Probing the internal structure of high-performance fibers by on-axis scanning diffractometry

Many high-performance fibers exhibit radial anisotropy or a skin-core morphology. This influences their mechanical properties, affects the interfacial characteristics of composite systems, and needs consideration when interpreting results collected using localized probing techniques. This study reports on the direct observation of crystallographic texture and rotational disorder within a single high-performance fiber. This is possible using a microfocused X-ray beam to obtain diffraction patterns along the fiber axis. This enables radial anisotropy to be investigated without the need for modeling. The results indicate that the high-performance fiber studied exhibits a rotationally disordered skin and core, with preferred orientation extending throughout the fiber. Variations in the skin's width and core position are taken as evidence of heterogeneous coagulation. The experimental results can be explained by a fiber formation model in which oriented crystalline domains extend inward, toward the fiber center. These results allow a number of findings from previous model-based studies to be validated.