Preparation Of Micro/Nano Polyaniline And Its Application In Anti-Corrosion Coatings

Micro/nanostructures of polyaniline (PANI) have excellent physical and chemical properties owing to their unique doping, diverse molecular structure, and environmental-friendly properties. It is widely applied in the field of anticorrosive and antifouling coatings, conductive materials and electromagnetic shielding materials. Micro/nanostructure of PANI and anticorrosive coatings containing PANI were prepared, and their physical and electrochemical properties were studied in this thesis.(1) Twelve kinds of PANI with different morphologies were prepared by "direct mixed reaction" method using ammonium persulfate (APS) as initiator and dihydric phosphate as dopant. Resultant PANIs were characterized by FT-IR, UV-vis and XRD studies. The morphologies of PANI were observed by SEM and TEM. It was found that sodium dihydrogen phosphate doped PANI showed the highest yield. With the increase of dihydric phosphate concentration, the apparent yield of PANI was also increased. It was concluded that PANI-nanofibers could be prepared at low temperature, while PANI-nanorods could be prepared at high temperature. With increasing temperature, the apparent yield of PANI was first increased and then decreased. PANI-nanofibers and nanotubes with good morphology and high apparent yield were obtained by controlling reaction conditions.(2) Sixteen different phosphoric acid doped PANI with different morphologies were prepared by "direct mixed reaction" method using APS as initiator. The apparent yields were calculated, and the morphologies were observed by SEM and TEM. The influence of phosphate acid concentration, aniline concentration and reaction time on apparent yields and morphologies were discussed. The results indicated when the amounts of aniline and APS were fixed, the apparent yield of PANI was increased with the increasing of phosphate acid concentration. With increasing temperature, the apparent yield of PANI was first increased and then decreased. PANI-nanofibers, nanotubes and nanosheets with good morphology and high apparent yield were obtained by controlling reaction conditions.(3) One PANI-based epoxy resin coating, one epoxy resin coating and nine different PANI-based PVB coatings were prepared. Their adhesion, hardness, impact resistance, open circuit potential, tafel plot and electrochemical impedance resistance were determined. Equivalent electrical circuit was used to fit the changes of electrochemical parameters during the corrosion. These coatings were immersed in 3.5 wt% NaCl aqueous solutions for different time, and their corrosion results were observed. PANI-based epoxy resin exhibited good adhesion and impact resistance. Based on the fitting results of equivalent circuit, PANI-based epoxy resin coatings exhibited better anti-corrosion properties than pure epoxy resin coatings. PANI-based epoxy resin coating formed dense oxide film on metal surface, which was proved by X-ray Photoelectron Spectroscopy (XPS). PVB coating with PANI-nanosheet showed higher corrosion potential and lower current density, which meant good anti-corrosion properties. In conclusion PVB coatings with PANI-nanosheet showed best anti-corrosion properties.