a new hypothesis for self-quenching

The strong vibronic one-phonon side-bands of the 5D0 → 7F0 emission of Eu3+ in {(C4H9)4N}3 EuxY1−x(NCS)6 are used to compute the Huang-Rhys electron-phonon coupling factor (S0) of Eu3+ with the mode at 35 cm-1. Increasing concentration from 1 to 100 is found to lead to a doubling of the electron-phonon coupling strength. Generalization of such an effect is proposed as a new hypothesis for part of the self-quenching process of rare-earth ions.

Polyaniline nanofilms as a monitoring label and dosimetric device for gamma radiation

Abstract In this work, an optical dosimeter for gamma radiation ( 60 Co) based on the color change of polyaniline nanofilms in the emeraldine oxidation state was developed by spin coating of the polymer films on glass substrates. After irradiation, the nanofilms were characterized by UV-visible (UV-Vis) absorption spectroscopy as a function of the 60 Co radiation dose. The deep blue color, characteristic of undoped polyaniline films before irradiation subsequently becomes green as the film is irradiated, and the film absorption coefficient exhibits a linear dependence with logarithm of the irradiation dose from 1 to 10 kGy. These results strongly suggest that polyaniline nanofilms can be used as a qualitative and quantitative dosimeter for gamma radiation in the analyzed dose range.

Semiempirical calculations of aniline oligomers hyperpolarisabilities

Theoretical study of the hyperpolarisabilities β and γ of aniline oligomers is presented. The results obtained for β at the AM1/TDHF level are promising for the emeraldine form, indicating a potential use as a second-order nonlinear optical material. The calculations of static cubic hyperpolarisability of trimers agree with the experimentally observed trends for polyaniline.