pH effects on the ohmic properties of bromophenol blue-doped polypyrrole film

Abstract

A resposta ôhmica durante medidas de resistência in situ de filmes de polipirrol (ppy) dopados com azul de bromofenol (BPB) foi analisada para se estudar o efeito do pH nas propriedades analíticas dos filmes. As moléculas de BPB foram inseridas na matriz polimérica através de síntese eletroquímica sobre eletrodos digitalizados de ouro. Os filmes de ppy-BPB não apresentaram diminuição da resistência ôhmica linear com relação ao aumento do pH do meio, no intervalo de 1,5 a 11, sendo observado um aumento da resistência do filme após imersão em pH 7,5. O comportamento não linear é uma desvantagem para a aplicação do ppy-BPB como sensor de pH, no entanto, importantes informações sobre a interação entre o dopante e o polímero conjugado podem ser obtidas deste sistema. O comportamento ôhmico do filme de ppy-BPB pode ser explicado em termos da variação no equilíbrio entre as formas neutra e aniônica do corante preso na matriz de ppy. O estudo neste trabalho contribui para o desenvolvimento de sensores eficientes baseados em polímeros condutores.The ohmic response of bromophenol blue (BPB) doped polypyrrole (ppy) films obtained by in situ resistance measurements was studied to evaluate the pH effect on their analytical properties. BPB molecules were inserted into the ppy matrix by electrochemical synthesis onto digitized gold electrodes. Ppy-BPB films do not present decrease in the linear ohmic resistance when increasing pH values over the pH range 1.5-11.0, displayed by an increase in resistance after immersion in pH 7.5. The nonlinear behavior is a disadvantage for the application of the ppy-BPB film as pH sensor, however, meaningful information about the interaction between the dopant and the conjugated polymer can be obtained from the system. The ohmic behavior of the ppy-BPB films are explained in terms of the equilibrium between neutral and anionic dye species embedded in the ppy matrix. This work brings important contributions to the development of efficient conducting polymer-based sensors.Keywords: polypyrrole, bromophenol blue, ohmic properties, doped films IntroductionConducting polymers are well known materials with interesting optical, magnetic and electrical properties. 1-3The oxidation process in the electronic structure of a heterocyclic conjugated polymer, such as polypyrrole (ppy), 4,5 leads to the formation of polaron and bipolaron states. These energy states are related to remarkable properties of conjugated polymers that take place with the introduction of anion dopants into the polymer matrix to stabilize those charges (polaron and bipolaron) formed during oxidation. 6 The dopant used during the polymer synthesis can directly affect the electrical and structural properties of the conjugated polymer. 2,7,8 Study of the interaction between polymer and dopant is meaningful for the comprehension and applications of these materials. 9The literature have demonstrated the application of electroactive conjugated polymers in the solar cells development, 10,11 organic light-emitting devices, 12,13 and electro...

Degradation of bromophenol blue molecule during argon plasma jet irradiation

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