Formation of supra-amphiphilic self-cleaning surface through sun-illumination of titania-based nanocomposite coatings

Titania-based nanocomposite coatings were prepared by mixing titania nanoparticles (Degussa P25) with a sol–gel derived silica sol and methoxysilane group-bearing styrene-co-acrylate (SA) oligomer, and curing with aminopropyltriethoxysilane at ambient temperature. The amphiphilic, mechanical and optical properties of the nanocomposite coatings with different titania contents and matrix compositions were investigated before and after sun-illumination. Supra-amphiphilic surfaces were achieved just after the coatings were placed in the sunshine for a short time. Accelerated weathering tests showed a good durability especially for the coatings with low fraction of organic phase while photocatalytic activity experiments with methylene blue demonstrated an excellent self-cleaning property of the coatings even with titania content less than 2.0 wt.%. The mechanism for the rapid formation of supra-amphiphilic surface with self-cleaning performance was explained.