Preparation and characterization of hydrophilic silicon dioxide film on acrylate polyurethane coatings with self-cleaning ability

A hydrophilic silicon dioxide film which was prepared by silicon dioxide sol could be coated on the acrylate polyurethane coating and translate the wettability of the coating from hydrophobic (CA = 85°) to hydrophilic (CA = 16°). The silicon dioxide sol was prepared by hydrolyzing tetraethoxysilane (TEOS) in aqueous medium and formed a hydrophilic film on acrylate polyurethane surface at 60 °C. The concentration of silicon dioxide sol influenced the film wettability and the hydrophilicity was studied by static contact angle and sliding angle measurements. It was observed that with increase in the ratio of the water/silicon dioxide sol from 0:1 to 3:1, the contact angle decreased from 35° to 16° and the sliding angle decreased obviously. Compared with hydrophobic acrylate polyurethane coating, the hydrophilic silicon dioxide film exhibited better self-cleaning ability which was confirmed by the self-cleaning test through measuring the specular gloss of coatings before contamination and after water droplets spray. Furthermore, there was little dust left on the hydrophilic silicon dioxide film after exposed to an outdoor environment for ca. 50 days.