Influence of Steric Hindrance on Ferro‐ and Piezoelectric Performance of Poly(vinylidene fluoride)‐Based Ferroelectric Polymers

Tuning the Ferroelectric Phase Transition of P(VDF-TrFE) through a Simple Approach of Modification by Introducing Double Bonds

Electroactive polymer (EAP) is a kind of intelligent material that, driven by external electric field, could produce changes in shape or volume. As an important class of EAP materials, poly(vinylidene fluoride) (PVDF) based relaxor ferroelectric polymers show remarkable potential for applications in sensors, actuator, and artificial muscles because of their excellent electrostrictive properties. However, the strain of PVDF-based relaxor ferroelectrics relies strongly on a high electric field, which seriously damages their reliability and limits their practical applications as wearable devices. To explore more suitable materials for actuator applications, in this present work, we report the influences of a double bond (DB) on the electroactive properties of P(VDF-TrFE) (TrFE: trifluoroethylene). The crystalline phase of P(VDF-TrFE) is partially destroyed after the DB is introduced, and the molecular chain flexibility of the product P(VDF-TrFE-DB) can be greatly improved. Therefore, P(VDF-TrFE-DB) has a larger electric displacement while having a lower dipole orientation electric field compared with that of P(VDF-TrFE). The result confirms that the DB could tune the ferroelectric properties and effectively reduce the driving electric field of the PVDF-based relaxor ferroelectric polymers. This work offers a strategy for the preparation of novel EAPs with low driving electric fields.

Facile fabrication of ferroelectric poly(vinylidene fluoride) thin films with pure γ phase

A simple heating-cooling procedure is employed to make pure polar γ-PVDF thin films. By controlling the relaxation state of the crystals, pure γ crystals are induced by two kinds of mechanism including self-seeding and self-nucleation upon cooling within 30 min. The methodology paves a new way for PVDF homopolymers in flexible ferroelectric device applications.

Controllable synthesis and structural design of novel all-organic polymers toward high energy storage dielectrics

As the core unit of energy storage equipment, high voltage pulse capacitor plays an indispensable role in the field of electric power system and electromagnetic energy related equipment. The mostly utilized polymer materials are metallized polymer thin films, which are represented by biaxially oriented polypropylene (BOPP) films, possessing the advantages including low cost, high breakdown strength, excellent processing ability, and self-healing performance. However, the low dielectric constant (εr < 3) of traditional BOPP films makes it impossible to meet the demand for increased high energy density. Controlled/living radical polymerization (CRP) and related techniques have become a powerful approach to tailor the chemical and physical properties of materials and have given rise to great advances in tuning the properties of polymer dielectrics. Although organic-inorganic composite dielectrics have received much attention in previous studies, all-organic polymer dielectrics have been proven to be the most promising choice because of its light weight and easy large-scale continuous processing. In this short review, we begin with some basic theory of polymer dielectrics and some theoretical considerations for the rational design of dielectric polymers with high performance. In the guidance of these theoretical considerations, we review recent progress toward all-organic polymer dielectrics based on two major approaches, one is to control the polymer chain structure, containing microscopic main-chain and side-chain structures, by the method of CRP and the other is macroscopic structure design of all-organic polymer dielectric films. And various chemistry and compositions are discussed within each approach.

P(VDF-TrFE) nanofibers: structure of the ferroelectric and paraelectric phases through IR and Raman spectroscopies

This study elucidates the complex morphology and the related spectroscopic response of poly(vinylidene fluoride-co-trifluoroethylene) copolymer, with 80% molar VDF content, namely P(VDF-TrFE) (80/20). We investigate the molecular structure, the morphology and the thermal behaviour of P(VDF-TrFE) samples obtained as electrospun nanofibers; we discuss their thermal evolution crossing the Curie temperature and the structure resulting after annealing, giving a comparison with P(VDF-TrFE) films. The new experimental data here obtained, combined with previous spectroscopic studies carried out on piezoelectric fluorinated polymers and copolymers, allow identifying spectroscopic markers sensitive to the molecular structure, the molecular orientation, the conformational defects and the kind of crystalline phase. We assign the vibrational modes localized on TrFE units by combining experimental observation and density functional calculations carried out on suitable molecular models. This work provides a sound set of diagnostic tools, which can be exploited for the assessment of structure/property relationships aimed at clarifying the molecular mechanisms leading to the piezoelectric performance of fluorinated copolymers.

This study elucidates the complex morphology and the related spectroscopic response of poly(vinylidene fluoride-co-trifluoroethylene) copolymer, with 80% molar VDF content, namely P(VDF-TrFE) (80/20).