Electrostrictive behavior of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene)

Abstract

The mechanism underlying the large electric-field-induced strains in terpolymers of vinylidene fluoride, trifluoroethylene, and chlorotrifluoroethylene was investigated. The electrostrictive strain increased by an order of magnitude with increasing temperature, up to the Curie transition, and was essentially invariant to temperature thereafter. Infrared absorption spectra, obtained as a function of both temperature and electric field strength, revealed no change in the crystal phase structure for electric fields sufficient to induce longitudinal strains of ∼1%. Thus, the electrostriction observed herein is not due to crystal phase conversion. The Maxwell strain was also negligible under all conditions, because of the terpolymer’s high mechanical modulus (10 to 100 MPa). The mechanical properties exhibit an anomalous change in behavior near the Curie transition, whose origin is unclear.

Advances in Dielectric Elastomers for Actuators and Artificial Muscles

“…[101] For efficient room temperature operation, the Curie temperature must be reduced to around room temperature and the hysteresis must be suppressed. Zhang and others have shown this can be achieved by irradiating P(VDF-TrFE) with high-energy electrons or protons [101][102][103][104] or adding bulky side groups to the copolymer, [102,[105][106][107] thus introducing polarization defects that destabilize the ferroelectric phase. Bulky side groups can be introduced though the formation of copolymers containing PVDF, TrFE, and either chloride containing monomers such as cholorofluoroethylene (CFE) [102,105] and chlorotrifluoroethylene (CTFE) [106,107] or hexafluoropropylene (HFP).…”

“…Zhang and others have shown this can be achieved by irradiating P(VDF-TrFE) with high-energy electrons or protons [101][102][103][104] or adding bulky side groups to the copolymer, [102,[105][106][107] thus introducing polarization defects that destabilize the ferroelectric phase. Bulky side groups can be introduced though the formation of copolymers containing PVDF, TrFE, and either chloride containing monomers such as cholorofluoroethylene (CFE) [102,105] and chlorotrifluoroethylene (CTFE) [106,107] or hexafluoropropylene (HFP). [108][109][110] The actuation mechanism is essentially the same as for ferroelectric polymers; a transition between paraelectric and ferroelectric phases is induced by the application of a high electric field as represented in Figure 4.…”

Giant Electrostriction in Relaxor Polymers

“…Typical representatives are the electron-irradiated ferroelectric copolymer poly(vinylidene fluoride-trifluoroethylene) or P(VDF-TrFE) [3] and its terpolymer with chlorofluoroethylene P(VDF-TrFE-CFE) [4]. In P(VDF-TrFE) and related systems, high energy electron irradiation is needed in order to transform the normal ferroelectric structure into an amorphous one, thus strongly enhancing their electro-mechanical properties.…”

Dielectric and electroactive strain properties of poly(vinylidene fluoride–trifluoroethylene–chlorotrifluoroethylene) terpolymers

“…The explanations of the contributions of the piezoelectric effect, electrostrictive effect, and ''Maxwell-stress'' effect are controversial in some cases. Very recently, the temperature dependence of the strain of terpolymers from Ϫ5 to ϳ50°C is reported by Garrett et al, 12 and the physical mechanism of the large electroactive strain is discussed, including the possible origin of the large strain observed in the terpolymers, the conversion of the nonpolar phase to the polar phase, and the Maxwell strain. Obviously, more dielectric and strain data in a wide temperature range are desirable to further understanding of the physical mechanism of high strains in the polymers.…”