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MEMS Devices
Published in Bogdan M. Wilamowski, J. David Irwin, Fundamentals of Industrial Electronics, 2018
José M. Quero, Antonio Luque, Luis Castañer, Angel Rodríguez, Adrian Ionescu, Montserrat Fernández-Bolaños, Lorenzo Faraone, John M. Dell
Figure 13.22 shows the principle of electrowetting and an example of an electrowetting-based microlens [60]. When a drop of liquid is placed on a solid, the shape of the droplet is generally spherical. The spherical shape of the liquid can then be used to form a lens, and since the surface of the lens is flexible, there exist the possibility of changing the focal length of the lens, by changing the contact angle between the solid and liquid. The contact angle between the solid and liquid is determined by the values of surface tension at the liquid–solid, liquid–vapor, and solid–vapor interfaces. Electrowetting is a physical effect in which the surface tension between a liquid and a solid can be controlled by a voltage applied across the interface.
Light-Driven Microfluidic Systems
Published in George K. Knopf, Kenji Uchino, Light Driven Micromachines, 2018
In the electrowetting process, the surface tension between the liquid-solid interfaces is altered by an external electrical field which then reduces the contact angle. The general mechanism for electrowetting involves placing a droplet of polarized liquid on a substrate with an insulating dielectric layer between the liquid and electrode (Chiou et al. 2003). The surface tension at the solid-liquid interface is altered when an external voltage is applied. The voltage potential also changes the contact angle, θs(vA), by
Introduction to Microfuidics
Published in Simona Badilescu, Muthukumaran Packirisamy, BioMEMS, 2016
Simona Badilescu, Muthukumaran Packirisamy
When immiscible fluids having different electrical properties are present simultaneously, surface tension forces become dominant. In this case, the electric field can inject electrostatic energy into the interface and, as a result, the contact angle can be modified. The consecutive changes in the contact angle will result in fluid movement. Electrowetting is a technique that explores the above-mentioned wetting force through the electric field. Electrowetting on dielectric (EWOD), also known as electrowetting on insulator-coated electrodes (EICE), is a technique that uses a thin insulation layer between the electrode and the fluid in order to avoid electrolysis at high voltages. In summary, electrophoresis exploits the electrically generated body force, while electroosmosis utilizes surface forces at the solid-electrolyte interface, and EWOD modulates wetting forces at the contact line. Electrophoresis has been largely used to manipulate biochemical species, while EWOD has been used to manipulate the carrier of the biochemical species.
Competition between dielectrophoresis and electrophoresis in fluids under an electric field
Published in Radiation Effects and Defects in Solids, 2022
This suggestion that dielectrophoretic forces are responsible for the transport of liquid matter within a strong electric field is apparently confirmed when liquid bridges are taken into consideration, at least when one focuses his attention on the transient phase of the bridge formation. From a general point of view, the formation of liquid bridges falls within the wide class of phenomena where deformation of the air/liquid interface is observed, due to an external electric field and is usually indicated as electrowetting (28). In principle, a deformation is observed also in non-polar liquids (16,29) even if only polar liquids seem capable of forming stable horizontal bridges (15–18). A high dielectric permittivity is required to obtain stable horizontal bridges. Without bulk charges, a simple capacitor model could describe the forces acting between the liquid/air interfaces, indicating critical field strength for the formation of the liquid bridge (16). A more rigorous description in terms of the Maxwell (19,30) pressure tensor confirms that the origin of the phenomenon must be found in electrodynamics more than in molecular details, leading to the formation of a catenary form of the bridge.
A review on control of droplet motion based on wettability modulation: principles, design strategies, recent progress, and applications
Published in Science and Technology of Advanced Materials, 2022
Mizuki Tenjimbayashi, Kengo Manabe
Figure 6(p–r) show droplet transport by electricity. Since polar droplets change their shape due to surface charging, electrically adjustable wetting has been widely studied as electrowetting. Figure 6(p) shows an example of droplet transport by electrowetting [117–119]; an induced effect between an electrode and a droplet on a solid surface attracts the droplet to a charged site. In Figure 6(q), droplets are transported using electrostatic repulsion on a superhydrophobic surface [120–122]. Figure 6(r) shows the control of droplet jump trajectory along an electric field on a superhydrophobic surface [123,124]. In controlling the charged droplet, both the coating surface and substrate permittivity also influence the droplet sliding behavior [125].