Flow-directed assembly of non-spherical titania nanoparticles into superhydrophilic thin films

Superhydrophilic thin films of 21 nm sized non-spherical titania nanoparticles are fabricated from a colloidal suspension by fixed blade flow coating without UV illumination. At a blade angle of a = 36° and a gap of d = 300 µm, hierarchically structured films with increasing surface roughness along with microscopic voids are formed depending on the substrate velocity and the titania volume fraction. Increasing the roughness is shown to be concomitant to an increase in the hydrophilicity, eventually leading to superhydrophilicity or water contact angle less than 5°.