A novel technique for automatically transporting a micro-droplet on a wafer surface which has a wettability gradient was demonstrated. Lithographic patterns of hydrophobic SiO_2 and hydrophilic amorphous fluoropolymer permitted wettability modification of a Si wafer surface. A series of alternate hydrophobic and hydrophilic wedge-shaped patterns generated a required gradient in wettability. A droplet on the patterned surface moved along the wettability gradient due to an imbalance between surface tension forces acting on the opposite sides of the droplet edge. Positions and velocities of a droplet were measured using the high speed CCD camera.
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