New process makes nanofibers in complex shapes and unlimit...( CHAMPAIGN Ill. The continuous fabri...)

CHAMPAIGN, Ill. The continuous fabrication of complex, three-dimensional nanoscale structures and the ability to grow individual nanowires of unlimited length are now possible with a process developed by researchers at the University of Illinois.

Based on the rapid evaporation of solvent from simple inks, the process has been used to fabricate freestanding nanofibers, stacked arrays of nanofibers and continuously wound spools of nanowires. Potential applications include electronic interconnects, biocompatible scaffolds and nanofluidic networks.

The process is like drawing with a fountain pen the ink comes out and quickly dries or solidifies, said Min-Feng Yu, a professor of mechanical science and engineering, and an affiliate of the Beckman Institute. But, unlike drawing with a fountain pen, we can draw objects in three dimensions.

Yu and graduate students Abhijit Suryavanshi and Jie Hu describe the drawing process in a paper accepted for publication in the journal Advanced Materials, and posted on its Web site.

To use the new process, the researchers begin with a reservoir of ink connected to a glass micropipette that has an aperture as small as 100 nanometers. The micropipette is brought close to a substrate until a liquid meniscus forms between the two. As the micropipette is then smoothly pulled away, ink is drawn from the reservoir. Within the tiny meniscus, the solute nucleates and precipitates as the solvent quickly evaporates.

So far, the scientists have fabricated freestanding nanofibers approximately 25 nanometers in diameter and 20 microns long, and straight nanofibers approximately 100 nanometers in diameter and 16 millimeters long (limited only by the travel range of the device that moves the micropipette).

To draw longer nanowires, the researchers developed a precision spinning process that simultaneously draws and winds a nanofiber on a spool that is millimeters in diameter. Using this technique,
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