Piezoelectric Effect and Electroactive Phase Nucleation in Self-Standing Films of Unpoled PVDF Nanocomposite Films

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.

Spin Coating and Micro-Patterning Optimization of Composite Thin Films Based on PVDF

“…As reported in previous sections, adding nano-fillers into the PVDF matrix has not only a technology goal of artificially coupling two different functionalities in the same nanostructures (i.e., piezoelectric and ferromagnetic), but comes basically from the idea that the nano-objects can promote the nucleation of a suitable electro-active phase. The enhancement of the β phase by using nano-fillers depends on the types of nano-inclusions as well as from the charges on their surface [25,[30][31][32][33][34][35]48,50]. The interaction between the electric charged surface of the nano-inclusions and the bonds of PVDF chains has already been proposed as a key factor for increasing the nucleation of the β phase of the polymer [8,24,25,[27][28][29][30][31][32].…”

“…As a matter of fact, in the near infrared region, each of the PVDF phases shows its own absorptions in the detectable transmittance. The intensity and the presence of these absorptions (indexed in Figure 7 from a comparison with the literature [35,[47][48][49][50]) depend on the amount of the absorbent phase. Figure 7a shows the FTIR spectra of the elaborated neat PVDF thin films on silicon substrates and Figure 7b of the correspondent elaborated neat PVDF thin films on silicon covered by aluminum.…”

“…We also recorded the substrate transmittance in order to verify a possible artefact from the substrates absorption. Putting in comparison IR spectra in Figure 7a,b, it is possible to notice that the Si substrate (black line in Figure 7a) has a very broad absorption for wave lengths smaller than 840 cm −1 which prevents the correct observation of the absorption band located at exactly 840 cm −1 , attributed to the TTT conformations existing in the β phase and also in the γ phase [35,[47][48][49][50]. This band is, in fact, remarkably visible in the twin-films deposited on Al/Si substrates where this broad absorption is absent thank to the good reflectivity properties of the aluminum layer within all the wavelength range.…”

“…12, x FOR PEER REVIEW 10 of indexed inFigure 7from a comparison with the literature[35,[47][48][49][50]) depend on the amount of the absorbent phase.…”

Solution Blow Spinning of Polyvinylidene Fluoride Based Fibers for Energy Harvesting Applications: A Review

“…Similar results were reported by Li et al [41] where fraction of β-phase significantly dropped with unmodified zinc oxide (ZnO) nanoparticles mainly due to their agglomeration. The hybrid nanofillers produce synergistic effects in polymers that are useful to improve mechanical properties; however, when ZnO nanorods and graphene nanoplatelets were incorporated into PVDF along with hydrated metal salts, a drastic reduction in d 33 was recorded [42]. It can be because of nanofillers assuming a competitive role with respect to H-bond formation between PVDF and the dissolved metal salt.…”