Multilayered Electrospun/Electrosprayed Polyvinylidene Fluoride+Zinc Oxide Nanofiber Mats with Enhanced Piezoelectricity

Abstract

Electrospun polyvinylidene fluoride (PVDF) nanofibers have been widely used in the fabrication of flexible piezoelectric sensors and nanogenerators, due to their excellent mechanical properties. However, their relatively low piezoelectricity is still a critical issue. Herein, a new and effective route to enhance the piezoelectricity of PVDF nanofiber mats by electrospraying zinc oxide (ZnO) nanoparticles between layers of PVDF nanofibers is demonstrated. As compared to the conventional way of dispersing ZnO nanoparticles into PVDF solution for electrospinning nanofiber mats, this approach results in multilayered PVDF+ZnO nanofiber mats with significantly increased piezoelectricity. For example, 6.2 times higher output is achieved when 100% of ZnO (relative to PVDF quantity) is electrosprayed between PVDF nanofibers. Moreover, this new method enables higher loading of ZnO without having processing challenges and the maximum peak voltage of ≈3 V is achieved, when ZnO content increases up to 150%. Additionally, it is shown that the samples with equal amount of material but consisting of different number of layers have no significant difference. This work demonstrates that the proposed multilayer design provides an alternative strategy to enhance the piezoelectricity of PVDF nanofibers, which can be readily scaled up for mass production.

Enhanced Piezoelectricity of PVDF-TrFE Nanofibers by Intercalating with Electrosprayed BaTiO3

“…Upon increasing the BTO content to 15 and 25%, the crystallinity increased to 82.24 and 92.66% (maximum with 27% enhancement), respectively. This increase in crystallinity could be ascribed to the higher f (β)% in the PVDF-TrFE polymer. , However, further increases in BTO content (50, 75, and 100%) led to a decrease in crystallinity to 77.83, 80.03, and 78.93%, respectively, which could correspond to reduced f (β)% in the PVDF-TrFE nanofibers. , …”

“…The calculated β-phase content for each sample is presented in Figure b, from which it can be noted that the β-phase content of unmodified PVDF-TrFE nanofibers is 65.15% and it increases to 79.35% for D.PVDF-TrFE + 15% BTO and maximizes at 89.54% (37% increase) for D.PVDF-TrFE + 25% BTO. The higher β-phase content might stem from the new arrangement of the polymer chain’s dipoles influenced by BTO and its interaction with the applied electric field during the electrospinning. ,, However, with further increases in BTO content (50, 75, and 100%), the β-phase content decreased to 75.65, 71.94, and 68.34%, respectively, which might result from BTO agglomeration within the nanofibers. ,, …”

“…However, upon further increasing the loading of BTO, BTO potentially forms agglomeration in the PVDF-TrFE nanofibers, which resulted in a decrease in f (β)% and crystallinity. This likely led to decreases in the output voltages. , The short-circuit current, presented in Figure b,c, was measured by testing with a resistor having optimized resistance, based on which the power density was calculated. The same trend as the output voltage was observed for short-circuit current and power density, with D.PVDF-TrFE + 25% BTO having a ∼ 514% and a ∼ 3662% increase in short-circuit current output and power density, respectively, as compared to the unmodified PVDF-TrFE nanofibers.…”

“…The nanofiber mats consisting of PVDF-TrFE and BTO but with two distinct designs, dispersed and layered, showed different piezoelectric performances. The maximum BTO content achieved in “dispersed PVDF-TrFE + BTO” nanofiber mats was 100% (PVDF-TrFE:BTO = 1:1) as higher loading results in solution to be too viscous for electrospinning Figure a–d compares the piezoelectric performance of the “layered PVDF-TrFE + BTO” and “dispersed PVDF-TrFE + BTO” nanofibers made of the same quantity of materials.…”

“…To enhance their piezoelectricity, it is therefore crucial to increase their β-phase content. Some techniques have been found effective including adding piezoelectric − and/or nonpiezoelectric fillers , as well as engineering the nanofiber structures such as coaxial nanofibers, coated nanofibers, and other hierarchical structures. , For example, Jiang et al developed flexible piezoelectric pressure tactile sensors based on PVDF/BTO nanocomposite nanofibers via electrospinning. The addition of BTO nanoparticles to PVDF enhanced the piezoelectric performance, with the highest β-phase content (at 10 wt % of BTO) reaching 91%, and mechanical strength increased up to 26.7 MPa, surpassing the properties of unmodified PVDF.…”