Droplet transport by electrowetting: lets get rough

• Published in: Microfluidics and nanofluidics 2013-09, Vol.15 (3), p.327-336
• Main Authors: Lapierre, Florian, Jonsson-Niedziolka, Martin, Coffinier, Yannick, Boukherroub, Rabah, Thomy, Vincent
• Format: Article
• Language: English
• Subjects: Analytical Chemistry; Applied fluid mechanics; Biomedical Engineering and Bioengineering; Condensed matter: structure, mechanical and thermal properties; Engineering; Engineering Fluid Dynamics; Exact sciences and technology; Fluid dynamics; Fluidics; Fundamental areas of phenomenology (including applications); Hydrodynamics; Nanotechnology; Nanotechnology and Microengineering; Physics; Research Paper; Solid-fluid interfaces; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Wetting
• ISSN: 1613-4982; 1613-4990
• DOI: 10.1007/s10404-013-1149-1

Since the pioneering works of Wenzel and Cassie Baxter in the 1930s, and now with the trivialization of the micro- and nanotechnology facilities, superhydrophobic surfaces have been announced as potentially amazing components for applications such as fluidic, optical, electronic, or thermal devices. In this paper, we show that using superhydrophobic surfaces in digital microfluidic devices could solve some usual limitations or enhance their performances. Thus, we investigate a specific monophasic (air environment) microfluidic device based on electrowetting integrating either a hydrophobic or a superhydrophobic surface as a counter-electrode. The droplet transport using a superhydrophobic surface compared with a classical hydrophobic system led to some original results. Characterization of the dynamic contact angle and the droplet shape allows us to get new insight of the fluid dynamics. Among the remarkable properties reported, a 30 % lower applied voltage, a 30 % higher average speed with a maximum instantaneous speed of 460 mm/s have been measured. Furthermore, we have noticed a huge droplet deformation leading to an increase by a factor 5 of the Weber number (from 1.4 to 7.0) on SH compared to hydrophobic surfaces. Finally, we discuss some of the repercussions of this behaviour especially for microfluidic device.