Localized flow control in microchannels using induced-charge electroosmosis near conductive obstacles

Abstract

In this paper, we investigate the use of inducedcharge electroosmosis (ICEO) as a means of providing localized flow control near conductive obstacles within bulk pressure-driven flow. In an experimental device, this ICEO flow was induced by an on/off switchable AC field applied across a section containing gold post(s). A simple numerical model, adapted from Levitan et al. (Colloids Surf A 267:122-132, 2005), was implemented and used to provide guidance for the design of the experimental devices. The induced flow was combined with an applied bulk pressure-driven flow to modify flow patterns. We have specifically observed single and multiple stream patterns downstream of the posts in the experimental devices, suggesting the presence of ICEO flow in the experimental system. The custom devices were obtained using a fabrication process that relies on relatively standard steps in the MEMS community, however, unlike other fabrication processes, it has been shown to create fully conductive posts with vertical sidewalls. Utilizing various combinations of number(s) of post(s), geometry and position, useful flow patterns can be created.

Hydrodynamic mechanisms of cell and particle trapping in microfluidics

“…157 Within a typical microfluidic experimental setup 149,156 the streaming velocity is on the order of mm/s to cm/s, which makes the manipulation of the liquid and particles in microchannels using oscillating bubbles a powerful yet efficient and simple technique compared to electrokinetics and electrophoresis. 144,[166][167][168] Recently, Wang et al 156,157 used the cavitation microstreaming of a bubble together with Poiseuille flow to manipulate particles and their spatial concentration for enrichment, filtering and focusing applications in microfluidic devices. The working mechanism is based on the fact that particles behave differently around the oscillating bubbles depending on their finite-size.…”

Bacterial aggregation and biofilm formation in a vortical flow

“…More quantification reveals that collection is faster and more intense for bacteria with higher motility. Although there are other promising techniques to create microvortices in order to trap or collect particles in microfluidic systems, [9][10][11][12][13][14][15] cavitation microstreaming was used here due to its simple formation, ease of control, and the fact that collection is independent of the particle charge. Unexpectedly, within a matter of minutes after bacterial collection in the vortical flow, microbial colonies similar to biofilm streamers are observed which, to the best of our knowledge, have not been reported before.…”

Induced charge electroosmosis micropumps using arrays of Janus micropillars

“…Others have successfully demonstrated local ICEO flows using high aspect ratio conducting micropillars, for example via Bosch etching, 41 electroplating, 43 or C-MEMS. 44 These methods could potentially be used to create ICEO pumps by fabricating asymmetric shapes, which can be designed to exert a net ICEO flow, 20 eliminating the need for Janus micropillars.…”

“…[37][38][39] Previous experiments have investigated ICEO flows near individual polarizable objects, 19,22,[35][36][37] measured the induced-charge electrophoretic velocity of metallodielectric colloids, 40 and used conductive micropillars for ICEO-driven mixing. 41,42 More recently, experimental application of ICEO has focused on local flow control within microchannels, for example by using electroplated gold 43 47 and surface conduction. [48][49][50][51][52] Surface conductivity can suppress ICEO flows near electrode edges and corners, or along surfaces with nanoscale roughness 50 or nonuniform ζ.…”