In conventional Electrowetting on Dielectric (EWOD) devices a static change of the contact angle is observed when a voltage is applied to the electrodes, usually correlated to the Lippmann equation. In this paper we analyze the contact angle changes by using two different dielectrics of different materials and thicknesses and also comparing two different ways of creating the field singularity at the contact line. Although it is known that the contact design may induce a tangential electric field and a spontaneous front wetting, we have observed in our devices that the change in the contact line is still due to the interfacial changing at the air-liquid interface. Several devices were fabricated using Teflon and PDMS coating on top of pyrex wafer and silicon wafer previously oxidized. The results obtained using these devices were compared to a conventional EWOD sample having PDMS deposited on top of metal electrodes previously laid out on top of pyrex wafer. We have compared the static contact angle change, produced using conventional voltage drive source, with a similar measurement after charges were generated in the gas phase. We have observed quite different behaviour of the two films used as coatings, for similar charge densities created, the contact angle on Teflon samples changed much less than in the PDMS samples.
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