Interface Profiles near Three-Phase Contact Lines in Electric Fields

Abstract

Long-range electrostatic fields deform the surface profile of a conductive liquid in the vicinity of the contact line. We have investigated the equilibrium profiles by balancing electrostatic and capillary forces locally at the liquid vapor interface. Numerical results show that the contact angle at the contact line approaches Young's angle. Simultaneously, the local curvature displays a weak algebraic divergence. Furthermore, we present an asymptotic analytical model, which confirms these results and elucidates the scaling behavior of the profile close to the contact line.

An Electrowetting Model for Rough Surfaces Under Low Voltage

“…Its effect is just to locate the contact angle around the contact line and its influence distance from the contact line only approximately equals the thickness of the dielectric layer [8,29,30]. As the contact angle studied in this paper is at the macroscopic scale, the approach to minimize the free energy of the system is also used to extend the electrowetting equation to rough surfaces.…”

“…In the case that the surface is rough but without trapped air, f 2 is zero, and equation (19) reduces to the Wenzel equation. Similarly, when the surface is smooth, the equation reduces to the Lippmann-Young equation (8).…”

“…The classical effect of electrowetting on dielectric (EWOD) [5,6] is to make a droplet flatten and spread by applying voltage between the electrodes in the droplet and under the dielectric coating. As the electrical control of the microfluidic motion is significantly more promising for microdevices and easy to manipulate, electrowetting has attracted much research interest [7][8][9][10][11][12][13].…”

Electrowetting of a 3D drop: numerical modelling with electrostatic vector fields

“…One can also establish estimates on the rate of convergence of the method. 6 Numerical analysis in the case of curved boundaries is not available, however a series of numerical experiments carried out in [14] showed that the standard numerical analysis (case of plane faces) is valid when k ≤ 5.…”

“…In particular one needs to describe more precisely the geometry of the drop near the triple line. In this prospect, Buehrle et al in [6] considered a second approximate model for the drop near the triple line: the drop is viewed as a 2D section of cylindrical 3D drop infinite in the direction perpendicular to the section. A physical analysis of this model yields a surprising result: the contact angle (the angle between the drop and the solid at the triple line) should remain constant, independently of the applied voltage.…”