SYNTHESIS OF SOLUBLE AND CONDUCTING POLYANILINE SALTS AS ANTI-CORROSION AGENTS FOR STEEL

We report an exciting study undertaken to improve desirable properties such as solubility, \ud electroactivity, electrical conductivity, thermal stability, molecular weight of polyaniline \ud (PANI). To fulfill these objectives, emulsion polymerization pathway was developed in \ud which, for the first time, the polymerization of aniline was carried out in the presence of \ud two dopants i.e. dodecylbenzenesulfonic acid (DBSA) and sulfuric acid, in order to \ud enhance the solubility and conductivity simultaneously. The obtained (PANI) co-doped \ud with dodecylbenzene sulfonic acid (DBSA) and sulfuric acid (PANI-DBSA-H2SO4) was \ud found to be completely soluble in a large number of common organic solvents and was \ud found to be highly conducting. Presumably the DBSA moiety enhanced the solubility and \ud H2SO4 further added to the conductivity. Reaction parameters were optimized for highest \ud yield and the synthesized polymers were systematically characterized by cyclic \ud voltammetry (CV), in situ conductivity measurements, UV-Vis spectroscopy and in-situ \ud UV-Vis spectroelectrochemical measurements, fourier transform infrared (FT-IR) \ud spectroscopy, elemental analysis, X-ray diffraction and scanning electron microscopy. \ud These PANI salts also show so far highest intrinsic viscosity i.e. up to 212 mL/g. The very \ud high intrinsic viscosity of the polymers indicates its large molecular weight, and hence its \ud good quality. It also exhibit very good electroactivity and electrochromic reversibility, very \ud similar to the response of electrochemically synthesized PANI. \ud Thermogravimetric analysis (TGA) revealed the excellent thermal stability up to 500 °C. \ud For detail investigation of thermal stability, TGA curves were recorded at different heating rates i.e. 6, 7, 8, 9 and 10 °C/min and three methods (Horowitz and Metzger method, Coats \ud and Redfern method and Chan et al. method) were used for calculation of activation energy \ud for the degradation of PANI-DBSA-H2SO4. It showed that activation energy slightly \ud increases with increase in heating rates which indicates that heating rate has no significant \ud influence on the activation energy for degradation process of the PANI. Furthermore, \ud thermally analyzed sample was collected at various temperatures (250, 490, 500, 1000 °C) \ud during TGA study. CV, FT-IR and UV-Vis spectroscopy of these samples also confirmed \ud the high thermal stability up to 500 °C. This is very welcoming for the use of PANI in \ud higher temperature applications. \ud Cyclic voltammetry was carried out to investigate the electrochemical properties PANI\ud DBSA-H2SO4 salts. The polymer was found to have high specific capacitance (392 F/g), \ud long cycle life and good environmental stability. Their performance at various scan rates \ud indicated a high power delivery/uptake of the PANI salts. These characteristics suggest the \ud synthesized PANI-DBSA-H2SO4 salts as efficient electrode materials for supercapacitor \ud application. The corrosion performance of PANI-DBSA-H2SO4 coating on stainless and mild steels has \ud been studied in natural water of Indian and Pacific Oceans. Results demonstrate that PANI\ud DBSA-H2SO4 coated steel is highly corrosion resistant in the water of both oceans. \ud Keywords: co-doped PANI, H2SO4, DBSA, complete solubility, cyclic voltammetry, in\ud situ conductivity, in-situ UV-Vis spectroelectrochemistry, X-ray diffraction, thermal grav\ud imetric analysis, supercapacitor, corrosion protection, natural water of oceans