Silmara Neves

Characterization of self-assembled thiols monolayers on gold surface by electrochemical impedance spectroscopy

Thiols with different alkyl chain length and containing COOH terminal group were self-assembled on gold electrodes. The electron transfer of Fe(CN)63-/4- couple to the electrode was studied at different pH by means cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Changes in solution pH resulted in the charge variation of the self-assembled monolayer (SAM) terminal group and, consequently, the electrostatic interaction of SAM with the electroactive species in the solution.

Influence of template synthesis on the performance of polyaniline cathodes

Abstract A composite using polyaniline (PAni) as the conducting polymer and silica sol–gel as the host matrix was prepared by the template method. To evaluate the electrochemical performance of the PAni/silica composite, PAni films were synthesized under the same conditions, directly on ITO substrates and the results were compared. Cyclic voltammetry, impedance spectroscopy, charge–discharge cycles and lifetime tests were done in organic medium. The PAni/silica composite showed excellent performance in all of the tests. This composite may therefore be useful for cathodes in lithium microbatteries.

Compósitos termoplásticos com madeira

Resumo: Dentre muitas fibras naturais de interesse tecnologico, o residuo de madeira substitui com vantagens as cargas e reforcos tradicionalmente empregados em compostos e compositos polimericos, particularmente os de ori- gem mineral, tais como talco, CaCO 3 e fibra de vidro. A tecnologia dos chamados Wood-Plastic Composites (WPCs) envolve conceitos de compatibilidade e processabilidade e apresenta grandes desafios tecnologicos para a formula- cao e estabilizacao da mistura devido a baixa estabilidade termica da celulose. Muitos dos avancos tecnologicos em WPCs dependem de uma analise criteriosa das caracteristicas fisicas de seus componentes e das condicoes de processamento do sistema, particularmente aspectos relacionados a sua compatibilizacao. No presente trabalho sao apresentados estudos sobre a reatividade do polipropileno modificado com anidrido maleico (PP-MAH) utilizado como compatibilizante em compositos termoplasticos de polipropileno com farinha de madeira. A influencia da carga celulosica e a eficiencia do compatibilizante nas propriedades reologicas, termicas, mecânicas e morfologicas do sistema foi avaliada atraves de medidas de rigidez, grau de cristalinidade, temperatura de cristalizacao e fusao cristalina levando-se em conta as caracteristicas da resina, a distribuicao granulometrica e o teor de umidade da farinha de madeira. Observou-se que os compositos compatibilizados com PP-MAH apresentaram ganhos significa- tivos de rigidez em relacao aos compositos nao-modificados independentemente do tipo de farinha de madeira em- pregada. As propriedades termicas do polimero mostraram-se sensiveis a distribuicao granulometrica e algumas com- posicoes apresentaram tendencia ao escurecimento e a elevacao da temperatura de cristalizacao do polimero na presenca do reforco celulosico. Imagens obtidas por microscopia eletronica de varredura ilustram o molhamento da fibra celulosica pela resina termoplastica quando na presenca do compatibilizante indicando a possivel ocorrencia de reacoes de esterificacao na interface polimero-madeira. Palavras-Chave: Compositos termoplastico-celulosicos, tecnologia polimero-madeira, compatibilizacao, reometria de torque, analise termica. Wood-Plastic Composites Abstract: Wood waste fibers (WWF), mostly known as wood flour, can replace mineral fillers such as talc, CaCO 3 and fiberglass in the reinforcement of thermoplastics with great advantage. Wood-plastics composites (WPCs) technol- ogy includes concepts of compatibility and processing and yet presents technical challenges in grade formulation and stabilisation of the composite system. Owing to thermal constraints in wood flour processing, commodities such as polyolefins (PP, PEAD/PEBD), styrenics (PS e HIPS) and vinyls (PVC) represent the bulk of the thermoplastics used in WPCs applications. In the present work, a brief overview of the latest developments in WPCs processing technol- ogy is discussed in the light of technical characteristics and performance of this novel class of thermoplastics com- posites in emerging applications. Some investigations on compatibilizing efficiency of the polypropylene modified with maleic anhydride (PP-MAH) are presented for polypropylene formulations compounded with different types of pinus wood waste. The influence of the cellulosic filler and the efficiency of compatibilizers on thermal, mechanical and morphology of the composite system was evaluated through stiffness measurements, degree of cristallinity, crystallization and melt temperatures in regard to the resin intrinsic properties and sawdust characteristics. Electron microscopy micrographs illustrate in great detail the filler wetting by the resin in the presence of the maleic anhy- dride in the polypropylene used as compatibilizer suggesting that sterification reactions may take place at the wood- polymer interface.

Determination of fractal dimension of polyaniline composites by SAXS and electrochemical techniques

The surface morphology of polyaniline (PAni) composite films was studied by using the fractal dimension concept. This work presents the utilization of the cyclic voltammetry and electrochemical impedance spectroscopy to determine the fractal dimension. The small angle X-ray scattering (SAXS) technique has been extensively used to investigate the structure of several materials and it was used here to verify the confidence of electrochemical methods by comparison. All techniques employed revealed that PAni/Silica and PAni/PVDF composites present surface fractals.