Abstract
Capillary pressures due to the wetting behaviour of a liquid on a material can be exploited to control the pressure drop of the liquid into microchannels. The pressure can be estimated by the Young-Laplace equation and for a given liquid, high values can be achieved by having small microchannel diameters and high wetting contact angles. An original actuation method for a microvalve can be derived from this, if reversible wettability behaviour can be achieved, i.e. the switching between hydrophobic to hydrophilic states implies that the microvalve can be turned on and off. In the present work a wettability controlled microvalve with UV/dark actuation is proposed. The valve microchannels are obtained by laser microdrilling on commercially pure titanium foil. Then the drilled titanium foil is anodic oxidized to grow on the microchannel surfaces a nanostructured TiO2 layer, which exhibits reversible wettability behaviour upon the alternate application of UV and darkness. Finally, the concept is demonstrated in a prototype microvalve controlled between OFF and ON states by UV light application.
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