Obtenção e comportamento eletroquímico de nanopartículas de polianilina e seus derivados

Conducting polymers are electroactive materials which can be used for different purposes as organic electronics, electrochromic devices, protective and antistatic coatings etc. The electronic properties of these materials can be significantly improved if they are obtained as nanoparticles. In this study, polyaniline nanoparticles (np-PAni), poly(o-methoxyaniline) nanoparticles (np-POMA) and Ani and OMA copolymer nanoparticles (np-PAOMA; molar ratio 3:1 Ani:OMA) were synthetized by interfacial polymerization using 0.5 mol L-1 H2SO4 + 0.08 mol L-1 (NH4)2S2O8 aqueous solution as polar phase and 1.6 mol L-1 of monomer dissolved in toluene as non-polar phase. The produced polymers were deposited as films on Pt plates from their respective NMP solutions and the electrochemical properties of these films were assessed by cyclic voltammetry. Polymerization of Ani and OMA occurs at the water/toluene interface because of the respective monomer salt formation and its further oxidation by (NH4)2S2O8. If Ani is used, an interfacial anilinium sulfate layer is formed in the first minutes of reaction resulting in an interfacial np-PAni layer, which is the exceeding polymer precipitates from the interface. Interestingly, this interfacial salt or polymer layer is not formed during the polymerization of OMA, but a thinner salt layer is observed during the co-polymerization; however, no polymer layer is observed at the end of the polymerization. np-PAni and np-POMA showed similar solubility in NMP whereas np-PAOMA showed a slightly higher solubility in this solvent. The voltammetric profiles of these polymer films on Pt in H2SO4 0.05 mol L-1 solution agrees with the literature, except that the redox peaks are anodically shifted regarding the expected values1. This is possibly not only characteristic of the synthesis conditions, but also a result of using the dipping method for film deposition. It is noteworthy that np-PAOMA films showed the smallest separation between the anodic and the cathodic peaks attributed to the polaron formation (64 mV smaller than np-PAni and 101 mV smaller than np-POMA). The np-PAni films showed the highest electrical charge density (0.545 C mg-1 cm-2) followed by np-PAOMA (0.164 C mg-1 cm-2) and np-POMA (0.053 C mg-1 cm-2), suggesting that PAni reaches the highest levels of doping and is therefore the most conducting of these materials. Therefore, conducting polymer nanoparticles with different electronic properties and electroactivity can be obtained from Ani, OMA and their copolymers by interfacial polymerization.