Complementary Electrowetting Devices on Plasma-Treated Fluoropolymer Surfaces

A reversal of the normal two-fluid competitive (water vs oil) electrowetting (nEW) on dielectric has been achieved by plasma irradiation of the normally hydrophobic fluoropolymer followed by thermal annealing. This process first renders the surface hydrophilic and then returns it to its normal hydrophobic properties as measured by water droplet contact and rolling angles. In the plasma-irradiated and annealed EW device (pEW), the normal two-fluid EW action is reversed after an initial charging step, with the oil layer being displaced at zero voltage and being returned at high voltage. A possible explanation of this effect is a plasma-induced modification of the fluoropolymer, rendering it more susceptible to charge injection and trapping at high voltage. nEW and pEW devices exhibit complementary EW operation, as verified by oil movement and optical transmission. This method can lead to low-power operation of two-fluid EW devices.