Fabrication and Actuation of an Electrowetting Droplet Array on a Flexible Substrate

Abstract

Electrowetting-on-dielectric (EWOD) is a fast, well-established actuation method for a variety of applications, from microfluidics to electrowetting displays to electrowetting lenses. We therefore seek to develop a robust, scalable fabrication method for the realization of EWOD on a flexible polydimethylsiloxane (PDMS) substrate in order to increase the range of possible applications. We fabricated a 5 × 5 array of individually controlled electrowetting cells to manipulate silicone oil droplets via EWOD. The fabrication process utilized exclusively flexible materials to improve the robustness of the overall device, and processing methods were adapted to accommodate the particular challenges posed by flexible materials. Simulation of the EWOD devices was conducted using ANSYS Fluent and showed the change in contact angle in response to voltage applied. Fabricated devices were also tested, with actuation of the oil droplet observed with up to 100 V (RMS) AC applied across underlying electrodes. We demonstrated fabrication of a fully flexible array and verified actuation to center droplets over the electrodes. This work may be expanded to address more specific flexible applications for EWOD.

Flexible Electrowetting-on-Dielectric Microlens Array Sheet

“…Our actuation mechanism makes use of an areal density modulated electrode design with which we previously demonstrated electrowetting on dielectric (EWOD) functionality. While previous work focused on characterizing a single EWOD lens on a rigid substrate [15], or on developing methods to fabricate EWOD devices on flexible substrates [16], in this work we demonstrated a completely functional tunable lens array utilizing EWOD, and also turned our attention to the imaging capabilities of an array of lenses, making improvements to the design and fabrication methods in the process. The areal-density-modulated electrode design used by each liquid lens in our array can be seen in Figure 1a.…”

“…There are a large variety of actuation methods that have been demonstrated for liquid lenses, including fluidic pressure [1,2,3], liquid crystal [4,5], hydrogel [6,7], thermal [8,9], dielectrophoretic [10,11], and electrowetting [12,13,14,15]. Electrowetting is particularly attractive thanks to its fast response times [16,17] and low power consumption. Additionally, since we plan to fabricate an array of lenses, it is relatively simple to electrically insulate neighboring electrowetting lenses from one another, something not easily implemented in, for example, thermally actuated lenses.…”

Tunable Liquid Lenses: Emerging Technologies and Future Perspectives

“…[85] Grinsven et al fabricated a fully flexible, focally tunable microlens array on thin sections. [86,87] Each liquid lens in the array was individually tuned by electrowetting and located on a PDMS substrate, as shown in Figure 12b. In particular, by wrapping this microlens array on a cylindrical surface, the FOV could be significantly increased from 21.5°obtained in a plane to 40.4°.…”

Self-Cleaning: From Bio-Inspired Surface Modification to MEMS/Microfluidics System Integration

“…Depending on the application, two popular EWOD configurations are often used, shown in Figure 9b, the parallel-plate system, and Figure 9c, the co-planar system. For the parallel-plate system, the water droplet was sandwiched in between the top and bottom electrodes, insulated by dielectric layer (SU8, SiO 2 [120] or parylene [125]) and hydrophobic (Teflon TM AF [126,127] or Cytop ® [128,129] coatings. The electrode on one plate was patterned and the electrode on the other was fully grounded.…”