Liquid handling and actuation by means of controlling surface tension has proven to have many advantages in small-scale applications due to the surface tension force dominance over body forces. In 1875, Lippmann first explored the phenomenon of the surface tension of liquids modulated with an electric field, which is called an electrowetting effect. When an electric potential is applied between a liquid and a solid electrode, the charge redistribution modifies the surface tension at the liquid−solid interface where the like-charge repulsion decreases the work by expanding the surface area. Due to the benefits of large forces in micro/meso scales, a fast response time in the range of microseconds, and low-power operation, the electrowetting technology has been used for numerous applications, including lab-on-a-chip, electronic display, thermal management, energy harvesting, and surface science.
In this talk, a broad perspective of the electrowetting technology will be presented from materials to its optics and solar applications. A novel high-capacitance dielectric material, called an ion gel, is first introduced which not only offers 2 to 3 orders higher capacitance (c ≈ 10 μF/cm2) than that of conventional dielectrics such as SiO2, but also is simply fabricated by either a spin or dip-coating method. This high-capacitance ion gel dielectric is used for an electrowetting-driven liquid prism that achieved the highest beam steering performance ever demonstrated. We further discuss an arrayed form of the liquid prisms with a large aperture area and potential applications for a tunable Fresnel lens and solar indoor lighting.