Determination of internal structure of complex polymeric materials often requires a variety of analytical techniques. One technique that we have developed and recently employed for the first time for quantitative analysis is x-ray linear dichroism microscopy. With sensitivity to the presence and orientation of specific chemical functionalities within polymer molecules, x-ray linear dichroism microscopy provides a powerful tool to probe the internal structure of such molecules. We have used this ability to quantitatively analyze the lateral orientational order (tangential and radial orientation of transverse sections) within different grades of poly(p-phenylene terephthalamide) (Kevlar) fibers.

Kevlar fibers are highly crystalline and possess a complicated internal structure that exhibits lateral radial orientation. Figure 1 shows x-ray micrographs of (a) Kevlar 149, (b) Kevlar 49 and (c) Kevlar 29 fibers imaged at a photon energy specific to the aromatic functionality.