Previously, inorganic nanomaterials such as lead zirconate
titanate (PZT) [4–7] and zinc oxide (ZnO) [8–10]
have demonstrated considerable progress toward self-powered
energy harvesters. These piezoelectric fibers can be fabricated
using various methods, including chemical vapor deposition
and physical vapor deposition [11, 12]. On the other hand,
electrospinning processes have been used to make organic
nanofibers, and, with the right selection of piezoelectric
materials, electrospun fibers could also be used as energy
harvesters [13]. Yee et al have demonstrated the feasibility
of using far-field electrospinning (FFES) and a rotating disk
to collect aligned electrospun PVDF fibers [14]. These fibers
are emitted from the Taylor cone in the fabrication process
by overcoming the surface tension and viscoelasticity of
polymer droplet solutions [15]. Electrostatic force is used to
stretch the fiber and the polymer jet can chaotically bend into
complex paths, causing random deposition of nanofibers [16].
As a result, it is difficult to produce aligned PVDF fibers
using FFES. Fennessey [17] and Kim [18] have investigated
different techniques to align electrospun fibers using a rotating
collector. Wang [19] has modified the electric field for better
alignments and the application of fundamental physics and
chemistry for better process controls [20]. Recently, the
direct-write electrospinning technique using NFES has been
introduced [21–23]. Unlike the conventional FFES process,
NFES only needs a small electric bias voltage to produce
continuous fibers with ultrafine diameters. Under the in situ
electrical poling procedure, the solidified PVDF polymer
solution can transform PVDF polymer from the non-polar
α-phase into the polar β-phase [13]. However, the breakdown
voltage of air is ∼106 V m−1
, which is too low for the
electric poling process, and a polymer thin film has been
proposed to replace air to apply higher electric field for
a better poling process [24]. In this work, in order to
prevent possible electrical shorts during the electrospinning
process [25], direct-write NFES on a glass tube under a
high applied voltage has been demonstrated. Furthermore,
a strong mechanical stretching effect is implemented by
rotating the glass tube collector with a tangential speed