In the early part of this decade, two researchers working independently -- Princeton graduate student Hak Poon and Cornell University physicist Harold Craighead -- found that the jet was stable for a very short distance after leaving the nozzle, but the result was still not practical and the reasons were still elusive.
To understand how to control the jet in any engineering application we had to understand why this was happening, Aksay said.
Korkut took up the challenge and worked for nearly six years to nail down the mechanisms at play. In the end, she found that a key factor was that the liquid jet was transferring some of its electrical charge to the surrounding gas, which breaks into charged particles and carries some of the electrical current. Korkuts predecessors and other scientists had looked only at the density of the electrical charges on the surface of the liquid jet.
Expanding her view of the system led Korkut to a simple way to control the stability of the jet by changing the gas and the amount of water vapor. She was able to produce an extremely straight and stable jet more than 8 millimeters from the nozzle. (See video image of straight and whipping jets here: www.princeton.edu/~cml/html/EHDPself-assembly.html.)
The result is highly practical not only because of the fineness of the stream but also because the large size of the nozzle and the distance from the nozzle to the printed surface will prevent clogs or jams.
Aksay said a chief use for the technique could be in printing electrically conducting organic polymers (plastics) that could be the basis for large electronic devices. Conventional techniques for making wires of that size (100 nanometers) require laboriously etching the lines with a beam of electrons,
|Contact: Steven Schultz|
Princeton University, Engineering School