TiO2coated microfluidic devices for recoverable hydrophilic and hydrophobic patterns

We report a simple method for modifying the surfaces of plastic microfluidic devices through dynamic coating process with a nano-colloidal TiO 2 sol. The surface of the thermoplastic, cyclic olefin copolymer (COC) was coated with the TiO 2 film, that displayed an effective photocatalytic property. The hydrophilic surface is obtained in the TiO 2 -coated zone of a microfluidic channel, and TiO 2 coated surface degradation can be reversed easily by UV irradiation. The present work shows a photocatalytic activity concerning the effect of TiO 2 coating density, which is controlled by the number of coating cycles. The hydrophilized surface was characterized by the contact angle of water and the TiO 2 coated COC surface reduced the water contact angle from 85° to less than 10° upon UV irradiation. The photocatalytic effect of the layer that was coated five times with TiO 2 was excellent, and the super-hydrophilicity of the TiO 2 surface could be promptly recovered after 10 months of storage at atmospheric conditions. The COC microfluidic devices, in which TiO 2 has been freshly deposited and aged for 10 months, were capable of generating water-in oil-in water (W/O/W) double emulsions easily and uniformly by simple control of the flow rates for demonstration of excellent hydrophilic patterning and recovery of the TiO 2 coated in the microchannels.