3.2. Nanofiber diameter
Fig. 2 shows the fiber diameter distribution of the PVA fibers at
different polymer concentrations. The nanofibers with lower and
higher PVA concentrations (10 wt% and 14 wt%) had a wider diameter
distribution from 65 to 137 nm and 175 to 332 nm. The wide
distribution of fiber diameters was mainly dependent on the formation
of some droplets at lower PVA concentration (10 wt%)
and the adhesion of partial nanofibers at higher PVA concentration
(14 wt%) as observed in SEM images above. When the PVA concentration
was 12 wt%, the fibers were smooth and homogeneous as
shown in Fig. 1 and thereby this nanofiber had a narrower fiber
diameter distribution.
Average diameters of the electrospun nanofibers at different
polymer concentrations were evaluated from the SEM images
using Photoshop CS5 software and the results were listed in
Table 1. It could be seen that with the increasing of PVA concentration
from 10 wt%, 12 wt% to 14 wt%, the average diameter of the
resultant nanofibers increased consistently from 91.2, 157.2 to
241.8 nm. The smaller average diameter in the lower concentrations
is due to the higher mobility of the polymer chains and the
stronger instabilities of the jets during the electrospinning. As
the PVA concentration increased to 14 wt%, the fibers were
adhered together leading to the larger average diameter. As listed
in Table 1, the standard deviation of the nanofiber diameter with
14 wt% PVA concentration was the largest. This suggested that
the diameter distribution of the whole fiber was not uniform and
it was also due to the adhesion of partial fibers [16]. As for the
PWA/PVA nanofiber with 8 wt% PVA concentration, the fiber aver