Abstract
The role of Ag addition on the structural, dielectric, and mechanical harvesting response of 20%(xAg − (1 − x)BaTiO3) − 80%PVDF (x = 0, 2, 5, 7 and 27 vol.%) flexible composites is investigated. The inorganic fillers were realized by precipitating fine (~3 nm) silver nanoparticles onto BaTiO3 nanoparticles (~60 nm average size). The hybrid admixtures with a total filling factor of 20 vol.% were embedded into the PVDF matrix. The presence of filler enhances the amount of β-PVDF polar phase and the BaTiO3 filler induces an increase of the permittivity from 11 to 18 (1 kHz) in the flexible composites. The addition of increasing amounts of Ag is further beneficial for permittivity increase; with the maximum amount (x = 27 vol.%), permittivity is three times larger than in pure PVDF ( ~ 33 at 1 kHz) with a similar level of tangent losses. This result is due to the local field enhancement in the regions close to the filler-PVDF interfaces which are additionally intensified by the presence of silver nanoparticles. The metallic addition is also beneficial for the mechanical harvesting ability of such composites: the amplitude of the maximum piezoelectric-triboelectric combined output collected in open circuit conditions increases from 0.2 V/cm2 (PVDF) to 30 V/cm2 for x = 27 vol.% Ag in a capacitive configuration. The role of ferroelectric and metallic nanoparticles on the increasing mechanical-electric conversion response is also been explained.
Highlights
No agglomeration of silver nanoparticles is noticed, even in the regions of larger aggregates, which means that the synthesis method allowed the formation of welldispersed Ag nanoparticles onto the BaTiO3 template surfaces
Polyvinylidene difluoride (PVDF)-based composites induced by the addition of a total amount of 20 vol.% hybrid fillers composed of variable quantities of Ag and BaTiO3 nanopowders are presented
Composed by ultrafine (~3 nm) silver nanoparticles directly precipitated onto BaTiO3 (~60 nm average diameter) nanoparticles were realized by solution casting
Summary
New dielectric and piezo-/pyro-/ferroelectric polymer-based materials are of high interest in recent years for flexible electronics applications such as portable or wearable sensors and transducers, energy harvesting elements, implantable devices for real-time health parameters monitoring, flexible building blocks for specific industrial applications, and soft robotics, etc. [1–3]. Ferroelectric polymers and in particular, Polyvinylidene difluoride (PVDF) with the formula –(C2 H2 F2 )n – (which is mostly used because it is ferroelectric and piezoelectric in specific molecular arrangements), and its co-polymers are highly flexible, i.e., they present good bending and tensile properties, they have a low mechanical impedance, low dielectric loss, and a lower permittivity with respect to one corresponding to oxides (ε r ≤ 10) [4,5] Their combination in hetero-structural composites with polymer matrix and inorganic fillers as active phase is natural, in order to combine the advantages of both types of materials and provide solutions for flexible electrical and electromechanical devices [6]. Permittivity as high as ~50–150 was reported for over-percolated compositions [16,17], but such values are produced as a result of the slow
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