Room temperature ionic liquids (RTILs or ILs) have emerged as a novel class of versatile solvent and soft material due to their negligible vapor pressure, wide liquid temperature range, intrinsic
ionic conductivity and acceptable electrochemistry stability.1 Besides these well-known properties, ILs could have good transparence in visible light, near-infrared and even in some other infrared regions, which renders them potential soft optic materials for multiple applications. 2 Recently, electrowetting of ILs has been studied and our previous results showed a reversible and wide contact angle modulation of ILs using oil as the medium and under an AC electric field,
as compared to that in air or under a DC electric field.3 In particular at a high frequency of 1 kHz, stable, sensitive, reversible and wide contact angle modulation (122–137 ) was obtained.4
Electrowetting-based variable focus liquid lenses (EVFLL) have attracted considerable attention in mobile phones, barcode readers, medical equipment and various other optical systems.5 Nevertheless, the most frequently used conductive liquid in EVFLL has been limited to saline. The traditional saline-based EVFLL could only work in a narrow temperature range ( 20–60 C), which may suffer from problems such as high focusing voltage, evaporating or freezing at relatively higher/lower temperatures, opacity in the near-infrared and even in most of the infrared range.6 Therefore, development of liquid media with lower focusing voltage, wide temperature stability and wide light spectra ranges for EVFLL should be highly desirable. Herein, based on our previous efforts on IL electrowetting, we report the first IL-based EVFLL. The IL based EVFLL can not only overcome the problems mentioned above but also work more efficiently than saline-based EVFLL, for example, it can focus...
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