Nanofibers go with the flow

Almost a decade's worth of research into making micro- and nano-particles has culminated in a technique for making large volumes of polymer nanofibers dispersed in liquid, according to research published by scientists at North Carolina State University and their local colleagues at startup company Xanofi. [Adv Mater, 2015; DOI: 10.1002/adma.201404616]

The process involves injecting a polymer solution into a spinning cylinder containing glycerin and water (as an antisolvent) within a beaker containing a spinning cylinder. When you take out the rotating cylinder, explains Orlin Velev, you find a mat of nanofibers wrapped around it. The technique was discovered almost accidentally while the team was trying to generate polymer nanorods rather than mats of fibers. They noticed that the rods they were making seemed to be nothing more than broken fibers. "We didn't quite have the conditions set perfectly at that time. If you get the conditions right, the fibers don't break." Initially, they were able to make microfibers and nanoribbons. "Microfibers, nanorods and nanoribbons are interesting and potentially useful, but you really want nanofibers," Velev explains. "We achieved this during the scaling up and commercialization of the technology." The researchers took out  patents on the basic process in 2006.

Other approaches to making polymer fibers, such as mechanical drawing, force spinning, electrospinning, phase separation, template synthesis and self-assembly, are well-established but have drawbacks such as producing large diameter dry fibers that may not be suitable for many of the applications for which researchers would like to use such materials. By using a simple continuous flow process the team can now make a scaled-up 'nanofiber gusher,' generating several kilograms of nanofiber material per hour in a small desk-sized flow device. "Depending on the concentrations of liquids, polymers and antisolvents, you can create multiple types of nanomaterials of different shapes and sizes." Moreover, liquid processing means that three-dimensional nanofiber substrates with very high surface area can be made, which might have applications in separation science, tissue engineering, bio-inks, and battery separators.

Developing the process further to allow them to make large quantities is essential to exploiting these fibers in nanomanufacturing. "When we produce the nanofibers via continuous flow, we get exactly the same nanofibers you would get if you were producing small quantities of them," explains Miles Wright, CEO of Xanofi.

"We believe that we have a method that over time could contribute immensely to the nanofabrication industry," Velev told Materials. Today. "The technology of nanofiber fabrication and process scale-up has already been translated to the startup company Xanofi (thanks partially to a couple of NSF grants)," he adds.

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".