Abstract
Novel polymer-based piezoelectric nanocomposites with enhanced electromechanical properties open new opportunities for the development of wearable energy harvesters and sensors. This paper investigates how the dissolution of different types of hexahydrate metal salts affects β-phase content and piezoelectric response (d33) at nano- and macroscales of polyvinylidene fluoride (PVDF) nanocomposite films. The strongest enhancement of the piezoresponse is observed in PVDF nanocomposites processed with Mg(NO3)2⋅6H2O. The increased piezoresponse is attributed to the synergistic effect of the dipole moment associated with the nucleation of the electroactive phase and with the electrostatic interaction between the CF2 group of PVDF and the dissolved salt through hydrogen bonding. The combination of nanofillers like graphene nanoplatelets or zinc oxide nanorods with the hexahydrate salt dissolution in PVDF results in a dramatic reduction of d33, because the nanofiller assumes a competitive role with respect to H-bond formation between PVDF and the dissolved metal salt. The measured peak value of d33 reaches the local value of 13.49 pm/V, with an average of 8.88 pm/V over an area of 1 cm2. The proposed selection of metal salt enables low-cost production of piezoelectric PVDF nanocomposite films, without electrical poling or mechanical stretching, offering new opportunities for the development of devices for energy harvesting and wearable sensors.
Highlights
During the last decade, flexible piezoelectric films have been attracting a great deal of interest for the realization of devices capable of converting low-frequency mechanical energy into electrical signals
Several experimental and theoretical studies have confirmed that the use of carbon nanotubes (CNTs) as filler in the polyvinylidene fluoride (PVDF) matrix can lead to a relevant increase in the β-phase content [16,17]
In our previous works we have investigated the influence of graphene nanoplatelets (GNPs) dispersion in PVDF nanocomposites on both β-phase formation [18] and d33 enhancement through piezoresponse force microscopy (PFM) [22]
Summary
Flexible piezoelectric films have been attracting a great deal of interest for the realization of devices capable of converting low-frequency mechanical energy into electrical signals. GNPs are 2D nanostructures having a high aspect ratio and a large surface area, which promotes a very strong interfacial interaction with the polymeric chains in nanocomposites This results in an enhancement of the electric [20], mechanical [18], piezoresistive [21], and piezoelectric [22] properties of the host polymer. The developed production route of piezoelectric PVDF nanocomposite film is fast and cost effective because it requires only 3 h of magnetic stirring (against days of processing) and makes use of inexpensive and low-toxicity commercially available hexahydrate salts of magnesium
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