Randomly deposited or partially aligned electrospun nylon-6 nanofibers were prepared by using a rotating collector with linear velocity from 0 to 900 m/min, and their molecular orientation was characterized with polarized Fourier-transform infrared (FT-IR) spectroscopy. At a linear velocity of 0 m/min, electrospun nylon-6 nanofibers are randomly deposited onto a collector owing to the bending instability of the charged jet. In this case the parallel polarized FT-IR spectrum (obtained at two mutually perpendicular directions) is the same as the perpendicular polarized spectrum, indicating that there is no molecular orientation in the electropun membrane. When the linear velocity of the collector was increased from 0 to 300 m/min, several changes in IR band intensity are observed, including the NH stretching band at 3303 cm -1 and the amide I and II vibrations (1647 and 1543 cm -1 , respectively) in the two polarized FTIR spectra. Also, the intensity of the amide II vibration is observed to gradually increase in the parallel polarized FT-IR spectrum, with an increase in the linear velocity of the collector, whereas its intensity is observed to decrease in the perpendicularly polarized spectrum. This indicates that the polymer chains are preferentially oriented along the fiber axis. Also, a decrease in the average fiber diameter (from 250 to 125 nm) is observed in SEM micrographs, indicating that the fibers are stretched and aligned by the high-speed rotating collector.
Isotactic poly(1-butene) (i-PB) fibrous membranes with fiber diameters on the order of microns
were prepared from polymer solutions using mixed solvents via electrospinning. As demonstrated by FE-SEM,
unexpected structures such as curled, twisted ribbon fibers and hollow hemisphere (HHS) on a string appeared
depending on the type of solvents used. Furthermore, it was observed that electrospun fibrous membranes and
solvent cast films gave rise to different crystalline modifications even though they were formed from the same
solutions. This may be due to different crystallization times and stresses induced during the electrospinning process.
The electrospun fibrous membrane contained both form I (twinned hexagonal structure) and metastable form II
(tetragonal structure) immediately after spinning. The metastable form II gradually transformed into the stable
form I at room temperature over the span of several days. This transformation was observed to occur more
rapidly with increased temperature. In comparison, solvent cast films contained a mixture of form III (orthorhombic
structure) and a small amount of form I‘ (untwinned hexagonal structure) and was stable at room temperature.
However, form III is the dominant crystal structure in the solvent cast film, as determined by WAXD. These
transformations were investigated as a function of aging time by Fourier transform infrared and Raman spectroscopy
as well as X-ray diffraction and differential scanning calorimetry.
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