Phase Inversion in PVDF Films with Enhanced Piezoresponse Through Spin-Coating and Quenching

In the present work, poly(vinylidene fluoride) (PVDF) films were produced by spin-coating, and applying different conditions of quenching, in order to investigate the dominant mechanism of the β-phase formation. The influence of the polymer/solvent mass ratio of the solution, the rotational speed of the spin-coater and the crystallization temperature of the film on both the β-phase content and the piezoelectric coefficient (d33) were investigated. This study demonstrates that the highest values of d33 are obtained when thinner films, produced with a lower concentration of polymer in the solvent (i.e., 20 wt.%), go through quenching in water, at room temperature. Whereas, in the case of higher polymer concentration (i.e., 30 wt.%), the best value of d33 (~30 pm/V) was obtained through quenching in liquid nitrogen, at the temperature of 77 K. We believe that in the former case, phase inversion is mainly originated by electrostatic interaction of PVDF with the polar molecules of water, due to the low viscosity of the polymer solution. On the contrary, in the latter case, due to higher viscosity of the solution, mechanical stretching induced on the polymer during spin-coating deposition is the main factor inducing self-alignment of the β-phase. These findings open up a new way to realize highly efficient devices for energy harvesting and wearable sensors.

Download Full-text

Characterization and Application of PVDF and Its Copolymer Films Prepared by Spin-Coating and Langmuir–Blodgett Method

Polymers ◽

10.3390/polym11122033 ◽

2019 ◽

Vol 11 (12) ◽

pp. 2033 ◽

Cited By ~ 9

Author(s):

Zerun Yin ◽

Bobo Tian ◽

Qiuxiang Zhu ◽

Chungang Duan

Keyword(s):

Spin Coating ◽

Vinylidene Fluoride ◽

Medical Applications ◽

Ongoing Research ◽

Langmuir Blodgett ◽

Copolymer Films ◽

The Past ◽

Β Phase ◽

Poly Vinylidene Fluoride ◽

Ε Phase

Poly(vinylidene fluoride) (PVDF) and its copolymers are key polymers, displaying properties such as flexibility and electroactive responses, including piezoelectricity, pyroelectricity, and ferroelectricity. In the past several years, they have been applied in numerous applications, such as memory, transducers, actuators, and energy harvesting and have shown thriving prospects in the ongoing research and commercialization process. The crystalline polymorphs of PVDF can present nonpolar α, ε phase and polar β, γ, and δ phases with different processing methods. The copolymers, such as poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), can crystallize directly into a phase analogous to the β phase of PVDF. Since the β phase shows the highest dipole moment among polar phases, many reproducible and efficient methods producing β-phase PVDF and its copolymer have been proposed. In this review, PVDF and its copolymer films prepared by spin-coating and Langmuir–Blodgett (LB) method are introduced, and relevant characterization techniques are highlighted. Finally, the development of memory, artificial synapses, and medical applications based on PVDF and its copolymers is elaborated.

Download Full-text

Enhancement of the piezoelectric coefficient in PVDF-TrFe/CoFe2O4 nanocomposites through DC magnetic poling

Beilstein Journal of Nanotechnology ◽

10.3762/bjnano.12.93 ◽

2021 ◽

Vol 12 ◽

pp. 1262-1270

Author(s):

Marco Fortunato ◽

Alessio Tamburrano ◽

Maria Paola Bracciale ◽

Maria Laura Santarelli ◽

Maria Sabrina Sarto

Keyword(s):

Piezoelectric Coefficient ◽

Vinylidene Fluoride ◽

Piezoelectric Materials ◽

Low Cost ◽

Wearable Sensors ◽

Polymer Nanocomposite ◽

Sample Surface ◽

Β Phase ◽

Phase Alignment ◽

Poly Vinylidene Fluoride

In the last years flexible, low-cost, wearable, and innovative piezoelectric nanomaterials have attracted considerable interest regarding the development of energy harvesters and sensors. Among the piezoelectric materials, special attention has been paid to electroactive polymers such as poly(vinylidene fluoride) (PVDF) and its copolymer poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFe), which is one of the most extensively investigated piezoelectric polymers, due to the high β phase content resulting from specific curing or processing conditions. However, to obtain a high piezoelectric coefficient (d33) alignment of the β phase domains is needed, which is usually reached through applying a high electric field at moderate temperatures. This process, usually referred to as electrical poling, requires the deposition of contact electrodes on the sample surface and the use of high-voltage apparatus. In the present work, in order to overcome these constraints, we have produced, characterized, and studied a polymer nanocomposite consisting of CoFe2O4 nanoparticles dispersed in PVDF-TrFe with enhancement of the β phase alignment through an applied DC magnetic field. The magnetic poling was demonstrated to be particularly effective, leading to a piezoelectric coefficient d33 with values up to 39 pm/V. This type of poling does not need the use of a top electrode or of high magnetic fields (the maximum value of d33 was obtained at 50 mT, using a current of 0.4 A) making the PVDF-TrFE/CoFe2O4 nanocomposite suitable for the fabrication of highly efficient devices for energy harvesting and wearable sensors.

Download Full-text

Influences of poling temperature and elongation ratio on PVDF-HFP piezoelectric films

Nanotechnology Reviews ◽

10.1515/ntrev-2021-0070 ◽

2021 ◽

Vol 10 (1) ◽

pp. 1009-1017

Author(s):

Zhaonan Jin ◽

Dan Lei ◽

Yang Wang ◽

Liangke Wu ◽

Ning Hu

Keyword(s):

High Efficiency ◽

Vinylidene Fluoride ◽

Low Cost ◽

Maximum Output ◽

Elongation Ratio ◽

Scanning Calorimetry ◽

Poling Process ◽

Β Phase ◽

Poly Vinylidene Fluoride ◽

Mechanical Stretching

Abstract Poly(vinylidene fluoride) (PVDF) and its copolymers exhibit excellent piezoelectric properties and are potential materials for high efficiency energy harvesting devices. In this study, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) films are prepared by the solution casting method. The prepared film is then subjected to mechanical stretching and poling process. By adjusting the temperature of the poling process and the elongation ratio of the mechanical stretching process, the relative content of β-phase F(β) increases significantly, leading to high piezoelectric performance. The maximum output voltage of the PVDF-HFP films poled at 40°C reaches 3.67 V, 71% higher than that of the films poled at room temperature. Fourier transform infrared spectroscopy analysis (FTIR), XRD (X-ray diffraction), and differential scanning calorimetry are used to investigate the influences of mechanical stretching and poling process on the crystal structure to discover the enhancement mechanism. This work provides a straightforward and low-cost route to prepare high piezoelectric PVDF-HFP-based materials.

Download Full-text

High Efficient and Continuous Triboelectric Power Harvesting based on Porous β-phase Poly (vinylidene fluoride) Aerogel

New Journal of Chemistry ◽

10.1039/d0nj05134a ◽

2021 ◽

Author(s):

Minmin Wang ◽

Weiqun Liu ◽

Xu Shi ◽

Jinyang Pan ◽

Bing Zhou ◽

...

Keyword(s):

Vinylidene Fluoride ◽

High Electron ◽

Exchange Method ◽

Power Harvesting ◽

Β Phase ◽

Output Performance ◽

High Electron Affinity ◽

High Efficient ◽

Poly Vinylidene Fluoride ◽

High Output

Non-additive β-phase porous poly (vinylidene fluoride) (PVDF) aerogel with high electron affinity is successfully prepared through simple solvent exchange method. The as-prepared additive-free PVDF aerogel shows high output performance used...

Download Full-text

Comparative Study of PVDF Sheets and Their Sensitivity to Mechanical Vibrations: The Role of Dimensions, Molecular Weight, Stretching and Poling

Nanomaterials ◽

10.3390/nano11071637 ◽

2021 ◽

Vol 11 (7) ◽

pp. 1637

Author(s):

Miroslav Mrlík ◽

Josef Osička ◽

Martin Cvek ◽

Markéta Ilčíková ◽

Peter Srnec ◽

...

Keyword(s):

Molecular Weight ◽

Comparative Study ◽

Vinylidene Fluoride ◽

Initial Thickness ◽

Complementary Method ◽

Β Phase ◽

Vibration Sensing ◽

Poly Vinylidene Fluoride ◽

Processing Techniques ◽

The Comparative Study

This paper is focused on the comparative study of the vibration sensing capabilities of poly(vinylidene fluoride) (PVDF) sheets. The main parameters such as molecular weight, initial sample thickness, stretching and poling were systematically applied, and their impact on sensing behavior was examined. The mechanical properties of prepared sheets were investigated via tensile testing on the samples with various initial thicknesses. The transformation of the α-phase to the electro-active β-phase was analyzed using FTIR after applying stretching and poling procedures as crucial post-processing techniques. As a complementary method, the XRD was applied, and it confirmed the crystallinity data resulting from the FTIR analysis. The highest degree of phase transformation was found in the PVDF sheet with a moderate molecular weight (Mw of 275 kDa) after being subjected to the highest axial elongation (500%); in this case, the β-phase content reached approximately 90%. Finally, the vibration sensing capability was systematically determined, and all the mentioned processing/molecular parameters were taken into consideration. The whole range of the elongations (from 50 to 500%) applied on the PVDF sheets with an Mw of 180 and 275 kDa and an initial thickness of 0.5 mm appeared to be sufficient for vibration sensing purposes, showing a d33 piezoelectric charge coefficient from 7 pC N−1 to 9.9 pC N−1. In terms of the d33, the PVDF sheets were suitable regardless of their Mw only after applying the elongation of 500%. Among all the investigated samples, those with an initial thickness of 1.0 mm did not seem to be suitable for vibration sensing purposes.

Download Full-text

Studies on the electrostatic effects of stretched PVDF films and nanofibers

Nanoscale Research Letters ◽

10.1186/s11671-021-03536-9 ◽

2021 ◽

Vol 16 (1) ◽

Author(s):

Yixuan Lin ◽

Yuqiong Zhang ◽

Fan Zhang ◽

Meining Zhang ◽

Dalong Li ◽

...

Keyword(s):

Vinylidene Fluoride ◽

Polarized Light ◽

Transition Process ◽

Open Circuit ◽

Wearable Electronics ◽

Energy Harvesters ◽

Β Phase ◽

Poly Vinylidene Fluoride ◽

Piezoelectric Effects ◽

Energy Harvesting Devices

AbstractThe electroactive β-phase in Poly (vinylidene fluoride, PVDF) is the most desirable conformation due to its highest pyro- and piezoelectric properties, which make it feasible to be used as flexible sensors, wearable electronics, and energy harvesters etc. In this study, we successfully developed a method to obtain high-content β-phase PVDF films and nanofiber meshes by mechanical stretching and electric spinning. The phase transition process and pyro- and piezoelectric effects of stretched films and nanofiber meshes were characterized by monitoring the polarized light microscopy (PLM) images, outputting currents and open-circuit voltages respectively, which were proved to be closely related to stretching ratio (λ) and concentrations. This study could expand a new route for the easy fabrication and wide application of PVDF films or fibers in wearable electronics, sensors, and energy harvesting devices.

Download Full-text