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Two different types of nano-silica (i.e., hydrophilic Aerosil 200 and hydrophobic Aerosil R805) were employed in the preparation of 2-pack acrylic polyol polyurethane nano-coatings so that the electrochemical properties of the resultant coatings could be investigated. Electrochemical impedance spectroscopy was used to evaluate the corrosion performances of such nano-coatings applied onto mild steel substrates that were immersed in 3.5% (w/w) NaCl solutions. It was observed coatings that contained nanosilica increased the barrier properties of the binder, as well as the coatings' electrochemical resistance compared with pure polyurethane coatings. The surface tension of pure polyurethane was measured by a tensiometer. Rheological properties were also determined at various shear rates by a rotaviscometer. Results showed that the surface tension of hydrophobic nanosilica is very close to the pure polyurethane matrix, giving the better compatibility of the two. This was further confirmed by transmission electron microscopy and by the fact that the hydrophobically filled nano-silica coatings showed shear thinning behavior in the fluid state. Also observed was better corrosion performance of the resultant hydrophobic nano-coatings compared to coatings embedded with hydrophilic nano-silica.

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