Capillary Micro Motor

Abstract

A micro structure supported on a droplet is subjected to capillary force and aligned depending on its shape as we explained in Chap. 4. If the droplet’s boundary condition at the bottom and the micro structure are non-circular, a capillary torque is exerted on the structures. The direction of the torque is determined by the boundary condition and the position of the structure. By changing the boundary condition continuously, the rotational motion of the plate was achieved. The boundary condition of the droplet was controlled by electrowetting. We patterned electrodes in annular shape on the plate supporting the droplet. By changing the voltage-applied electrodes, the boundary condition is changed and the plate is rotated. With this method, the droplet and the plate work as a capillary motor. In this chapter, we describe the relationship between the characteristics of the capillary motor and its rotational motion. We sandwiched $3.0\,{\upmu }\mathrm L$ water droplet between 2 mm plate and achieved the rotational motion of 720 rpm at the maximum (Content of this chapter, including all pictures and tables, originally published in [21] $\copyright$ 2010 Royal Society of Chemistry (available at: http://pubs.rsc.org/en/Content/ArticleLanding/2010/LC/c001211d). Presented hereby in revised form with permission of The Royal Society of Chemistry).