Efeito do solvente sobre o crescimento e as propriedades de filmes compósitos a base de polianilina

Polyaniline (PAni) and its composites are materials which properties strongly depend on their syntheses conditions. Therefore, it is necessary to understand the effect of each parameter on the synthesis product. In this study, ethanol was used as the solvent for the electrosynthesis of PAni films and PAni/magnetite nanoparticles (MgteNP) composite films. These materials were obtained on a gold substrate by cyclic voltammetry coupled to the electrochemical quartz crystal microbalance (EQCM). A precursor solution composed by 0.5 mol L-1 H2SO4 and 0.1 mol L-1 aniline was used. The growth voltammograms obtained in ethanol are similar to those collected in aqueous medium except for the absence of the redox peaks attributed to the oxidation by-products. Moreover, the ratio between cathodic charge and product mass is lower for ethanol than for water; these features suggest that PAni is obtained with higher purity in ethanol than in water. The dependence of the cathodic charge and product mass with the number of cycles shows that the PAni grows significantly slower in ethanol than in aqueous medium. The behaviors described above are also observed for the growth of PAni/MgteNP films however, the presence of MgteNP causes a decrease in growth rate in the two media. This behavior may be associated with the increase in the resistance to the ion transfer caused by the presence of the oxide particles. Furthermore, an increase of the intensity of redox peaks attributed to the oxidation by-products is related to the presence of MgteNP. The EQCM curves obtained in the absence of the monomer show different profiles for the process of inflow and outflow of counter ions during the leucoemeraldine-emeraldine transition, suggesting distinct film morphologies. The ion flow is less intense in the films obtained in ethanol, which possibly results of the relatively low rate of the redox transition and of the more ordered morphology of these films, both provided by the use of ethanol. In summary, PAni and PAni/MgteNP films are obtained with a lower growth rate in ethanol than in water however, both films present higher purity and more ordered morphology. Thus, considering also the increase in the ion transfer resistance provided by the MgteNP, PAni and PAni/MgteNP, it may be assumed that the films obtained in ethanol are very suitable when electroactivity and barrier effect are required.