Electrowetting of Aqueous Solutions of Ionic Liquid in Solid-Liquid-Liquid Systems

The influence of water on the electrowetting performance of the ionic liquid (IL) [BMIM][BF4] in contact with an ambient phase of hexadecane was studied. Electrowetting experiments on a fluoropolymer surface with IL concentrations between 0 and 99% enabled investigation of various electrowetting parameters, including the maximum range of accessible contact angles, the saturation contact angle (and voltage), and spreading dynamics. Experiments carried out using dc and ac potentials were successfully described with the Young-Lippmann equation prior to contact angle saturation. The saturation contact angles differed for ac and de electrowetting, indicating distinct saturation mechanisms. The dilution of [BMIM][BF4] by water, within the range of concentrations studied, had no direct impact on the electrowetting behavior, aside from indirect effects due to altered viscosity and interfacial tension.