Polyaniline Micro/Nano Structures With Different Wettability As Anticorrosion Coating

Conductive polyaniline has a wide range of applications because of its specificproperties, such as highly conjugated molecular structure, controllable conductivity,environmental stability, easy synthesis, low cost and so on. One of the applications iscorrosion protection. In order to obtain information on the inhibition mechanism ofpolyaniline, the polyaniline were usually coated on metal surface as solution-castpolymer coating, electrodeposited coating and additives of resins coating. Recently,considerable interest has been given to the development of superhydrophobic films asanticorrosion coatings. Water serves as a medium for the diffusion of corrosivechemicals from reaching the metal-coating interface, so increasing the water repellantproperty of the coating increases its ability to protect the underlying substrate fromcorroding. On the basis of using conductive polyaniline and superhydrophobic filmsas protective coatings, our research of this thesis was focused on the correlationbetween the contact angle (θ) of the polyaniline micro/nanostructures coatings and thecorrosion protection efficiency (η) of the polyaniline micro/nanostructures. The mainresults are summarized as follows:1. A “template-free” method was used to prepare the polyanilinemicro/nanostructures with different wettability by changing the dopant. The corrosionprotection performance of the PANI with different wettability was evaluated in0.1mol/L H2SO4using the potentiodynamic polarization curves and electrochemicalimpedance spectroscopy (EIS). The effect of the wettability on the anticorrosionperformance was investigated. Superhydrophobic PANI micro/nano structures showgood anticorrosion properties. This is due to the superhydrophobic conducting PANIcoating not only inhibited water from being absorbed by the coating, thus preventingthe corrosive chemicals and corrosion products from diffusing through the coating,but also promoting a thin oxide film on the electrode surface.2. Firstly, sulfonic acid groups (-SO3H) which were strongly hydrophilic substituent group were introduced into the polyaniline molecular structure by thecopolymerization of aniline (ANI) and3-aminobenzenesulfonic acid (metanilic acid,MA). The anti-corrosion behavior of PANIMA coated carbon steel electrodes wasinvestigated in1mol/L H2SO4solutions by the potentiodynamic polarizationtechnique and electrochemical impedance spectroscopy (EIS). Results show that lowsulfur content in the PANIMA coatings afforded the best protection, though theperformance of all PANIMA coatings was inferior to PANI itself under the appliedtesting conditions. Secondly, a hydrophobic group, ethyl groups (-C2H5) wereintroduced into the polyaniline molecular structure by the copolymerization of aniline(ANI) and o-ethylaniline (OEA). The results of potentiodynamic polarization curvesand electrochemical impedance spectroscopy (EIS) indicate that corrosion protectionefficiency depends on the water repellent property of the PANIOEA copolymersmicro/nanostructures. And there is a well-fitting correlation between the contact angle() of the PANIOEA copolymers micro/nanostructures coatings and the corrosionefficiency () of the PANIOEA copolymers micro/nanostructures coatings which canbe expressed as=132.04–128.62exp (-/137). The POEA polymer showed thelargest static water contact angle (CA=145°) and the most effective protection withinhibition efficiency of87.29%. Lastly, a series of polyaniline (PANI) copolymersmicro/nanostructures were prepared by copolymerization of aniline (ANI) and3-aminobenzenesulfonic acid,3-aminobenzoic acid,3-toluidine and2-ethylaniline.The corrosion protection of PANI or PANI copolymers increased with increasingwater repellent property of the PANI or PANI copolymers micro/nanostructures. Awell-fitting correlation between the contact angle () of the PANI or PANIcopolymers micro/nanostructures coatings and the corrosion protection efficiency ()of the PANI or PANI copolymers micro/nanostructures coatings was found and can beexpressed as=102.22–102.78exp (-/84). The PANI copolymer with thehydrophobic-C2H5group (PANI-C2H5) showed the largest static water contact angle(CA=125°) and the most effective protection with an inhibition efficiency of78.98%.3. Polyaniline micro/nano fibers with different wettability was obtained byre-doping with Sodium Dodecyl Sulfonate (SDS) and perfluoro caprylic acid (PFOA). It was found that the wettability of the polyaniline micro/nano fibers was controlledby the content of SDS and PFOA. Standard electrochemical measurements revealedthat the corrosion protection of PANI increased with increasing the water repellentproperty of the PANI micro/nano fibers. And there are well-fitting correlationsbetween the contact angle () of the PANI micro/nano fibers coatings and thecorrosion efficiency () of the PANI micro/nano fibers coatings which can beexpressed as=234.32–205.31exp (-/442)(re-doped with PFOA) and=5.971–7.10exp (-/84)(re-doped with SDS).