Interfacial waves generated by electrowetting-driven contact line motion

Ha, Jun Seok; Park, Jaebum; Kim, Yun-Hee; Shin, Beomju; Bae, Jong‐Soo; Kim, Ho-Young

doi:10.1063/1.4963863

Cited by 13 publications

(5 citation statements)

References 31 publications

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“…Theoretically, this propulsion mechanism is adaptable to interfaces beyond the air‐water boundary. Employing different fluids to form the interface alters the fluid properties and interfacial tension, consequently modifying the swimmer's waveform, interfacial wave propagation, [ 20 ] and the resultant hydrodynamic forces. The dynamic interaction between the flexible swimmer and the dual liquid phases constitutes a complex system.…”

Section: Discussionmentioning

confidence: 99%

Undulatory Propulsion at Milliscale on Water Surface

Ren,

Ucak,

Yan

et al. 2024

Advanced Science

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The oscillatory pitch motion at the leading edge of a millimeter‐scale flexible sheet on the water surface can generate undulatory locomotion for swimming, similar to a honeybee vibrating its wings for propulsion. The influence of various parameters on such swimming strategy remains unexplored. This study uses magnetic milliswimmers to probe the propulsion mechanics and impact of different parameters. It is found that this undulatory propulsion is driven by capillary forces and added mass effects related to undulatory waves of the milliswimmers, along with radiation stress stemming from capillary waves at the interface. Modifying the parameters such as actuation frequency, pitch amplitude, bending stiffness, and hydrofoil length alters the body waveform, thus, affecting the propulsion speed and energy efficiency. Although undulatory motion is not a prerequisite for water surface propulsion, optimizing body stiffness to achieve a proper undulatory waveform is crucial for efficient swimming, balancing energy consumption, and speed. The study also reveals that the induced water flow is confined near the water surface, and the flow structures evolve with varying factors. These discoveries advance the understanding of undulatory water surface propulsion and have implications for the optimal design of small‐scale swimming soft robots in the future.

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Section: Discussionmentioning

confidence: 99%

Undulatory Propulsion at Milliscale on Water Surface

Ren,

Ucak,

Yan

et al. 2024

Advanced Science

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“…where γ is the surface tension, ∆ρ is the density difference, and g is the gravitational acceleration. When a droplet's critical dimension is smaller than its capillary length (λ c ), the surface tension dominates, and it mostly remains spherical [30,31]; otherwise, the droplet will be affected by gravity [18], and its contact lines will become susceptible to kinetic movement [32]. Designs 2 and 3, therefore, allowed the droplets to have larger critical dimensions and capillary lengths (λ c ), making their contact lines prone to kinetic movements.…”

Section: Capillary Lengthmentioning

confidence: 99%

Droplet Transportation through an Orifice on Electrode for Digital Microfluidics Modulations

Chu

2021

Micromachines

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A digital microfluidic modular interface (chip-to-chip interface) which possesses an electrode with an orifice to vertically transport core–shell droplets is presented. The electrodes were geometrically designed to promote droplet deformation and suspension. The droplets were then applied with an electrical potential for insertion into and passage through the orifice. The concepts were tested with three types of droplets at the volume of 0.75~1.5 μL, which is usually difficult to transfer through an orifice. The integration of electrowetting on dielectric (EWOD) with paper-based microfluidics was demonstrated: the droplet could be transported within 10 s. More importantly, most of the core droplet (~97%) was extracted and passed through with only minimal shell droplets accompanying it.

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“…This phenomenon has inspired the rapid development of diverse applications. − For example, the asymmetric wetting-induced droplet movement on a planar EWOD device with patterned electrodes enables the booming of digital microfluidics for chemical and biomedical applications. − Furthermore, the EWOD configuration in an oil/aqueous interface has been widely employed in the development of focal-length-tunable lenses − and advanced display technologies. − In recent years, EWOD has been expanded to a free air/aqueous interface with an AC electric signal. The variation of wettability in EWOD devices drives sessile droplet oscillations − or continuous surface contact line variations, − inducing the formation of capillary waves. A very interesting application of EWOD is a new type of capillary propulsion, which offers the advantages of having no moving components, requiring little power, and achieving good sonic and infrared concealment.…”

Section: Introductionmentioning

confidence: 99%

Effects of Liquid Viscosity on the Formation and Attenuation of Capillary Waves Induced by AC Electrowetting-on-Dielectric

et al. 2022

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The capillary waves induced by electrowetting-ondielectric have great potential in terms of capillary propulsion and other applications. At present, these applications are limited by a lack of research on the effects of liquid viscosity, which is an important parameter in controlling this phenomenon. This paper examines the formation, propagation, and attenuation of electrowetting-on-dielectric-induced capillary waves (EWCWs) on a liquid-free surface with different levels of liquid viscosity. The formation and propagation of the capillary waves are visualized using a high-speed camera and a free-surface synthetic Schlieren method. A theoretical model is established to describe the wave amplitude and wave propagation of EWCWs. The results show that the liquid viscosity, as well as the surface tension, significantly affects the formation and propagation of EWCWs. Using the results presented in this paper, a new type of Stokes viscometer based on EWCWs is proposed, enabling accurate measurements of liquid viscosity over a wide range of viscosity and temperature conditions.

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Interfacial waves generated by electrowetting-driven contact line motion

Cited by 13 publications

References 31 publications

Undulatory Propulsion at Milliscale on Water Surface

Undulatory Propulsion at Milliscale on Water Surface

Droplet Transportation through an Orifice on Electrode for Digital Microfluidics Modulations

Effects of Liquid Viscosity on the Formation and Attenuation of Capillary Waves Induced by AC Electrowetting-on-Dielectric

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