Controlling Fluids At The Nanoscale

Scientists have modeled a method of controlling the direction of fluid flow at the nanoscale without the use of mechanical pumps or electrodes.

AsianScientist (Jul 8, 2014) – Researchers have developed a method of pumping fluid at the nanoscale level that has potential use for desalinating water and lab-on-a-chip devices. This research has been published in the journal Langmuir.

Their simple, highly accurate model to predict fluid movement for highly confined fluids has been used to drive flow without mechanical pumping or the use of electrodes.

“Conventional fluid dynamics modeling works perfectly with things we can see such as the flow of air over an aircraft,” Swinburne University of Technology’s Professor Billy Todd explains. “But when devices get to nanometre size or 1 billionth of a meter—about one ten-thousandth the diameter of a human hair—the fundamental assumptions of fluid mechanics break down. It is difficult to force fluid to flow in confined dimensions that are just a few atoms thick.”

Together with colleagues at Swinburne, RMIT and Roskilde University in Denmark, Prof. Todd used supercomputers to look at what happens at the interface between the solid surface and the fluid at nanometre dimensions.

“Several years ago, researchers in France and Germany developed a theory that a rotating electric field could induce water molecules to spin and that this spin motion could be converted into linear streaming fluid motion,” he said.

“If the symmetry of the confining walls could be broken such that one wall was hydrophilic and attracted water, while the other was hydrophobic and repelled water, then mathematically it was demonstrated that water could be made to flow in just one direction, namely along the channel.”

Prof. Todd’s team further developed that theory and performed the first molecular dynamics computer simulations to demonstrate this effect, mimicking nanoconfined water under the application of a rotating microwave field.

What they found was that the use of circularly polarized microwaves could drive substantial flow at the nanoscale without significantly heating the water.

“Flow can be sustained when the fluid is driven out of equilibrium by an external uniform rotating electric field and confined between two flat surfaces with different degrees of hydrophobicity, thus opening up an entirely new way to pump and control fluid flow confined to nano or micro-metre scale dimensions,” Professor Todd said.

He added that this discovery has potential application for desalinating water as well as for biotech diagnostic tools such as lab-on-a-chip devices and is now seeking an experimental partner to verify this model in a lab.

The article can be found at: De Luca et al. (2014) Molecular Dynamics Study of Nanoconfined Water Flow Driven by Rotating Electric Fields under Realistic Experimental Conditions.

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Source: Swinburne University of Technology; Photo: Masakazu Matsumoto/Flickr/CC.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

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