Facile construction of silica-based surface coating onto polypropylene microporous film through dopamine-assisted hydrolysis of tetraethoxysilane

Surface modification with silica-based coating is widely used to attain high performance and construct special functions for thin films. In this paper, dopamine (DA) and tetraethoxysilane (TEOS) were used as initial building blocks to construct a biomimetic hydrophilic and mechanical robust silica-based coating onto polypropylene (PP) microporous film. It was found that the final DA/TEOS coating can be steadily immobilized onto PP film and greatly improve the hydrophilic property of PP film as evidenced by the decreased contact angle. Furthermore, the coating structures were comparatively investigated through one-step synthesis and two-step synthesis of DA and TEOS with a fixed ratio. Interestingly, the one-step synthesized coating possesses a loosely-packed layer with dispersed SiO2 nanoparticles within polydopamine matrix while the two-step synthesized coating shows a high loading of SiO2 nanoparticles. As a result, the two-step approach leads to a continuous SiO2 layer with abundant hydroxyl groups, indicating a better lyophilic property and depressed thermal shrinkage. In addition, the concentric SiO2 layer results in a significant increase of the tensile strength of PP films.