Synergistic Effects of Maxwell Stress and Electrostriction in Electromechanical Properties of Poly(vinylidene fluoride)-Based Ferroelectric Polymers

Abstract

Poly(vinylidene fluoride) (PVDF)-based relaxor ferroelectric polymers, synthesized from the physical or chemical modification of β-PVDF and P(VDF−TrFE) (TrFE refers trifluoroethylene), show high thickness strain under an external field, which allows them to be employed as electroactive materials for actuation, sensor, and artificial muscle applications. In an effort to disclose the formation mechanism of electrostrain, a series of P(VDF−TrFE−CTFE) (CTFE is chlorotrifluoroethylene) copolymers are synthesized and carefully characterized. By correlating the crystalline and ferroelectric phase transitions to their dielectric, ferroelectric, and electromechanical performances, a new model combining both the Maxwell stress and electrostrictive effect is proposed. The contribution of each effect to the overall strain and its dependence on the electric field, material composition, and the fabrication process of the films have been well addressed. The perfect synergism of two effects is responsible for the large strain under a low field, which offers a strategy to design and fabricate electroactive polymers with excellent electrostrain performances.

Phase diagram of poly(VDF-ter-TrFE-ter-CTFE) copolymers: Relationship between crystalline structure and material properties

“…Three studies exploring such a range of CTFE compositions have been already published. Two of them relate to Piezotech terpolymers [51] [53] obtained by direct terpolymerization, while the third considered terpolymers obtained after hydrogenation of P (VDF-co-CTFE) [52]. The comparison with this last study cannot be considered.…”

Soft, tough, and fast polyacrylate dielectric elastomer for non-magnetic motor

“…Up to now, the intrinsic features of electromagnetic motors like low specific power, bulky frame, rigid structure, and complicated control system, cannot meet the requirement of light weight, high flexibility, and easy control for soft micromotors, which have a wide range of applications in flexible electronics 1,2 , soft robotics 3,4 , biomedical implantation 5 , and aerospace 6,7 . Recently, soft actuators made of various types of electroactive polymers (EAPs) with electric-field-induced deformation have received considerable attention in the aforementioned fields [8][9][10][11][12][13] . Different from the actuators with ferroelectric polymers 11,13 , dielectric elastomer actuator (DEAs), an electrically stimulus-responsive actuator, show great potential for the large strain and superior flexibility 8,12,14,15 .…”

Towards Poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene)-Based Soft Actuators: Films and Electrospun Aligned Nanofiber Mats

“…Figure 8 reports the contraction forces , which have been measured in the uniaxial load tests on the specimen of the P(VDF-TrFE-CTFE) film, the specimen of P(VDF-TrFE-CTFE) nanofibers (NF) mat, and the specimen of PFA film when an electric field of 15 MV/m is applied. This specific value of applied electric field is sufficiently high to demonstrate the electrostrictive properties of the P(VDF-TrFE-CTFE)-based materials [ 17 ], while avoiding the risk of dielectric breakdown especially in the nanofibers mat, which is characterized by low density. In the figure, it can be noted that, after a transient of ∼10 s from the application of the electric field, the contraction forces of the P(VDF-TrFE-CTFE)-based specimens reach a steady state, whereas, as expected, the PFA film specimen does not show any contraction force.…”

“…Therefore, to evaluate electrostriction, it is required to experimentally measure it separately from the Maxwell stress. Due to the experimental challenges in separating the two effects, mathematical models have been used in, e.g., poly(vinylidenefluoride)-based polymers [ 17 ] and ideal polar rubbers [ 18 ], or different approaches have been proposed to determine the electrostrictive coefficients [ 19 ], i.e., electrostrictive coefficients are derived by measuring the strain-polarization and the strain-electric field curves [ 20 , 21 ], or by using the relationship between dielectric permittivity versus the applied stress [ 22 ], the piezoelectric coefficients, dielectric permittivities, and spontaneous polarization [ 23 ], the lattice parameters [ 24 ], the dielectric permittivity under a DC-biased electric field [ 25 ].…”