Manufacturing and characterisation of a wettability controlled microvalve with darkness/UV actuation

A contactless microvalve actuation method through UV irradiation and darkness application was developed, based on the control of the capillary pressures created in microchannels. This paper reports the design and the manufacturing phases, along with the demonstration of the concept and characterization of a manufactured prototype. To realize the wettability microvalve with UV/darkness actuation concept, commercially pure titanium sheet was microdrilled with a pulsed fiber laser system, then chemical etching was applied to remove spatter created during the laser process and finally anodic oxidation was employed to functionalize the microchannel surfaces with TiO₂ nanotubes. The alternate application of UV and darkness allows commuting between hydrophobic and hydrophilic states of the nanotubular surface.. Two aims have driven the manufacturing parameters investigation: i) to reach contact angle values towards the extremes in the hydrophobic and hydrophilic regions, ii) to obtain smallest hole diameters possible. A prototype microvalve was in the end realized and tested. The concept was validated, as switching from off to on, and on to off phases were achieved. The break pressure was measured and compared to the theoretical value. Finally the temporal behaviour of the wetting change under the UV irradiation as a function of contact angle was evaluated.