Relaxor Ferroelectric Polymer Research Articles

A self-regenerative heat pump based on a dual-functional relaxor ferroelectric polymer.

Electrocaloric (EC) cooling presents a promising approach to efficient and compact solid-state heat pumps. However, reported EC coolers have complex architectures and limited cooling temperature lift. In this work, we introduce a self-regenerative heat pump (SRHP) using a cascade of EC polymer film stacks, which have electrostrictive actuations in response to an electric field that are directed to realize efficient heat transfer, eliminating the need for additional transportive or regenerative mechanisms. The SRHP demonstrates a cooling of 8.8 kelvin below ambient temperature in 30 seconds and delivers a maximum specific cooling power of 1.52 watts per gram. The temperature lift of the SRHP is 14.2 kelvin. These results underscore the potential of the compact solid-state cooling mechanism to address the increasing need for localized thermal management.

Intrinsic Elastomer with Remarkable Dielectric Constant via Elastification of Relaxor Ferroelectric Polymer.

High-dielectric-constant elastomers always play a critical role in the development of wearable electronics for actuation, energy storage, and sensing; therefore, there is an urgent need for effective strategies to enhance dielectric constants. The present methods mainly involve adding inorganic or conductive fillers to the polymer elastomers, however, the addition of fillers causes a series of problems, such as large dielectric loss, increased modulus, and deteriorating interface conditions. Here, the elastification of relaxor ferroelectric polymers is investigated through slight cross-linking, aiming to obtain intrinsic elastomers with high-dielectric constants. By cross-linking of the relaxor ferroelectric polymer poly(vinylidene fluoride-ter-trifluoroethylene-ter-chlorofluoroethylene) with a long soft chain cross-linker, a relaxor ferroelectric elastomer with an enhanced dielectric constant is obtained, twice that of the pristine relaxor ferroelectric polymer and surpassing all reported intrinsic elastomers. This elastomer maintains its high-dielectric constant over a wide temperature range and exhibits robust mechanical fatigue resistance, chemical stability, and thermal stability. Moreover, the ferroelectricity of the elastomer remains stable under strains up to 80%. This study offers a simple and effective way to enhance the dielectric constant of intrinsic elastomers, thus facilitating advancements in soft robots, biosensors, and wearable electronics.

Ultra‐High Energy Density in Cyanoethyl Biomass Polymers

AbstractDielectric polymers are essential to capacitive capacitors widely used in modern electronic and electrical systems. Most useful dielectric polymers are derived from petroleum while environmentally sustainable dielectric biomass remains mostly unexplored although they are abundant, renewable, and cost‐effective. Here an ultrahigh energy density in cyanoethyl cellulose (CEC) and cyanoethyl pullulan (CEP) obtained by replacing the hydroxyl groups of cellulose and pullulan with cyanoethyl is reported. Large dielectric constants of 16.7 and 20.0 in CEC and CEP due to the strong polarity of cyanoethyl which are comparable to high‐dielectric ferroelectric polymers are shown. CEC and CEP show nearly no degradation of the dielectric constant with increasing electric fields, inhabiting the early polarization saturation and thus leading to improved energy density, which is different from relaxor ferroelectric polymers. Consequently, solution‐processable CEP films exhibit an ultrahigh discharged energy density of 28.2 J cm−3 with an efficiency of 72% at 600 MV m−1, outperforming other all‐organic dielectric biomass materials. The work paves the way for the development of high‐performance dielectric biomass for energy storage applications.

Solution-processable low-voltage carbon nanotube field-effect transistors with high-k relaxor ferroelectric polymer gate insulator

Achieving energy-efficient and high-performance field-effect transistors (FETs) is one of the most important goals for future electronic devices. This paper reports semiconducting single-walled carbon nanotube FETs (s-SWNT-FETs) with an optimized high-k relaxor ferroelectric insulator P(VDF-TrFE-CFE) thickness for low-voltage operation. The s-SWNT-FETs with an optimized thickness (∼800 nm) of the high-k insulator exhibited the highest average mobility of 14.4 cm2 V−1s−1 at the drain voltage (I D) of 1 V, with a high current on/off ratio (I on/off >105). The optimized device performance resulted from the suppressed gate leakage current (I G) and a sufficiently large capacitance (>50 nF cm−2) of the insulating layer. Despite the extremely high capacitance (>100 nF cm−2) of the insulating layer, an insufficient thickness (<450 nm) induces a high I G, leading to reduced I D and mobility of s-SWNT-FETs. Conversely, an overly thick insulator (>1200 nm) cannot introduce sufficient capacitance, resulting in limited device performance. The large capacitance and sufficient breakdown voltage of the insulating layer with an appropriate thickness significantly improved p-type performance. However, a reduced n-type performance was observed owing to the increased electron trap density caused by fluorine proportional to the insulator thickness. Hence, precise control of the insulator thickness is crucial for achieving low-voltage operation with enhanced s-SWNT-FET performance.

Inkjet printing P(VDF-TrFE-CTFE) actuators for large bending strains

Additive manufacturing of sensors and actuators together with structural materials and electronics will make it possible to fabricate innovative system designs that are overly laborious to realise with conventional methods. While printing of the structural materials and electronics are advancing fast, the additive manufacturing methods for actuators and sensors are in an earlier stage of development. This research will develop a manufacturing process for entirely inkjet printed electroactive polymer (EAP) actuators basing on the P(VDF-TrFE-CTFE) relaxor ferroelectric polymer and Ag electrodes. The process consists of (1) printing an Ag layer on a polyethylene terephthalate (PET) substrate for the bottom electrode; (2) formulating, printing and annealing a P(VDF-TrFE-CTFE) ink for the EAP layer; and (3) printing and sintering an Ag layer on the plasma-treated EAP surface to form the top electrode. Two actuator variations, addressed as DMC and KM512, are manufactured and characterised by their: (a) response to quasi-static excitation (1 Hz sine wave); (b) hysteresis behaviour; (c) actuation amplitude variation with the input voltage; and (d) frequency response. The 18 mm long actuators showed 91.4 µm (DMC, 200 Vpp ) and 224 µm (KM512, 275 Vpp ) deflections in response to 1 Hz sinusoidal excitation, and 1.10 mm (DMC, 113 Hz, 200 Vpp ) and 1.72 mm (KM512, 114 Hz, 200 Vpp ) deflections in resonant operation. It is 55% more quasi-static strain and 470% more resonant strain than in earlier fully inkjet-printed polyvinylidene fluoride (PVDF) -based actuators, and comparable to similar partially inkjet-printed actuators. This is the first time that inkjet printing of all three layers of a relaxor ferroelectric actuator have been achieved.

Electrically and mechanically driven rotation of polar spirals in a relaxor ferroelectric polymer

Topology created by quasi-continuous spatial variations of a local polarization direction represents an exotic state of matter, but field-driven manipulation has been hitherto limited to creation and destruction. Here we report that relatively small electric or mechanical fields can drive the non-volatile rotation of polar spirals in discretized microregions of the relaxor ferroelectric polymer poly(vinylidene fluoride-ran-trifluoroethylene). These polar spirals arise from the asymmetric Coulomb interaction between vertically aligned helical polymer chains, and can be rotated in-plane through various angles with robust retention. Given also that our manipulation of topological order can be detected via infrared absorption, our work suggests a new direction for the application of complex materials.

Electron-beam writing of a relaxor ferroelectric polymer for multiplexing information storage and encryption.

To meet the strong demand for high-level encryption security, several efforts have been focused on developing new encryption techniques with high density and data security. Herein we employed a template-free electron beam lithography (EBL) technique to write various nanopatterns on poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CTFE)) films and applied it to electron-beam/electric multiplexing memory. Furthermore, electron beams can arbitrarily tailor down the domain structure evolutions and dipole directions, as proved by a combination of AFM-IR and PFM. Finally, our devices could function concurrently as an electron-beam write-only-memory (EB-WOM) and FeRAM, where the information could be encoded with the metastable phase evolutions from the ferroelectric phase to the paraelectric phase and variable bi-level ferroelectric signals. Our systematic study provides an inspiring idea for the design of information encryption devices with high-security requirements in flexible electronic fields.

Highly elastic relaxor ferroelectric via peroxide crosslinking.

Relaxor ferroelectrics are well-known for their high dielectric constants, low dielectric losses, and excellent electromechanical properties, making them valuable for various electronic devices. Despite recent efforts to enhance the durability of ferroelectrics through chemical cross-linking, achieving elasticity in relaxor ferroelectric materials remains a significant challenge. These materials inherently possess traits such as low crystallinity and small crystal size, while chemical crosslinking tends to diminish polymer crystallinity considerably. Thus, a key obstacle to making relaxor ferroelectric polymers elastic lies in safeguarding their crystalline regions from the effects of slight crosslinking. To tackle this issue, we selected P(VDF-CTFE-DB) with highly reactive C[double bond, length as m-dash]C double bonds as crosslinking sites, reducing the amount of cross-linking agents added and thereby lessening their impact on crystallinity. Through peroxide crosslinking, we transformed linear P(VDF-CTFE-DB) into a network structure, successfully producing a resilient relaxor ferroelectric material with maintained polarization intensity for ferroelectricity. Notably, this elastic relaxor ferroelectric was synthesized at relatively low temperatures, exhibiting a remarkable dielectric constant, superior resilience, fatigue resistance, and a stable ferroelectric response even under strains of up to 80%. Our approach paves the way for developing low-cost, high-dielectric-constant elastomers suitable for wearable electronics and related applications.

High-temperature electromechanical actuation of relaxor ferroelectric polymers blended with normal ferroelectric polymer

Soft actuators that can operate at high temperatures are of great interest in emerging research fields such as microfluidics, soft robotics, automotive, aircraft, and bioelectronics. However, most polymer-based flexible actuators suffer from performance degradation at elevated temperatures above 60 °C. In this paper, we present the high-temperature electromechanical actuation of relaxor ferroelectric polymers solution-blended with normal ferroelectric polymers. We conduct a systematic analysis of the electromechanical properties of three unimorph actuators with relaxor ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene)s [P(VDF-TrFE-CFE)s] containing different amounts of chlorofluoroethylene (CFE) moieties (approximately 1, 3.5, and 9 wt%). In this study, we propose the film stress, given as Young's modulus times strain, as the measure of the electromechanical performance of soft bending actuators under loading, rather than strain or strain energy density. We demonstrate that a relaxor ferroelectric actuator with 1-wt% CFE, which mixes high-modulus ferroelectric crystal domains with an optimized electrostrictive relaxor phase, develops a high film stress of ∼3.5 MPa. When blended with the normal ferroelectric P(VDF-TrFE), the actuator exhibits excellent film stress of approximately 3.1 MPa at an elevated temperature of 60 °C comparable with that at 25 °C. The high-modulus ferroelectric crystals in P(VDF-TrFE) reinforce the mechanical properties of the actuator at elevated temperatures, generating high-temperature electromechanical actuation with a large strain and strain energy density of approximately 1.6% and 23 mJ/cm², respectively. We also demonstrate successful microfluidic pump operation at 60°C with our actuator using a relaxor ferroelectric polymer blended with an intrinsic ferroelectric polymer.

Nanostructured relaxor ferroelectric polymers enable full utilization of nickel-rich cathode at wide-temperature

The sluggish Li+ replenishment and surface structural transformation issues are major bottlenecks that limit the full utilization of Ni-rich cathodes (NLOs) in high-energy rechargeable batteries. Here, a relaxor ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF + TrFE)) copolymer coated on commercial polypropylene (PP) separator is proposed to tackle these problems for NLO cathodes. It is discovered that the relaxor ferroelectric P(VDF + TrFE) nanostructures with high spontaneous polarization and high dielectric constant at ambient temperature, acts as an ion-selective pump to accelerate the migration of lithium ions and reduce the accumulation of anions at the coating/cathode interface, thereby significantly improving the lithium-ion utilization rate of the cathode, reducing the interfacial side reactions, and stabilizing the cathode structure. As a result, the NCM811/Li cell with the relaxor ferroelectric coating shows extraordinary rate performance and cycling durability at a wide-temperature range of −40 ∼ 55 ℃. This work sheds light on the possibility to improve the electrochemical performance of other intercalated electrode materials by engineering ferroelectric interlayers.

Giant Electrostriction Enabled by Defect-Induced Critical Phenomena in Relaxor Ferroelectric Polymers

Polymers that generate large shape changes under electric stimulation are of great interest for many applications. Recently, it was shown that converting a small amount of chlorofluoroethylene (CFE) in relaxor ferroelectric poly(vinylidene fluoride–trifluoroethylene–CFE) (PVDF-TrFE-CFE) terpolymer into fluorinated alkyne (FA) creates P(VDF-TrFE-CFE-FA) tetrapolymers with giant electromechanical (EM) response at ultralow electric fields (<50 MV/m). We investigate the microscopic origin of this effect and show that converting the bulky CFE into small-size FA defects dramatically weakens the relaxor behavior. Importantly, P(VDF-TrFE-CFE-FA) tetrapolymers with near 2 mol % FA exhibit a diffused critical endpoint transition region at which the energy barriers for switching from nonpolar to polar molecular conformations become small. Consequently, a small change of the electric field induces a large electroactuation, which can enable novel applications. This work opens up a totally new approach to designing ferroelectric polymers that generate large responses at ultralow electric fields.

Ultralow loading of carbon quantum dots leading to significantly improved breakdown strength and energy density of P(VDF-TrFE-CTFE)

The scheme of the CQD structure and its interaction with the polymer matrix; the comparison between the 0.1 wt% CQD nanocomposite and pristine polymer.

Design and control of a new electrostrictive polymer based continuum actuator for endoscopic robot

Minimally Invasive Surgery (MIS) consists of the insertion of a flexible endoscope into the patient body through natural orifices. Over the past few decades, the growing interest in microelectromechanical systems (MEMS) has paved the way for ubiquitous miniaturized integrated sensors and actuators in medical endoscopy. Nowadays, recent advances in materials have opened a promising way to fulfill the surgical requirements and size constraint for the development of smart continuum structures. Among smart materials, electroactive polymers (EAPs) exhibit exceptionally large, fast, repeatable, and reversible motions while perfectly meeting the requirements of micro-integration. However the high applied voltage required for the actuation is not compatible with in vivo medical application. To overcome these issues, a multilayered concept has been proposed. In this work a relaxor ferroelectric electrostrictive polymer is studied for its large electromechanical strain. A wide range of parameters involved in the active material has led us to the development of a finite element model on Abaqus to guide the experimental development. Then, to control this smart endoscopic robot a kinematic and a dynamic models have been built. To test and validate these models a Co-simulation procedure has been developed. This procedure coupled Abaqus and Matlab-Simulink allowing testing proposed control algorithms.

Study on relaxor polymer interface matrix for piezoelectric nanocomposite generators

Piezoelectric nanocomposites consisting of a polymer matrix and ceramic fillers are candidate components of flexible, wearable, and self-powered electronic devices. The physical discrepancy between ferroelectric polymers and ceramics in a piezoelectric interface makes it difficult to assemble efficient hybrid piezoelectric nanocomposites without polarization and extraneous artifacts. Here, we describe the effect of a relaxor ferroelectric terpolymer matrix on the piezoelectric output, which can enhance the energy harvesting or sensor performance of piezoelectric composite device of nanocomposite generators with filler nanoparticles of lead zirconium titanate. The dielectric property and reduced ferroelectric hindrance of the proposed terpolymer matrix provides more poling to align the polarization of piezoelectric ceramic fillers compared with a normal ferroelectric copolymer matrix. Therefore, relaxor ferroelectric polymers can be better than normal ferroelectric polymers as the matrix of hybrid polymer-ceramic piezoelectric nanocomposite. This research provides important physical information about the interface between a polymer matrix and ceramic fillers in flexible piezoelectric nanocomposite applications.

Direct measurement of electrocaloric effect in P(VDF-TrFE-CFE) film using infrared imaging

Poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) P(VDF-TrFE-CFE) is a relaxor ferroelectric polymer, which exhibits a temperature-independent electrocaloric effect at room temperature. In this work, the electrocaloric effect in P(VDF-TrFE-CFE) film was directly analysed using infrared imaging. P(VDF-TrFE-CFE) 64.8%/27.4%/7.8% (in mole) film of (15 ± 1) μm thickness was deposited on polyethylene naphthalate substrate. Direct ECE of P(VDF-TrFE-CFE) film was measured from 15 to 35 °C at different electric fields. A maximum adiabatic temperature change (ΔTad) of 3.58 K was measured during the cooling cycle at a field of 100 V/μm at 30 °C. Finite element analysis of temperature dissipation through the sample estimated that the actual temperature change within P(VDF-TrFE-CFE) film was 4.3 K. Despite the thermal mass of the substrate, a substantial ECE was observed in P(VDF-TrFE-CFE) films. This electrocaloric terpolymer composition could be of interest for electrocaloric cooling applications.

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.

A pyrotoroidic transition in ferroelectric polymer

<h2>Summary</h2> Emergent topological textures coupled with ferroic orders have become the promising basis for exotic phenomena and application advances. While the number of materials observed with polar topological textures is growing, manipulation of these emergent polar topologies with the aid of external stimuli (e.g. electric field, strain, thermal perturbation) remains rare. Here, we report a pyrotoroidic transition accompanying the Curie transition in face-on lamellae of poly(vinylidene fluoride-<i>ran</i>-trifluoroethylene) (P(VDF-TrFE)), with a chirality reversal revealed in the polar topology. The existence of toroidal order in paraelectric polymers has been validated by further confirming the toroidal order in face-on lamellae of relaxor ferroelectric polymer induced by physical defects. This work demonstrates the manipulation of polar topological texture with the controls of the thermal condition. It should also expand the reach of toroidal polar topologies to a range of flexible materials and offer an insight into their formation.

Relaxor ferroelectric polymer exhibits ultrahigh electromechanical coupling at low electric field.

Electromechanical (EM) coupling-the conversion of energy between electric and mechanical forms-in ferroelectrics has been used for a broad range of applications. Ferroelectric polymers have weak EM coupling that severely limits their usefulness for applications. We introduced a small amount of fluorinated alkyne (FA) monomers (<2 mol %) in relaxor ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (PVDF-TrFE-CFE) terpolymer that markedly enhances the polarization change with strong EM coupling while suppressing other polarization changes that do not contribute to it. Under a low-dc bias field of 40 megavolts per meter, the relaxor tetrapolymer has an EM coupling factor (k33) of 88% and a piezoelectric coefficient (d33) >1000 picometers per volt. These values make this solution-processed polymer competitive with ceramic oxide piezoelectrics, with the potential for use in distinct applications.

Structure-property relationships in three-phase relaxor-ferroelectric terpolymers

Poly(vinylidenefluoride-trifluoroethylene)-based (P(VDF-TrFE)-based) terpolymers represent a new class of electroactive polymer materials that are relaxor-ferroelectric (RF) polymers and that offer unique and attractive property combinations in comparison with conventional ferroelectric polymers. The RF state is achieved by introducing a fluorine-containing termonomer as a “defect” into the ferroelectric P(VDF-TrFE) copolymer, which reduces the interaction between the VDF/TrFE dipoles. The resulting terpolymer exhibits a low Curie transition temperature and small remanent and coercive fields yielding a slim hysteresis loop that is typical for RF materials. Though the macroscopic behavior is similar to RF ceramics, the mechanisms of relaxor ferroelectricity in semi-crystalline polymers are different and not fully understood yet. Structure-property relationships play an important role in RF terpolymers, as they govern the final RF properties. Hence, a review of important characteristics, previous studies and relevant developments of P(VDF-TrFE)-based terfluoropolymers with either chlorofluoroethylene (CFE) or chlorotrifluoroethylene (CTFE) as the termonomer is deemed useful. The role of the termonomer and of its composition, as well as the effects of the processing conditions on the semi-crystalline structure which in turn affects the final RF properties are discussed in detail. In addition, the presence of noteworthy transition(s) in the mid-temperature range and the influence of preparation conditions on those transitions are reviewed. A better understanding of the fundamental aspects affecting the semi-crystalline structures will help to elucidate the nature of RF activity in VDF-based terpolymers and also help to further improve their applications-relevant electroactive properties.

Chemical adsorption on 2D dielectric nanosheets for matrix free nanocomposites with ultrahigh electrical energy storage

Relaxor ferroelectric polymers display great potential in capacitor dielectric applications because of their excellent flexibility, light weight, and high dielectric constant. However, their electrical energy storage capacity is limited by their high conduction losses and low dielectric strength, which primarily originates from the impact-ionization-induced electronmultiplication, low mechanical modulus, and low thermal conductivity of the dielectric polymers. Here a matrix free strategy is developed to effectively suppress electron multiplication effects and to enhance mechanical modulus and thermal conductivity of a dielectric polymer, which involves the chemical adsorption of an electron barrier layer on boron nitride nanosheet surfaces by chemically adsorbing an amino-containing polymer. A dramatic decrease of leakage current (from 2.4 × 10−6 to 1.1 × 10−7 A cm−2 at 100 MV m−1) and a substantial increase of breakdown strength (from 340 to 742 MV m−1) were achieved in the nanocompostes, which result in a remarkable increase of discharge energy density (from 5.2 to 31.8 J cm−3). Moreover, the dielectric strength of the nanocomposites suffering an electrical breakdown could be restored to 88% of the original value. This study demonstrates a rational design for fabricating dielectric polymer nanocomposites with greatly enhanced electric energy storage capacity.