Influence of the electrical double layer in electrowetting

Electrowetting (wetting under the influence of an applied electric field) of three fluoropolymer surfaces (amorphous Teflon, DuPont) by electrolyte solutions was studied with the sessile drop method. The electrowetting curve (contact angle/potential) is analogous to the electrocapillary curve (surface tension/potential) and may be described by a combination of the Young and Lippmann equations. The influence of the electrical double layer at the polymer/solution interface has been neglected in the past because the overall interfacial capacitance is mainly determined by the capacitance of the insulating polymer layer. We demonstrate that for some surfaces a systematic deviation occurs at positive potentials. This departure from the constant capacitance regime is attributed to double layer effects, namely, the adsorption of hydroxide and halide anions. The pH, ionic strength, and polymer composition can all influence electrowetting behavior.