J. Adhesion Sci. Technol. (2011) DOI:10.1163/156856111X600190 brill.nl/jast Adhesion Force Change by Electrowetting on a Polymer Microlens Array Maesoon Im ∗ , Kyungyong Choi, Dong-Haan Kim ∗∗ , Joo-Hyung Lee, Jun-Bo Yoon and Yang-Kyu Choi ∗∗∗ Department of Electrical Engineering, KAIST, 335 Gwahangno, Yuseong-gu, Daejeon 305-701, Republic of Korea 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.  Koninklijke Brill NV, Leiden, 2011 Keywords Electrowetting, hydrophobicity, adhesive force, work of adhesion, microlens, parylene, poly(dimethylsilox- ane) (PDMS) 1. Introduction Wettability switching has been studied intensively in various physical or chemi- cal approaches such as switching of electrical potential, electrochemical properties, light intensity, or temperature [1–7]. In numerous practical applications [8–15], electrowetting has been utilized due to its ease of implementation and electri- cal programmability in array operations. The contact angle of a liquid droplet * Present address: Department of Neurosurgery, Massachusetts General Hospital (MGH) and Harvard Medical School, Boston, MA 02114, USA. ** Present address: Doosan Heavy Industries and Construction Co., Ltd, 1303-22 Seocho-dong, Seocho-gu, Seoul, Republic of Korea. *** To whom correspondence should be addressed. Tel.: +82-42-350-3477; Fax: +82 42 350 8565; e-mail: ykchoi@ee.kaist.ac.kr  Koninklijke Brill NV, Leiden, 2011 DOI:10.1163/156856111X600190 Downloaded by [Yang-Kyu CHOI] at 05:48 22 May 2012