R.A. Zoppi

Hybrids of perfluorosulfonic acid ionomer and silicon oxide by sol-gel reaction from solution: Morphology and thermal analysis

NAFION®/silicon oxide hybrids were prepared from solution by hydrolysis/polycondensation of alkoxy silanes. Transparent, but brittle films were obtained when TEOS was used as the inorganic polymer precursor, showing a lamellar structure by transmission electron microscopy. Part of the TEOS was substituted by TMDES to increase the film flexibility. For substitution higher than 10% phase separation was clearly observed by scanning and transmission electron microscopy. The thermal analysis of NAFION® and hybrids with different inorganic contents showed two main endothermic transitions, one assigned to the NAFION® ionic clusters and the other to the melting of the perfluorinated matrix. The cluster transition temperature decreases as the TEOS content increases up to 50 wt%, but than increases as the TEOS content reaches 80 wt%.

Electrochemical impedance studies of hybrids of perfluorosulfonic acid ionomer and silicon oxide by sol-gel reaction from solution

Hybrids of Nafion® and silica were prepared from solution, growing the inorganic phase by hydrolysis/condensation of alkoxy silanes. Using tetraethoxysilane (TEOS) as the inorganic precursor, transparent and rigid films were obtained. Substituting part of the TEOS (20 wt% substitution) by 1,1,3,3 tetramethyl-1,3-diethoxydisiloxane (TMDES) more flexible films were obtained. These films were translucent and showed a phase segregation which was clearly observed by transmission electron microscopy. The ionic conductivity of the hybrids was measured by electrochemical impedance spectroscopy using two stainless steel electrodes, a frequency range of 0.1 to 105 Hz, and temperatures from 25 to 100°C. Samples were also characterized by modulated differential scanning calorimetry.

Hybrids of SiO2 and poly(amide 6-b-ethylene oxide)

Hybrids of poly(amide-6-b-ethylene oxide), Pebax®, and silica were prepared by using a sol-gel process. The inorganic phase was grown by hydrolysis-condensation of tetraethoxysilane, TEOS, by acid catalysis, in presence of Pebax/n-butanol or Pebax/formic acid:tetrahydrofuran (1 : 1 w/w). Pebax/silica hybrids, with different compositions, were obtained and characterized by stress-strain tests, dynamic-mechanical analysis, X-ray diffraction, transmission electron and scanning electron microscopy. The effect of the preparation conditions on the hybrid properties is discussed.

Solid electrolytes based on poly(amide 6-b-ethylene oxide)

Abstract An amide 6- b -ethylene oxide copolymer (Pebax ® ) was investigated as an ionic conducting matrix. Transparent and flexible films containing LiClO 4 were prepared with ionic conductivities in the range of 10 −6 S cm −1 at room temperature. The conductivity values gradually increased when the films were heated (10 −4 S cm −1 at 100 °C). The conductivity dependence on temperature could be described according to the classical Arrhenius plots over the temperature range of 22 to 100 °C. The glass transition temperature was determined by differential scanning calorimetry. The T g of the Pebax/LiClO 4 system increases for samples containing high salt concentration, as expected. The polymer electrolyte morphology was analyzed by transmission electron microscopy. Salt aggregation was observed in all samples. This was confirmed by electron spectroscopic images selective for chlorine. The electrochemical stability window of the Pebax/LiClO 4 electrolytes as investigated by cyclic voltammetry was in the range of 4.0 V.

Chemical preparation of conductive elastomeric blends: polypyrrole/EPDM—II. Utilization of matrices containing crosslinking agents, reinforcement fillers and stabilizers

Abstract Semi-interpenetrating networks (semi-IPN) of polypyrrole and ethylene-propylene-5-ethylidene-2-norbornene rubber, EPDM, were prepared by chemical oxidation of the monomer using two different methods of synthesis. In the first method, EPDM rubber samples containing CuCl2 (powder with granulometry

Hybrids of poly(ethylene oxide-co-epichlorhydrin) and silica : phase separation, morphology and thermal properties

Abstract Hybrid materials of poly(ethylene oxide- co -epichlorhydrin), HYDRIN, and silica were prepared by a sol-gel process. An inorganic network was grown in a tetrahydrofuran/organic polymer solution from acid hydrolysis and polycondensation of tetraethoxysilane, TEOS. During solvent evaporation and simultaneous growth of the inorganic network, phase separation was observed. The mechanism of phase separation of these sol-gel systems was investigated by light scattering. Spinodal decomposition (SD) was observed for HYDRIN/TEOS systems with composition equal to 71/29, 67/33, 60/40, 50/50, 40/60, 33/67 and 29/71. The morphology of the final HYDRIN/TEOS hybrid material was investigated by scanning electron microscopy. The thermal properties of these materials were investigated by differential scanning calorimetry and their hydrophilicity was evaluated by contact angle measurements.

Chemical preparation of conductive elastomeric blends: polypyrrole/EPDM. III. Electrochemical characterization

Abstract Polypyrrole and polypyrrole/EPDM rubber blends were prepared by chemical oxidation of the monomer with FeCl3. EPDM rubber an ethylene-propylene-5-ethylidene-2-norbornene terpolymer. Pure polypyrrole and polypyrrole/EPDM blends were characterized to cyclic voltammetry and electrochemical impedance spectroscopy. Their spectro- and photoelectrochemical behavior were also investigated.

Synthesis and characterization of a composite containing poly(3-methylthiophene) and nitrilic rubber

Abstract The electrochemical synthesis of a composite of poly(3-methylthiophene) and poly(acrylonitrile-co-butadiene), nitrilic rubber, is described. The effect of the synthesis conditions on the electrochemical properties of the material was studied by cyclic voltammetry and chronoamperometry. I. r. spectroscopy thermogravimetry, d.s.c., elemental analysis and scanning electron microscopy were used to characterize the inclusion of the conductive polymer in the rubber matrix. The data indicated a low miscibility between the composite components. Stress-strain measurements indicated a toughening of the composite material in relation to the pure rubber. The electrical conductivity of the composite is one order of magnitude lower than that of the pure polymer.

Uso do processo sol-gel na obtenção de materiais híbridos organo-inorgânicos: preparação, caracterização e aplicação em eletrólitos de estado sólido

In this work it was described the preparation of hybrid materials constituted by a organic copolymer, which contains ethylene oxide blocks, and silica. The inorganic network was formed by the hydrolysis and condensation of tetraethoxysilane, TEOS, into the polymeric solution. As a copolymer, it was used poly(ethylene oxide-b-amide-6), PEBAX. Hybrids containing lithium perchlorate, known as hybrid electrolytes, were also prepared. The materials were characterized by transmission electron microscopy, stress-strain tests, dynamic-mechanical analysis and X-ray diffractometry. The PEBAX/TEOS/LiClO4 systems were also characterized by electrochemical impedance spectroscopy and cyclic voltammetry to evaluate their properties as a solid state electrolyte.