Particle focusing by AC electroosmosis with additional axial flow

• Published in: Microfluidics and nanofluidics Vol. 18; no. 5-6; pp. 1115 - 1129
• Main Authors: Liu, Zhipeng, Frijns, Arjan J. H., Speetjens, Michel F. M., van Steenhoven, Anton A.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.05.2015; Springer Nature B.V
• Subjects: Analytical Chemistry; Biomedical Engineering and Bioengineering; Engineering; Engineering Fluid Dynamics; Nanotechnology and Microengineering; Research Paper; AC electroosmosis; Vortex; Microflows; 3D velocity measurement
• ISSN: 1613-4982; 1613-4990
• DOI: 10.1007/s10404-014-1504-x

ACEO-induced vortices have been used to manipulate fluids and particles for chemical and biochemical analysis in microscale systems. In such applications, a pressure-driven background flow is often applied to deliver the samples or particles into the target region. In the present study, the influence of an axial background flow on ACEO-induced vortices is experimentally investigated. An array of symmetric electrodes is used, perpendicular to the axial flow. Velocity fields of vortical flow are measured using astigmatism μ -PTV. The strength of vortex is quantified as a function of the axial background velocity. Flow measurements with 2- μ m tracer particles reveal that the background flow compresses the ACEO-induced vortices and decreases the vortex size. This vortex region, separated from the background flow, can be seen as an “isolated area” in the microchannel. Next, 5- μ m particle dynamics in such flow with isolated vortical area is investigated. Experimental observations expose that 5- μ m particles do not follow the vortical flow and are focused toward the upper side of the channel. The velocity components of the 5- μ m particles are found to be different with the local flow visualized by the 2- μ m particles. This velocity difference of 5- μ m particles is probably due to the dielectrophoretic force acting on the particles. Furthermore, such particle focusing appears to be strongly related to the background velocity.