Session: 17-01-01: Research Posters

Paper Number: 145099

145099 - Contactless and Reversible Electrowetting by Controlled Charge Deposition 

Reversible wettability modulation makes great contributions to various technologies including fog collection, soft machines, and sensor devices. Electrowetting and di-electrowetting can be used to actively modulate the wettability, which usually rely on a conductive wire connected to a droplet or an electrode pair under a film.  These active strategies are benefited by its controllability and reversibility, but limited by the requirements of contact and complex electrode. Wettability increase by inducing the corona ionization has been proven on dielectric surfaces. This charge injection approach is widely used owing to its non-contact and simple structure. It demonstrates a memorability property that wetting can be maintained for a long time due to the long-term surface charge storage. This irreversibility nevertheless limits the performance and applicability as well. In our research, we propose a reversible wettability modulation strategy by flexible opposite corona injections. Without changing the original layout, which only consists of a sharp conductive tip, a conductive plate and a dielectric film. Wetting (from 106° to 58°) and dewetting (from 59° to 95°) are realized by charge deposition (corona ionization) and charge neutralization (opposite corona ionization), respectively. The wetting process is confirmed in that the charge is accumulated at the edge of droplet, which therefore is subjected to a net electrostatic force to its outside. After the electrostatic force ceases to act due to charge neutralization, on account of the surface tension, a droplet rapidly transforms to that with a bigger contact angle. It is also noted that the final contact angle is slightly less than the initial state due to the contact angle hysteresis.

By ingeniously combining memorability and reversibility, we offer an idea to overcome the problems of traditional wetting patterns, such as limited wettability difference and unmovable patterns. Relying on the memorability, droplets can hang over the downward hydrophobic plate after the charge injection. The reversibility is then used for selective droplet dropping, while the high adhesion and accurate selecting function could be used for programmable printing. Besides, by using a conductive copper to create a mobilizable wetting pattern, together with the reversible wettability, the wettability difference can be established repeatably. Long-distance transport thus can be realized. Contrary to a fixed structure, the wetting pattern can be rearranged on-demand to achieve various functions. This reconfigurable platform greatly increases the application potential. Owing to the flexibility and practicability of this noncontact and reversible wettability modulation method, diverse applications in energy conservation, water harvesting, and bioengineering are demonstrated.

Presenting Author: Sang W. Joo Yeungnam University

Presenting Author Biography: Sang W. Joo graduated from Seoul National University (B.S. and M.S) and the University of Michigan, Ann Arbor (Ph.D), and worked as a professor at University of Illinois at Chicago, Wayne State University, and currently Yeungnam University. His research interest includes thermos-fluid science, micronanotechnology, and functional materials for energy, biomedicine, and environment. His a member of the Korea Academy of Science and Technology, and served in national committees, including the National Commission for Science and Technology.

Authors:

Yifan Zhou Wuhan University
Huai Zheng Wuhan University
Sang W. Joo Yeungnam University