A fundamental study on electrowetting by traditional and multifunctional ionic liquids: Possible use in electrowetting on dielectric-based microfluidic applications

Water or aqueous electrolytes are the dominant components in electrowetting on dielectric (EWOD)-based microfluidic devices. Low thermal stability, evaporation, and a propensity to facilitate corrosion of the metal parts of integrated circuits or electronics are drawbacks of aqueous solutions. The alternative use of ionic liquids (ILs) as electrowetting agents in EWOD-based applications or devices could overcome these limitations. Efficient EWOD devices could be developed using task-specific ILs. In this regard, a fundamental study on the electrowetting properties of ILs is essential. Therefore electrowetting properties of 19 different ionic liquids, including mono-, di-, and tricationic, plus mono- and dianionic ILs were examined. All tested ILs showed electrowetting of various magnitudes on an amorphous flouropolymer layer. The effects of IL structure, functionality, and charge density on the electrowetting properties were studied. The enhanced stability of ILs in electrowetting on dielectric at higher voltages was studied in comparison with water. Deviations from classical electrowetting theory were confirmed. The physical properties of ILs and their electrowetting properties were tabulated. These data can be used as references to engineer task-specific electrowetting agents (ILs) for future electrowetting-based applications.