| High molecular weight polyamides have attained considerable practical importance as Nylon fibers. One of the commercially most successful polyamides is made by the condensation of hexamethylene diamine and adipic acid, known as Nylon 6,6. Hydrogen bonding could occur between Nylon polymer chains, leading to the β-sheet structure similar to that of polypeptides. The most common structure of Nylon 6,6 is called α form with triclinic unit cell. Previous work has shown that lath shaped and faceted single crystals could be obtained in certain crystallization conditions. Four types of spherulites have been observed from bulk samples, including positive, negative, zero-birefringence spherulites and spherulitic aggregates. With extensive studies on Nylon 6,6 structure and properties during the past 60 years, however, the detailed phase structure and morphology are still remaining unclarified.; In this dissertation, we conducted systematic work on solution crystallized Nylon 6,6 single crystals and spherulites. Both self-seeding and non self-seeding methods have been applied. Lath shaped and regularly faceted single crystals have been grown from glycerin solution. The aspect ratio of each facet of the single crystals changes with crystallization temperature. Furthermore, novel triangular and scrolled/tubular single crystals have been, for the first time, grown from solution. Both these two crystal habits exhibit peculiar crystal structures constructed by twinning of the previously reported α unit cell. Scrolled/tubular single crystals are of particular interests. The diameter of the tubes/scrolls is approximately 350 nm. It is envisioned that the scroll/tube is due to the asymmetric fold of the top and bottom lamellar surfaces. Spherulitic aggregates have been grown from concentrated glycerin solution. In particular, our study has shown that the solution concentration, crystallization temperature and self-seeding temperature have dramatic effects on spherulitic growth of Nylon 6,6. Morphology maps of Nylon 6,6 at different growth conditions have been established. |
