Wettability Manipulation by Interface-Localized Liquid Dielectrophoresis: Fundamentals and Applications

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.

Dynamics Behaviors of Droplet on Hydrophobic Surfaces Driven by Electric Field

“…The electric force F e , as a source term of the Navier-Stokes equations, can be calculated by the divergence of the Maxwell stress tensor, τ M (SI unit: N/m 2 ) [31,32]. Under the conditions of the perfect dielectric model and incompressible fluid, the electric force per unit volume is given as: Fe=∇⋅τM=∇ε0ε[trueE→trueE→−12E2normalI]…”

Fluorinated Metal–Organic Coatings with Selective Wettability

“…Lower surface tension liquids (e.g., oil) will wet better than higher surface tension liquids (e.g., water) for most surfaces. − This phenomenon largely explains the challenge in creating surfaces with both water affinity and oil repellence properties . Nevertheless, achieving simultaneous controlled surface affinity − and repellence to various liquids is important for engineering advanced materials and holds promise and broad interest for a wide range of wetting-related applications such as self-cleaning, chemical sensing, and membrane separations. − Externally induced wetting, through, e.g., shear and strain − or by combining surface active additives (e.g., chromophores), − can initiate responsive wettability. − However, externally induced wetting strategies do not lead to selective wetting without the application of external stimuli/energy or super-repellence to conventional wetting oils, in air or under water (e.g., droplet bouncing). Therefore, to date, a mechanistic understanding of selective wetting is largely unexplored.…”

Static and Dynamic Optical Analysis of Micro Wrinkle Formation on a Liquid Surface

“…A spatially periodic voltage applied via an interdigital array of striped coplanar electrodes embedded into the solid surface produces a surface localized periodic and non-uniform electric field that decays into the underside of the liquid. This causes a dielectrophoresis force to act on the liquid, which is a polarizable dielectric material, in the direction of the increasing magnitude of the electric field [19,20]. This force results in the liquid spreading over the surface, eventually forming into a uniform thin film with average thickness h ave .…”