Ferroelectric Polymer Nanocomposites Research Articles

Electro-thermal actuation in percolative ferroelectric polymer nanocomposites.

The interconversion between electrical and mechanical energies is pivotal to ferroelectrics to enable their applications in transducers, actuators and sensors. Ferroelectric polymers exhibit a giant electric-field-induced strain (>4.0%), markedly exceeding the actuation strain (≤1.7%) of piezoelectric ceramics and crystals. However, their normalized elastic energy densities remain orders of magnitude smaller than those of piezoelectric ceramics and crystals, severely limiting their practical applications in soft actuators. Here we report the use of electro-thermally induced ferroelectric phase transition in percolative ferroelectric polymer nanocomposites to achieve high strain performance in electric-field-driven actuation materials. We demonstrate a strain of over 8% and an output mechanical energy density of 11.3 J cm-3 at an electric field of 40 MV m-1 in the composite, outperforming the benchmark relaxor single-crystal ferroelectrics. This approach overcomes the trade-off between mechanical modulus and electro-strains in conventional piezoelectric polymer composites and opens up an avenue for high-performance ferroelectric actuators.

Correlating the Interfacial Polar-Phase Structure to the Local Chemistry in Ferroelectric Polymer Nanocomposites by Combined Scanning Probe Microscopy

HighlightsA strategy that combines multi-mode scanning probe microscopy-based electrical characterization and nano-infrared spectroscopy is developed.A series of samples with different coupling agents and nanoparticles are characterized to unveil the local structure-property correlation of the interface in ferroelectric polymer nanocomposites.The formation of hydrogen bond between the surface modifiers and the ferroelectric polymer enhances the β-phase content and reduces the domain size of the interface, and hence promotes the local piezoelectric effect and breakdown strength.

Ultralow contents of AgNbO3 fibers induced high energy storage density in ferroelectric polymer nanocomposites

Polymer dielectric films have been widely used in electronic and power systems due to their unique dielectric properties, processing properties, and excellent cost performance. Although the dielectric constant of dielectric polymers can be improved by adding high contents of ceramic fillers, this approach comes at the expense of the breakdown strength (Eb). This work is inspired by the idea that high-aspect-ratio fibers can induce a larger electric dipole moment without sacrificing too much Eb compared to zero-dimensional nanoparticles, thereby effectively improving the energy storage performance of the composites. We synthesized antiferroelectric AgNbO3 (ANO) fibers by using an in situ topotactic transition reaction which were then introduced into the polyvinylidene fluoride (PVDF) matrix for energy storage applications. The results show that the nanocomposite film with an ultralow loading of 0.4 wt. % ANO fibers achieves a high discharge energy density of 12.97 J cm−3 at 490 MV m−1. Nanocomposites based on ultralow content ANO fibers show great promise as one-dimensional antiferroelectric fillers for high energy density capacitor applications.

Electrocaloric Effect of Structural Configurated Ferroelectric Polymer Nanocomposites for Solid-State Refrigeration.

To successfully complete the design of high-performance electrocaloric devices for advanced flexible cooling systems, it is necessary to comprehensively consider the optimization of composite materials, structural design of nanocomposites, and device integration. The cooling power density and energy storage density of various structural configurated poly(vinylidene fluoride) (PVDF)-based polymer nanocomposites are investigated using a phase-field model through the general formulation of a partial differential equation of COMSOL Multiphysics and finite element analysis through Maxwell's equation of conservation of charge. It is revealed that ferroelectric polymer nanocomposites composed of boron nitrate fibers (BNf) + BCZT@BaTiO3(f) + PVDF possess the optimal result regarding their cooling power as well as the energy storage density. The cooling power density of the core-shell-structured BNf + BCZT@BaTiO3(f) + PVDF nanocomposites is evaluated as a function of the volume content, frequency, and electric field, where a remarkable cooling power density of 162.2 W/cm3 is achieved at 4 Hz with energy storage density of 33.4 J/cm3 under a 500 MV/m field. Therefore, by performing the systematic study of the electrocaloric effect in structural configurated ferroelectric polymer nanocomposites for solid-state refrigeration, this opens an avenue for developing remarkably improved power density with reduced weight in aerospace energy storage technology.

Significant Improvements in Dielectric Constant and Energy Density of Ferroelectric Polymer Nanocomposites Enabled by Ultralow Contents of Nanofillers.

Polymer dielectrics with excellent processability and high breakdown strength (Eb ) enable the development of high-energy-density capacitors. Although the improvement of dielectric constant (K) of polymer dielectric has been realized by adding high-K inorganic fillers with high contents (>10 vol%), this approach faces significant challenges in scalable film processing. Here, the incorporation of ultralow ratios (<1 vol%) of low-K Cd1- x Znx Se1- y Sy nanodots into a ferroelectric polymer is reported. The polymer composites exhibit substantial and concurrent increase in both K and Eb , yielding a discharged energy density of 26.0 J cm-3 , outperforming the current dielectric polymers and nanocomposites measured at ≤600 MV m-1 . The observed unconventional dielectric enhancement is attributed to the structural changes induced by the nanodot fillers, including transformation of polymer chain conformation and induced interfacial dipoles, which have been confirmed by density function theory calculations. The dielectric model established in this work addresses the limitations of the current volume-average models on the polymer composites with low filler contents and gives excellent agreement to the experimental results. This work provides a new experimental route to scalable high-energy-density polymer dielectrics and also advances the fundamental understanding of the dielectric behavior of polymer nanocomposites at atomistic scales.

Electrocaloric cooling over high device temperature span

Summary Electrocaloric cooling demonstrates direct electricity utilization and high energy efficiency, and is often proposed as an environmentally benign, solid-state alternative to the conventional vapor compression cooling technology. As a result, the fabrication of effective electrocaloric materials and engineering of electrocaloric cooling devices have attracted increasing attention in the cooling community. However, the limited material adiabatic temperature change under safe operation field poses a major challenge to practical electrocaloric cooling device development, since real-world applications usually require device temperature span over 20 K. This perspective presents recent efforts devoted to design electrocaloric cooling devices based on active heat regeneration and cascading approaches; both strategies have achieved significant device temperature lift ~10 K with adiabatic temperature change of 2~3 K. The strategies discussed in this work are broadly applicable to the design of efficient and compact cooling systems.

Structural Insight in the Interfacial Effect in Ferroelectric Polymer Nanocomposites.

Both experimental results and theoretical models suggest the decisive role of the filler-matrix interfaces on the dielectric, piezoelectric, pyroelectric, and electrocaloric properties of ferroelectric polymer nanocomposites. However, there remains a lack of direct structural evidence to support the so-called interfacial effect in dielectric nanocomposites. Here, a chemical mapping of the interfacial coupling between the nanofiller and the polymer matrix in ferroelectric polymer nanocomposites by combining atomic force microscopy-infrared spectroscopy (AFM-IR) with first-principles calculations and phase-field simulations is provided. The addition of ceramic fillers into a ferroelectric polymer leads to augmentation of the local conformational disorder in the vicinity of the interface, resulting in the local stabilization of the all-trans conformation (i.e., the polar β phase). The formation of highly polar and inhomogeneous interfacial regions, which is further enhanced with a decrease of the filler size, has been identified experimentally and verified by phase-field simulations and density functional theory (DFT) calculations. This work offers unprecedented structural insights into the configurational disorder-induced interfacial effect and will enable rational design and molecular engineering of the filler-matrix interfaces of electroactive polymer nanocomposites to boost their collective properties.

Enabling High‐Energy‐Density High‐Efficiency Ferroelectric Polymer Nanocomposites with Rationally Designed Nanofillers

AbstractFerroelectric polymers have been regarded as the preferred matrix for high‐energy‐density dielectric polymer nanocomposites because of their highest dielectric constants among the known polymers. Despite a library of ferroelectric polymer‐based composites having been demonstrated as highly efficient in enhancing the energy density, the charge–discharge efficiency remains moderate because of the high intrinsic loss of ferroelectric polymers. Herein, a systematic study of the oxide nanofillers is presented with varied dielectric constants and the vital role of the dielectric match between the filler and the polymer matrix on the capacitive performance of the ferroelectric polymer composites is revealed. A combined experimental and simulation study is further performed to specifically investigate the effect of the nanofiller morphology on the electrica properties of the polymer nanocomposites. The solution‐processed ferroelectric polymer nanocomposite embedded with Al2O3 nanoplates exhibits markedly improved breakdown strength and discharged energy density along with an exceptional charge–discharge efficiency of 83.4% at 700 MV m−1, which outperforms the ferroelectric polymers and nanocomposites reported to date. This work establishes a facile approach to high‐performance ferroelectric polymer composites through capitalizing on the synergistic effect of the dielectric properties and morphology of the oxide fillers.

Largely enhanced energy storage performance in multilayered ferroelectric polymer nanocomposites with optimized spatial arrangement of ceramic nanofillers

Dielectric materials with ultrahigh power density play an important role in modern electrical applications. Herein, we propose and demonstrate a class of newly designed multilayered polymer nanocomposites prepared via a systemically optimized electrospinning method. These multilayered nanocomposites are stacked with P(VDF-HFP) layers and P(VDF-HFP)/BaTiO3 layers alternately. Our results uncover that the heptalayered nanocomposites present superior breakdown strength among five different multilayered composites, which is owing to the increased layers interfaces. The further tailored spatial arrangement of BaTiO3 nanoparticles (BT NPs) in the hierarchical structure offers an additional increment in breakdown strength and energy density. The synergistic effects of hierarchical structure and gradient distribution of nanofillers furnish the resulting nanocomposites with much enhanced collective energy storage properties including a largely enhanced energy density of 17 J cm−3 and an ultrahigh breakdown strength of 635 MV m−1. This work provides a feasible route to improve the energy storage performance for dielectric nanocomposites.

Reseach progress of ferroelectric polymer nanocomposites with high energy storage density

Electrostatic capacitors based on dielectrics delivering an ultrahigh power density, low loss and high operating voltage, are widely used in energy storage devices for modern electronic and electrical systems. Dielectric polymers, especially ferroelectric polymers, are preferable for an energy storage medium in film capacitors due to their superiority in ultrahigh breakdown strength, low mass density, flexibility, and easy fabrication process. Ferroelectric polymer nanocomposites combining the advantageous properties of ferroelectric polymer matrix and high dielectric constant of ceramic fillers, show great potential applications in achieving superior energy storage performances and have aroused substantial academic interest. This review focuses on the recent research progress of high-energy-density ferroelectric polymer nanocomposites. First, the synthesis and properties of PVDF-based ferroelectric polymers are introduced. Second, the effects of nanofillers, composite structures and interfaces on the dielectric and energy storage properties of ferroelectric polymer nanocomposites are summarized. Third, the underline mechanism of dielectric and energy storage behaviors in ferroelectric nanocomposites are discussed in the aspect of phase-field simulation. Last, the existing challenges and future directions of ferroelectric polymer nanocomposites with high energy storage density are summarized and prospected.

Electrocaloric effect in relaxor ferroelectric polymer nanocomposites for solid-state cooling

Ferroelectric polymer nanocomposites demonstrate improved adiabatic change of temperature and isothermal change of entropy and markedly enhanced heating–cooling efficiency.

High-Energy-Density Ferroelectric Polymer Nanocomposites for Capacitive Energy Storage: Enhanced Breakdown Strength and Improved Discharge Efficiency

Emerging dielectric composites consisting of polymer and ceramic nano-inclusions or several polymers facilitate the development of capacitive energy storage materials, as they can preserve high breakdown strength and exhibit enhanced dielectric constant. Ferroelectric poly(vinylidene fluoride) (PVDF) and its copolymers have been intensively studied as the matrices because of their high intrinsic dielectric constant and breakdown strength. Here, we review the recent advances on improving the energy density of PVDF-based composite dielectrics. It is concluded that, promotion of energy density is mainly established on enhanced breakdown strength and improved discharge efficiency. The microstructure design, material performance, and mechanism associated with these parameters are described. Perspectives for future development on PVDF-based nanocomposites and application of other potential polymer matrices are presented at last.

Ferroelectric Nanocomposites: Direct Detection of Local Electric Polarization in the Interfacial Region in Ferroelectric Polymer Nanocomposites (Adv. Mater. 21/2019)

Ferroelectric Nanocomposites: Direct Detection of Local Electric Polarization in the Interfacial Region in Ferroelectric Polymer Nanocomposites (Adv. Mater. 21/2019)

Direct Detection of Local Electric Polarization in the Interfacial Region in Ferroelectric Polymer Nanocomposites.

Ferroelectric polymer nanocomposites are widely used in capacitive energy storage, electrocaloric refrigeration, and mechanical energy harvesting due to their exceptional electric polarization property and ease of fabrication. It is generally considered that the abnormal performance of ferroelectric nanocomposites stems from the interfacial region between the polymer matrix and embedded nanoparticles. However, direct evidence of the distinct local electric polarization property at the interfacial region is not yet accessible. Herein, a modified Kelvin probe force microscopy (KPFM) method with nanoscale spatial resolution is reported for direct detection of local polarization property at the matrix/particle interface in ferroelectric nanocomposites. Typical ferroelectric nanocomposites are studied using the present method. It is quantitatively probed that the electric polarization at matrix/particle interfacial region is higher than the polymer matrix under applied electric fields. Taking into account the enhanced local electric polarization gauged by the modified KPFM, the dielectric property of ferroelectric polymer nanocomposites matches with bulk experimental characterizations, indicating that the established method is reliable. It is anticipated that the present method, opening up new possibilities in understanding the matrix/particle interfacial region, may help with judicious design and engineering of high-performance ferroelectric polymer nanocomposites.

Tuning of dielectric and impedance properties of PVDF by incorporation of Mg doped PZT

Ferroelectric polymer nanocomposites of poly(vinylidene fluoride) (PVDF) and Mg doped PZT (PMZT) have been prepared by solvent casting method. The existence of β, γ and δ polar phases and α nonpolar phase of PVDF have been observed from the X-ray diffraction (XRD) and FTIR analysis. Both rhombohedral as well as tetragonal crystal phases of PZT at morphotropic phase boundary (MPB) is also observed. The characteristic peaks of PVDF in the FTIR spectra are unaffected with the incorporation of PMZT. Dielectric properties were studied as a function of frequency and temperature. The microstructure of PVDF–PMZT composite has been studied by employing SEM technique. Maximum dielectric constant of 32 with minimum dielectric loss of 0.0053 were obtained at 100 kHz for 6 mol% PMZT composite. The ac conductivity follows the Jonscher power law which exhibits the least value of interaction between mobile ions and lattice. Both grain and grain boundary contributions have been considered to explain the impedance behavior of the sample. The optimum loading percentage of PMZT in PVDF matrix is found to be 6 mol%. The structural results obtained from XRD and FTIR are well correlated with the physical parameters obtained from impedance measurement.

Enhanced energy storage performance of ferroelectric polymer nanocomposites at relatively low electric fields induced by surface modified BaTiO3 nanofibers

Polymer nanocomposite dielectrics with high energy densities have shown great potential in electrical energy storage applications. However, these high energy densities are normally achieved at ultrahigh applied electric fields (≥400 MV/m), which is inconvenient for certain applications such as aerospace power systems and microelectronics. In this study, uniform BaTiO3 nanofibers (BT nfs) with a large aspect ratio were prepared via the electrospinning method, surface modified by poly(vinyl pyrrolidone) (PVP) and utilized as the fillers in the poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) nanocomposites. It is found that the nanocomposite with 3 vol% BT nfs possesses a much enhanced discharged energy density of 8.55 J/cm3 at an applied electric field of 300 MV/m, which is 43% higher than that of the neat polymer matrix (i.e. 5.98 J/cm3) and more than four times that of the commercial biaxial oriented polypropylene dielectric (2 J/cm3 at over 600 MV/m). Comparative studies have been performed on the corresponding nanocomposites with BT nanoparticle fillers and pristine BT nfs. The improved energy storage performance is ascribed to the synergetic effects of surface modification and large aspect ratio of BT nfs. Our research provides a facile and effective approach to high-performance electrical energy storage materials which work efficiently at relatively low operating voltages.

Ferroelectric Polymer Nanocomposites with Complementary Nanostructured Fillers for Electrocaloric Cooling with High Power Density and Great Efficiency

The exploration of electrocaloric cooling is of great importance to address the environmental and energy-efficiency issues in the currently available refrigeration technologies. Although pronounced electrocaloric effect (ECE) has been demonstrated in ferroelectric materials, it is a necessary but far from sufficient condition to achieve substantial cooling. For instance, the narrow operation temperature windows and limited thermal conductivities of ferroelectric materials pose challenging obstacles for ferroelectric materials to realize high cooling power density and great cooling efficiency. In this work, we present polymer nanocomposites with multiple nanostructured fillers, including barium strontium titanate nanowires (BST NWs) with systematically varied Curie temperatures and boron nitride nanosheets (BNNSs). The introduced BST NWs effectively enhance EC strength and significantly extend the operating temperature so that giant ECE is achieved at relatively low electric fields in a wide temperature ra...

Solution-processed white graphene-reinforced ferroelectric polymer nanocomposites with improved thermal conductivity and dielectric properties for electronic encapsulation

The recent surge in graphene research has stimulated interest in the investigation of various two-dimensional (2D) nanomaterials, including 2D boron nitride (BN) nanostructures. Among these, hexagonal boron nitride nanosheets (h-BNNs; also known as white graphene, as their structure is similar to that of graphene) have emerged as potential nanofillers for preparing thermally conductive composites. In this work, hexagonal boron nitride nanoparticles (h-BNNPs) approximately 70 nm in size were incorporated into a polyvinylidene fluoride (PVDF) matrix with different loadings (0–25 wt.%). The PVDF/h-BNNP nanocomposites were prepared by a solution blending technique and characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), polarized optical microscopy (POM) and scanning electron microscopy (SEM). In addition, the thermal conductivity and dielectric properties of the nanocomposites were investigated. The incorporation of h-BNNPs in the PVDF matrix resulted in enhanced thermal conductivity. The highest value, obtained at 25 wt.% h-BNNP loading, was 2.33 W/mK, which was five times that of the neat PVDF (0.41 W/mK). The thermal enhancement factor (TEF) at 5 wt.% h-BNNP loading was 78%, increasing to 468% at 25 wt.% h-BNNP loading. The maximum dielectric constant of approximately 36.37 (50Hz, 150 °C) was obtained at 25 wt.% h-BNNP loading, which was three times that of neat PVDF (11.94) at the same frequency and temperature. The aforementioned results suggest that these multifunctional and high-performance nanocomposites hold great promise for application in electronic encapsulation.

Graphene and temperature controlled butterfly shape in permittivity-field loops of ferroelectric polymer nanocomposites

We report on the field-dependent polarization of graphene (GE) filled poly[vinylidene fluoride-co-trifluoroethylene] P(VDF-TrFE) nanostructures fabricated by mechanical melt mixing. This study shows an increase in effective permittivity of these nanomaterials on increasing the GE loading in a manner that is consistent with standard mixing law. Detailed characterization of the unsaturated ferroelectric hysteresis, as well as the butterfly shape of the effective permittivity versus electric bias, of the samples are presented. For GE content set to 9.1 wt. % in the samples containing 50/50 wt. % (VDF/TrFE), the maximum polarization increases by 260% with respect to that of the neat polymer matrix. With a higher VDF content, 73 wt. %, the coercive field remains constant over the range of GE content explored. Additionally, our results highlight the strong impact of the GE loading and temperature on the butterfly shape in permittivity-field loops of these nanocomposites. The experimental findings are consistent with theoretical predictions of the modified Johnson's model [Narayanan et al., Appl. Phys. Lett. 100, 022907 (2012)]. Our findings can open avenues for interplay between conductive nanofillers and ferroelectricity in soft nanomaterials with controlled phase transitions.

Effects of internal and external electronic conduction in sodium titanate nanotubes on dielectric loss mechanisms in relaxor ferroelectric polymer nanocomposites

In this report, we studied dielectric loss mechanisms in a 1–3 type of polymer nanocomposites, i.e., nanofibers or nanotubes in a polymer matrix. Sodium titanate nanotubes (TiNTs, 8–10 nm outer diameter and 300–500 nm long), which were synthesized by the hydrothermal method, were used as the fillers. The polymer matrix was a high permittivity relaxor ferroelectric polymer, poly(vinylidene fluoride-co-trifluoroethylene-co-chlorotrifluoroethylene). The nanocomposites were fabricated using solution-blending followed by hot-pressing above the melting temperature. Because of the high aspect ratio of TiNT fillers, the percolation threshold was found to be around 10–12.5 vol%. Below the percolation threshold, significant dielectric losses (both linear and nonlinear) were identified using bipolar and unipolar electric displacement – electric field (D-E) loop tests. For aggregated/percolated TiNTs, external electronic conduction was the major linear dielectric loss. For isolated TiNTs, internal electronic conduction contributed significantly to the nonlinear dielectric loss. From this study, we conclude that it is better to develop highly insulating nanofibers or nanotubes for the 1–3 type polymer nanodielectrics and the nanofillers content should be kept far below the percolation threshold in order to avoid significant dielectric losses.