'Electrospun' polymer yields supertough, strong nanofibres
25 April 2013
Engineers have developed a structural nanofibre that is both strong and tough, a discovery that could transform everything from aircraft to bridges.
A high-resolution scanning electron microscopy image of the nanofibres that can be easily aligned and bundled for handing and processing into various applications (photo: Joel Brehm, Dimitry Papkov, Yuris Dzenis)
"Whatever is made of composites can benefit from our nanofibres," says development team leader, Professor Yuris Dzenis, a member of the University of Nebraska-Lincoln's (UNL's) Nebraska Centre for Materials and Nanoscience. "Our discovery adds a new material class to the very select current family of materials with demonstrated simultaneously high strength and toughness."
In structural materials, conventional wisdom holds that strength comes at the expense of toughness. Strength refers to a material's ability to carry a load. A material's toughness is the amount of energy needed to break it; so the more a material dents, or deforms in some way, the less likely it is to break.
Dzenis and colleagues have developed an exceptionally thin polyacrilonitrile nanofibre, a type of synthetic polymer related to acrylic, using a technique called electrospinning. The process involves applying high voltage to a polymer solution until a small jet of liquid ejects, resulting in a continuous length of nanofibre.
They discovered that by making the nanofibre thinner than had been done before, it became not only stronger, as was expected, but also tougher.
Dzenis suggests that toughness comes from the nanofibres' low crystallinity. In other words, it has many areas that are structurally disorganised. These amorphous regions allow the molecular chains to slip around more, giving them the ability to absorb more energy.
Most advanced fibres have fewer amorphous regions, so they break relatively easily. In an aircraft, which uses many composite materials, an abrupt break could cause a catastrophic failure. To compensate, engineers use more material, which makes aircraft, and other products, heavier.
"If structural materials were tougher, one could make products more lightweight and still be very safe," says Dzenis. Body armour, such as bulletproof vests, also requires a material that's both strong and tough. "To stop the bullet, you need the material to be able to absorb energy before failure, and that's what our nanofibres will do," he adds.