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Energy harvesting is one of the most promising research areas to produce sustainable power sources from the ambient environment. Which found applications to attain the extensive lifetime self-powered operations of various devices such as MEMS wireless sensors, medical implants and wearable electronic devices. Piezoelectric nanogenerators can efficiently convert the vastly available mechanical energy into electrical energy to meet the requirements of low-powered electronic devices. Among the piezoelectric materials, poly (vinylidene fluoride) (PVDF) and its copolymers are extensively studied for the development of energy harvesting devices. Due to the outstanding properties such as high flexibility, ease of processing, long-term stability, biocompatibility makes them a promising candidate for piezoelectric generators. Nevertheless, compared to piezoceramic materials, PVDF based generators produce lower piezoresponse. Over the last decades, tremendous research activities have been reported to endorse the performance of PVDF based energy harvesters. This review article mainly focused on the recent progress in the performance improvement with processing methods, piezoelectric materials, different filler loading. The new developments and design structures will lead to an increase in piezoelectricity, alignment of dipoles, dielectric properties and subsequently enhance the output performance of the device. Electronic circuits play a vital role in energy harvesting to efficiently collect the developed charge from the device. Here, we have proposed a detailed description of the electronic circuits. Also, in the application part deals with the recent progress in flexible, biomedical and hybrid generators based on PVDF polymers.

This study deals with the deagglomeration of nanoparticles in low concentration suspensions in water, protic polar solvent for polymers such as poly(vinyl alcohol) (PVA). The influence of the main parameters of ultrasonication such as time, power and irradiation modes (continuous, pulsed) on the cluster size of aluminium oxide nanoparticles 1 mg/ml in aqueous solutions was investigated. Power-law dependence of size reduction on ultrasonic time was observed. The study indicated an optimum power input, i.e. at higher vibration amplitude the break up of nanoparticle clusters was no better and there was a risk of reagglomeration occurring during a long ultrasonication. Under optimal conditions, continuous and pulsed irradiations showed almost the same efficiency of deagglomeration over a given time. This result provides alternative operating conditions for attaining the smallest size of the alumina aggregates in suspension. The influence of stabilization on the cluster size was also studied. Alumina nanoparticles were stabilized by electrostatic forces against reagglomeration without the need for dispersants, and the enhancement of dispersion stability using electrostatic, steric effects had no significant effect on the aggregate size. On the contrary, the adsorption of high molecular weight polyelectrolytes onto the particle surface could lead to reagglomeration due to material bridges between particle surfaces and even flocculation.

This work presents a new synthesis of nano-sized lithium niobate particles by a low temperature three steps procedure. The complete protocol implies a LiH induced reduction of NbCl5 followed by in situ spontaneous oxidation into low valence niobium nano-oxides. These niobium oxides are exposed to air atmosphere leading to pure Nb2O5 formation. Finally, the stable Nb2O5 is converted into lithium niobate LiNbO3 nanoparticles during the controlled hydrolysis of the LiH excess. The nano-sized lithium niobate particles as well as their formation processes were characterized using X-ray photoelectron spectroscopy.

A detailed experimental investigation of the formation mechanisms of acentric iron iodate [Fe(IO 3 ) 3 ] nanocrystals in AOT-based reverse micelles according to the water-in-oil (w/o) microemulsion (ME) composition and temperature was performed. A low chemical reaction rate was first demonstrated by means of UV-vis absorption spectroscopy. Attainment of iron iodate crystalline nanorods was then attributed to an oriented aggregation mechanism of 10-20-nm amorphous primary nanoparticles. As for the intermicellar exchange of reactants, the aggregation mechanism was also found to be determined by the ME composition because clear effects of the surfactant and reactant concentrations, the nature of the oil phase, and the water droplet size were observed. Moreover, a combination of dynamic light scattering, X-ray diffraction, and transmission electron microscopy experiments revealed that hyper-Rayleigh scattering is a fast, valuable, and nondestructive alternative to probe, in real time, the crystallization and formation dynamics of acentric nanoparticles in microemulsions. This experimental approach can be extended to studies dealing with the formation of metal nanoparticles for which scattering of second-harmonic light is readily observed.

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Hybrid nanocomposites based on crystalline nanoparticles dispersed in polymer matrix have been widely studied in the past few years because of the ability of these materials to combine the properties of organic polymer and inorganic nanoparticles. The aim of this work is to tune the mechanical properties of a piezoelectric polymer by adding nanoparticles to the matrix. In this paper, alumina nanoparticles were dispersed in the copolymer P(VDF-TrFE), which exhibits high piezoelectric coefficient after polarization under high electric field without needing stretching during the polarization process. Transmission electron microscopy and scanning electron microscopy demonstrate the high rate of welldispersed nanoparticles with 10% of alumina nanoparticles added to the matrix. Piezoelectric measurements indicate that P(VDF-TrFE) may be filled by up to 10 wt% of alumina while retaining its high piezoelectric properties and increasing its elastic constant by more than 20%, measured by Brillouin spectroscopy. This work opens a wide range of applications using nanoparticles with nonlinear optical, pyroelectric, magnetic, or ferroelectric properties.