Flexible Nanogenerator and Nano-Pressure Sensor Based on Nanofiber Web of PVDF and its Copolymers - Soft Fibrillar Materials: Fabrication and Applications - page 228

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Flexible Nanogenerator and Nano-Pressure Sensor Based on
Nanofiber Web of PVDF and its Copolymers
Chunye Xu and Kap Jin Kim
8.1
Introduction
Films consisting of polyvinylidene fluoride (PVDF) and its copolymer
poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), which exhibit piezo-,
pyro-, and ferroelectric behavior, have been investigated by many researchers
in the last three decades. PVDF promises potential applicability in diverse
fields of technology because of its high piezoelectric activity and availability as a
flexible thin film [1]. The copolymer of PVDF, namely P(VDF-TrFE), has another
advantage over PVDF due to its ferroelectricity, with a definite Curie transition
temperature ( T c ) and an adequately large electromechanical coupling coefficient
[1, 2]. However, because of several disadvantages such as non-breathability and
non-selectivity of directional deformation by external pressure and elongation,
PVDF and P(VDF-TrFE) films are not suitable as pressure sensors for a smart and
intelligent garment capable of detecting the position and magnitude of external
physical impact.
Recently, Wang et al . put forward a new research field of nanopiezoelectronics
which promises that piezoelectric materials can be an alternative choice for energy
harvesting applications [3]. They demonstrated the excellent concept of a nano-
generator based on zinc oxide (ZnO) nanorod or nanowire arrays. However, due
to rigidity, fragility, and low power generation caused by difficulty in fabricating
in a large area, realistic application of this technology is still questionable. In
contrast, piezoelectric polymers are good alternatives for similar kinds of applica-
tions. Recently we have shown the possibility of fabricating polymeric sensors and
nanogenerators based on the nanofiber webs of PVDF and P(VDF-TrFE) [4]. The
nanofiber webs are prepared by the electrospinning method, because this simple
and scalable process can eliminate the need for direct-contact poling or corona
poling to induce spontaneous dipolar orientation. Furthermore, flexibility and air
permeability of the nanofiber webs make them more suitable for integration with
self-power garments [5, 6]. Chang et al . showed the feasibility of fabricating a nano-
generator with a high energy conversion efficiency based on a single PVDF fiber
prepared by near-field electrospinning [6]. Now, some observations have shown that