Ferroelectric Polymer Poly Vinylidene Fluoride Research Articles

Selective localization of carbonized polymer dots in amorphous phase towards high breakdown strength and energy density of PVDF-based dielectric composites

In a general way, there is a contradictory between dielectric constant (εr) and breakdown strength (Eb) in dielectric materials, and improving the discharge energy density (Ud) of dielectric polymers has become a great challenge. The semicrystalline ferroelectric polymer polyvinylidene fluoride (PVDF) is favored for its high εr, but its relatively weak Eb in amorphous regions makes it still difficult to obtain appreciable Ud. In response to the fact that the current method of introducing rigid chain amorphous polymers into the amorphous regions of PVDF has limited capability to enhance its Eb, in this work, due to the crystallization induced phase separation, carbonated polymer dots (CPDs) as well as PMMA were introduced into the amorphous region of PVDF, and CPDs/PVDF/PMMA composites were prepared towards high Eb and Ud. It is confirmed that, CPDs significantly increase the entanglement density of molecular chains in amorphous regions of PVDF; in addition, CPDs rely on their inorganic carbon cores with unique electrical properties to resist carrier migration in amorphous regions of PVDF under high electric fields. In brief, CPDs are used as a reinforcing agent for the amorphous region of PVDF to further enhance its Eb and Ud. The composite loaded with 0.1 wt% CPDs exhibits the superior Ud of 12.4 J/cm3 at the Eb of 652.0 MV/m. This work provides new understanding on the dielectric response of ultrasmall-sized CPDs on polymer dielectrics, which could help us design new dielectric polymer composites with suppressed segmental motions for high breakdown strength and high energy density applications.

Significantly Enhanced Energy Density of Polyvinylidene Fluoride/Polyimide-Based Nanocomposites by Core-Shell BaTiO3@SiO2.

Improving the limited energy storage capacity of dielectric materials has long been an attractive challenge. In this work, a four-phase hybridized nanocomposite was designed. The linear polymer polyimide (PI) was added to the ferroelectric polymer polyvinylidene fluoride (PVDF) and compounded with a nanoceramic BT@SiO2 with a core-shell structure. The results show that PVDF-PI/BT@SiO2 nanocomposites prepared by a straightforward spin-coating method have a significantly increased discharge energy density. The polymer blends obtain a tightly extended conformation in the amorphous region. Also, this provides an excellent matrix environment for the homogeneous dispersion of fillers. The core-shell structure, as a physical barrier, not only hinders the expansion of the breakdown path but also extends multiple polarization surfaces with gradient variations at the microscopic level. Therefore, the synergistic effect generated by polymer blending and core-shell structure effectively enhances the dielectric and stored energy characteristics of nanocomposites. The dielectric constant is stable at 11.39-18.7, and the dielectric loss is always lower than 0.136. The discharge energy density is 2.5 J/cm3, almost 110% higher than that of the BOPP films (about 1.2 J/cm3). These experimental results suggest that the composite system using core-shell structure and polymer blending is a new way to improve the energy density of dielectric materials.

Multi-functionally ferroelectric polymer promotes highly-efficient large-area organic solar cells with excellent comprehensive performance

Developing high-performance active layer with excellent comprehensive performance is very crucial for the commercialization of organic solar cells (OSCs). Here, we demonstrate the multi-function of ferroelectric polymer polyvinylidene fluoride (PVDF) in improving the device comprehensive performance including device efficiency, stability, green-solvent large-area printing and mechanical property. Addition of PVDF not only enhances the build-in field to promote charge kinetics, but also develops robust network through strong interaction and chain entanglement between polymer donor and PVDF. Importantly, such robust network effectively protects the active layer from excessive flushing/swelling between D/A component to optimize layer-by-layer (LBL) deposition, induce a favorable vertical phase distribution and prolong the film-forming process, consequently facilitating green-solvent blade-coating printing, improving device efficiency and stability, and enhancing device mechanical flexibility. Due to the multiple advantages of PVDF, the PM6/BTP-eC9 obtains an excellent efficiency of 18.35% for BTP-eC9-based LBL devices. By blade-coating printing with green solvent, one of the highest efficiencies of 16.40% is achieved for large-area (1.21 cm2) binary device. Particularly, toughness is used to comprehensively evaluate mechanical property of OSCs, showing significant improvement with simultaneously enhanced fracture strength and tensile strain, and enabling small molecule-based system even have comparable mechanical flexibility and comprehensive performance to the all-polymer system.

Tuning Ba/Sr ratios of BaxSr1-xTiO3 of polymer nanocomposites toward significant enhancement of energy storage performance by optimized phase composition

The rapid development of portable electronic equipment, hybrid electric vehicles and pulse power systems have put forward higher requirements for new dielectric materials, making flexible polymer dielectrics attractive. Barium strontium titanate nanoparticles with different compositions were successfully prepared by using oxalate. A series of PVDF/BaxSr1-xTiO3 nanoparticles nanocomposites were prepared using the semi-crystalline ferroelectric polymer polyvinylidene fluoride PVDF as the polymer matrix. The microstructure and electrical properties of the nanocomposites were characterized to explore the effects of the composition and intrinsic properties of the filling phase on the nanocomposites. Among all the groups of nanocomposites, the 1 vol% PVDF/Ba0.6Sr0.4TiO3@DA NPs has the highest discharge energy density at the breakdown field strength, which is 7.8 J/cm3. The excellent discharge energy efficiency of 1 vol% PVDF/Ba0.6Sr0.4TiO3@DA NPs is maintained at 65 % at 300 kV/mm. This paper can provide experimental guidance and theoretical basis for the development of high energy storage density dielectric materials and their application in dielectric energy storage capacitors.

Existence of ferroelectric resistive switching memory in MoS2/PVDF heterojunction devices

The heterostructure device based on polyvinylidene fluoride (PVDF)/MoS2 films was succesfully prepared and showed a good hysteresis feature with a unique resistive switching perpromance, where the logarithmic I–V curve looks like a butterfly. The on-off ratio for the resistive switching in the device based on PVDF/MoS2 films reaches 2.5 × 102 and the resistive switching happens at −0.9 V and −4.9 V for a half loop. The influence of the introduction of MoS2 and ferroelectric PVDF film was also studied and compared to a device based on a single film. The underlying physical mechanism for the unique resistive transition was attributed to the polarization field from the ferroelectric polymer PVDF and the S vacancies in MoS2.

Acoustic energy harvesting with irradiated cross-linked polypropylene piezoelectret films

Piezoelectret films prepared by irradiated cross-linked polypropylene (IXPP) not only feature a large figure of merit (d33 · g33, FoM) and a nearly flat response of the sensitivity as a microphone (4 mV Pa−1) in the audio range, but also exhibit a good impedance match to air. Therefore, this material is appropriate for air-coupled sonic and ultrasonic applications. In this work, we report acoustic energy harvesting using IXPP piezoelectret films without mass loading both in ultrasonic and low-frequency ranges. Under an input sound pressure level (SPL) of 100 dB (or 2 Pa) and a resonance frequency of 53 kHz, a maximum output power of 7.2 nW is obtained for an IXPP film harvester. Despite its high resonance frequency, the large FoM of IXPP piezoelectret films suggests itself to be a promising candidate also for low-frequency acoustic energy harvesting with the help of Helmholtz resonators. An output power of 10.3 nW is achieved for a harvester with a 16 cm2 large IXPP film within a Helmholtz resonator, which features a resonance frequency of 900 Hz, with an optimized load resistance of 962 kΩ under an input SPL of 100 dB. In comparison to acoustic energy harvesters based on ferroelectric polymer polyvinylidene fluoride cantilever beams, our devices have much higher output power density under the same conditions and much broader bandwidth. Theoretical analysis and numerical simulations are performed to confirm the experimental results. Moreover, the output power of the IXPP acoustic energy harvesters can be further improved by increasing the active area of the piezoelectret films.

Electrospun polyvinylidene fluoride nanofibers by bubble electrospinning technique

This work reports, for the first time, the electrospinning of the piezoelectric and ferroelectric polymer polyvinylidene fluoride (PVDF) by means of the bubble electrospinning technique. We focus our study in the effect of different applied voltages on the morphological and crystalline features of the PVDF bubble-electrospun nanofibers. The crystallinity of PVDF nanofibers that were obtained by this process was higher than that observed in traditionally synthesized PDVF powders. Is important to highlight that production rate of the obtained PVDF nanofibers was higher (13.93mL/h) than that of the reported traditional electrospinning (1–5mL/h).

Molecular modeling of the piezoelectric effect in the ferroelectric polymer poly(vinylidene fluoride) (PVDF)

In this work, computational molecular modeling and exploration was applied to study the nature of the negative piezoelectric effect in the ferroelectric polymer polyvinylidene fluoride (PVDF), and the results confirmed by actual nanoscale measurements. First principle calculations were employed, using various quantum-chemical methods (QM), including semi-empirical (PM3) and various density functional theory (DFT) approaches, and in addition combined with molecular mechanics (MM) methods in complex joint approaches (QM/MM). Both PVDF molecular chains and a unit cell of crystalline β-phase PVDF were modeled. This computational molecular exploration clearly shows that the nature of the so-called negative piezo-electric effect in the ferroelectric PVDF polymer has a self-consistent quantum nature, and is related to the redistribution of the electron molecular orbitals (wave functions), leading to the shifting of atomic nuclei and reorganization of all total charges to the new, energetically optimal positions, under an applied electrical field. Molecular modeling and first principles calculations show that the piezoelectric coefficient d 33 has a negative sign, and its average values lies in the range of d 33 ~ -16.6 to -19.2 pC/N (or pm/V) (for dielectric permittivity ε = 5) and in the range of d 33 ~ -33.5 to -38.5 pC/N (or pm/V) (for ε = 10), corresponding to known data, and allowing us to explain the reasons for the negative sign of the piezo-response. We found that when a field is applied perpendicular to the PVDF chain length, as polarization increases the chain also stretches, increasing its length and reducing its height. For computed value of ε ~ 5 we obtained a value of d31 ~ +15.5 pC/N with a positive sign. This computational study is corroborated by measured nanoscale data obtained by atomic force and piezo-response force microscopy (AFM/PFM). This study could be useful as a basis for further insights into other organic and molecular ferroelectrics.

Structure and properties of polymer core-shell systems: Helium ion microscopy and electrical conductivity studies

Peculiarities of the structural organization and electrical properties of two core-shell polymer systems under different fabrication protocols have been studied with a combination of helium ion microscopy (HIM) and current-voltage characterization. The systems under study included a submicrometer core of a ferroelectric polymer polyvinylidene fluoride and a shell of intrinsically conducting or semiconducting polymer polyaniline (PANI) or poly(3-methylthiophene) (P3MT). Application of HIM allowed identification of the polymer components, visualization of the electrically conductive percolation network of PANI or P3MT, and its variation due to thermal annealing and/or interaction with the environment. HIM is proved to be a powerful tool for characterization of not only the morphology but also of the charge distribution and conductivity properties on the nanoscale. The specific contrast formation in HIM imaging is due to differences in local electrical conductivity of the components. The authors have demonstrated that the polymer core-shell systems under study can serve as a universal platform for development of nanostructured multifunctional materials. Specifically, it is shown that they can be used for preparation of conducting and semiconducting polymer films or layers having promising nonlinear electrical and sensor properties.

Ferroelectric PVDF cladding terahertz waveguide

A new type of flexible terahertz-wave hollow waveguide has been developed using ferroelectric polymer poly vinylidene fluoride (PVDF) as the cladding material. The transmission efficiency of the PVDF waveguide was better than a metal hollow waveguide with the same size and structure as the PVDF waveguide. This paper also reports the bent-angle dependencies of the transmission efficiency of the hollow PVDF.

Simulation of nonlinear dielectric properties of polyvinylidene fluoride based on the Preisach model

The nonlinear dielectric properties of a ferroelectric material were studied based on the concepts of the Preisach model. In this work, the ferroelectric polymer polyvinylidene fluoride was chosen as an example. The electric displacement D in the material when subjected to a sinusoidal electric field of a given frequency was calculated by use of the Preisach model. Both in-phase and out-of-phase components as well as higher harmonics emerged naturally from the model calculation. D-E loops at different field amplitudes were simulated and Fourier analyzed. The Fourier coefficients obtained were compared with the experimental data [T. Furukawa, K. Nakajima, T. Koizumi, and M. Date, Jpn. J. Appl. Phys., Part 1 26, 1039 (1987)]. Essentially, almost all the broad experimental features were reproduced by the simulations. This model is able to account for finer features than the theoretical model used in the original paper.

Large and broadband piezoelectricity in smart polymer-foam space-charge electrets

Charged closed-cell microporous polypropylene foams are shown to exhibit piezoelectric resonance modes in the dielectric function, coupled with a large anisotropy in the electromechanical and elastic material properties. Strong direct and converse dynamic piezoelectricity with a piezoelectric d33 coefficient of 140 pC/N at 600 kHz is identified. The piezoelectric d33 coefficient exceeds that of the ferroelectric polymer polyvinylidene fluoride by a factor of 5 and compares favorably with ferroelectric ceramics. Applications of similar concepts should provide a broad class of easily fabricated “soft” piezoelectric materials.

Large piezoelectric effects in charged, heterogeneous fluoropolymer electrets

Large piezoelectric d33 coefficients around 600 pC/N are found in corona-charged non-uniform electrets consisting of elastically “soft” (microporous polytetrafluoroethylene PTFE) and “stiff” (perfluorinated cyclobutene PFCB) polymer layers. The piezoelectric activity of the two-layer fluoropolymer stack exceeds the d33 coefficient of the ferroelectric ceramic lead zirconate titanate (PZT) by more than a factor of two and that of the ferroelectric polymer polyvinylidene fluoride (PVDF) by a factor of 20. Soft piezoelectric materials may become interesting for a large number of sensor and transducer applications, in areas such as security systems, medical diagnostics, and nondestructive testing.

The role of high pressure in the study and applications of the ferroelectric polymer polyvinylidene fluoride and its copolymers

Abstract The effects of frequency, temperature and hydrostatic pressure on the dielectric properties, molecular relaxations, and phase transitions of PVDF and a copolymer with 30 mol% trifluoroethylene will be discussed. Pressure causes large slowing down of the β molecular relaxations as well as large increases in the ferroelectric transition temperatures and melting points, but the magnitudes of the effects are different for the different “transitions.“ These effects can be understood in terms of pressure-induced hindrance of the molecular motions and/or reorientations. A unique application of these polymers as time-resolved, dynamic stress gauges, based on PVDF studies under very high pressure shock compression, is briefly discussed.