Crystalline Morphology and Polymorphic Phase Transitions in Electrospun Nylon-6 Nanofibers
Uniform nylon-6 nanofibers with diameters around 200 nm were prepared by electrospinning. Polymorphic phase transitions and crystal orientation of nylon-6 in unconfined (i.e., as-electrospun) and a high T{sub g} (340 C) polyimide confined nanofibers were studied. Similar to melt-spun nylon-6 fibers, electrospun nylon-6 nanofibers also exhibited predominant, metastable {gamma}-crystalline form, and the {gamma}-crystal (chain) axes preferentially oriented parallel to the fiber axis. Upon annealing above 150 C, {gamma}-form crystals gradually melted and recrystallized into thermodynamically stable {alpha}-form crystals, which ultimately melted at 220 C. Release of surface tension accompanied this melt-recrystallization process, as revealed by differential scanning calorimetry. For confined nanofibers, both the melt-recrystallization and surface tension release processes were substantially depressed; {gamma}-form crystals did not melt and recrystallize into {alpha}-form crystals until 210 C, only 10 C below the T{sub m} at 220 C. After complete melting of nanoconfined crystals at 240 C and recrystallization at 100 C, only {alpha}-form crystals oriented perpendicular to the nanofiber axis were obtained. In the polyimide-confined nanofibers, the Brill transition (from the monoclinic {alpha}-form to a high-temperature monoclinic form) was observed at 180-190 C, which was at least 20 C higher than that in unconfined nylon-6 at {approx}160 C. This, again, was attributed to the confinement effect.
- Research Organization:
- Brookhaven National Laboratory (BNL) National Synchrotron Light Source
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- AC02-98CH10886
- OSTI ID:
- 929949
- Report Number(s):
- BNL--80544-2008-JA
- Journal Information:
- Macromolecules, Journal Name: Macromolecules Vol. 40
- Country of Publication:
- United States
- Language:
- English
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