Effects of gravity on the shape of liquid droplets

We report the gravity effects on the shape and focal length changes of liquid droplets. As the droplet size decreases, the gravity effect is gradually weakened. Moreover, if the outside space of the droplet is filled with another immiscible liquid rather than air, the filled liquid helps to offset the gravity effect even though their densities do not match well. Good agreement between experiment and simulation is obtained. The negligible gravity effect enables us to improve the optical performances of the liquid lens by choosing suitable liquids without worrying their density mismatch.