Carlos A. Brunello

Electrochromic and conductivity properties: a comparative study between melanin-like/V2O5 nH2O and polyaniline/ V2O5 nH2O hybrid materials

In this work, we report the synthesis and some properties of melanin-like/V2O5·nH2O and polyaniline/V2O5·nH2O hybrid materials that have potential applications in optics and electronics. The hybrid materials were obtained by an oxidative polymerization/intercalation process reacting the gel with the monomers of the polymers. The optical properties of the compounds in film forms were measured using ultraviolet–visible (UV–Vis) spectroscopy. Thermogravimetric analysis, differential gravimetric analysis and dc conductivity techniques were also used to study the compounds. The X-ray diffractograms indicate that the lamellar structure of the V2O5 is preserved with the increase of the inter-planar space from 1.18±0.05 to 1.40±0.05 nm. The presence of the organic phase induced the reduction of V(V) ions to V(IV) and increased the dc conductivity and affected the spectroelectrochemical properties of the samples.

Nitric oxide release using natural rubber latex as matrix

Received: March 16, 2011; Revised: June 16, 2011Nitric oxide (NO) is a diffusible messenger that has been involved in numerous physiological processes ranging from vasodilatation and antimicrobial properties to wound healing. The beneficial effects can be attributed to the role NO plays in angiogenesis, inflammation and tissue remodeling. In the present work, a polymeric device for the sustained site specific delivery of nitric oxide using a latex rubber matrix from

Magnetic and thermal induced ordering in V2O5 xerogel films

Abstract In this work we investigated the possibility of using magnetic fields and thermal treatments to induce ordering in V 2 O 5 xerogels in film form. The xerogel was prepared by standard procedures. The films were prepared either by dip-coating or casting. X-ray powder diffraction, cyclic voltammetry as well as conductivity were used to monitor the changes. We found that the freshly made films are unstable, needing at least 48 h of rest at room temperature to have reproducible X-ray diffractograms, as well as conductivities. The changes are attributed to a decrease in film water content. Magnetic field treatments of several hours were observed to increase the ordering of the V 2 O 5 ribbons, as well as the conductivity. For freshly deposited films the effects were larger than those in films left for a few days at room temperature. The electrochemical response of films exposed to magnetic fields did also show an increase in surface homogeneity.

Thermal Annealing Effects on Synthetic Melanin

The influence of adsorbed moisture on the ESR signal of the free radical in synthetic melanin is investigated. Water is found to correspond to 10% to 20% of melanin mass in the as synthesized state. Water removal is responsible for an increase in spin density induced by extended heating at temperatures above 60 °C. This enhanced spin concentration is stable at room temperature but can be quenched by rehydratation. A systematic study on the time dependence of the spin enhancement is presented along with a macroscopic model based on rate equations.

Aging effects in polyaniline studied by electrically detected magnetic resonance

The effects of thermal treatments in inert atmosphere on polyaniline films have been investigated by electrically detected magnetic resonance (EDMR) and Electron Spin Resonance (ESR). Two lines are observed both by ESR a narrow resonance line with a lincwidth of approx. 0.24 mT and a broader line with 1.6 mT linewidth, with similar g-factors (2.003), for EDMR with sandwich contacts only the broader line is observed. The broad EDMR signal is not sensitive to the presence of oxygen or moisture, as is the case of electron spin resonance and conductivity.

Melanin-like units concentration effects in melanin-like/vanadium pentoxide hybrid compounds

An intercalated material has been prepared consisting of a regular alternation of organic/inorganic layers. The films were obtained by reacting 3,4-dihydroxy-phenylalanine (dl-DOPA) with varying concentrations in a solution with freshly prepared HVO3, which suffered a oxidative polymerization/intercalation ‘in situ’ process, forming a green suspension, in which after de-hydration at room temperature produces a nanocomposite with a dark blue metallic color. Films (C8H9NO2)xV2O5·nH2O were characterized using FT–IR, ESR, powder X-ray diffraction, conductivity, and cyclic voltammetry. The X-ray diffractograms indicate that the lamellar structure of the V2O5 is preserved for low concentrations of melanin-like units (x<0.02), but the inter-planar space increases from 1.2 nm to ca. 1.5 nm. The FT–IR and ESR spectra confirm that the V2O5 structure is preserved, however the presence of melanin-like units induces the reduction of V(V) ions to V(IV) ions. The melanin insertion is observed to increase the stability and reproducibility of the electrochemical insertion/de-insertion of Li+. The incorporation of melanin-like structures increases the conductivity, followed by a decrease in its temperature activation energy.

Thermal annealing effects on polyaniline studied by electrically detected magnetic resonance

Abstract The effects of thermal treatments in inert atmosphere on polyaniline films have been investigated by electrically detected magnetic resonance (EDMR). For small electric fields (F

The effects of Sb incorporation into vanadium pentoxide xerogel

Abstract In this work we report the effects on structural and conductivity properties of incorporating different amounts of antimony ions into vanadium pentoxide xerogel. Powder X-ray diffraction, Fourier-transform infrared spectroscopy, electronic paramagnetic resonance and thermogravimetric analysis were used in order to characterise the obtained products. Powder X-ray diffraction data indicate that the presence of Sb ions induces a decrease in crystallinity with the maintenance of the lamellar organisation, evidenced by 001 reflection with a higher basal distance (d=1.26 nm). FT-IR spectra show the characteristic vibrational modes of the matrix, indicating that the presence of Sb ions did not affect the short range structure. EPR spectra, in addition, show that Sb ions induce a reduction of V5+ ions to V4+. The conductivity is enhanced by small amounts of Sb ions with a decrease in activation energy.