Abstract
Electric field-based smart wetting manipulation is one of the extensively used techniques in modern surface science and engineering, especially in microfluidics and optofluidics applications. Liquid dielectrophoresis (LDEP) is a technique involving the manipulation of dielectric liquid motion via the polarization effect using a non-homogeneous electric field. The LDEP technique was mainly dedicated to the actuation of dielectric and aqueous liquids in microfluidics systems. Recently, a new concept called dielectrowetting was demonstrated by which the wettability of a dielectric liquid droplet can be reversibly manipulated via a highly localized LDEP force at the three-phase contact line of the droplet. Although dielectrowetting is principally very different from electrowetting on dielectrics (EWOD), it has the capability to spread a dielectric droplet into a thin liquid film with the application of sufficiently high voltage, overcoming the contact-angle saturation encountered in EWOD. The strength of dielectrowetting depends on the ratio of the penetration depth of the electric field inside the dielectric liquid and the difference between the dielectric constants of the liquid and its ambient medium. Since the introduction of the dielectrowetting technique, significant progress in the field encompassing various real-life applications was demonstrated in recent decades. In this paper, we review and discuss the governing forces and basic principles of LDEP, the mechanism of interface localization of LDEP for dielectrowetting, related phenomenon, and their recent applications, with an outlook on the future research.
Highlights
In the last few decades, the wettability of liquids on a solid surface became a very extensively researched topic in surface science due to its fundamental and crucial role in various aspects of domestic life and industry, such as water collection by plant leaves, the self-cleaning effect observed in lotus leaves and feathers of birds, and the paint industry, to name a few [1]
This paper provided a brief overview of the liquid dielectrophoresis (LDEP) phenomenon for liquid manipulation and its latest version of the dielectrowetting phenomenon, in which the contact angle of a dielectric liquid droplet can be modified reversibly though the localization of the LDEP force at the solid–liquid interface
LDEP is a bulk force of electrical origin which penetrates into the bulk of the dielectric liquid through the polarization of liquid molecules to produce a movement toward the higher-intensity direction of a non-homogeneous electric field
Summary
In the last few decades, the wettability of liquids on a solid surface became a very extensively researched topic in surface science due to its fundamental and crucial role in various aspects of domestic life and industry, such as water collection by plant leaves, the self-cleaning effect observed in lotus leaves and feathers of birds, and the paint industry, to name a few [1]. The active manipulation of wettability of a liquid on a solid surface through external stimuli, such as electric field, magnetic field, pH, heat treatment, ultraviolet (UV) irradiation, etc., became a modern trend in microfluidics and optofluidics devices [3,4] Of these external stimuli, the electric field controls the wettability of a liquid through an electrohydrodynamics effect at the three-phase contact line of a droplet via two mechanisms in particular: electrowetting and liquid dielectrophoresis (LDEP) [5]. The dielectric liquid droplet could be spread into a thin liquid film with wrinkles, overcoming the contact-angle saturation problem in EWOD This ability generated many exciting applications based on the principle of dielectrowetting [25,26]. The observations in dielectrowetting are apparently similar to those in EWOD; fundamentally, it involves the manifestation of the LDEP force highly localized near the three-phase contact line using co-planar interdigitated electrode geometry
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