The orientation of molecules in fibers

This paper reviews various methods for measuring molecular alignment and various interpretations of results. It is emphasized that exact knowledge of the molecular arrangement in fibers is non‐existent; many interpretations and models exist but none of them are accurate representations of the true state. Deformation causes reorganization at all of these dimensional levels: the segments of the basic molecule, the aggregate called a crystallite, the crystalline‐amorphous entity, the single crystal lamella, the larger aggregation called spherulite. Each of these levels may have its own deformation behavior and may be involved differently in the results from a particular experimental technique. No single technique describes the alignment of all molecules for their entire length. Most techniques represent an average orientation, whereas the distribution of orientation is ideally sought. These techniques were reviewed: x‐ray diffraction, birefringence, infrared dichroism, magnetic anisotropy, softening, shrinkage tension, dichroic dyestuffs, stress optical coefficient, sonic velocity, differential thermal analysis, and light scattering. The most useful data have been those for the relationship of orientation to physical properties. The seldom recognized increase of T g by orientation is emphasized. Speculation is made of the morphology associated with stress‐crystallization and the role of dislocation motion in deformation.