The difference between the smooth precursor film and the beads, Li says, is that in the thinner film, each molecule of liquid is close enough to directly interact, through quantum-mechanical effects, with the molecules of the solid buried beneath it; this force suppresses the Rayleigh instability that would otherwise cause beading. But with or without beading, the upward flow of the liquid, defying the pull of gravity, is a continuous process that could be harnessed for small-scale liquid transport.
Although this upward pull is always present with wires at this tiny scale, the effect can be further enhanced in various ways: Adding an electric voltage on the wire increases the force, as does a slight change in the profile of the wire so that it tapers toward one end. The researchers used nanowires made of different materials silicon, zinc oxide and tin oxide, as well as two-dimensional graphene to demonstrate that this process applies to many different materials.
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 researc
|Contact: Sarah McDonnell|
Massachusetts Institute of Technology