Electrowetting of ionic liquids (ILs) in different alkane ambient and at different temperatures were studied under different AC voltages. The performance of IL-based electrowetting at elevated temperatures and that at room temperature was compared. It turns out that the electrowetting of ILs at elevated temperatures resulted in faster response and lower operation voltage. Furthermore, the relationship between the structure of the ion and the contact angle change was specifically investigated and theoretically explained. Finally, the properties of IL-based electrowetting in different alkane ambient were studied. It was demonstrated that the long length of the alkyl chain guaranteed a smaller contact angle under the same applied voltage. All the experimental results showed attractive features involving wide operating temperatures and in particular high stability, fast response, and good reversibility at elevated temperatures. The performance of IL-based electrowetting could be further improved through an optimal choice of an ambient phase or a rational design and synthesis of ionic liquids.

Keywords: electrowetting; ionic liquids; temperature; alkanes ambient; AC voltage; response time

★★★☆☆ Hu XD,Zhang SG,Lu XJ,et al. On The Performance Of Thermostable Electrowetting Agents[J]. Surf. Interface Anal.,2011.

Electrocapillarity is the basis of modern electrowetting. And room temperature ionic liquids, an increasingly important set of electrolytes and organic salts that are liquid at room temperature, are considered a novel class of electrowetting agents, because of non-significant vapor pressure, nonflammability, good thermal stability, and a wide useable temperature range. In this paper, a simple device has been fabricated to investigate the electrocapillarity of ionic liquids. It shows attractive features involving wide operating temperature and in particular high stability, fast response and good reversibility at high temperatures. Besides, electrocapillarity of ionic liquids is strongly dependent on power supply frequency. In particular, high frequency, stable, reversible and wide height of rise modulations were obtained. The phenomenon of ionic liquids-based electrocapillarity was found to be affected by the structure and physicochemical properties of ionic liquids such as density, surface tension, alkyl carbon chain length of cation, type of the anion, etc., and the efficiency could be further improved through optimal choice of ambient phase or rational design and synthesis of ionic liquids.

Keywords: Electrocapillarity, ionic liquids, height of rise, response time, high temperature, AC electric fields

★★★☆☆ Hu XD,Zhang SG,Qu C,et al. Electrically Switchable Capillarity Of Ionic Liquids[J]. J. Adhesion Sci. Technol.,2011,0:1-10.

We demonstrated an infrared variable focus ionic liquids lens using electrowetting, which could overcome the problems caused by use of water, e.g., evaporation and poor thermostability, while keeping good optical transparency in visible light and near-infrared region. Besides, the type of lens (convex or concave) could be tuned by applied voltage or refractive index of ILs used, and the transmittance was measured to exceed 90% over the spectrum of visible light and near-infrared. We believe this infrared variable focus ionic liquids lens has a great application prospect in both visible light and infrared image systems.

★★★☆☆ Hu XD,Zhang SG,Liu Y,et al. Electrowetting Based Infrared Lens Using Ionic Liquids[J]. Appl. Phys. Lett.,2011,99:213505(1-3).

This work presents ionic liquid based variable focus lenses using electrowetting, which exhibit excellent performance over a conventional saline based lens such as good tolerance of sharp temperature variation, wide operating temperature range (which is up to 100 ℃) and in particular high stability at high temperatures.

★★★☆☆ Hu XD,Zhang SG,Qu C,et al. Ionic Liquid Based Variable Focus Lenses[J]. Soft Matter,2011,7:5941–5943.