Effects of Inhomogeneous Substrate and Molecular Orientation on the AC Electrowetting Behavior of Liquid Crystal Droplet

Abstract In this paper, the dynamic ac electrowetting (EW) behavior of liquid crystal (LC) droplets was investigated on inhomogeneous substrates by inducing LC molecules to orient themselves on a pre-rubbed polyimide substrate. For the first time, we studied the influence of inhomogeneous molecular orientation on the oscillation response of dielectric droplets during ac EW. The experimental results show that the ac EW oscillation amplitude of LC droplet is also inhomogeneous depending on the polyimide-induced molecular orientations on the substrate. The oscillation amplitude that is parallel to the LC molecular orientation is about ∼40% larger than the oscillation amplitude that is vertical to the LC molecular orientation. The oscillation amplitude on the homogeneous un-rubbed polyimide substrate falls in between. Meanwhile, the droplet oscillation amplitude decreases as the ac EW driving frequency increases. An analysis of the EW driving force and various resistance forces for dielectric droplet revealed...