Advanced Materials Letters

The electrospun PVDF (Polyvinylidene Fluoride) nanofiber web is commonly agreed on a kind of new sensitive materials for the sensor testing the dynamic pressure and energy harvesting, and has the characteristics of fast response and high sensitivity of pressure. As a result of the nanofiber web, it must be packaged to collect piezoelectric charge and bear strong mechanical behavior before industrial practice. The packaging of PVDF nanofiber web is usually sandwiched by incorporating a pair of flexible electrode. However, the effects of the surface and mechanical properties of electrodes such as morphology, roughness and compressibility have not been well investigated yet. This work will introduce three common types of packaging electrode materials (adhesive copper foil tape, indium tin oxide (ITO) thin film, adhesive conductive cloth.) in previously published literatures, compares the piezoelectric output of their sensor prototypes under a periodic impact, and discusses the effect of surface morphology, electrical resistance, and compressibility. The results showed that it has higher output of PVDF piezoelectric sensor packaged by electrode materials with the smooth surface and low mechanical compressibility. This result provides a guideline for designing the textile electrode material for the PVDF nanofiber web.

Polyvinylidene fluoride (PVDF) nanofiber mats prepared using electrospinning technique have been used for making mechanical-to-electrical energy conversion devices. However, the effect of residual charges on this energy conversion process has never been seriously considered yet. In this study, by removing residual charges from electrospun PVDF nanofiber mats using a solvent treatment method, the contribution of the charges to device energy harvesting performance was carefully examined. It has been found that isopropanol treatment could effectively remove most of residual charges from the nanofiber mats, without obviously affecting crystal structure of the fibers. The electric outputs decreased from 1.0 V and 1.2 μA to 0.45 V and 0.5 μA after the residual charges removal. It can be concluded that residue charges play an important role in mechanical-to-electrical energy conversion of electrospun nanofibers. The understanding obtained from this study may supply a strategy for enhancing electric outputs of piezoelectric devices in future. Copyright © 2017 VBRI Press.

Herein, we report the synthesis of poly (vinylidene fluoride) (PVDF) based novel nanocomposites reinforced with graphene nanoplatelets (GNP) and vanadium pentoxide (V2O5) as nanofillers. The PVDF/V2O5/GNP nanocomposite films were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), polarized optical microscopy (POM) and scanning electron microscopy (SEM). The electrical properties of nanocomposites were investigated to ascertain the synergistic effect of fillers on the quality factor (Q-factor) of nanocomposites. The FTIR and XRD results infer good interaction between PVDF and V2O5 and the good dispersion of nanofillers in the PVDF matrix. The TGA results revealed that the thermal stability of PVDF/V2O5/GNP nanocomposite has improved at higher loading of nanofillers due to the good interaction between the nanofillers and the polymer matrix. The electrical analysis of nanocomposite films demonstrates high Q-factor value (1099.04) at 4.7 wt % V2O5 and 0.3 wt % GNP loading. With further increase in GNP loading to 1 wt %, the Q-factor becomes lower (356.52) which could be due to the enhanced conductivity of the samples. The significant enhancement in the value of Q-factor shows that the nanocomposites can be used as a potential candidate for high-Q capacitor applications. 

This work proposes an energy harvester that captures the mechanical energy caused by water flow and converts into an electrical energy through the piezoelectric effect. A flexible piezo-film has been used as a transducer in the energy harvesting system and the kinetic energy of the water flow is produced by using the vortex induced vibration technique. When placing in water way the transducer is fluctuating in the vortex of the fluid flow, producing the kinetic energy of 44 mW at a low fluid velocity of 6.8 m/s and low frequency of 0.4 Hz. This configuration generates a corresponding open-circuit voltage of 6.6 mV at a matching load of 1 MW, leading to the maximum output power of 0.18 mW. An efficiency power conversion of the harvesting system was evaluated to be about 4.4 %.  It is possible to use the proposed unit under gravitational force where there is a difference in the levels of the fluid no matter in water way or transporting parts such as petroleum pipes. However, rectifying the output voltage generated by the present micro generator is compulsory in order to feed small scale electronics and communication, for instance, wireless sensor networks. Furthermore, multiple arrays of the piezoelectric unit are also promising for delivering higher output power.