Structure of mesophase pitch fibers

The as-spun structure of mesophase pitch-based carbon fibers has been characterized by darkfield electron microscopy of microtomed fiber sections. Three levels of organization have been observed. At the molecular range, the pitch molecules are stacked together creating small coherent domains. At the intermediate range, microdomains are observed, consisting of molecular assemblies with long range orientational order. They are several μm long in the fiber direction, but their lateral extension is limited by wedge disclinations to a few hundred nm or less. Finally, the role of fluctuations of the microdomain density in controlling the degree of very long range statistical orientation over the fiber crosssection is described. The variety of observed textures encompasses the many types eventually observed in the carbonized fibers. The effect of pitch type on the microtexture and texture is demonstrated.