Adhesion Force Change by Electrowetting on a Polymer Microlens Array

Abstract

In addition to contact angle changes, adhesion force changes by electrowetting on a polymer microlens are reported in this paper. A flexible poly(dimethylsiloxane) (PDMS) microlens array was fabricated with an embedded Cr/Au double-layered electrode and a dielectric layer of parylene and Teflon. On microlens structures with a Teflon layer, a deionized water droplet on the microlens array surface shows a high contact angle of 137° before electrowetting. The contact angle is decreased to 63° by electrowetting with an external bias of 250 V. The electrowetting process carried out on the microlens array also enhances the adhesion force between the water droplet and the microlens array. This change in the adhesion force after electrowetting is demonstrated by a water droplet that hangs upside down on the fabricated microlens array. From the computed work of adhesion, it is shown that a larger difference in the adhesion force by electrowetting can be achieved on the fabricated microlens array than on a flat Teflon surface.