Hydrophobic–hydrophilic conversion in microfluidic polymer channels with TiO2 thin films

Abstract

In this study, recoverable and maintainable hydrophilic micropatterns on polymer-based microfluidic devices were developed through liquid phase deposition of a photocatalytic TiO2. The TiO2-coated region in the microchannel could be hydrophilized through brief UV irradiation upon request. A titanium oxide film was deposited either on bare polymer substrates or on a titanium-sputtered surface using an aqueous TiCl3 solution at 80 °C. A cyclic olefin copolymer (COC) coated with the TiO2 film displayed effective photocatalytic activity, which reduced the water contact angle from 50° to less than 5°. The Ti seed layer was facilitated to pave the substrate with TiO2 grains during the liquid phase deposition. Thus, the photocatalytic effect could be achieved with less number of LPD cycles. Even after contamination from an organic solvent or photoresist, the surface became hydrophilic upon 5 min of UV irradiation. The photocatalytic effect was so stable that super-hydrophilicity of the surface could be promptly recovered after a month of storage under atmospheric conditions. A COC microchannel was fabricated with TiO2 patterns to allow for controlled delivery of the aqueous liquid without the need for external pumps or valves. A hydrogel pattern self-organized along the TiO2 pattern demonstrated a practical application of the recoverable hydrophilicity in microchannels. Functional hydrogels can easily and stably be integrated into a polymer microchannel using this approach.