  Electrowetting on dielectric (EWOD) has emerged as a powerful tool to
electrically manipulate tiny individual droplets in a controlled manner.
Despite tremendous progress over the past two decades, current EWOD operating
in ambient conditions has limited functionalities posing challenges for its
applications, including electronic display, energy generation, and microfluidic
systems. Here, we demonstrate a new paradigm of electrowetting on
liquid-infused film (EWOLF) that allows for complete reversibility and tunable
transient response simultaneously. We determine that these functionalities in
EWOLF are attributed to its novel configuration, which allows for the formation
of viscous liquid-liquid interfaces as well as additional wetting ridges,
thereby suppressing the contact line pinning and severe droplet oscillation
encountered in the conventional EWOD. Finally, by harnessing these
functionalities demonstrated in EWOLF, we also explore its application as
liquid lens for fast optical focusing.
