A Fundamental Study on Electrowetting by Traditional and Multifunctional Ionic Liquids: Possible Use in Electrowetting on Dielectric-Based Microfluidic Applications

Abstract

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.

A Tunable Ionic Liquid Based RC Filter Using Electrowetting: A New Concept

“…Use of [bmim][NTf 2 ] has several practical advantages: (i) having negligible or no vapor pressure so that evaporation is not a concern and no special sealing or packaging is needed for the filter (11), (ii) resistance to vibrations and satellite drop formation, particularly compared to water or aqueous electrolytes (3), (iii) a lower viscosity than most ILs so that response times are faster than other ILs (11) (3,11), and (vi) negligible effect of water when compare to other ionic liquids (3,11).…”

“…Also, the ∆θ is different for different ILs, i.e., some ILs exhibit higher ∆θ at a given voltage, whereas other ILs show lower ∆θ at the same voltage (3,11,12). Therefore, if one needs a wide tunability range of f c , it is desirable to use the first type of ILs, and for fine-tunability the latter types of ILs are desirable.…”

“…The ionic liquid (IL), 1-butyl-3-methylimidazolium bis-(triflouromethylsulfonyl)imide, is commonly abbreviated [bmim][NTf 2 ] (Figure 1) was synthesized in our laboratory as reported previously (11). Before use, the IL was kept in a vacuum oven for 18 h with phosphorus pentoxide (P 2 O 5 ) at room temperature to minimize the water content.…”

Electrowetting Effect: Theory, Modeling, and Applications

“…Most conductive electrolyte solutions (including many common solvents) can be used in EWOD to achieve a reasonable level of contact angle modulation (30,31). A systematic study was conducted by Nanayakkara et al to show the actuation of room temperature ionic liquids (IL) using EWOD and the results were also satisfactory (32). Liquid metals such as mercury have been used extensively in continuous electrowetting in the development of dropletbased micro electromechanical systems (MEMS) in both continuous electrowetting and EWOD setups (5,33).…”

Synthesis of tetracationic organic salt from 4,4'-bipyridine

“…This is due to the potential to change their structural features simply by: varying the nature of the cation and/or the anion; tuning them by introducing small structural changes in the constituting ions, or of the spacers separating them provides the opportunity to obtain materials with sets of desired properties suitable for different applications. They have been applied as a chemical anchorage on a solid support [10], starting materials for the synthesis of molecular devices [11,12], reaction media or catalysts, immobilization of catalysts [9], reaction media for high-temperature organic reactions [13,14], catalysts [15], receptors for anion recognition [16], low-molecular-weight gelators [17], fluorescent organic salts [18,19], energetic materials [20,21], for use in the preparation of solid films for organic electronic applications [22] and electrowetting materials [23]. Heteromolecules including imidazole, 1,10-phenanthroline, pyridine and others have been used as the starting materials for the synthesis of polycationic organic salts.…”