Oriented hierarchical structure in synthetic fibers

All oriented polymers (net axial orientation function greater than 0.7) possess a microfibrillar morphology and all show significant fibrillation upon failure. Typical microfibrillar dimensions are 10 Nm in diameter and of essentially infinite length. Synthetic fibers comprise the most common form of oriented polymers, and all synthetic fibers possess a hierarchical structure in the sense that they possess a structural repeat of fiber symmetry from the molecular to the macroscopic. The microstructure of synthetic fibers is comprised of crystalline and non-crystalline elements. The choice of polymer and the details of the processing conditions control the ratio of crystalline to non-crystalline units, the net orientation associated with each phase (or subphase), and the connections between them. The microstructure of the typical 100 angstrom diameter microfibril can be between them. The microstructure of the typical 100 angstrom diameter microfibril can be described as an array of crystalline (or at least, mesogenically correlated) and non-crystalline elements in series. The ordered portions of the fibrils are characterized by size (normally 100s of angstrom by about 100 angstrom), net orientation and the nature of the order-disorder interface. While an equilibrium polymer crystal is comprised of fully extended chains, kinetic conditions during practical crystallization almost inevitably cause the chains to fold, forming thin lamellar structures with the chains parallel to the thin dimension. The regular nature of this folding and the concentration of tie molecules between lamellae is still debated in the literature, it is clear that tie molecule formation and less regular fold surfaces are aided by fast crystallization and chain orientation during or prior to the crystallization event. The thickness of the lamellar crystals is a function of the time and temperature of crystallization and lamellar crystals are subject to perfecting and thickening during annealing.