This Novel Stretching Process Could Matter for Nanotech

The MIT-developed technique exploits the cold-drawing process used to make synthetic fibers. It is designed to break sheets of any material into tiny, nearly uniform segments ranging in various sizes down to a nanoparticle.

Kristopher Sturgis

The discovery was made by an interdisciplinary team of researchers at MIT, and could be used to mass-produce high tech optical devices and other electronics. The new method was designed to produce sectioned particles out of a variety of different materials including plastics, metals, glass, and even natural materials like silk.

"The process we describe can produce nanoparticles from any material that is available in the form of a thread or thin sheet," says Ayman Abouraddy, associate professor of optics and photonics at the University of Central Florida, and one of the lead authors on the research. "Consequently, a very broad range of materials can be tackled in this way, as we show. Nanoparticles are useful for a wide range of applications, spanning the gamut from cosmetics and sunscreens, to biotechnology and drug delivery, all the way to paints and coatings."

The technology that makes it all possible is a process called cold-drawing, a technique that has been used for years to produce synthetic fibers like nylon. In their new research, Abouraddy and his team expanded this technique to include fibers from multiple materials, including ones that were previously expected to shatter when subjected to this kind of stretching.

"The serendipitous discovery of this process grew out of previous work on fluid instabilities in fibers comprised of multiple materials," Abouraddy said. "Our efforts were focused on what happens when the fiber is heated and the materials soften to the point where surface tension can lead to a core running the whole length of the fiber, and is converted into a necklace of spheres--just as a jet of water out of a faucet is reduced to droplets when the flow rate drops."

It was during this investigation that Soroush Shabahang, one of their students and first author on the work, happened to observe that the core along a very thin thread seemed to shatter when the fiber was pulled, ever so gently, from its two ends. Once they moved to larger diameters and larger axial stresses, they found that the phenomenon happens ubiquitously.

"Very few nanoparticle fabrication strategies rely on mechanical forces, especially if it is a complex internal architecture," Abouraddy says. "Grinding processes can produce small particles, but size uniformity is usually lacking, and it's impossible to create complex structures. Our process uses a mechanical force at room temperature, thus low energy expenditure, and nevertheless produces uniformly sized particles from a wide variety of materials."

Since cold-drawing has been a staple in the business of manufacturing synthetic fibers for years, this routine practice could now be used to produce structures made from a myriad of different materials at the micro and nanoscale.

"This is routinely carried out at tremendous quantities and high speed," Abouraddy says. "Now, this well established manufacturing process can be exploited to produce micro and nano-structures, and as such, we anticipate that the adoption of our strategy will have a tremendous impact."

Abouraddy says that, in the context of biological science, complex particle structures can be fabricated using polymeric fibers as a scaffold. His team envisions that this technique can be used as imaging contrast agents, and possibly even vehicles for drug delivery. He says that in addition to applications in spectroscopy, the technique will effectively serve as a tool for anyone involved with materials science and engineering.

"Gratings are used in spectroscopy to identify compounds by examining their diffracted optical spectrum. But in addition to their scientific interest, this process is a valuable educational tool for young students--bringing together ideas and concepts from materials science, mechanical engineering, and optics."

As they move forward, the team is confident this technique could be used as an important tool to produce larger quantities of nanoparticles, nanorods, and nanowires of a wide variety of different compositions--all in an effort to advance the the use of multimaterial fibers.