writer：Shuangyang Liu, Yanyan Liang, Yabo Quan, Kun Dai, Guoqiang Zheng(通讯作者), Chuntai Liu, Jingbo Chen , C
keywords：Electrospinning Self-similar morphology Orientation
source：期刊
specific source：Polymer
Issue time：2013年
Macroscopically aligned isotactic polypropylene (iPP) fibers with different diameters ranging from 0.7 to
13.2 mmwere successfully fabricated by high-temperature solution electrospinning using an infrared (IR)
heating system. Polarized optical microscope (POM), scanning electron microscope (SEM), wide-angle Xray
diffraction (WAXD), differential scanning calorimetry (DSC) and polarized Fourier transform infrared
(FTIR) were employed to characterize the surface morphology and microstructure of the electrospun
fibers. From SEM images, three macroscopically structural models have been found: (1) cylindrical fibers,
(2) twisted fibers and (3) beaded fibers. Interestingly, regardless of fiber’s shape and size, they (especially
for cylindrical fibers) exhibit well-defined self-similar morphology. That is, the tertiary, secondary and
primary morphology are similar with each other. Thermally induced phase separation (TIPS) is the most
pertinent origin to explain the formation of self-similar morphology.WAXD and DSC results show that aform
crystal prevails in the electrospun iPP fibers. For comparison, the solution-cast film was also prepared
under the same conditions as those adopted in electrospinning except that the voltage was 0 kV.
Compared with the solution-cast film, lower crystallinity, smaller average crystallite size and higher
melting point are achieved in the electrospun iPP fibers. The results of polarized FTIR spectra demonstrate
that the macroscopically aligned electrospun fibers are highly oriented along the fiber’s longitudinal
axis at molecular level. Furthermore, when the electrospun iPP fibers were embed in iPP matrix,
surface-induced crystallization is significantly enhanced and finally develops into transcrystalline layer
which can be even revived after recrystallization. As a result, it is logical that long-lived thermodynamically
stable structure has been formed in the electrospun iPP fiber. Combined with FTIR result, the
a-form crystal formed in the fiber is conjectured to be a kind of oriented structure with thermodynamically
long-lived stability which is similar to "shish-kebab" structure.