Electrowetting of water and aqueous solutions on poly(ethylene terephthalate) insulating films

The wettability of poly(ethylene terephthalate) (PET) films by water and aqueous solutions is increased by applying a voltage between the water and a rear electrode placed under the polymer film. We show that this electrowetting effect can decrease contact angles by more than 30 degrees under applied voltages of 200 V-eff. At low voltage, we observe the expected variation, but for high voltage, the electrowetting saturates, with other polymer films. In the case of PET, the increase in wettability is irreversible but only as a result of modification of the polymer at the edge of the drop, near the three-phase contact line, where the electric field is high and inhomogeneous. At very high fields, we observe that the liquid contour becomes unstable, the liquid drop expelling little droplets around it. We investigate the influence of the composition of the aqueous solution with simple solutes as well as water soluble polymers. In all these cases, the electrowetting effect can help the solutions to wet the solid surface. (C) 1996 Elsevier Science Ltd.