Polarized FT-IR study of macroscopically oriented electrospun nylon-6 nanofibers

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.