Cambridge, United States (ISJ) ? MIT researchers have developed polymer filaments only a couple of hundred nanometres (one nanometre is one thousand-millionth of a metre) in diameter, called Nanofibers. The new nanofibers reduces energy consumption by 90 percent, thus holding out the prospects of cheap efficient nanofiber production.
?We have demonstrated a systematic way to produce nanofibers through electrospinning that surpasses the state of the art,? says Luis Fernando Vel�squez-Garc�a, a principal research scientist in MIT?s Microsystems Technology Laboratories, who led the new work.
Nanofibers are useful for any application that benefits from a high ratio of surface area to volume ? solar cells, for instance, which try to maximize exposure to sunlight, or fuel cell electrodes, which catalyse reactions at their surfaces. Nanofibers can also yield materials that are permeable only at very small scales, like water filters, or that are remarkably tough for their weight, like body armour.
The standard technique for manufacturing nanofibers is called electrospinning, and it comes in two varieties. In the first, a polymer solution is pumped through a small nozzle, and then a strong electric field stretches it out.� The process is slow, however, and the number of nozzles per unit area is limited by the size of the pump hydraulics.
The other approach is to apply a voltage between a rotating drum covered by metal cones and a collector electrode. The cones are dipped in a polymer solution, and the electric field causes the solution to travel to the top of the cones, where it?s emitted toward the electrode as a fibre. That approach is erratic, however, and produces fibres of uneven lengths; it also requires voltages as high as 100,000 volts.
The researchers adopted the second approach, but on a much smaller scale, using techniques common in the manufacture of microelectromechanical systems to produce dense arrays of tiny emitters. The emitters? small size reduces the voltage necessary to drive them and allows more of them to be packed together, increasing production rate.
At the same time, a nubbly texture etched into the emitters? sides regulates the rate at which fluid flows toward their tips, yielding uniform fibres even at high manufacturing rates. ?We did all kinds of experiments, and all of them show that the emission is uniform,? Vel�squez-Garc�a says.
In the latest issue of the journal Nanotechnology, the researchers described the new technique will increase the rate of production of nanofibers fourfold while reducing energy consumption by more than 90 percent, holding out the prospect of cheap, efficient nanofiber production. The application of nanofibers so far has been relegated to just a few niche industries due to high cost of manufacture. �
Image courtesy: MIT (A scanning electron micrograph of the new microfiber emitters, showing the arrays of rectangular columns etched into their sides).