Influence of various loadings of hydrophilic or hydrophobic silica nanoparticles on water uptake and porosity of a polyurethane coating

In this paper, water uptake, porosity and corrosion behaviours of two‐pack polyurethane coatings separately loaded with two types of silica nanoparticles (i.e. hydrophilic and hydrophobic silica nanoparticles) are presented. Water uptake of such coatings was measured by the aid of electrochemical impedance spectroscopy whereas porosity of the coatings was determined according to the ASTM D 6583 standard. Transmission electron microscopy and Fourier transform infrared spectroscopy were also utilised to examine morphology and chemical structure of the nanoparticles filled coatings. These techniques show that the hydrophobic SiO2 nanoparticles could be easily dispersed throughout the polyurethane matrix while negatively influence the curing process of the coatings. The results reveal that the incorporation of both hydrophilic and hydrophobic silica nanoparticles into the polyurethane matrix, generally, reduces the percent porosity of the resultant coatings. However, obtained results show that the type and content of silica nanoparticles influence the capacitance and therefore water uptake of the coatings to various extents.