Electrokinetic flow in a free surface-guided microchannel

Abstract

The purpose of this study is to investigate electro-osmotic flow in a free surface-guided microchannel. Although multiphase microfluidics has attracted interests over the past few years, electro-osmotic flow involving free surfaces has yet to be studied in great detail. Several proposed theoretical models describing this type of electro-osmotic flow need to be verified by experiments. In this work, a surface-guided microchannel was fabricated using an innovative fabrication process. Because the liquid stream was confined by surface properties, solid sidewalls did not exist in this microchannel. Instead, the sidewalls were water-air or water-oil interfaces. Using this microchannel, two systems were investigated: water-air system and water-oil system. The experimental results were compared against three proposed models in order to gain more understandings on this type of electro-osmotic flow. Experimental results show that the liquid velocity near the liquid-fluid interface resembles a pluglike profile for both water-air and water-oil systems. Computer simulation results show that with the consideration of the electrical double layer and the surface charges, the electric forces inside the electrical double layer are counteracted by the surface forces at the liquid-fluid interface, also resulting in a pluglike velocity profile in the microchannel. Therefore, the model that considers both the electrical double layer and the surface charges at the liquid-fluid interface best describe the physical phenomenon observed in experiments.

Surface microfluidics fabricated by photopatternable superhydrophobic nanocomposite

“…Surface microfluidics, originally evolved from the surface-directed channels, can be categorized into three configurations: the microflow confined between two surfaces of identical hydrophobic micropatterns (Lam et al 2002;Besson et al 2006;Lee et al 2006;West et al 2007;Watanabe 2009a;2010), the microflow restricted between one wettability-patterned surface and another uniform hydrophobic substrate (Bouaidat et al 2005), and the microflow directed on a single planar substrate with ultrahigh wettability contrast (Juncker et al 2002;Piorek et al 2007;Hong and Pan 2010a, b), as will be compared in Sect. 3 (Open Surface Fluidic Configurations).…”

Electroosmotic flow at a liquid–air interface

“…The calculated velocities were compared against the fluid velocities predicted by the Fig. 1 Schematics of the PDMS microchannel with an opening to allow for the formation of a liquid-air interface model presented in Lee et al (2005) and Gao et al (2005a, b). The particle velocity in the bulk and the liquid interface regions is found to increase linearly with applied electric field.…”

“…Recently, the authors of this paper have analyzed the different theoretical models proposed for two-phase electroosmotic flow and evaluated them against experimental evidence (Lee et al 2005). The results show that the effect of surface charges must be considered along with the Gouy-Chapman-Stern model to produce results closed to that in experiments.…”

Surface instability of a thin electrolyte film undergoing coupled electroosmotic and electrophoretic flows in a microfluidic channel

“…The instabilities at the free surface of a thin liquid film undergoing EKF are engendered by the coupled interactions between the electric field applied in the flow direction and stress generated across the film because of the difference in zeta-potentials at the liquid-air and liquid-solid interfaces. Recent experimental [8,9] and theoretical [10,11] studies indicate that the charge accumulation at the free surface of a film undergoing EKF can even lead to immobilization of the free surface. Furthermore, theoretical studies by Joo [6,7] and Qian et al [12] consider a deformable liquid-air interface, and report the presence of a long-wave (LW) interfacial mode of instability.…”