Multi-functional Lagrangian flow structures in three-dimensional ac electro-osmotic micro-flows

Flow forcing by ac electro-osmosis (ACEO) is a promising technique for the actuation and manipulation of micro-flows. Utilization to date mainly concerns pumping and mixing. However, emerging micro-fluidic applications demand further functionalities. The present study explores the first ways to systematically realize this in three-dimensional (3D) micro-flows using ACEO. This exploits the fact that continuity 'organizes' Lagrangian fluid trajectories into coherent structures that geometrically determine the transport properties. Lagrangian flow structures typically comprise families of concentric tubular structures, acting both as transport barriers and as transport conduits, embedded in chaotic regions. Numerical simulations of representative case studies demonstrate that ACEO, possibly in combination with other forcing mechanisms, has the potential to tailor these features into multi-functional Lagrangian flow structures that can fulfill various transport purposes. This may greatly enhance the functionality and versatility of labs-on-a-chip.