How can you get information about tiny things,
like the individual molecules in Kevlar,
if they are too small
to be seen with a regular microscope?

   
  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.


If you have ever worn sunglasses, you are familiar with the idea of selective absorption of light. Some sunglasses, when you look through them, cause everything you see to take on a blueish tint. This occurs because the glasses are primarily absorbing yellow light, while allowing the blue tones of light to pass through to your eyes. Things look blueish because you see only the light that gets to your eyes.

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.


CLUE #5: The aromatic components of Kevlar polymers have a radial (spoke-like) orientation, which provides a high degree of symmetry and regularity to the internal structure of the fibers. This crystal-like regularity is the largest contributing factor in the strength of Kevlar. Only with bright synchrotron radiation could the secret strength of Kevlar be revealed.


Kevlar Introduction

Clue #1

Clue #2

Clue #3

Clue #4

Putting the Pieces Together

   
 

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