Engineers and physicists working together have discovered that under certain conditions liquid drops and gas bubbles were breaking at two separate points instead of one, leaving an extremely thin thread in between. This could lead to the creation of nanofibers and nanowires and to numerous applications, such as new kinds of composite materials, electronic circuits and pharmaceutical products.
Nanotechweb.org reports on this discovery in "Nanowires drop out of fluid research."
There is a widely accepted universal rule that drops and bubbles always break away from a nozzle in the same way, no matter what the liquid or gas. As the drop forms, it is attached to the nozzle by a thin segment of liquid or gas. This segment grows thinner before breaking at a single point, allowing the drop to fall away from the nozzle.
But Osman Basaran of Purdue University and his colleagues have discovered an exception to the rule. While studying how liquid drops and gas bubbles are formed by nozzles such as those in inkjet printers, the researchers found that for a nozzle immersed in a viscous liquid such as silicone oil, water drops formed differently to the way they would in air. The drops formed much more slowly and the segment of liquid between the growing drop and the tip of the nozzle grew longer than it would in air, before cutting away from the nozzle at two points rather than one.
Here is an illustration showing how a water drop breaks up in oil, leaving a thin thread (Credit: Itai Cohen and Sidney R Nagel).
The liquid separated from the nozzle at both the place where the drop formed and at a point nearer to the nozzle. This left a drop of liquid, along with an extremely thin liquid thread. “This thin thread forms so slowly that you have enough time to solidify it into a filament or wire,” said Basaran. By adding a prepolymer to the water and then exposing the liquid to light to bring about photopolymerization, the scientists were able to create solid fibres less than 100 nm wide.
For more information, you can read this news release from Purdue University, "Discovery could lead to new ways to create nano-fibers and wires."
[Basaran] said the method might one day be used to make flexible nano-wires out of many types of materials that conduct electricity, including polymers.
Scientists hope to eventually produce wires so thin that their diameter is smaller than the width of an electron's wavelength, which could be used to dramatically alter the flow of electricity and heat. It is possible that other researchers might use such wires to develop a new class of electronics, solid-state refrigerators, air conditioners and power generators.
The research paper was published on November 14, 2003 by Science Magazine. Here is the abstract of this paper, "Persistence of Memory in Drop Breakup: The Breakdown of Universality" (Registration needed). It's also available from the above reference at Purdue.
A low-viscosity drop breaking apart inside a viscous fluid is encountered when air bubbles, entrained in thick syrup or honey, rise and break apart. Experiments, simulations, and theory show that the breakup under conditions in which the interior viscosity can be neglected produces an exceptional form of singularity. In contrast to previous studies of drop breakup, universality is violated so that the final shape at breakup retains an imprint of the initial and boundary conditions. A finite interior viscosity, no matter how small, cuts off this form of singularity and produces an unexpectedly long and slender thread. If exterior viscosity is large enough, however, the cutoff does not occur because the minimum drop radius reaches subatomic dimensions first.
I'm not totally convinced that this discovery can lead to solid industrial processes, but it sure looks promising.
Sources: Liz Kalaugher, Nanotechweb.org, November 14, 2003;Purdue News, November 13, 2003
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