Self-Cleaning and Tunable Structural Color Generation by TiO₂/Ti nanostructures

Structural colors are known for its long term sustainability in comparison to dyes, pigments, etc., but generating self-cleaning structural colors by nano/micro structuring is quite challenging. Here, we report self-cleaning structural color generation by TiO₂ nanorods and thin films on Ti sputtered glass and polyethylene terephthalate (PET) substrates deploying glancing angle deposition (GLAD) method. Reflected colors are tuned by varying height of TiO₂ nanorods or thin film on Ti films. Both the front and back surface of the samples show different colors, called Janus optical effect, due to altered dielectric constant on both sides of Ti film. All as-deposited TiO₂ nanorods and thin film samples are hydrophobic and hydrophilic respectively while both is transformed to reversible superhydrophilic state, a self-cleaning state, by UV irradiation. Further, annealing of samples on glass substrates has made the samples semi-transparent or transparent having superhydrophilic surface. Besides, structural colors are demonstrated for information encryption and optical ethanol sensing. Nevertheless, these structural colored specimens are promising for immense applications in the field of color printing, smart windows etc.