Recebido em 7/12/98; aceito em 8/6/99 CONDUCTIVE POLYMER SYNTHESIS IN SOLID HOST MATRICES. This r... more Recebido em 7/12/98; aceito em 8/6/99 CONDUCTIVE POLYMER SYNTHESIS IN SOLID HOST MATRICES. This review discusses the methods used to prepare conductive polymers in confined environments. This spatial restriction causes formation of defect-free polymer chains in the interlayer as porous cavities of inorganic hosts. The properties of the different composites obtained are a synergist combination of the characteristics of the inorganic host and the polymer. This opens new perspectives for the preparation of these materials and widens its potential applications.
Resumo: Dentre muitas fibras naturais de interesse tecnológico, o resíduo de madeira substitui co... more Resumo: Dentre muitas fibras naturais de interesse tecnológico, o resíduo de madeira substitui com vantagens as cargas e reforços tradicionalmente empregados em compostos e compósitos poliméricos, particularmente os de origem mineral, tais como talco, CaCO 3 e fibra de vidro. A tecnologia dos chamados Wood-Plastic Composites (WPC´s) envolve conceitos de compatibilidade e processabilidade e apresenta grandes desafios tecnológicos para a formulação e estabilização da mistura devido à baixa estabilidade térmica da celulose. Muitos dos avanços tecnológicos em WPC's dependem de uma análise criteriosa das características físicas de seus componentes e das condições de processamento do sistema, particularmente aspectos relacionados a sua compatibilização. No presente trabalho são apresentados estudos sobre a reatividade do polipropileno modificado com anidrido maleico (PP-MAH) utilizado como compatibilizante em compósitos termoplásticos de polipropileno com farinha de madeira. A influência da carga celulósica e a eficiência do compatibilizante nas propriedades reológicas, térmicas, mecânicas e morfológicas do sistema foi avaliada através de medidas de rigidez, grau de cristalinidade, temperatura de cristalização e fusão cristalina levando-se em conta as características da resina, a distribuição granulométrica e o teor de umidade da farinha de madeira. Observou-se que os compósitos compatibilizados com PP-MAH apresentaram ganhos significativos de rigidez em relação aos compósitos não-modificados independentemente do tipo de farinha de madeira empregada. As propriedades térmicas do polímero mostraram-se sensíveis à distribuição granulométrica e algumas composições apresentaram tendência ao escurecimento e à elevação da temperatura de cristalização do polímero na presença do reforço celulósico. Imagens obtidas por microscopia eletrônica de varredura ilustram o molhamento da fibra celulósica pela resina termoplástica quando na presença do compatibilizante indicando a possível ocorrência de reações de esterificação na interface polímero-madeira.
The effect of adding a non-ionic surfactant to disperse oxide particles on the electrochemical pe... more The effect of adding a non-ionic surfactant to disperse oxide particles on the electrochemical performance of PAni/LiMnNiO4 composites is evaluated by using cyclic voltammetry (CV), impedance measurements and constant-current charge/discharge cycling techniques. Three surfactants based on ethoxylated (EO) and propoxylated (PO) lauryl alcohols (3EO/6PO, L306; 4EO/5PO, L405; and 6EO/3PO, L603) were investigated. For comparative purposes, the oxide and polyaniline were prepared by sol–gel and chemical methods and were also investigated for their physical and electrochemical performances. By galvanostatic charge–discharge tests, the PAni/LiMnNiO4 L306 composite showed a better electrochemical performance than each single component and other composites (PAni/LiMnNiO4 L405 and PAni/LiMnNiO4 L603). The electrical conductivity of this composite reached 21.7 S cm−1, and an initial discharge capacity of 198 mAh g−1 was obtained. After 21 cycles, the retention capacity was 91%. These results i...
One way to obtain orientation of polymer chains is to grow them inside a structurally organized h... more One way to obtain orientation of polymer chains is to grow them inside a structurally organized host framework. In this work we report on the preparation of nanocomposites by encapsulating polyaniline in three different hosts: (a) Tin IV 2-carboxyethyl phosphonate (lamellar host), (b) porous glass (Vycor - Corning 7930) and (c) sol-gel silica. The hosts and respective composites were characterized by X-Ray Diffractommetry, Cyclic Voltammetry and Scanning and Transmission Electron Microscopy. Each organized host determined the growth of the conductive polymer and the results obtained confirm the enhanced molecular order of polyaniline chains. Keywords: Conducting polymers; Composites; Template synthesis. Preparação de polímeros condutores em sistemas organizados Resumo Uma maneira de obtenção de cadeias poliméricas orientadas consiste na síntese do polímero no interior de hospedeiros organizados estruturalmente. Neste trabalho reportamos a preparação de nanocompósitos por meio do enc...
Dentre muitas fibras naturais de interesse tecnológico, o resíduo de madeira substitui com vantag... more Dentre muitas fibras naturais de interesse tecnológico, o resíduo de madeira substitui com vantagens as cargas e reforços tradicionalmente empregados em compostos e compósitos poliméricos, particularmente os de origem mineral, tais como talco, CaCO3 e fibra de vidro. A tecnologia dos chamados Wood-Plastic Composites (WPC´s) envolve conceitos de compatibilidade e processabilidade e apresenta grandes desafios tecnológicos para a formulação e estabilização da mistura devido a baixa estabilidade térmica da celulose. Muitos dos avanços tecnológicos em WPC?s dependem de uma análise criteriosa das características físicas de seus componentes e das condições de processamento do sistema, particularmente aspectos relacionados a sua compatibilização. No presente trabalho são apresentados estudos sobre a reatividade do polipropileno modificado com anidrido maleico (PP-MAH) utilizado como compatibilizante em compósitos termoplásticos de polipropileno com farinha de madeira. A influência da carga ...
Multi-wall carbon nanotubes (CNTs) were coated with protonated polyaniline (PAni) in situ during ... more Multi-wall carbon nanotubes (CNTs) were coated with protonated polyaniline (PAni) in situ during the chemical polymerization of aniline. Uniform coating of CNT with PAni was observed by scanning electronic microscopy. An improvement in the covering of CNT composites was found by the association of poly(2,5-dimercapto-1,3,4-thiadiazole) (PDMcT). The conductivity of composites has been compared with the conductivity of the PAni and CNT. A maximum conductivity of 96.8 S cm −1 has been found for a PAni/PDMcT/CNT composite. High capacitance value (289.4 F g −1 ) was also determined for this composite, indicating that all materials, PAni, PDMcT and CNT, remain active during the charge-discharge cycling. The reduction in the capacitance after 100 cycles was found to be less than 25%. The capacitive behavior of all materials was confirmed by impedance analysis.
The composite SnP-C/Fe/PAni was obtained as a powder by polymerization of aniline in the interlay... more The composite SnP-C/Fe/PAni was obtained as a powder by polymerization of aniline in the interlayer space of the host tin (IV) 2-carboxyethylphosphonate (SnP-C). The photoelectrochemical behavior of the composite was investigated as a function of applied potential, polyaniline concentration and direction of the polychromatic irradiation. The stability of the device using a liquid electrolyte was also determined. The photoelectrochemical response is sensitive to the oxidation state of the polymer. Depending on the potential applied to the electrode we observe cathodic or anodic photocurrents.
Photoelectrochemistry is based on interfacial electron transfer, where one of the phases is the e... more Photoelectrochemistry is based on interfacial electron transfer, where one of the phases is the excited state of a semiconductor. We used the a.c. impedance technique in order to investigate these interface processes. Polyaniline films galvanostatically grown on platinum electrodes showed variation of photocurrent responses with d.c. bias with two maxima, 0.4 and 0.7 V, and a minimum at 0.65 V.
Lithium manganese oxide powders were prepared via combustion reaction. Structural characterizatio... more Lithium manganese oxide powders were prepared via combustion reaction. Structural characterization of the powder using X-ray diffraction and scanning electron microscopy confirmed the formation of a LiMn2O4 nanosized powder. LiMn2O4 films were prepared by spin coating using 80 wt% of oxide, 15 wt% of polyaniline (PAni) as an electronic conductor and 5 wt% of polyvinylidene (PVDF) as a binder in
Water drop contact-angle measurements were used to monitor the organic contamination cleaning pro... more Water drop contact-angle measurements were used to monitor the organic contamination cleaning process of InP crystals by refluxing in a sequence of solvents. A single reflux in methanol reduces the contact angle by the same amount as a solvent sequence. MOCVD confirms the cleanliness of the InP crystals treated by a single reflux in methanol.
In this work we describe the preparation of hybrid organic-inorganic films using the sol-gel proc... more In this work we describe the preparation of hybrid organic-inorganic films using the sol-gel process. Poly(ethylene oxide-b-amide-6), PEBAX, was used as an organic matrix. Silicon oxide or titanium oxide were prepared by hydrolysis and polycondensation of tetraethoxysilane, TEOS, or titanium tetraisopropoxide, TiOP, respectively. Hybrid films were characterized by electron microscopy, stress-strain tests and their gas permeability and selectivity properties were evaluated. Small angle X-ray scattering was used to investigate structural heterogeneity caused by the presence of SiO 2 or TiO 2 particles in the organic matrix. For films containing silicon oxide as an inorganic filler, gas permeability decreased as a function of the inorganic component content. When titanium oxide was used as a filler, gas permeability was considerably lower than that measured for films containing silicon oxide (80/20 PEBAX/inorganic precursor compositions). In these cases, the morphologies were very similar, but films containing titanium oxide were much more rigid. For CO 2 /N 2 and CO 2 /H 2 separation factors up to 52.9 and 7.1, respectively, were obtained for 80/20 PEBAX/TiOP films. For higher titanium oxide contents, gas permeability increased. In these cases, a TiO 2 agglomeration was observed and the barrier performance decreased. Permeability and selectivity properties are discussed as a function of morphological and mechanical properties of these films. ᭧
Tióis de cadeias carbônicas com tamanhos diferentes e contendo grupo terminal COOH foram usados p... more Tióis de cadeias carbônicas com tamanhos diferentes e contendo grupo terminal COOH foram usados para formar monocamadas auto-organizadas sobre a superfície de eletrodos de ouro. A transferência de elétrons do par Fe(CN) 6 3-/4para o eletrodo foi estudada em diferentes pH usandose as técnicas de voltametria cíclica (CV) e de espectroscopia de impedância eletroquímica (EIS). Mudanças no pH da solução resultaram em variações na carga do grupo terminal das monocamadas auto-organizadas e, conseqüentemente, em alterações na interação eletrostática da SAM com as espécies eletroativas em solução.
Composite electrodes for supercapacitors are prepared via template synthesis by the electrochemic... more Composite electrodes for supercapacitors are prepared via template synthesis by the electrochemical polymerization of 3-methyl thiophene in the heterogeneous void spaces of polyvinylidene fluoride (PVDF) porous films. The large pore size distribution in the template matrix results in some of the poly(3-methyl thiophene) growing in a more ordered fashion than in films synthesized without spatial restriction, and this can lead to improved conductivity and kinetics. In this work, the capacitance properties of a poly(3-methyl thiophene)/PVDF composite were investigated using cyclic voltammetry, ac impedance spectroscopy and charge-discharge tests. The P(3-MeT)/PVDF|PC/EC/1 mol L −1 LiClO 4 |P(3-MeT)/PVDF type III capacitor had a specific capacitance of 616 F g −1 and a Coulombic efficiency of 93%. The power density decreased during ∼300 cycles and then became practically constant at 7.3 kW kg −1 . These results indicate that template synthesis is an useful alternative to enhance the properties of conducting polymers.
Films of poly[(R)-(−)-3-(1-pyrrolyl)propyl-N-(3,5-dinitrobenzoyl)-␣-phenylglycinate] (polyDNBP) w... more Films of poly[(R)-(−)-3-(1-pyrrolyl)propyl-N-(3,5-dinitrobenzoyl)-␣-phenylglycinate] (polyDNBP) were deposited, using the galvanostatic method, onto indium tin oxide electrodes in the presence of the electrolytes tetrabutylammonium tetrafluoro-borate [(C 4 H 9 ) 4 NBF 4 ] or LiClO 4 . Atomic force microscopy revealed that polyDNBP/(C 4 H 9 ) 4 NBF 4 films exhibited a grainy morphology with higher roughness and greater superficial area than polyDNBP/LiClO 4 films. Moreover, polyDNBP/(C 4 H 9 ) 4 NBF 4 films exhibited a higher capacitive electrochemical response when characterised in LiClO 4 rather than in (C 4 H 9 ) 4 NBF 4 . Since polyDNBP films exhibit both n-and p-doping, they may have considerable potential application as electrodes in type III capacitor assemblies.
Multi-wall carbon nanotubes (CNTs) were coated with protonated polyaniline (PAni) in situ during ... more Multi-wall carbon nanotubes (CNTs) were coated with protonated polyaniline (PAni) in situ during the chemical polymerization of aniline. Uniform coating of CNT with PAni was observed by scanning electronic microscopy. An improvement in the covering of CNT composites was found by the association of poly(2,5-dimercapto-1,3,4-thiadiazole) (PDMcT). The conductivity of composites has been compared with the conductivity of the PAni and CNT. A maximum conductivity of 96.8 S cm −1 has been found for a PAni/PDMcT/CNT composite. High capacitance value (289.4 F g −1 ) was also determined for this composite, indicating that all materials, PAni, PDMcT and CNT, remain active during the charge-discharge cycling. The reduction in the capacitance after 100 cycles was found to be less than 25%. The capacitive behavior of all materials was confirmed by impedance analysis.
Photoelectrochemistry is based on interfacial electron transfer, where one of the phases is the e... more Photoelectrochemistry is based on interfacial electron transfer, where one of the phases is the excited state of a semiconductor. In this work we investigated the photoelectrochemical response of polyaniline intercalated in a layered material. The photoelectrochemical response show cathodic or anodic photocurrents depending on the applied potential, hence on the oxidation state of the polyaniline. Above 0.40 V in the oxidation and reduction processes, polyaniline shows n-type semiconductor characteristics and below 0.40 V in the reduction process, its behavior is of a p-type semiconductor. The composite SnP-C/Fe/PAni was obtained as a powder by polymerization of aniline in the interlayer space of the host Tin (IV) 2-carboxyethylphosfonate (SnP-C). The polymerization was done in an acid solution after incorporation of Fe 3+ to the host. X-ray diraction and conductivity measurements indicated the formation of polyaniline in the interlayer space and cyclic voltammetry measurements showed that the product is electroactive. #
A new methodology that combines the sol–gel method and a template approach is used to synthesize ... more A new methodology that combines the sol–gel method and a template approach is used to synthesize porous LiNi1−xCoxO2 films. Conventional films are obtained through the sol–gel method. The films are used to evaluate the influence of this new methodology on the electrochemical performance. It was observed, from X-ray diffraction analysis on the conventional film that a further increase in the
Composite electrodes were prepared via electrochemical polymerization of 3-methylthiophene in por... more Composite electrodes were prepared via electrochemical polymerization of 3-methylthiophene in porous PVDF membranes of various thicknesses. The electrochemical properties were determined by cyclic voltammetry and charge-discharge tests and the possible correlation of the results with the morphology of the host membranes was examined. The best definition of n-and p-doping/undoping processes and the biggest capacitance (82 F g −1 ) were obtained with a 27.5 m-thick composite. Further characterization of this composite using electrochemical impedance spectroscopy revealed three behaviors associated with variation in the oxidation state of poly(3-methylthiophene) during transition from the nundoping to p-doping states. The behavior of the charge transfer resistance and the double layer capacitance as a function of the applied potential were also determined.
Recebido em 7/12/98; aceito em 8/6/99 CONDUCTIVE POLYMER SYNTHESIS IN SOLID HOST MATRICES. This r... more Recebido em 7/12/98; aceito em 8/6/99 CONDUCTIVE POLYMER SYNTHESIS IN SOLID HOST MATRICES. This review discusses the methods used to prepare conductive polymers in confined environments. This spatial restriction causes formation of defect-free polymer chains in the interlayer as porous cavities of inorganic hosts. The properties of the different composites obtained are a synergist combination of the characteristics of the inorganic host and the polymer. This opens new perspectives for the preparation of these materials and widens its potential applications.
Resumo: Dentre muitas fibras naturais de interesse tecnológico, o resíduo de madeira substitui co... more Resumo: Dentre muitas fibras naturais de interesse tecnológico, o resíduo de madeira substitui com vantagens as cargas e reforços tradicionalmente empregados em compostos e compósitos poliméricos, particularmente os de origem mineral, tais como talco, CaCO 3 e fibra de vidro. A tecnologia dos chamados Wood-Plastic Composites (WPC´s) envolve conceitos de compatibilidade e processabilidade e apresenta grandes desafios tecnológicos para a formulação e estabilização da mistura devido à baixa estabilidade térmica da celulose. Muitos dos avanços tecnológicos em WPC's dependem de uma análise criteriosa das características físicas de seus componentes e das condições de processamento do sistema, particularmente aspectos relacionados a sua compatibilização. No presente trabalho são apresentados estudos sobre a reatividade do polipropileno modificado com anidrido maleico (PP-MAH) utilizado como compatibilizante em compósitos termoplásticos de polipropileno com farinha de madeira. A influência da carga celulósica e a eficiência do compatibilizante nas propriedades reológicas, térmicas, mecânicas e morfológicas do sistema foi avaliada através de medidas de rigidez, grau de cristalinidade, temperatura de cristalização e fusão cristalina levando-se em conta as características da resina, a distribuição granulométrica e o teor de umidade da farinha de madeira. Observou-se que os compósitos compatibilizados com PP-MAH apresentaram ganhos significativos de rigidez em relação aos compósitos não-modificados independentemente do tipo de farinha de madeira empregada. As propriedades térmicas do polímero mostraram-se sensíveis à distribuição granulométrica e algumas composições apresentaram tendência ao escurecimento e à elevação da temperatura de cristalização do polímero na presença do reforço celulósico. Imagens obtidas por microscopia eletrônica de varredura ilustram o molhamento da fibra celulósica pela resina termoplástica quando na presença do compatibilizante indicando a possível ocorrência de reações de esterificação na interface polímero-madeira.
The effect of adding a non-ionic surfactant to disperse oxide particles on the electrochemical pe... more The effect of adding a non-ionic surfactant to disperse oxide particles on the electrochemical performance of PAni/LiMnNiO4 composites is evaluated by using cyclic voltammetry (CV), impedance measurements and constant-current charge/discharge cycling techniques. Three surfactants based on ethoxylated (EO) and propoxylated (PO) lauryl alcohols (3EO/6PO, L306; 4EO/5PO, L405; and 6EO/3PO, L603) were investigated. For comparative purposes, the oxide and polyaniline were prepared by sol–gel and chemical methods and were also investigated for their physical and electrochemical performances. By galvanostatic charge–discharge tests, the PAni/LiMnNiO4 L306 composite showed a better electrochemical performance than each single component and other composites (PAni/LiMnNiO4 L405 and PAni/LiMnNiO4 L603). The electrical conductivity of this composite reached 21.7 S cm−1, and an initial discharge capacity of 198 mAh g−1 was obtained. After 21 cycles, the retention capacity was 91%. These results i...
One way to obtain orientation of polymer chains is to grow them inside a structurally organized h... more One way to obtain orientation of polymer chains is to grow them inside a structurally organized host framework. In this work we report on the preparation of nanocomposites by encapsulating polyaniline in three different hosts: (a) Tin IV 2-carboxyethyl phosphonate (lamellar host), (b) porous glass (Vycor - Corning 7930) and (c) sol-gel silica. The hosts and respective composites were characterized by X-Ray Diffractommetry, Cyclic Voltammetry and Scanning and Transmission Electron Microscopy. Each organized host determined the growth of the conductive polymer and the results obtained confirm the enhanced molecular order of polyaniline chains. Keywords: Conducting polymers; Composites; Template synthesis. Preparação de polímeros condutores em sistemas organizados Resumo Uma maneira de obtenção de cadeias poliméricas orientadas consiste na síntese do polímero no interior de hospedeiros organizados estruturalmente. Neste trabalho reportamos a preparação de nanocompósitos por meio do enc...
Dentre muitas fibras naturais de interesse tecnológico, o resíduo de madeira substitui com vantag... more Dentre muitas fibras naturais de interesse tecnológico, o resíduo de madeira substitui com vantagens as cargas e reforços tradicionalmente empregados em compostos e compósitos poliméricos, particularmente os de origem mineral, tais como talco, CaCO3 e fibra de vidro. A tecnologia dos chamados Wood-Plastic Composites (WPC´s) envolve conceitos de compatibilidade e processabilidade e apresenta grandes desafios tecnológicos para a formulação e estabilização da mistura devido a baixa estabilidade térmica da celulose. Muitos dos avanços tecnológicos em WPC?s dependem de uma análise criteriosa das características físicas de seus componentes e das condições de processamento do sistema, particularmente aspectos relacionados a sua compatibilização. No presente trabalho são apresentados estudos sobre a reatividade do polipropileno modificado com anidrido maleico (PP-MAH) utilizado como compatibilizante em compósitos termoplásticos de polipropileno com farinha de madeira. A influência da carga ...
Multi-wall carbon nanotubes (CNTs) were coated with protonated polyaniline (PAni) in situ during ... more Multi-wall carbon nanotubes (CNTs) were coated with protonated polyaniline (PAni) in situ during the chemical polymerization of aniline. Uniform coating of CNT with PAni was observed by scanning electronic microscopy. An improvement in the covering of CNT composites was found by the association of poly(2,5-dimercapto-1,3,4-thiadiazole) (PDMcT). The conductivity of composites has been compared with the conductivity of the PAni and CNT. A maximum conductivity of 96.8 S cm −1 has been found for a PAni/PDMcT/CNT composite. High capacitance value (289.4 F g −1 ) was also determined for this composite, indicating that all materials, PAni, PDMcT and CNT, remain active during the charge-discharge cycling. The reduction in the capacitance after 100 cycles was found to be less than 25%. The capacitive behavior of all materials was confirmed by impedance analysis.
The composite SnP-C/Fe/PAni was obtained as a powder by polymerization of aniline in the interlay... more The composite SnP-C/Fe/PAni was obtained as a powder by polymerization of aniline in the interlayer space of the host tin (IV) 2-carboxyethylphosphonate (SnP-C). The photoelectrochemical behavior of the composite was investigated as a function of applied potential, polyaniline concentration and direction of the polychromatic irradiation. The stability of the device using a liquid electrolyte was also determined. The photoelectrochemical response is sensitive to the oxidation state of the polymer. Depending on the potential applied to the electrode we observe cathodic or anodic photocurrents.
Photoelectrochemistry is based on interfacial electron transfer, where one of the phases is the e... more Photoelectrochemistry is based on interfacial electron transfer, where one of the phases is the excited state of a semiconductor. We used the a.c. impedance technique in order to investigate these interface processes. Polyaniline films galvanostatically grown on platinum electrodes showed variation of photocurrent responses with d.c. bias with two maxima, 0.4 and 0.7 V, and a minimum at 0.65 V.
Lithium manganese oxide powders were prepared via combustion reaction. Structural characterizatio... more Lithium manganese oxide powders were prepared via combustion reaction. Structural characterization of the powder using X-ray diffraction and scanning electron microscopy confirmed the formation of a LiMn2O4 nanosized powder. LiMn2O4 films were prepared by spin coating using 80 wt% of oxide, 15 wt% of polyaniline (PAni) as an electronic conductor and 5 wt% of polyvinylidene (PVDF) as a binder in
Water drop contact-angle measurements were used to monitor the organic contamination cleaning pro... more Water drop contact-angle measurements were used to monitor the organic contamination cleaning process of InP crystals by refluxing in a sequence of solvents. A single reflux in methanol reduces the contact angle by the same amount as a solvent sequence. MOCVD confirms the cleanliness of the InP crystals treated by a single reflux in methanol.
In this work we describe the preparation of hybrid organic-inorganic films using the sol-gel proc... more In this work we describe the preparation of hybrid organic-inorganic films using the sol-gel process. Poly(ethylene oxide-b-amide-6), PEBAX, was used as an organic matrix. Silicon oxide or titanium oxide were prepared by hydrolysis and polycondensation of tetraethoxysilane, TEOS, or titanium tetraisopropoxide, TiOP, respectively. Hybrid films were characterized by electron microscopy, stress-strain tests and their gas permeability and selectivity properties were evaluated. Small angle X-ray scattering was used to investigate structural heterogeneity caused by the presence of SiO 2 or TiO 2 particles in the organic matrix. For films containing silicon oxide as an inorganic filler, gas permeability decreased as a function of the inorganic component content. When titanium oxide was used as a filler, gas permeability was considerably lower than that measured for films containing silicon oxide (80/20 PEBAX/inorganic precursor compositions). In these cases, the morphologies were very similar, but films containing titanium oxide were much more rigid. For CO 2 /N 2 and CO 2 /H 2 separation factors up to 52.9 and 7.1, respectively, were obtained for 80/20 PEBAX/TiOP films. For higher titanium oxide contents, gas permeability increased. In these cases, a TiO 2 agglomeration was observed and the barrier performance decreased. Permeability and selectivity properties are discussed as a function of morphological and mechanical properties of these films. ᭧
Tióis de cadeias carbônicas com tamanhos diferentes e contendo grupo terminal COOH foram usados p... more Tióis de cadeias carbônicas com tamanhos diferentes e contendo grupo terminal COOH foram usados para formar monocamadas auto-organizadas sobre a superfície de eletrodos de ouro. A transferência de elétrons do par Fe(CN) 6 3-/4para o eletrodo foi estudada em diferentes pH usandose as técnicas de voltametria cíclica (CV) e de espectroscopia de impedância eletroquímica (EIS). Mudanças no pH da solução resultaram em variações na carga do grupo terminal das monocamadas auto-organizadas e, conseqüentemente, em alterações na interação eletrostática da SAM com as espécies eletroativas em solução.
Composite electrodes for supercapacitors are prepared via template synthesis by the electrochemic... more Composite electrodes for supercapacitors are prepared via template synthesis by the electrochemical polymerization of 3-methyl thiophene in the heterogeneous void spaces of polyvinylidene fluoride (PVDF) porous films. The large pore size distribution in the template matrix results in some of the poly(3-methyl thiophene) growing in a more ordered fashion than in films synthesized without spatial restriction, and this can lead to improved conductivity and kinetics. In this work, the capacitance properties of a poly(3-methyl thiophene)/PVDF composite were investigated using cyclic voltammetry, ac impedance spectroscopy and charge-discharge tests. The P(3-MeT)/PVDF|PC/EC/1 mol L −1 LiClO 4 |P(3-MeT)/PVDF type III capacitor had a specific capacitance of 616 F g −1 and a Coulombic efficiency of 93%. The power density decreased during ∼300 cycles and then became practically constant at 7.3 kW kg −1 . These results indicate that template synthesis is an useful alternative to enhance the properties of conducting polymers.
Films of poly[(R)-(−)-3-(1-pyrrolyl)propyl-N-(3,5-dinitrobenzoyl)-␣-phenylglycinate] (polyDNBP) w... more Films of poly[(R)-(−)-3-(1-pyrrolyl)propyl-N-(3,5-dinitrobenzoyl)-␣-phenylglycinate] (polyDNBP) were deposited, using the galvanostatic method, onto indium tin oxide electrodes in the presence of the electrolytes tetrabutylammonium tetrafluoro-borate [(C 4 H 9 ) 4 NBF 4 ] or LiClO 4 . Atomic force microscopy revealed that polyDNBP/(C 4 H 9 ) 4 NBF 4 films exhibited a grainy morphology with higher roughness and greater superficial area than polyDNBP/LiClO 4 films. Moreover, polyDNBP/(C 4 H 9 ) 4 NBF 4 films exhibited a higher capacitive electrochemical response when characterised in LiClO 4 rather than in (C 4 H 9 ) 4 NBF 4 . Since polyDNBP films exhibit both n-and p-doping, they may have considerable potential application as electrodes in type III capacitor assemblies.
Multi-wall carbon nanotubes (CNTs) were coated with protonated polyaniline (PAni) in situ during ... more Multi-wall carbon nanotubes (CNTs) were coated with protonated polyaniline (PAni) in situ during the chemical polymerization of aniline. Uniform coating of CNT with PAni was observed by scanning electronic microscopy. An improvement in the covering of CNT composites was found by the association of poly(2,5-dimercapto-1,3,4-thiadiazole) (PDMcT). The conductivity of composites has been compared with the conductivity of the PAni and CNT. A maximum conductivity of 96.8 S cm −1 has been found for a PAni/PDMcT/CNT composite. High capacitance value (289.4 F g −1 ) was also determined for this composite, indicating that all materials, PAni, PDMcT and CNT, remain active during the charge-discharge cycling. The reduction in the capacitance after 100 cycles was found to be less than 25%. The capacitive behavior of all materials was confirmed by impedance analysis.
Photoelectrochemistry is based on interfacial electron transfer, where one of the phases is the e... more Photoelectrochemistry is based on interfacial electron transfer, where one of the phases is the excited state of a semiconductor. In this work we investigated the photoelectrochemical response of polyaniline intercalated in a layered material. The photoelectrochemical response show cathodic or anodic photocurrents depending on the applied potential, hence on the oxidation state of the polyaniline. Above 0.40 V in the oxidation and reduction processes, polyaniline shows n-type semiconductor characteristics and below 0.40 V in the reduction process, its behavior is of a p-type semiconductor. The composite SnP-C/Fe/PAni was obtained as a powder by polymerization of aniline in the interlayer space of the host Tin (IV) 2-carboxyethylphosfonate (SnP-C). The polymerization was done in an acid solution after incorporation of Fe 3+ to the host. X-ray diraction and conductivity measurements indicated the formation of polyaniline in the interlayer space and cyclic voltammetry measurements showed that the product is electroactive. #
A new methodology that combines the sol–gel method and a template approach is used to synthesize ... more A new methodology that combines the sol–gel method and a template approach is used to synthesize porous LiNi1−xCoxO2 films. Conventional films are obtained through the sol–gel method. The films are used to evaluate the influence of this new methodology on the electrochemical performance. It was observed, from X-ray diffraction analysis on the conventional film that a further increase in the
Composite electrodes were prepared via electrochemical polymerization of 3-methylthiophene in por... more Composite electrodes were prepared via electrochemical polymerization of 3-methylthiophene in porous PVDF membranes of various thicknesses. The electrochemical properties were determined by cyclic voltammetry and charge-discharge tests and the possible correlation of the results with the morphology of the host membranes was examined. The best definition of n-and p-doping/undoping processes and the biggest capacitance (82 F g −1 ) were obtained with a 27.5 m-thick composite. Further characterization of this composite using electrochemical impedance spectroscopy revealed three behaviors associated with variation in the oxidation state of poly(3-methylthiophene) during transition from the nundoping to p-doping states. The behavior of the charge transfer resistance and the double layer capacitance as a function of the applied potential were also determined.
Uploads
Papers by Silmara Neves