|Chemists had a hint that the aromatic compounds in Kevlar
were related to its strength. The challenge was to find out how these aromatic
groups were oriented within a fiber of Kevlar. With synchrotron light, it
is possible to "see" (detect) the presence of different groups of atoms
by the selective absorption of light.
Click here to learn more about selective absorption of light:
Scientists can use a special type of x-ray microscopy called XANES to reveal the orientation of molecules in materials. At the National Synchrotron Light Source in New York, scientists exposed the cut end of a Kevlar fiber to produce this image:
The pattern shows that the aromatic components of Kevlar have a radial (spoke-like) orientation.
The radial orientation is important because it allows the polymer chains to be well-ordered and symmetric like the atoms in a crystal. Because of this highly ordered structure, a fiber of Kevlar has few structural flaws or weak places. This lack of flaws or weak places is the biggest reason for the exceptional strength of Kevlar.