Microvalve actuation with wettability conversion through darkness/UV application

In this work a new microvalve concept that employs wettability conversion through the alternate application of darkness and UV irradiation to switch between off and on states is studied. The control of pressure drop through capillary channels by wettability conversion is the exploited control mechanism to switch in between two states. As expressed in the Young–Laplace equation the pressure drop depends on the channel diameter and contact angle (CA) of a given fluid on the channel. In this application positive pressure values obtained in the hydrophobic region are used for blocking, and negative pressure values obtained at the hydrophilic region are used for releasing water through microchannels. In both regions the magnitude of the pressure drop can be increased by very small microchannel diameters and extreme values of the contact angle (i.e. 0° and 180°). Laser microdrilling was chosen to generate the microchannels on commercially pure titanium sheets. The spatter produced by the laser drilling was removed by chemical etching, to improve the hole quality. Anodic oxidation was used for functionalizing the titanium microchannels with TiO2 layers that exhibit convertible wettability behaviour by alternate UV and darkness application. The actuation principle was demonstrated with a prototype microvalve produced.