The Effect of AC Frequency on the Electrowetting Behavior of Ionic Liquids

This paper presents a study of electrowetting of ionic liquids (ILs) under AC voltages, where nine different ILs (including mono-, di-, and tricationic varieties) with three different AC frequencies (60 Hz, 1 kHz, 10 kHz) were experimentally investigated. The main foci of this study are (i) an investigation of AC frequency dependence on the electrowetting of ILs; (ii) obtaining theoretical relationships between the relevant factors that explain the experimentally achieved frequency dependence; and (iii) a systematic comparison of electrowetting of ILs using AC vs DC voltage fields. The frequency of the AC voltage was found to be directly related to the apparent contact angle change (Deltatheta) of the ILs. This relationship was further analyzed and explained theoretically. The electrowetting properties of ILs under AC voltages were compared to that under DC voltages. All tested ILs showed greater apparent contact angle changes with AC voltage conditions than with DC voltage conditions. The effect of structure and charge density also was examined. Electrowetting reversibility under AC voltage conditions was studied for few ILs. Finally, the physical properties and AC electrowetting properties of ILs were measured and tabulated.