Watching nanometer fluid flow

Research carried out at MIT has demonstrated for the first time that when inserted into a pool of liquid, nanowires naturally draw the liquid upward in a thin film that coats the surface of the wire.

The finding could have applications in microfluidic devices, biomedical research and inkjet printers.

The phenomenon had been predicted by theorists, but never observed because the process is too small to be seen by optical microscopes; electron microscopes need to operate in a vacuum, which would cause most liquids to evaporate almost instantly.

It is possible to deliver controlled volumes of liquid for novel applications in nanotechnology

To overcome this, the MIT team used an ionic liquid called DMPI-TFSI, which remains stable even in a powerful vacuum. Though the observations used this specific liquid, the results are believed to apply to most liquids, including water.

The work was carried out by a team of researchers led by Ju Li, an MIT professor of nuclear science and engineering and materials science and engineering, along with researchers at Sandia National Laboratories in New Mexico, the University of Pennsylvania, the University of Pittsburgh, and Zhejiang University in China.

While Li claims this research intended to explore the basic science of liquid-solid interactions, it could lead to applications in inkjet printing, or for making a lab on a chip. “We’re really looking at fluid flow at an unprecedented small length scale,” Li says – so unexpected new phenomena could emerge as the research continues.

Nanowires are less than one-tenth the diameter of fluidic devices now used in biological and medical research, such as micropipettes, and one-thousandth the diameter of hypodermic needles.

At these small scales, the researchers found, a solid nanowire is just as effective at holding and transferring liquids as a hollow tube. This smaller scale might pave the way for new kinds of microelectromechanical systems to carry out research on materials at a molecular level.

The methodology the researchers developed allows them to study the interactions between solids and liquid flow “at almost the smallest scale you could define a fluid volume, which is 5 to 10 nanometers across,” Li says.

The team now plans to examine the behavior of different liquids, using a “sandwich” of transparent solid membranes to enclose a liquid, such as water, for examination in a transmission electron microscope. This will allow “more systematic studies of solid-liquid interactions,” Li says – interactions that are relevant to corrosion, electrodeposition and the operation of batteries.

Erich Stach, head of the Electron Microscopy Group at Brookhaven National Laboratory in New York, says, “The dynamic observations from Huang and colleagues provide fascinating insight into the mechanisms of fluid flow at the deep nanoscale, and demonstrate that it is possible to deliver controlled volumes of liquid for novel applications in nanotechnology.”

The research was supported by Sandia National Laboratories, the U.S. Department of Energy, and the National Science Foundation.