Title: Electrowetting water droplet contact angle relaxation on coated stainless steel plates

Authors: Abdulwahab S. Aljuhani; George G. Chase

Addresses: Yanbu Industrial College, Yanbu, Saudi Arabia; Chemical and Bimolecular Engineering Department, The University of Akron, Akron, Ohio, USA ' Yanbu Industrial College, Yanbu, Saudi Arabia; Chemical and Bimolecular Engineering Department, The University of Akron, Akron, Ohio, USA

Abstract: Contact angle relaxation was investigated for water droplets on coated stainless steel surfaces. Contact angles of water droplets on electrowettable surfaces were measured to investigate the effects of the electrode geometry and electrical potential exposure time. Two geometric configurations were evaluated using a flat stainless steel plate as one electrode and either a horizontal or a vertical wire as the second electrode. The macroscopic contact angles were compared with the angles predicted by the Young-Lippmann equation. The results show that contact angle relaxation was higher in the horizontal electrode arrangement than for the vertical electrode arrangement. At 200 VDC the drops moved along the horizontal wire electrode whereas they did not move in the vertical wire electrode arrangement at the same voltage. The activation voltage for the reversible change in the macroscopic contact angle was found to be in the range of 40 VDC to 200 VDC.

Keywords: electrowetting; contact angle relaxation; contact angle; dielectric coating; microfluidics; water droplets; droplet movement; electrodes; FluoroPel; Young-Lippmann; coated stainless steel; stainless steel plates; activation voltage.

DOI: 10.1504/IJSURFSE.2016.076995

International Journal of Surface Science and Engineering, 2016 Vol.10 No.3, pp.224 - 239

Received: 27 Nov 2014
Accepted: 14 Mar 2015
Published online: 17 Jun 2016 *

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