Flexible Nanogenerator and Nano-Pressure Sensor Based on Nanofiber Web of PVDF and its Copolymers - Soft Fibrillar Materials: Fabrication and Applications - page 242

(a) Z (collector rotation direction)

Chain orientation

Perpendicularly
polarized IR beam

Applied electric field direction
during electrospinning
Induced dipole direction

E (electric field vector of
polarized IR beam)

ν as ( μ ν as )

ν s ( μ ν s )

Y

X (thickness direction)

0.7

B 1

(d)

0.6

B 2

Parallel polarization
Perpendicular polarization

0.5

0.4

B 1

B 2

(b) (c)

0.3

Symmetry
species

Vib. trans.
m oment
μ
μ

A 1

a

A 2

B 1

0.2

A 1 ,
B 1 ,
B 2 ,

A 1

b

0.1

b

c

0.0

μ a

1400 1200 1000 800 600 400

Ferroelectric phase

Wavenumber (cm − 1 )

Figure 8.14 (a) Schematic drawing for the
geometry of P(VDF-TrFE) nanofiber web
when the FTIR spectrum is measured using
the perpendicularly polarized IR, the electric
field vector of the incident IR beam, and the
vibrational transition moments of the electro-
active dipoles. The applied DC bias voltage
direction is parallel to the incident IR beam

direction. (b) The unit crystal lattice of the
ferroelectric phase of P(VDF-TrFE). (c) The
relationship between the vibrational transi-
tion moment and the crystal unit axis for
each vibrational symmetry species. (d) The
FTIR spectra of as-electrospun P(VDF-TrFE)
nanofiber web measured with parallel and
perpendicularly polarized IR beams.

in the parallel polarized spectrum. This indicates that the trans -zigzag chains
of P(VDF-TrFE) tend to orient preferentially parallel to the collector rotation
direction, and the preferential orientations of the electro-active CF 2 dipoles are
perpendicular to the trans -zigzag chains, as shown in Figure 8.14a. Therefore,
perpendicular polarization was chosen for further analysis of the induced dipolar
orientations. Let us consider two extreme cases. The first case is that there can
be no preferential orientation of dipoles toward the applied bias DC voltage