Low-temperature preparation of superhydrophilic coatings using tetraethoxysilane and colloidal silica by sol-gel method

In this study, a simple and facile method for producing superhydrophilic coatings by thermal curing at a low temperature of 100 °C or less for 2 h without a calcination process at high temperatures was reported. Hydrophilic coating solutions were prepared using tetraethoxysilane (TEOS) and colloidal silica as precursors by sol-gel method. After applying the prepared coating solution to a glass slide by dip-coating, a superhydrophilic coating was prepared by thermal curing at 100 °C for 2 h. In this process, the effect of the amount and concentration of colloidal silica added to the polysiloxane sol derived from TEOS on the superhydrophilicity of the coatings was observed. The coatings were characterized by water contact angle (WCA) analyzer, FT-IR spectroscopy, field emission scanning electron microscopy (FE-SEM), and atomic force microscope (AFM). In the coatings prepared using 10 wt% colloidal silica, as the content of colloidal silica added increased to 8 g, 16 g, 24 g, and 40 g, the WCA of the coating decreased to 56°, 37°, 10°, and 5°, respectively. From this result, it can be seen that a superhydrophilic coating, which shows a WCA of 5° or less, can be obtained when 40 g of colloidal silica is added. The FT-IR results suggest that the superhydrophilic coating consists of more hydrophilic components than the coating using only the polysiloxane sol without the addition of colloidal silica. In addition, the superhydrophilic coating showed a rough surface morphology in SEM and AFM observations. It was considered that the superhydrophilicity of the coating was derived from the increase of hydrophilic chemical components and surface roughness by adding colloidal silica. Moreover, the superhydrophilic coating showed an excellent anti-fogging property and a self-cleaning ability.