Abstract:The spatial distribution of the piezoelectric coefficient in polarized PVDF has been investigated by several authors using different methods / 1-6/. In addition also the time deve lopment of the polarization distribution in PVDF under external electfic fields was studied for a variety of commercially available PVDF films from different suppliers using the piezoelectric pressure step (PPS) technique / 7 J. For a field strength ranging from 0.5 to 1 MV fem, samples from different suppliers developped either i) a… Show more
“…This crystalline phase transition requires only low activation energy. Above 200 MV/m in Figure a and 150 MV/m in Figure b, the polarization curves show a slight but noticeable up-turn trend, which may be associated with the poling effect to alter the chain conformation from TGTG ‘ to TTTG and also to alter the crystalline phase from a δ-phase to a polar γ-phase . The hysteresis loop also expends with the increase of remnant polarization and the coercive field.…”
Section: Resultsmentioning
confidence: 88%
“…This poling effect is much more obvious in unipolar polarization curves (discussed later). With a further increase in the electric field (>350 MV/m), the polymer chain conformation eventually becomes an all-trans (TTTT) conformation with β-phase crystals that exhibit an even larger hystersis loop. 2 Bipolar D − E hysteresis loops of (a) PVDF homopolymer (control), (b) VDF/CTFE (92.2/7.8 mol %) copolymer (run A-2), (c) VDF/TrFE (63.3/36.7 mol %) copolymer (run B-3), and (d) VDF/TrFE/CTFE (65.6/26.7/7.7 mol %) terpolymer (run C-6).…”
This paper systematically examines the family of poly(vinylidene difluoride) (PVDF)-based
fluoropolymers, including homo-, co-, and terpolymers containing vinylidene fluoride (VDF), trifluorethylene
(TrFE), and chlorotrifluoroethylene (CTFE) units, with the objective of tuning the polymer chain conformation
and crystal structure in order to identify the most suitable polymer for energy storage (capacitor) applications.
All polymers have high molecular weight, uniform composition distribution, semicrystallinity, and high purity.
They were prepared by a borane/oxygen control radical initiator in a homogeneous solution at ambient temperature.
The resulting polymers were solution-cased, then melt-conditioned into uniform (defect-free) thermoplastic thin
films (thickness 10−20 μm). The combination of thermal, dielectric, and uni- and bipolar charge displacements
reveals their polarization profiles, which are dependent on chain conformation, crystal phase, crystal size, Curie
temperature, and ac and dc fields. Ferroelectric VDF/TrFE copolymers, having all-trans chain conformation and
polar β-phase crystals, exhibiting huge remnant polarization, are not suitable for energy storage (capacitor)
applications. Some poled PVDF homopolymer and VDF/CTFE copolymers with γ-phase crystals show potential
for dc (not ac) powered applications. The most suitable polymer is the VDF/TrFE/CTFE terpolymer having a
TTTG chain conformation, small polar γ-phase crystals, relaxed dielectric properties, and a Curie transition at
near ambient temperature, providing both ac and dc powered capacitors with a balance of properties, high-energy
density and low-energy loss.
“…This crystalline phase transition requires only low activation energy. Above 200 MV/m in Figure a and 150 MV/m in Figure b, the polarization curves show a slight but noticeable up-turn trend, which may be associated with the poling effect to alter the chain conformation from TGTG ‘ to TTTG and also to alter the crystalline phase from a δ-phase to a polar γ-phase . The hysteresis loop also expends with the increase of remnant polarization and the coercive field.…”
Section: Resultsmentioning
confidence: 88%
“…This poling effect is much more obvious in unipolar polarization curves (discussed later). With a further increase in the electric field (>350 MV/m), the polymer chain conformation eventually becomes an all-trans (TTTT) conformation with β-phase crystals that exhibit an even larger hystersis loop. 2 Bipolar D − E hysteresis loops of (a) PVDF homopolymer (control), (b) VDF/CTFE (92.2/7.8 mol %) copolymer (run A-2), (c) VDF/TrFE (63.3/36.7 mol %) copolymer (run B-3), and (d) VDF/TrFE/CTFE (65.6/26.7/7.7 mol %) terpolymer (run C-6).…”
This paper systematically examines the family of poly(vinylidene difluoride) (PVDF)-based
fluoropolymers, including homo-, co-, and terpolymers containing vinylidene fluoride (VDF), trifluorethylene
(TrFE), and chlorotrifluoroethylene (CTFE) units, with the objective of tuning the polymer chain conformation
and crystal structure in order to identify the most suitable polymer for energy storage (capacitor) applications.
All polymers have high molecular weight, uniform composition distribution, semicrystallinity, and high purity.
They were prepared by a borane/oxygen control radical initiator in a homogeneous solution at ambient temperature.
The resulting polymers were solution-cased, then melt-conditioned into uniform (defect-free) thermoplastic thin
films (thickness 10−20 μm). The combination of thermal, dielectric, and uni- and bipolar charge displacements
reveals their polarization profiles, which are dependent on chain conformation, crystal phase, crystal size, Curie
temperature, and ac and dc fields. Ferroelectric VDF/TrFE copolymers, having all-trans chain conformation and
polar β-phase crystals, exhibiting huge remnant polarization, are not suitable for energy storage (capacitor)
applications. Some poled PVDF homopolymer and VDF/CTFE copolymers with γ-phase crystals show potential
for dc (not ac) powered applications. The most suitable polymer is the VDF/TrFE/CTFE terpolymer having a
TTTG chain conformation, small polar γ-phase crystals, relaxed dielectric properties, and a Curie transition at
near ambient temperature, providing both ac and dc powered capacitors with a balance of properties, high-energy
density and low-energy loss.
“…results for the growth of the polarization distribution during room-temperature poling of a PVDF film containing , -. , 20% 0-phase [99]. The results indicate that the polarization is initially homogeneous due to the homogeneous field.…”
Section: Polwl Nyliden Efluori De and Its Copolymersmentioning
confidence: 75%
“…The poling is completed after a much shorter time, charge injection does not significantly distort the field, and the polarization is considerably higher. After field removal and short-circuiting, a smaller but homogeneous remanent polarization is present [99]. Poling at 118°C is affected by charge injection from the electrodes although at a time scale a factor of lo4 faster than at room temperature.…”
Section: Polwl Nyliden Efluori De and Its Copolymersmentioning
Experimental work on charge distributions and charge transport in polymer films is reviewed. For studying the charge distributions in the thickness dimension, thermal or acoustic techniques are used with resolutions down to N 1 pm. The polymer samples usually are charged with corona, electron beam or thermal methods. Observation of the change of charge and polarization distributions with time allows one to draw conclusions about charge transport and charge injection phenomena. In some cases theoretical models have been established, based on excess-charge drift due to a finite carrier mobility and on charge compensation due to intrinsic or radiation-induced conductivity Other models are concerned with the interaction of injected or intrinsic space charge with a dipole polarization. Comparisons of measured and calculated charge distributions and their change with time show the applicability of these models and shed new light on charge trapping and charge transport phenomena.
“…22 It has been shown previously that non-uniform poling of thin P͑VDF-TrFE͒ film can occur, with the polarization starting at the anode, and the mechanism has been discussed in detail. 8,10,11,[23][24][25] In this paper we study the poling of thick copolymer films at elevated temperature. The resonance frequencies of these films have been measured.…”
Thick ͑800 m͒ polyvinylidene fluoride/trifluoroethylene ͑P͑VDF-TrFE͒͒ copolymer films for transducer applications are poled under applied voltage at elevated temperatures. By using different heat treatments, poling temperatures, and poling time, we are able to prepare a uniformly poled film with a single resonance peak at 1.3 MHz, or a nonuniformly poled film with two resonances ͑1.3 and 2.6 MHz͒, or a film with bimorph structure with a single resonance at 2.6 MHz. The nonuniform polarization which arises from charge injection from the cathode is checked by the pressure wave propagation method. The polarization mechanisms in these thick films are expected to be similar to those previously reported for thin films. The results obtained in this work may lead to practical applications because they suggest a means for controlling transducer frequency by poling.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
