A research team of engineers at Purdue University and physicists at the University of Chicago has made a discovery about the formation of drops that could lead to new methods for making threads, wires and particles only a few nanometers wide. These nano-threads, wires and particles could have numerous applications, including new kinds of composite materials, electronic circuits and pharmaceutical products.
The discovery was made while studying how liquid drops and gas bubbles are formed by nozzles, such as those in inkjet printers. The widely accepted rule holds that, no matter what the liquid or gas is made of, drops and bubbles always break away from a nozzle the same way: As the drop is forming, it is attached to the nozzle by a thin segment of liquid or gas. This connecting segment grows progressively thinner, and as its width gets closer and closer to zero it breaks at a single point and the drop falls away from the nozzle. The researchers, however, have discovered an exception.
Drops usually form in air, which has much lower viscosity than the liquid. However, if a nozzle is immersed into a sticky liquid like honey or silicone oil, which is thousands of times thicker than water, the water drops form differently than they would in air.
The drops take longer to form and instead of abruptly breaking off, the segment of liquid between the forming drop and the nozzle's tip continues to grow into a narrow thread. Rather than separating from the nozzle at a single point, the liquid cuts away in two places: at the point where the drop has formed and at a point closer to the nozzle. The drop falls away, but an extremely thin thread of liquid or gas also separates from the nozzle.
With certain chemicals in the liquid, the threadlike segment can be quickly solidified by exposing it to "photo-polymerizing" light, creating extremely thin filaments or fibers of uniform thickness. Fibers have been created by this method that are less than 100 nanometers wide.
By varying the viscosity ratios, filaments can be made to varying lengths and widths. The greater the difference in viscosity, the thinner and longer the filaments become.
The 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 may then be possible to use such wires to develop a new class of electronics, solid-state refrigerators, air conditioners and power generators.