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The great development potential of polymer dielectric capacitors in harsh environments urgently requires enhancing capacitive performance at high temperatures. However, the exponentially increased conduction loss at high temperature and high field results in a drastic drop in energy density and charge-discharge efficiency. Here, a bilayer-structured polyimide (PI) composite film containing a wide-band gap inorganic layer as a charge blocking layer is designed. The inorganic layer improves the charge trapping ability and regulates the charge mobility at the electrode/dielectric interface. The charge injection mechanism in the interface-optimized PI/boron nitride nanosheet (BNNS) composite films is investigated by finite element simulation, and the effect of the BNNS layer on high temperature conduction is further understood. An appropriate thickness of the charge blocking layer establishes an effective energy barrier. Therefore, the composite films exhibit significantly suppressed conduction loss and excellent capacitive performance at a high temperature. A high energy density of 4.37 J cm

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The high operating temperature of dielectric capacitors applied in electric vehicles, aerospace and underground exploration require dielectric materials with high temperature resistance and high energy density. Polyimide (PI) turns out to be a potential dielectric material for capacitors applications at high temperature. In this review, the key parameters related to high temperature resistance and energy storage characteristics were introduced and recent developments in all-organic PI dielectrics and PI-matrix dielectric nanocomposites were discussed. Synthetic strategies of new functional PI via modification at the molecular level together with the design engineering of nanofillers and multilayer structures of PIs were also analysed. Finally, a systematic summary of the current challenges and future developments for capacitor materials used at high temperatures were presented.

Sandwich-structured polymer nanocomposites exhibit remarkable capacitive energy storage performance, including high energy density, great charge–discharge efficiency and excellent dielectric stability at elevated temperatures.

The interchain space of polyimide is optimized to hinder charge carrier transport, thus improving the energy storage performance at high temperatures.

Polymer dielectrics with high energy density are of urgent demand in electric and electronic devices, but the tradeoff between dielectric constant and breakdown strength is still unsolved. Here we report the synthesis and molar mass control of three alternating [1.1.1]propellane-(meth)acrylate copolymers, denoted as P-MA, P-MMA, and P-EA, respectively. These copolymers exhibit high thermal stability and are semi-crystalline with varied glass transition temperatures and melting temperatures. The rigid bicyclo[1.1.1]pentane units in the polymer backbone promote the orientational polarization of the polar ester groups, thus enhancing the dielectric constants of these polymers, which are 4.50 for P-EA, 4.55 for P-MA, and 5.11 for P-MMA at 10 Hz and room temperature, respectively. Moreover, the high breakdown strength is ensured by the non-conjugated nature of bicyclo[1.1.1]pentane unit. As a result, these copolymers show extraordinary energy storage performance; P-MA exhibits a discharge energy density of 9.73J/cm

Polymer dielectrics are insulators or energy storage materials widely used in electrical and electronic devices. Polymer dielectrics are needed with outstanding dielectric characteristics than current technologies. In this study, the self-assembly of boron nitride nanosheets (BNNSs) was applied to form an inorganic–organic nanocoating on various common polymer dielectrics. It is inexpensive and easy to fabricate this thin coating on a large scale. The coating has a wide bandgap and thus can significantly improve the breakdown strength of polymer dielectrics. The charge characteristics and trapping parameters of nano-domains on the surfaces of polymer dielectrics were measured, and the coating had shallow trap levels. This facilitated the dissipation of surface charges and thus greatly increased the flashover voltage. The coating also effectively improved the temperature stability and dielectric constant of the polymer dielectric. This nanocoating shows potential as a method to effectively improve the dielectric characteristics of polymer dielectrics and outperform existing composite polymer dielectrics, which are crucial for large-scale applications in energy storage and power and electronic devices.

Conductive-filler filled polymer composites have exhibited great potential due to the high dielectric constant that can be reached near the percolation threshold, yet the associated high dielectric loss prohibits wide use in practice. Recently, extensive efforts have been devoted to encapsulating conductive fillers with an insulating shell, with the aim to constrain the dielectric loss; but such efforts also significantly reduce dielectric constant. This dilemma raises the question of whether core-shell structured fillers are ultimately beneficial for the dielectric performance of composites, which is less explored. In this study, we investigate polymer nanocomposites containing a series of Al@Al2O3 nanofillers with different shell thicknesses. It shows that the high dielectric constant of percolative composites is contributed by a fast intra-particle polarization and a slow inter-particle polarization. Formation of an insulating shell enables the independent control of the two polarizations, which are otherwise coupled (increasing or decreasing together) in regular percolative composites. By promoting intra-particle polarization and suppressing inter-particle polarization, the core-shell structured nanocomposites can obtain a high dielectric constant and concurrently low dielectric loss, far surpassing the unmodified nanofiller composites. Moreover, the thermal conductivity and high field resistivity are also improved, resulting in a stable and low temperature during operation. This work offers a new paradigm for the design of percolative polymer composite with high dielectric constant and low dielectric loss as well as improved thermomechanical properties.

Metallized Film Capacitors (MFC) are vital devices in many important fields such as energy, transportation, and aviation, whilst Digital Twin (DT) technology opens a new channel to leverage existing data resources of metallized film capacitors. This paper review current knowledge about metallized film capacitors and digital twin, list the key issues, propose frameworks, and provide the outlook to clarify the potential of digital twin’s application in metallized film capacitors. First, based on the development history and research status of metallized film capacitors, this review sorts out the key research issues of data utilization. Then, the connotation and typical characteristics of the digital twin definition are combed and refined, and the typical architecture of digital twin implementation is presented. Furthermore, the overall application architecture of digital twin in metallized film capacitors is constructed, and the technology system of each application scenario and the role of digital twin are analyzed. Finally, the main challenges in the application of the digital twin in metallized film capacitors and the future development directions are discussed. This review promotes the performance improvement, cost reduction and application expansion of metallized film capacitors, which can be used as a guide for the application of digital twin in other power equipment of energy system.

Flexible dielectric and electronic materials with high dielectric constant (k) and low loss are constantly pursued. Encapsulation of conductive fillers with insulating shells represents a promising approach, and has attracted substantial research efforts. However, progress is greatly impeded due to the lack of a fundamental understanding of the polarization mechanism. In this work, a series of core-shell polymer composites is studied, and the correlation between macroscopic dielectric properties (across entire composites) and microscopic polarization (around single fillers) is investigated. It is revealed that the polarization in polymer conductor composites is determined by electron transport across multiple neighboring conductive fillers-a domain-type polarization. The formation of a core-shell filler structure affects the dielectric properties of tpolymer composites by essentially modifying the filler-cluster size. Based on this understanding, a novel percolative composite is prepared with higher-than-normal filler concentration and optimized shell's electrical resistivity. The developed composite shows both high-k due to enlarged cluster size and low loss due to restrained charge transport simultaneously, which cannot be achieved in traditional percolative composites or via simple core-shell filler design. The revealed polarization mechanism and the optimization strategy for core-shell fillers provide critical guidance and a new paradigm, for developing advanced polymer dielectrics with promising property sets.

Polymer dielectrics with super dielectric constant (e'), low loss as well as high thermal conductivity (TC) are gaining tremendous momentum owing to the ever-increasing demands on microelectronic devices. Introduction core–shell fillers into polymers has been demonstrated as a promising strategy for high-e' but low loss. Herein, nickel (Ni) particles were encapsulated by an insulating layer of NiO with various thicknesses via controlling calcination times at 550 °C under air, and the as-prepared core–shell Ni@NiO was incorporated into poly(vinyli-dene fluoride) (PVDF). The results verify the formation of a NiO shell outside of the Ni, and manifest that the PVDF with Ni@NiO particles exhibit a high e', a signally suppressive loss and conductivity, as well as a high-TC compared with raw Ni. The reason can be ascribed to multiple effects of NiO interlayer including the enhancement of interface compatibility and interface polarizations and the blocking of leakage current. Furthermore, the thickness of NiO shell exerts different influences on long-range and short-range charge migration, and it should be rationally tuned to optimize the dielectric properties and TC. This study provides an effective idea to regulate and control the dielectric properties and TC of polymer composites.

To suppress the high dielectric loss of graphene oxide (GO)/poly(vinylidene fluoride) (PVDF) while still maintaining a high dielectric constant (k) near the filler percolation threshold, herein, GO...

Polymer nanocomposites have attracted increased attention for use in the field of high‐voltage direct current (HVDC) cable insulation. To study the use of polymer nanocomposites for this purpose, 3D flower‐like MgO (flower‐MgO) particles with hierarchical surface morphology are first synthesised. Polypropylene (PP) was simultaneously mixed with styrene‐(ethylene‐co‐butylene)‐styrene triblock copolymer (SEBS) and flower‐MgO to obtain PP/SEBS/flower‐MgO composites. The microstructural, thermal, electrical, and mechanical properties of the obtained nanocomposites were then studied in detail. The results showed that flower‐MgO particles loaded at low concentration were well dispersed in the PP/SEBS matrix. The incorporation of flower‐MgO particles has been found to significantly suppress the injection of homocharges and strengthen the ability to release the charge, thus containing accumulation of the space charge. The DC breakdown strength of PP/SEBS/flower‐MgO composites was increased to 323 MV/m. Meanwhile, the tensile strength and elongation at break of the obtained composites was improved by loading 0.5 phr flower‐MgO because of the synergistic toughening effects of SEBS and MgO. The investigation demonstrates the immense potential to replace nonrecyclable cross‐linked polyethylene as an HVDC cable insulating material.

Developing a high dielectric constant (er) polymer dielectrics with low dielectric loss and high thermal conductivity (TC) is still continuous demands for advanced electrical power systems. Herein, nickel (Ni) particles were encapsulated by silica (SiO2) via a sol–gel process using sodium silicate as a precursor, and the obtained core–shell Ni@SiO2 powders were blended into poly(vinylidene fluoride) (PVDF) to investigate the effects of SiO2 insulating layer and its thickness on dielectric properties and TC of composites. Compared with pristine Ni, the Ni@SiO2/PVDF composites exhibit a superior er, and remarkably suppressed loss and conductivity, attributable to the SiO2 interlayer between the core Ni particles which effectively prevents them from direct contacts and significantly reduces the leakage loss. Moreover, the Ni@SiO2/PVDF composites still possess a high TC owing to the restrained thermal interfacial resistance and enhanced interfacial compatibility between the fillers and the matrix. The developed Ni@SiO2/PVDF composites with high k and TC but low loss are potential for microelectronic industry.

Polymer dielectrics for energy storage applications usually endure high electric field strength. Adjustment of the composition and structure of the dielectric bulk phase to enhance the dielectric breakdown strength has been widely studied. However, the effect of electrode–dielectric interface on the breakdown strength has received little attention, which greatly hinders further development in this field. In this work, an all-organic double-layer dielectric film consisting of poly(vinylidene fluoride) (PVDF) as the matrix and polymethyl methacrylate (PMMA) as the organic nano-interlayer was prepared. By adjusting the electrode–dielectric interface, remarkably improved electric breakdown strength (767.05 MV m−1) and discharged energy density (19.08 J cm−3) were realized concurrently without sacrificing the charge–discharge efficiency. The experimental results and computational simulations reveal that the surface morphology of dielectrics has a great effect on the electric field distribution at the electrode–dielectric interface, and further affects the leakage current and breakdown strength of the dielectric. The PMMA nano-interlayer modifies the surface defects and increases the Young's modulus at the electrode–dielectric interface, leading to the improvement of insulation performance. These findings offer a new perspective to understand the impact of the electrode–dielectric interface on the polymer dielectric breakdown strength. This work provides a novel paradigm for fabricating polymer dielectrics with high breakdown strength for energy storage.

Flaky Cu (f-Cu) particles with surface modification by polystyrene (PS) coating layer were incorporated into poly(vinylidene fluoride) (PVDF), to obtain high dielectric constant (k) and thermal con...

High-performance epoxy (EP) composites with excellent thermal conductivity and dielectric properties have attracted increasing attention for effective thermal management. In this work, three-dimensional (3D) structural functional fillers were prepared by an electrostatic self-assembly approach. The negatively charged carbon nanotubes (nCNTs) prepared by carboxylation on the surface of CNTs were attached to the positively charged boron nitride (pBN) to form the 3D pBN@nCNTs functional fillers. The morphological characterizations of the formed 3D pBN@nCNTs fillers and epoxy composites were established, illustrating that nCNTs were linearly overlapped between the BN sheets, thus forming a 3D heat conduction network in the epoxy matrix. The synergistic effect of pBN with nCNTs on the enhancement of thermal conductivity and dielectric properties of composites was systematically studied. The experimental results demonstrated that the thermal conductivity of pBN@nCNTs/EP composites could reach 1.986 W m−1K−1 with the loading of 50 wt% fillers at 10:1 mass ratio of pBN:nCNTs, which is 464% and 124% higher than that of pure EP and BN/EP, respectively. Simultaneously, the dielectric permittivity was successfully increased to 15.14. Moreover, the thermal stability of the composites was synchronously enhanced. This study provides a facile path to fabricate thermosetting polymer composites with high thermal conductivity and dielectric properties.

Electroactive polymer (EAP) is a kind of smart material, which can change its shape under the stimulation of electric field. Dielectric elastomer (DE) is an important member of the EAP. DE has the characteristics of excellent performance, such as light weight, low noise, low cost, and so on, which guarantee its wide applications in the fields of actuators, generators, sensors. In this review, the principles of energy conversion, the research status and latest development of new technologies for DEs, and the performance characteristics of DEs are summarised. Simultaneously, it points out the development problems and feasible countermeasures. At last, the application prospects of DE are discussed, combined with the research direction of the international frontier.

Polymer nanocomposites with improved dielectric permittivity and high breakdown strength are extremely desirable for the flexible electronic devices and power systems. The compatibility of fillers and polymer matrix is important in determining the dielectric and breakdown strength properties. The core–shell structure concept is useful to improve the compatibility of fillers with polymer matrix. Herein, an organic thermoplastic urethanes (TPU) polymer shell was successfully grafted on the surface of barium titanate (BaTiO(3), BT) and such a TPU shell improved the permittivity and breakdown strength of TPU@BT/PVDF polymer nanocomposites greatly. The permittivity of TPU@BT/PVDF nanocomposites with 12 wt% fillers at 10^2 Hz was up to 13.5, which was 1.5 times higher than that of pure poly(vinylidene fluoride) (PVDF). The improvement of the dielectric properties could be attributed to the enhanced interfacial polarisation between BT nanoparticles and TPU shell. Besides, the compatibility of BT nanoparticles and PVDF matrix was improved after the introduction of TPU shell. Accordingly, a highest breakdown strength value about 373 MV/m was obtained for the TPU@BT/PVDF nanocomposites with 7 wt% fillers. The core–shell strategy could be extended to a variety of inorganic fillers to improve the dielectric and breakdown strength properties of polymer nanocomposites.

Atmospheric pressure needle-to-plane negative corona discharges have been studied considering the effect of photoionization in electrode gap spacing from 2.9 to 3.9 mm. Trichel pulses, spatial distributions of electron density and electric field, pulse duration time, and pulse frequency under different gap spacing were investigated in this work. It is found that peak value and duration time of the first Trichel pulse decrease with the increase of gap spacing. The movement of charged particles is faster in narrow gap spacing, which leads to higher pulse frequency. Moreover, the effect of photoionization on negative corona discharge under different gap spacing is also studied by numerical simulation. It is found that electric field, as well as electron density, is weakened due to the effect of photoionization. Besides, the magnitude of Trichel pulses, duration time of the first pulse, and pulse frequency are relatively small when taking the effect of photoionization into consideration. These results are of great importance to fully understand the mechanism of negative corona discharge under different conditions.

Film capacitor, one typical type of electrostatic capacitors, exhibits its unique advantages in the high-power energy storage devices operating at a high electric field due to the high electrical breakdown strength (Eb) of the polymeric films. However, the development of film capacitor towards high energy storage density is severely hindered by the low dielectric constant (e) and low charge-discharge efficiency (η) of the polymeric films. The film of polypropylene (PP), the most used polymeric film with a market share of 50%, owns a high η due to its low inherent hysteresis loss. Yet the low e (2.2 ​at 103 ​Hz) impedes the increase of its energy storage density (1–2 ​J/cm3). Here we demonstrate that the discharged energy density (Ue) of PP film could be largely increased from 1.40 ​J/cm3 of pure PP film to 3.86 ​J/cm3 of PP nanocomposite film by incorporating a small loading of core-shell structured PMMA@BaTiO3 (PMMA@BT) nanoparticles (2.27 ​vol%) into PP matrix. The obtained Ue of 3.86 ​J/cm3, to the best of our knowledge, is the highest reported value for the PP based films using commercial PP resin. Meanwhile, the η merely undergoes a slight decrease from 99.5% to 94.1%. Similarly, the obtained η of 94.1%, to the best of our knowledge, is also the highest value for the polymeric films reported in the previous works. The significant increase of Ue (175.7%) and negligible decrease of η (5.4%) are mainly attributed to the increases of e from 2.2 to 3.7 and Eb from 361 ​MV/m to 448 ​MV/m. Compared with the films of raw BT/PP nanocomposites, the Ue exhibits a significant increase of 365.1% from 0.83 ​J/cm3 to 3.86 ​J/cm3 and the η also displays an increase of 7.4% from 87.6% to 94.1%. The significant improvement of energy storage performance achieved in the film of PMMA@BT/PP nanocomposite suggests that the organic PMMA shell plays an important role in the amelioration of compatibility of BT nanoparticles and PP matrix and the alleviation of local electric field concentration. Moreover, the PMMA shell could also provide a robust scaffold to hinder the early breakdown failure of nanocomposites due to its high Eb (425 ​MV/m). Thus, high e, low loss and high Eb are simultaneously achieved. Specifically, the high hot stretch ratio (1:4) of nanocomposite film indicates the strong feasibility of industrialized film processing. Apart from the experimental analysis, theoretical analysis using the simulation of finite element is also carried out to figure out the influence of organic PMMA shell on the dielectric performance of PP nanocomposites films. These findings enable the development of film capacitor using non-polar PP based film towards high energy storage density.

High-voltage direct current (HVDC) power cables have been paid more attention due to the big issue concerning the main insulation materials. The residues in the industrial production process will cause space charge generation and accumulation in the materials, which has become one bottleneck to limit the development of power cables up to higher voltage levels. In this paper, the LDPE matrix was modified by three types of ethylene-butyl acrylate (EBA) copolymers (1.0 wt%) with different polarities (BA content) via melt blending to optimize the space charge behavior of the LDPE insulation. The micromorphology and structure of the blends are examined by polarized light microscope and differential scanning calorimetry. The space charge distribution is tested by the pulsed electroacoustic method. The trap level is studied by the thermally stimulated current. The results show that EBA introduces more deep traps and decreases the shallow traps. The medium-polar EBA (16% BA content) can effectively suppress charge accumulation, and have the same suppressed effect on XLPE/EBA blends. This study will provide important insights into the design and development of advanced HVDC power cable applications.

Polymer dielectrics have been widely used in electrical energy storage devices. However, the relatively low operating temperature hinders their applications in harsh environments. Herein, the molecular structure of polyimide (PI) is optimized by adjusting the reaction kinetics of polyamic acid, which improves the energy storage performance of PI at elevated temperature. The PI film with an optimal imidization degree achieves a simultaneous increase in dielectric permittivity (ϵ r) and breakdown strength (E b), resulting in a maximum discharged energy density (U e) of 6.9 J cm −3 with a charge-discharge efficiency of 90.0% at room temperature and a high U e of 3.9 J cm −3 at 150 °C. The introduced -COOH/-CN-OH- polar groups increase the ϵ r through the enhancement of dipole polarization. Moreover, an appropriate number of -COOH/-CN-OH- groups as deep traps reduce the mobility of carriers, thereby increasing the E b. Finite element simulation reveals that PI with an appropriate imidization degree exhibits suppressed space charge accumulation and improved electric field distortion. This method reduces the PI processing temperature, which effectively reduces the production energy consumption. For verifying the universality of the design strategy, two other PIs prepared from different monomers are also demonstrated to have simultaneous improvement in ϵ r and E b.Finally, this production process of only reducing the preparation temperature without adjusting the original commercial PI production equipment is crucial for the practical application of capacitor films in the future.

Metallic zinc anodes in zinc-ion batteries suffer from problematic Zn dendrite chemistry. Previous works have shown that preferred-orientation crystal planes can help dendrite-free metal anodes. This work reports a nanothickness (≈570 nm) AgZn

With the development of advanced electronic devices and electric power systems, polymer-based dielectric film capacitors with high energy storage capability have become particularly important. Compared with polymer nanocomposites with widespread attention, all-organic polymers are fundamental and have been proven to be more effective choices in the process of scalable, continuous, and large-scale industrial production, leading to many dielectric and energy storage applications. In the past decade, efforts have intensified in this field with great progress in newly discovered dielectric polymers, fundamental production technologies, and extension toward emerging computational strategies. This review summarizes the recent progress in the field of energy storage based on conventional as well as heat-resistant all-organic polymer materials with the focus on strategies to enhance the dielectric properties and energy storage performances. The key parameters of all-organic polymers, such as dielectric constant, dielectric loss, breakdown strength, energy density, and charge-discharge efficiency, have been thoroughly studied. In addition, the applications of computer-aided calculation including density functional theory, machine learning, and materials genome in rational design and performance prediction of polymer dielectrics are reviewed in detail. Based on a comprehensive understanding of recent developments, guidelines and prospects for the future development of all-organic polymer materials with dielectric and energy storage applications are proposed.

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Herein, graphene oxide (GO) nanosheets coated with insulated polyvinyl pyrrolidone (PVP) were integrated into poly(vinylidene fluoride) (PVDF) to investigate the effects of the insulating PVP shell...

To suppress dielectric loss while still harvesting high dielectric constant (k) and thermal conductivity in polymer composites, core–shell structured fillers are synthesized via controlled calcination under air, where the conductive copper (Cu) particles are encapsulated by a thin insulating oxidation layer (CuO). The dielectric constant can be substantially improved in the poly(vinylidene fluoride) PVDF composites filled with Cu@CuO fillers, and the dielectric loss is strongly restrained even at high filler loadings. The improved dielectric performance can be ascribed to the insulating CuO shell, which promotes the multiple interfacial polarization and meanwhile impedes the long-range electron migration. Additionally, the Cu@CuO/PVDF composites exhibit higher thermal conductivity (TC) than the unfilled polymer and the Cu/PVDF, owing to the reduced interfacial thermal resistance between the fillers and the matrix. Composites with high TC and k but low loss are promising materials for potential applications in microelectronic, electrical and energy storage devices.

Polymer-based composites with ceramic fillers could combine the advantages of both, which can be potentially used in electrical and electronic technology. In this work, the barium titanate (BaTiO 3 ) nanofibres and the core-shell structured BaTiO 3 @Al 2 O 3 nanofibres with Al 2 O 3 insulation layer coated on the BaTiO 3 surface were both prepared via the electrospinning method. The appropriate incorporation of the ceramic nanofibres effectively improves the dielectric properties and energy density of the polymer. Moreover, the poly(vinylidene fluoride- co -hexafluoropropylene)-based composite films with the three-layer sandwich structure were fabricated to further promote the dielectric properties. The results show that the outer two layers with a higher content of BaTiO 3 nanofibres can make more contribution to the improved permittivity of the composites. In addition, the introduction of the interlayer with low loading of BaTiO 3 @Al 2 O 3 nanofibres promotes the breakdown strength. This work gives rise to the potential in high energy storage applications.

Dynamic dielectric properties of nickel (Ni)/epoxy composites are investigated by broadband dielectric spectroscopy over a wide frequency range (approximately 1–107 Hz) and temperature range (approximately −20 to 200°C). Multiple dielectric relaxation processes in the Ni/epoxy composites are identified, corresponding to conductivity, interfacial polarization (IP), and α-relaxation. With increasing temperature, both dielectric permittivity and loss of composites increase, arising from enhanced dipolar mobility; approaching the glass transition temperature ( T g), a clear α-relaxation appears, which can be attributed to the onset of cooperative chain movement. Further increasing temperature activates the long-range movement of space charges, as manifested by an IP superimposed on the ionic conductivity. A transition from insulator (below T g) to semiconductor (above T g) is also observed for the studied composite system.

The dielectric elastomers have been widely studied in last decades due to their excellent electromechanical conversion ability. Herein, two kinds of polyurethanes (PU) with different molecular weights were used and the results demonstrated that incorporating low molecular weight (MW) PU into high MW PU not only caused the decrease in elastic modulus but also induced a high elongation at break. The optimal performances of PU mixture were observed when the content of low MW PU was 20 wt% and the PU mixture with 20 wt% low MW PU was used as the matrix in this work. In order to achieve a high electromechanical conversion performance, the surface modification of BaTiO3 (BT) nanoparticles by 4,4′-diphenylmethane diisocyanate (MDI) was carried out and the obtained BT products (BT-MDI) were used as fillers for the PU nanocomposites. The permittivity of BT-MDI/PU nanocomposites with 6 wt% fillers increased to 8.6 at 1 kHz and the elongation at break of nanocomposites at this filler loading still remained as high as 1070%. Because of the enhanced properties, the achieved energy-conversion density reached 2.88 mJ/cm3 at 900 V, and the conversion efficiency was up to 1.56 %. The results reveal that an effective surface modification of nanoparticles is beneficial for the improvement of electromechanical conversion behavior of composite dielectric elastomers due to both the excellent dispersion of BT-MDI nanofillers and the improved compatibility between BT-MDI nanoparticles and PU matrix.

To suppress the high dielectric loss of graphene oxide (GO)/poly(vinylidene fluoride) (PVDF) while maintaining high dielectric constant (high- k) near the percolation threshold, in this study, GO nanosheets coated with polydopamine (PDA) were integrated into PVDF to investigate the effects of the PDA shell and its concentrations on the dielectric properties of the nanocomposites. The results indicate that the dissipation factor and conductivity of the GO@PDA/PVDF are significantly suppressed to very low values compared with the pristine GO/PVDF composites, attributable to the PDA interlayer between the GO nanosheets which prevents them from direct contact with each other and remarkably reduces the leakage loss. Furthermore, activation energies of the GO/PVDF and GO@PDA/PVDF composites were calculated as 1.247 and 0.884 eV, respectively, indicating that the presence of PDA interlayer reduces the relaxation activation energy and makes the relaxation occur at low temperature for the GO@PDA/PVDF. The prepared GO@PDA/PVDF nanocomposites with high- k but low loss have potential applications in microelectronic engineering.

Motivated by a broad temperature span, we performed a strain-induced broadening temperature range of electrocaloric effects in PbZr0.6Ti0.4O3/PbTiO3 ferroelectric superlattices based on phenomenological Landau-Devonshire thermodynamic theory. The results indicated that interlayer misfit strain and substrate misfit strain in superlattices modulate the Curie temperature. Considering two types of strains coexist in ferroelectric superlattices, there exist a balance between interlayer misfit strain and substrate misfit strain to broaden temperature range (281 K) of electrocaloric effects. The present study therefore contributes to the understanding of strain effects of electrocaloric cooling and provides guidance towards experimental design of high efficiency cooling devices.