Poly(ethylene glycol)-grafted silica nanoparticles for highly hydrophilic acrylic-based polyurethane coatings

A silane coupling agent bearing polyethylene glycol) (PEG) chains was synthesized using triethoxysilylpropyl isocyanate and excess PEG, with molecular weights of 400 or 1000 g/mol (PEG400 and PEG1000) and chemically bonded to SiO2 nanoparticles, to obtain PEG-modified SiO2 nanoparticles (SiO2-PEG) with pendant hydroxyl groups. The PEG modification was demonstrated by Fourier transformed infrared spectroscopy, thermogravimetric analysis, and through the dispersion behavior of SiO2-PEG nanoparticles in water. The SiO2-PEG nanoparticles were further incorporated into acrylic-based polyurethane (APU) coatings. Transparent and crack-free nanocomposite coatings with SiO2-PEG content up to 35 and 40 wt.% were achieved for SiO2-PEG400 and SiO2-PEG1000, respectively. The high quality of the product was owed to the improved compatibility of SiO2 nanoparticles with the APU matrix after PEG modification. Due to the rearrangement of hydrophilic/hydrophobic segments, a highly hydrophilic surface, with a water contact angle (WCA) as low as 38.7, was attained for the SiO2-PEG embedded coatings after induction with water. Moreover, SiO2-PEG400 was more efficient in enhancing the surface hydrophilicity of the APU coatings than SiO2-PEG1000 at the same SiO2-PEG content. In contrast, pure APU coatings and the APU coatings containing unmodified SiO2 nanoparticles displayed WCA5 of 68.2 and 70.1, respectively. Outdoor exposure experiments showed that the APU coatings containing SiO2-PEG nanoparticles had excellent dirt-resistance. (C) 2017 Elsevier B.V. All rights reserved.