TrFE Copolymer Research Articles

Ferroelectric properties of vinylidene fluoride–trifluoroethylene copolymer thin films fabricated on amorphous alloy electrode

We have investigated the structure and ferroelectric properties of vinylidene fluoride–trifluoroethylene (VDF–TrFE) copolymer thin films fabricated on amorphous alloy electrodes. Thin films of amorphous Pd–Cu–Si alloys with various compositions were successfully prepared by sputtering deposition. An atomically flat surface resulting from a fully amorphous structure of Pd–Cu–Si was obtained upon achieving a uniform surface of a spin-coated VDF–TrFE copolymer thin film. X-ray diffraction (XRD) measurements revealed that the crystalline structure of the VDF–TrFE copolymer thin films was of ferroelectric β-phase, being independent of the composition and crystalline state of the Pd–Cu–Si alloy. The clearly observed D–E hysteresis loops showed a remanent polarization of 0.075 C/m2 and a coercive field of 90 MV/m at a measurement frequency of 10 Hz for a 50-nm-thick film, which is almost consistent with the results obtained with Pt electrode samples. We also observed the thinning-induced reduction of remanent polarization, which was explained by the depolarization field induced by the surface dead layer in VDF–TrFE copolymer rather than the oxidized layer in Pd–Cu–Si alloy electrode.

Enhanced Piezoelectricity of Nanoimprinted Sub-20 nm Poly(vinylidene fluoride–trifluoroethylene) Copolymer Nanograss

In this paper, sub-20 nm ferroelectric PVDF–TrFE copolymer nanograss structures with aspect ratios up to 8.9 were developed. This study demonstrated sub-20 nm PVDF–TrFE nanograss structures that are nanoimprinted using a silicon nanograss mold in a single step. Vertically oriented PVDF–TrFE nanopillars were poled using the developed flip-stacking poling method. According to the PFM measurements, the piezoelectricity of flat thin films fabricated in this work reaches 14.0 pm/V. The maximum output voltage of the single PVDF–TrFE nanopillar was 526 mV, and the maximum piezoelectricity of the single PVDF–TrFE nanopillar was 210.4 pm/V. The piezoelectricity of the developed PVDF–TrFE nanograss structures was 5.19 times larger than that of the PVDF–TrFE flat thin films. The developed technique is simple, economical, and easy to fabricate. The developed ferroelectric PVDF–TrFE copolymer nanograss structures, which showed enhanced piezoelectricity compared to the PVDF–TrFE flat thin films, have potential applicat...

Evaluation of piezoelectric PVDF polymers for use in space environments. III. Comparison of the effects of vacuum UV and gamma radiation

AbstractFilms of piezoelectric PVDF and P(VDF‐TrFE) were exposed to vacuum UV (115–300 nm VUV) and γ‐radiation to investigate how these two forms of radiation affect the chemical, morphological, and piezoelectric properties of the polymers. The extent of crosslinking was almost identical in both polymers after γ‐irradiation, but surprisingly, was significantly higher for the TrFE copolymer after VUV‐irradiation. Changes in the melting behavior were also more significant in the TrFE copolymer after VUV‐irradiation due to both surface and bulk crosslinking, compared with only surface crosslinking for the PVDF films. The piezoelectric properties (measured using d33 piezoelectric coefficients and D‐E hysteresis loops) were unchanged in the PVDF homopolymer, while the TrFE copolymer exhibited more narrow D‐E loops after exposure to either γ‐ or VUV‐radiation. The more severe damage to the TrFE copolymer in comparison with the PVDF homopolymer after VUV‐irradiation is explained by different energy deposition characteristics. The short wavelength, highly energetic photons are undoubtedly absorbed in the surface layers of both polymers, and we propose that while the longer wavelength components of the VUV‐radiation are absorbed by the bulk of the TrFE copolymer causing crosslinking, they are transmitted harmlessly in the PVDF homopolymer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3253–3264, 2006

Evaluation of piezoelectric poly(vinylidene fluoride) polymers for use in space environments. I. Temperature limitations

AbstractSmart materials, such as thin‐film piezoelectric polymers, are interesting for potential applications on Gossamer spacecraft. This investigation aims to predict the performance and long‐term stability of the piezoelectric properties of poly(vinylidene fluoride) (PVDF) and its copolymers under conditions simulating the low‐Earth‐orbit environment. To examine the effects of temperature on the piezoelectric properties of PVDF, poly(vinylidenefluoride‐co‐trifluoroethylene), and poly(vinylidenefluoride‐co‐hexafluoropropylene), the d33 piezoelectric coefficients were measured up to 160 °C, and the electric displacement/electric field (D–E) hysteresis loops were measured from −80 to +110 °C. The room‐temperature d33 coefficient of PVDF homopolymer films, annealed at 50, 80, and 125 °C, dropped rapidly within a few days of thermal exposure and then remained unchanged. In contrast, the TrFE copolymer exhibited greater thermal stability than the homopolymer, with d33 remaining almost unchanged up to 125 °C. The HFP copolymer exhibited poor retention of d33 at temperatures above 80 °C. In situ D–E loop measurements from −80 to +110 °C showed that the remanent polarization of the TrFE copolymer was more stable than that of the PVDF homopolymer. D–E hysteresis loop and d33 results were also compared with the deflection of the PVDF homopolymer and TrFE copolymer bimorphs tested over a wide temperature range. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1310‐1320, 2005

Normal and Relaxor Behaviors of Ferroelectric P(VDF-TrFE) Copolymers

Structural and dielectric techniques were used to investigate semi-crystalline ferroelectric P(VDF-TrFE) copolymers. These materials undergo normal diffuse phase transition without any relaxation character of the Curie temperatures. By submitting them to high doses of γ-irradiation we were able to destroy the stability of their ferroelectric domains, and thus, to induce the appearing of relaxor features. The irradiation provokes the appearing of cross-linking bonds in the amorphous phase of the polymer. This effect is more important for the 50 mol% TrFE copolymer, while no effect was observed for the PVDF homopolymer. The cross-linking rate is surely the parameter that controls the crossover from normal to relaxor state in this system.

Effects of annealing on the structure and switching characteristics of VDF/TrFE copolymers

Structure-property relationship has been investigated in concern with the ferroelectric switching characteristics of a VDF(78)/TrFE(22) copolymer. Unoriented and oriented film samples prepared by melt-quenching and melt-extrusion, respectively, were subjected to annealing and resulting structural changes were characterized by SEM, X-ray, density and DSC measurements. It was found that annealing just above the Curie point (120–130°C) caused a marked increase in crystallinity, whereas annealing in the paraelectric state (130–145°C) induced a crystal growth into thick lamellae. Such structural changes resulted in the ferroelectric switching characteristics with larger remanent polarization and shorter switching time. The unoriented sample yielded a smaller remanent polarization than the oriented sample by a factor of π/4, which substantiated that polarization reversal occurred as a result of rotation of molecules rotation about their chain axis. The melt-extruded and well-annealed sample consisted of regularly stacked large lamellae, thus providing information on the switching process occurring in constituent crystallites. Analysis of the observed switching transient has shown that polarization reversal progresses through a conventional nucleation-growth mechanism with a large waiting time.

An accurate equivalent circuit for the unloaded piezoelectric vibrator in the thickness mode

An equivalent circuit model for the unloaded piezoelectric vibrator in the thickness mode is presented. The model contains two branches, the motional branch and the static branch, like the lossless resonator model, but the circuit elements are generalized by making each a complex constant. The mechanical, dielectric and piezoelectric losses associated with the vibrator are accounted for by the imaginary components of the circuit elements. The model produced impedance curves that closely matched the impedance calculated by using equations derived from vibration theory and the data measured for lead zirconate titanate and PVDF - TRFE co-polymer samples. The calculation of the circuit parameters from the complex elastic, dielectric and piezoelectric material constants is straightforward and the model accurately fits both the baseline dielectric behaviour and the piezoelectric resonance around and below the fundamental resonance. Conversely, when the complex circuit parameters are known, the complex material constants can be derived by straightforward calculations without any loss of information.

Domains in ferroelectric VDF/TrFE copolymer thin films: Investigated by a new optical probe method

Abstract A new optical probe method was developed by using electro-optic and piezoelectric effects and a phase sensitive detection to determine the polarization of domains in ferroelectric thin films. Ferroelectric domains within a region smaller than 1 μm were detected in annealed VDF(65)/TrFE(35) copolymer thin films. The switching dynamics of these individual domains were also investigated by using this method.

A novel TGS/70:30 VDF:TrFE copolymer composite material for pyroelectric sensors

Abstract A novel thin composite film has been fabricated in which both phases are electroactive. Triglycine sulphate crystals (5μm in size), grown by rapid quenching and freeze drying of an aqueous solution, were mixed (10% w/w) with 70:30 vinylidene fluoride:trifluoroethylene copolymer in butanone. When spin cast, the material possessed a pyroelectric coefficient of (60±2)μCm−2K−1 and a figure of merit (pyroelectnc coefficient/√(relative permittivity x dielectric loss)) of 150μCm−2K−1, some 18% and 35% larger, respectively, than that of the pure copolymer.

The measurement of the piezoelectric effect in Langmuir-Blodgett films

Pyroelectric Langmuir-Blodgett (LB) films of 1-docosylamine alternated with ω-tricosenoic acid, and an organo-ruthenium complex alternated with behenic acid have been studied for their piezoelectric effect. A purpose built rig was designed for applying an oscillating bending flexure to the composite structure (comprised of a glass substrate, metal electrode, and active film), producing tensile and compressive stresses in the film on its surface. The piezoelectric d 31 coefficient was determined from the stress state in the active layer, the resultant charge, and the elastic properties of the composite. The accuracy of this experimental method was verified by measuring the piezoelectric response of a thin (1.3 μm) spuncoat, polarized film of a 70:30 VF TrFE copolymer with known piezoelectric and elastic properties. Piezoelectric coefficients of 0.023 pC N −1 and 0.17 pC N −1 have been obtained from the acid/amine and the alternate layer ruthenium complex, respectively. The higher degree of piezoelectric activity in the ruthenium complex is believed to be due to the higher molecular mobility in this material.

Pressure Dependence of the Ferroelectric Transition in Copolymers of Vinylidene Fluoride and Trifluoroethylene

Effect of the hydrostatic pressure p on the ferroelectric transition Tt in copolymers of vinylidene fluoride VDF and trifluoroethylene TrFE with 47.2 and 35.4 mol-% TrFE has been investigated for dielectric behavior and thermal expansion. The permittivity peak and the abrupt increase in thermal expansion at the transition shifted markedly to higher temperature with increasing pressure. The pressure dependence of the transition dTt/dp observed was 0.31 KMPa-1 on heating for 47.2 mol-% TrFE copolymer and 0.38 KMPa-1 on heating and 0.40 KMPa-1 on cooling for 35.4 mol-% TrFE Copolymer. These values of dTt/dp were consistent with those calculated by the Clausius-Clapeyron relation. The bulk modulus evaluated from the expansion vs pressure curve exhibited a conspicuous minimum at the ferroelectric transition as found for other physical properties.

Ferroelectric Transition in Vinylidene–Trifluoroethylene Copolymer Studied by Nuclear Magnetic Resonance Method

NMR absorption lines for a uniaxially drawn film of VDF–TrFE copolymer (72:28) were measured as a function of the alignment angle γ between the drawn axis and the magnetic field, over a temperature range from 23 to 130°C. The line shape consisted of inner, intermediate and outer peaks below the Curie temperature Tc. The line width of the intermediate peak narrowed at about 40°C with increasing temperature, and above 80°C it increased gradually by 1—3 Oe up to Tc. This line width as well as the line width of the outer peak strongly depended on γ, indicating that the nuclear dipole interactions in the crystalline region contribute to these peaks. Above Tc the width of the outer peak and the second moment decreased markedly owing to the chain motion accompanying conformational changes from the all-trans sequence to the combination of TG, TḠ, T3G, and T3Ḡ groups. The remarkable γ-dependence of the line shape as well as the line width observed in the paraelectric phase may be interpreted by a one-dimensional diffusion motion of conformational defects, and compared well with the ESR of a one-dimensional magnetic substance (CH3)4 NMnCl3 (TMMC).