Volume 2, Issue 1, March 2008
- REGULAR ARTICLES
2(2008); http://dx.doi.org/10.1063/1.2894313View Description Hide Description
A focusing-based microfluidic mixer was studied. The micromixer utilizes the focusing process required for cytometry to reduce the diffusion distance of molecules to be mixed in order to facilitate the passive diffusion-controlled mixing process. It was found that both the high flow rate ratio of the sheath flow to the flows to be mixed and the low flow rate of the mixing fluids resulted in the short mixing length required within the microfluidic channel. It was shown that a complete mixing was achieved within a distance of 4 mm in the micromixer for the focused mixing fluids at a flow rate of and a flow rate ratio of the sheath flow to the flows to be mixed at 4:1. The mixer described here is simple and can be easily fabricated and controlled.
Dynamic superconcentration at critical-point double-layer gates of conducting nanoporous granules due to asymmetric tangential fluxes2(2008); http://dx.doi.org/10.1063/1.2904640View Description Hide Description
A transient -fold concentration of double-layer counterions by a high-intensity electric field is demonstrated at the exit pole of a millimeter-sized conducting nanoporous granule that permits ion permeation. The phenomenon is attributed to a unique counterion screening dynamics that transforms half of the surface field into a converging one toward the ejecting pole. The resulting surface conduction flux then funnels a large upstream electro-osmotic convective counterion flux into the injecting hemisphere toward the zero-dimensional gate of the ejecting hemisphere to produce the superconcentration. As the concentrated counterion is ejected into the electroneutral bulk electrolyte, it attracts co-ions and produce a corresponding concentration of the co-ions. This mechanism is also shown to trap and concentrate co-ion microcolloids of micron sizes too (macroions) and hence has potential application in bead-based molecular assays.