Microfluidic valves based on TiO2 coating with tunable surface wettability between super hydrophilic and super hydrophobic

A new simple microfluidic valve, which utilizes titanium dioxide (TiO₂) nanoparticles tunable surface wettability between super hydrophilic and super hydrophobic to switch the valve on/off, is presented in this paper. TiO₂ nanoparticals are coated using liquid phase deposition (LPD) technique in the selected areas of silicon microchannels. After coating, a fresh TiO₂ film is super hydrophilic, and liquid can flow over the TiO₂ coated channel easily due to the capillary (valve open). After baking the channel covered with a PDMS film at 200°C, the contact angle of the TiO₂ film increases to 154 degree quickly in 10 minutes, resulting in a stop of liquid flow at the TiO₂ film (valve closed). When the TiO₂ film is exposed to a UV illumination, the film becomes super hydrophilic, and the valve is open again. The switch duration of the microfluidic valve between on and off status is less than 15 minutes. This type of microfluidic valve provides potential applications to microfluidic systems, especially the lab-on-chip systems.