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February 01, 2007

Nanofibers thinner than critical diameters have more strength

Scientists at the Technion-Israel Institute of Technology have shown that tiny polymer nanofibers become much stronger when their diameters shrink below a certain size. Their research, published in the January issue of Nature Nanotechnology, could make possible stronger fabrics that use less material.

Professor Eyal Zussman and Dr. Oleg Gendelman of the Faculty of Mechanical Engineering are the first to propose an explanation for this surprising behavior in very thin fibers.

When the researchers measured the mechanical properties of nylon nanofibers, they found the critical diameter – the diameter at which the nylon nanofiber abruptly becomes stiffer—to be approximately 500 nanometers (about as thick as a spider web strand, or 100 times thinner than a human hair). They explained the abrupt increase in stiffness by considering the molecular structure inside the polymer fiber.

According to Zussman, each polymer nanofiber is made up of countless large, complex molecules called macromolecules. Macromolecules try to align themselves when the fiber is forming, but since they are so long and tangled, it is impossible for them to sort themselves out and align uniformly throughout the entire nanofiber. As a result, the nanofiber is a patchwork of differently oriented macromolecule regions. The researchers calculated the size of these regions to be roughly the same as the critical diameter of the nanofiber

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