Synthesis of ultra-thin superhydrophilic titanium oxide film and its effects on the capillary of microchannels

Ultra-thin superhydrophilic titanium oxide films were fabricated on silicon microchannels by an in situ reaction sol-gel method using titanium tetraisopropoxide as a starting material.. By changing the concentration of water in ethanol and reaction time, the thickness of synthesized TiO₂ films can be controlled from around 10 nm to 80 nm. The contact angle of as-synthesized TiO₂ films on flat silicon is around 20° and can be further decreased to zero by calcination at 700 °C in nitrogen atmosphere. X-ray diffraction spectra show the microstructure of the TiO ₂ films changed gradually from amorphous to anatase with the increase of calcination temperature. Surface morphology of the film before and after calcination also shows that a smoother coating with crystal structure was obtained by heat treatment. The flow velocity in the TiO₂ coated channel reached around 0.03 m/s, almost ten times of that in PDDA/PSS coated channel and 4 times of that in SiO₂ coated one. The ultra-thin superhydrophilic TiO₂ films fabricated by this method show the ability to strongly increase the wettability of microchannels without affecting the morphology of the sidewall of the channels, indicating potential applications to biomolecule analysis and surface tension driven microfluidic systems.