Making ‘nanospinning’ practical

Nanofibres - strands of material only a couple hundred nanometers in diameter - have a huge range of possible applications: scaffolds for bioengineered organs, ultra-fine air and water filters, and lightweight Kevlar body armour, to name just a few. But so far, the expense of producing them has consigned them to a few high-end, niche applications.

A tiny array of silicon tips sandwiched between electrodes spins out "nanofibers" of plastic that could be useful for a host of applications. Photo: Dominick Reuter

Luis Velásquez-García, a principal research scientist at MIT's Microsystems Technology Laboratories, and his group hope to change that. At the International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications in December, Velásquez-García, his student Philip Ponce de Leon, and Frances Hill, a postdoc in his group, will describe a new system for spinning nanofibers that should offer significant productivity increases while drastically reducing power consumption.

Using manufacturing techniques common in the microchip industry, the MTL researchers built a one-square-centimeter array of conical tips, which they immersed in a fluid containing a dissolved plastic. They then applied a voltage to the array, producing an electrostatic field that is strongest at the tips of the cones. In a technique known as electrospinning, the cones eject the dissolved plastic as a stream that solidifies into a fiber only 220 nanometers across.

In their experiments, the researchers used a five-by-five array of cones, which already yields a sevenfold increase in productivity per square centimeter over even the best existing methods.

But, Velásquez-García says, it should be relatively simple to pack more cones onto a chip, boosting productivity even more. Indeed, he says, in prior work on a similar technique called electrospray, his lab was able to cram almost a thousand emitters into a single square centimeter. And multiple arrays could be combined in a panel to further increase yields.

Surfaces, from scratch
Because the new paper was prepared for an energy conference, it focuses on energy applications. But nanofibres could be useful for any device that needs to maximise the ratio of surface area to volume, Velásquez-García says. Capacitors - circuit components that store electricity - are one example, because capacitance scales with surface area. The electrodes used in fuel cells are another, because the greater the electrodes' surface area, the more efficiently they catalyze the reactions that drive the cell.