Two-phase Electrokinetic Nanofluidics

In two-phase nanochannel flow two immiscible fluids will coexist in one system. They can either have different chemical compositions – for example oil/water, or different physical states – for example gas/liquid. If we can successfully generate such flow, it will have several advantages:

•	Immiscible phases separated from each other by flexible fluid interfaces

•	One fluid is confined by another immiscible fluid

•	We can continuously manipulate the small volume of fluid

•	We can sequentially control reaction or analysis in chemical, medical or biological fields

There are however real challenges to control two-phase flow in nanochannels. Firstly, two immiscible fluids, for example, gas (or oil) and aqueous phase, have different wettability and conductivity. A hydrophilic aqueous phase will spontaneously fill a hydrophilic micro- or nanochannel by capillary force, but a very high pressure (~10bar in 100 nm channels) is necessary to pump a hydrophobic phase in a hydrophilic nanochannel. Furthermore, the most efficient pumping method for micro- or nanofluidics, electro-osmotic flow (EOF), cannot be used to pump a two-phase flow in which one of the phases is a non-conductive dielectric.

Assignment

One of the interesting things we can do is to select and manipulate novel immiscible two-phase fluidic systems. Is it possible to obtain a two-phase fluidic system of two conductive immiscible liquids which can be pumped by EOF unlike the conventional oil/aqueous two-phase system? Yes, a novel designed liquid – room temperature ionic liquid (RTIL) provides us with this possibility now. A hydrophobic RTIL is conductive but immiscible with water. Therefore, a RTIL/water two-phase system may achieve the requirements. The scheme of two-phase flow generation and working principle is shown in Figure 1.

Electro-osmotic two-phase flow

In this assignment you will first select candidate immiscible two-phase systems consisting of water and a hydrophobic RTIL. Then you will test whether you can generate two-phase electro-osmotic flow in a simple micromachined channel system. If you are successful, the new system can be used to perform nanofluidic (bio)chemical experiments at the final stage.

Contact Information

Lingling Shui and/or Jan Eijkel

MESA+ Institute for Nanotechnology

University of Twente

P.O. Box 217

7500 AE Enschede

The Netherlands

Phone: +31 (0)53.489.2722(Shui) or (0)53 489 28 39 (Jan)

Fax: +31 (0)53 489 2287

E-mail: l.shui@ewi.utwente.nl or j.c.t.eijkel@utwente.nl