Development of micromotors using the backflow effect of liquid crystals

Abstract

We developed liquid crystal micromotors that exploit the backflow effect. The motors are composed of concentric glass cylinders, the gap being filled with a liquid crystal. A planar orientation layer coats the outer surface of the inner cylinder, whereas a homeotropic layer coats the inner surface of the outer cylinder, resulting in a hybrid orientation profile between the cylinders. The effects of motor size, frequency, and voltage of the applied electric field on the speed of rotation of the inner cylinder were studied in experiments. For a fixed gap between cylinders, the speed of rotation increases with increasing applied voltage and with decreasing inner cylinder diameter. Furthermore, the speed depends on the frequency of the applied voltage. The maximum speed of rotation obtained was approximately 20rpm for a pair of cylinders of 70 μm and 80 μm in diameter and a pulsed voltage of 10 V, duty ratio of 5%, and frequency of 1000 Hz. Increasing the gap results in a decrease in the speed of rotation because the strength of the electric field decreases. The principle underlying liquid crystal motors is not the usual rotational motion but a “translational motion along the circumference”, analogous to a linear actuator.