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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...

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.

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.

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.

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.

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...

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.

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.

The synthesis of core@double‐shells structured TiO2@C@SiO2 nanowires (NWs) with variable thickness of carbon inner shell and SiO2 outer shell was achieved by individually controlling the chemical vapour deposition time and amount of silicon precursor added in the sol–gel synthesis. The resultant TiO2@C@SiO2 NWs filled nanocomposites exhibited an excellent dielectric performance with simultaneously improved dielectric constant and suppressed dielectric loss, which could be further regulated by individually controlling the carbon inner shell and SiO2 outer shell thickness. More importantly, the influences of the conductive carbon inner shell and insulated SiO2 outer shell thickness on the dielectric performance of nanocomposites were clearly revealed. The increase of the conductive carbon inner shell thickness would lead to an increase in dielectric constant and loss of nanocomposites, while the insulated SiO2 outer shell exhibited a totally opposite law that the dielectric constant and loss of nanocomposites decrease with increasing SiO2 outer shell thickness. Numerical simulations were also carried out to theoretically verify the relationship between the dielectric loss and SiO2 outer shell thickness. This promising controllable multi‐shell structure could be extended to a variety of hybrids to develop high‐performance dielectric nanocomposites.

High-voltage direct current (HVDC) transmission plays an important role in the development of sustainable transmission networks and the conversion of energy systems. As an important medium in the transmission system, HVDC cables have become a hot research topic. Flexible DC transmission using HVDC plastic cables is the mainstream direction advocated by the international power grid. Therefore, the demand for high-performance HVDC plastic cables is increasing. Aiming at the development process of thermoplastic environmental polypropylene insulation materials for HVDC cables, the development status and technical bottlenecks of HVDC cable insulation materials were summarized. This chapter discussed the research progress of polypropylene insulation materials from the perspective of the basic structure of polypropylene, intrinsic modification, and its nanocomposite, etc. The necessity and urgency of research and development of insulation materials for HVDC cables were clarified. Finally, the future development direction of HVDC cables was summarized and prospected.

Polyvinylidene fluoride (PVDF), as an electroactive polymer, has been attracting increasingly attention for its broad potential applications ranging from film capacitors, actuators, to energy harvesters. The capability of a PVDF film to sustain a high working voltage is highly demanded to achieve these applications. Herein, we find that blending two PVDF polymers with low and high molecular weights can achieve higher dielectric strength (Eb = 479 MV/m) than either of the two original ones (PVDF-1 with Mw of ~180,000, Eb = 412 MV/m and PVDF-2 with Mw of ~441,000, Eb = 391 MV/m). The underlying synergetic effect is deduced from the analysis of the crystallization of PVDF by wide-angle X-ray diffraction and small-angle X-ray scattering from a synchrotron source. It involves crystallite polymorphism, the transition of crystalline phases, the variation of crystalline lattice spacing at different strain spaces, and the long periods and the distribution of crystallite sizes. Understanding these underlying influences is beneficial to process PVDF films with desirable and reliable dielectric properties.

Polypropylene (PP) has the potential to be used as insulation for high voltage direct current cables due to its high melting point, excellent recyclability and electrical insulation properties. The PP/SEBS composites filled with surface-modified ZnO (m-ZnO) nanoparticles were fabricated through melt blending. Scanning electron microscopy (SEM) showed that the m-ZnO nanoparticles were well dispersed in the PP/SEBS matrix. With doping of 0.5 wt% m-ZnO, the DC breakdown strength, space charge suppression and mechanical properties of the PP/SEBS were remarkably improved, and their DC conductivity was found to be lowered. Moreover, the incorporation of m-ZnO has little effect on the melting and crystallization process as well as dielectric properties of the PP/SEBS. Thus, the PP/SEBS/m-ZnO composites have shown promise to be used as insulation for recyclable HVDC cables.

In this work, graphene oxide (GO) nanosheets with surface modification by Tannic and Fe coordination complexes (TA-Fe) were incorporated into poly(vinylidene fluoride) (PVDF) to prepare high constant but low loss polymer nanocomposites, and the effect of TA-Fe interlayer on dielectric properties of the GO@TA-Fe/PVDF nanocomposites was investigated. The results indicate that the dosage, mixing ratio, and reaction time of TA-Fe complexes have obvious influences on the dielectric properties of the nanocomposites. Furthermore, the TA-Fe interlayer significantly influences the electrical properties of GO@TA-Fe nanoparticles and their PVDF composites, and the GO@TA-Fe/PVDF composites exhibit superior dielectric properties compared with raw GO/PVDF. Dielectric losses of the GO@TA-Fe/PVDF are significantly suppressed to a rather low level owing to the presence of TA-Fe layer, which serves as an interlayer between the GO sheets, thus preventing them from direct contacting with each other. Additionally, the dynamic dielectric relaxation of the GO/PVDF and GO@TA-Fe/PVDF nanocomposites was investigated in terms of temperature.

Dielectric elastomers (DEs) are kinds of advanced functional materials, attracting more attention due to that they can used to fabricate ingenious devices. In this work, a series of advanced DEs based on the copolymer of polyurethane (PU) and acrylate, were chemically prepared through the condensation polymerization between p (BA-HEA), the n-butyl acrylate (BA) and hydroxyethyl acrylate (HEA) copolymer and diphenyl methane diisocyanate (MDI), named as p (BA-HEA)@MDI. The absence of urethane group was confirmed by infrared spectroscopy measurements. And the DEs show a decreased elastic modulus and an improved elongation at break with the decreasing content of MDI. For the absence of strong polar urethane group, the dielectric permittivity of new DEs still keeps at a relatively high value. And the p (BA-HEA)@MDI-3 shows the highest electromechanical sensitivity and the foreseeable highest actuation strain (14.4%) at a relatively low electric field (15.2 kV/mm) without any pre-strains, which is almost 2 times of that of VHB 4910 (acrylic adhesive tape, 3 M Corporation). The present work provides a new strategy to design high performance dielectric elastomers.

Block polypropylene (BPP) is an eco-friendly material that has a good potential for cable insulation because of its high melting point and excellent electrical properties. To further improve the electrical insulation properties of BPP, 1 wt% AI 2 O 3 nanoparticles were added by melt blending to BPP. The electrical properties of the BPP/AI 2 O 3 composite were measured at 25 and 70 °C. The results show that the trap density increases by 3.2 times that of unfilled BPP. The conduction current in BPP and BPP/AI 2 O 3 composite decreased at 25 and 70 °C. The electrical breakdown strength of the composite also increases compared to BPP. Space charge accumulation is significantly suppressed in the composite at 70 °C. The results indicate that the improvements in electrical properties, especially the space charge suppression in the composite, can be attributed to the higher trap density. Permittivity and dielectric loss show little effect on temperature. The permittivity of the composite shows a slight increase which can be attributed to the higher permittivity of the AI 2 O 3 nanoparticles.

The low permittivity of the polypropylene (PP) film has become a barrier for the further development of film capacitors with high energy storage density. An advanced strategy of the high-permittivity filler/polymer nanocomposite turns out to be a promising way of solving this problem. In this work, we coated ethylene propylene diene monomer (EPDM) as the shell on the surfaces of BaTiO3 successfully to fabricate core-shell structural nanoparticles. The addition of surface rubberized BaTiO3 into PP matrix promotes the permittivity to about 5.8, while the dielectric loss is barely changed as compared with PP itself. In addition, the elongation at break is as high as 364%, which is over 4 times higher than that of PP. The influences of shell thickness (3 nm, 5 nm and 7 nm) for the nanoparticles and hot-stretching process for the nanocomposite films were also carefully investigated, both of which greatly affected the properties of nanocomposites. Finally, the optimum breakdown strength as high as 370 MV/m is obtained, leading to a maximum energy density of 3.06 J/cm3, which can be attributed to both high breakdown strength and high permittivity of the core-shell structural BaTiO3/PP nanocomposites.

The electrospun polyvinylidene fluoride (PVDF) based modified boron nitride (m-BN) composite with high thermal conductivity and flexible mechanical property was successfully fabricated by electrospinning method. The uniform dispersion and ordered orientation of m-BN in the m-BN/PVDF composites form a hot string, denoted as a series of thermal conduction fillers, in the direction of the fiber. Hence, the thermal conductivity of the m-BN/PVDF film could reach to 7.29 W m−1K−1 with the addition of 30 wt% m-BN. Besides, the obtained composites also show improved mechanical properties with the tensile strength of 24.06 MPa, low dielectric permittivity of 2.45 and dielectric loss of 0.0242 @ 103 Hz. Therefore, this work provides a new route to prepare the high thermal conductivity films with potential application as flexible power devices.

Most dielectric elastomers (DEs) need high operating electric field (>100 kV/mm) and the essential pre-strains to achieve satisfied actuation, which limits their widespread application. In this work, we prepare a series of high performance DEs using the common acrylate monomers through a versatile method. By adjusting the component of polymers, the advanced DE possess a high actuation coefficient β (51.54 MPa−1) and shows a high actuated strain of 52.08% at a low electric field of 21.57 kV/mm without pre-strain. It is also found that the actuated strain of the c-p (BA-GMA)-3 is almost 4.2 times higher than that of VHB 4910. Furthermore, the advanced DE material is used to fabricate into a bend actuator, which can bend a angel of 180° and show a good electromechanical response. The present work opens a new strategy for designing advanced dielectric elastomers displaying high actuated strain without pre-strain at very low electric field.

To achieve uniform dispersion of graphene in polypropylene, polypropylene-graft-maleic anhydride (PP-g-MA) as compatibilizer was compounded with graphene to obtain masterbatch, and then melt blended with polypropylene using a micro-compounder. Raman study showed the strong interfacial interaction between the surface of functionalized graphene sheets (FGS) and the compatibilizer, while morphologic study indicated the homogeneous dispersion of graphene in polypropylene. Remarkable enhancements in mechanical, thermal and dielectric properties were obtained at low graphene loading. At an effective graphene content of 1.5 wt%, the tensile strength and storage modulus of polypropylene increased by 18% and 33%, respectively. The electrical percolation threshold of the nanocomposites is about 0.55 vol%, which is lower than most of previously reported polypropylene composites prepared by similar melt processing. Near the percolation threshold (0.535 vol% graphene), the dielectric permittivity increased to 15.2 and the loss tangent was kept as low as 0.20 at 103 Hz.

All-solid-state batteries are proposed to have ultimate safety and higher power and energy densities over conventional lithium ion batteries with liquid electrolytes. The Li ion conductivity and interfacial resistance between electrolyte and electrodes are the major bottleneck of the development of all-solid-state batteries for practical uses. Here, we reported a novel composite electrolyte which is composed of uniform distributed Li ion conducting Li6.4La3Zr1.4Ta0.6O12 (LLZTO) fillers in PEO/LiClO4 matrix. The EO:Li+ ratio of 15:1 is being used to achieve lower interfacial resistance between electrolyte and electrodes through the melting process. The composite electrolyte is fabricated by simple solution casting method, which is more advantageous comparing with high temperature sintering or sol-gel method used in the fabrication of ceramic electrolytes. The composite electrolyte exhibits good Li ion conductivity of 4.8 × 10−4 Scm−1 at 60 °C and excellent interfacial stability against Li metal. The all-solid-state lithium battery using this composite electrolyte shows a specific capacity of 140mAhg−1 and an unprecedentedly high capacity retention of 83% after 500 cycles at 60 °C and the rate of 1C. It is concluded that good electrode/electrolyte interfacial stability and contact as well as fast Li ion conductivity obtained by the addition of active garnet particulates to PEO/LiClO4 matrix are essential criteria for good charge/discharge performance of all-solid-state lithium batteries.

High-permittivity (high-k) materials play a key role in advanced electronics and electrical power systems. How to prepare the flexible material with high permittivity and low dielectric loss turns out to be a hard work due to the essential low permittivity of polymers. In this work, a kind of ductile polymer-based composites was fabricated by incorporating ionic liquids into polymer matrices. The optimized permittivity of composite with 50 wt% ionic liquid reached up to 3.3 × 104, while the dielectric loss was as low as 0.65. The temperature dependence of dielectric properties was also investigated, and a high permittivity as well as low dielectric loss at 100 Hz of about 2.0 × 104 and 0.23 were achieved at 80 °C, respectively. Furthermore, the study reveals that the dielectric loss peaks of the composite films can be affected by the content of ionic liquid, temperature even the size of ions. In short, the finding indicates that the addition of ionic liquids into polymers provides a big opportunity to improve dielectric properties of polymer materials.

Oligomer-plasticized polyurethanes were fabricated and their mechanical properties, dielectric properties, and electro-mechanical actuations in a diaphragm configuration were investigated. The effect of the ramp rate of electric field and the diameter of actuators on the actuation was tested in detail. We found that choosing appropriate parameters can suppress the leakage current and reduce the visco-elastic resistance, resulting in improved actuated strain. Under near optimal conditions, the polyurethane with 1 phr (per hundred resin) plasticizer displayed a deflection strain as high as 1800% (around 12% of diameter) at 42 V/μm, providing an effective actuated work of 1.8 J/cm3. The optimized conditions are material specific, however the present analysis can be extended to other dielectric elastomers to aid in the design and fabrication of better actuators.

Flexible polymer based materials with excellent breakdown strength and weak space charge behavior have been widely used in the field of cable insulation and cable termination. The silicon carbide (SiC) is beneficial to homogenize the electric field distributions, suppress the space charge injection and enhance the dissipation in the polymer composite. In this work, the polydimethylsiloxane (PDMS) based composites filled with β-SiC nanoparticles were prepared by solution mixing and mechanical blending, respectively. Compared with the pure PDMS, the SiC/PDMS composites possess not only the increased nonlinear conductivity coefficient but also the largely enhanced capability of dissipation of space charge. Especially under high electric field environment, the impact caused by uneven distribution of the SiC fillers was significant. The results of the space charges measurement under high electric field revealed that the SiC nanoparticles could largely enhance the dissipation and accelerate the movement of space charge, which was due to less trap sites leading to the better dispersion of SiC nanoparticles.

The effect of selective localization and surface modification of iron (Fe) nanoparticles on the dielectric and magnetic properties of polystyrene/poly(vinylidene fluoride) (PS/PVDF) composites with co-continuous structure was systematically studied. The carbon nanotubes (CNT) were used as co-filler with fixed content in PVDF phase to increase the dielectric properties. The modified Fe nanoparticles ( p -Fe) were successfully prepared by coating the PS on the surface of Fe nanoparticles, which presented a good dispersion in the polymer matrix. The X-ray diffraction and fourier transform infrared spectroscopy results of composites show CNT and Fe/ p -Fe nanoparticles have the nucleation effect on β phase of PVDF. Meanwhile, the selective localization of Fe nanoparticles in PS phase produce a high dielectric constant (e) and the effect of selective localization of p -Fe nanoparticles in the e is stronger than that of Fe nanoparticles and restrains the increase of dielectric loss. The composites with the selective dispersion of 4 vol% Fe nanoparticles filled in PS phase have the highest saturation magnetization than the other three. The difference of real part (μ′) of the complex magnetic permeability of the composites can be ignored and the value of μ‘ have low frequency dependence. This work could shed some light on the better optimization of such polymer composites.

With the development of the long-distance DC electrical power transmission, high voltage direct current (HVDC) cables have attracted more attention as an important transmission medium. HVDC transmission systems offer the best technical and economical solutions for long distance transmission. Polypropylene (PP) has better prospect than cross-linked polyethylene (XLPE), which is attributed to its excellent performance as an eco-friendly material in HVDC cables. However, the main problem in restricting the development of HVDC cables is the space charge injection and accumulation which can cause the breakdown and aging of materials. In this paper, we prepared the nanocomposites with the modified MgO, PP and Styrene-Ethylene-Butylene-Styrene Block Copolymer (SEBS) through melt blending method. The space charge, breakdown strength and dielectric properties of the nanocomposites were also investigated. Results showed that the nanocomposites with 0.5 phr surface-treated MgO dispersed well in the matrix. The addition of MgO effectively suppressed the space charge accumulation compared to PP/SEBS blends and improved its breakdown strength. At last, we explained the mechanism of space charge suppression using the trap theory. This work could provide theoretical basis for PP used as an eco-friendly insulating material in HVDC cables.

In the recent decades, the phenomena of space charge accumulation in the high voltage direct current (HVDC) insulation have been attracted more attention. In this paper, the novel sandwich-structured low-density polyethylene (LDPE) nanocomposites filled with nano-sized Al 2 O 3 particles were prepared by layer-by-layer hot pressing method. For comparison, the homo-dispersed LDPE composites with nano-Al 2 O 3 were also prepared. Morphology, breakdown strength, space charge distribution and electrical conductivity of the specimens were investigated. Morphologies of the composites were characterized by scanning electron microscopy (SEM), and their space charge profiles were measured by pulsed electro-acoustic (PEA) method. SEM images showed that there are no obvious interfaces between the adjacent layers. The breakdown strength of the sandwich-structured LDPE nanocomposites is higher than that of the homo-dispersed ones. Besides, the charge profiles indicated that space charge suppression of the sandwich-structured LDPE composites was better than that of homo-dispersed ones. Under the electrical field of 50 kV/mm at 70 °C, the conductivity of homo-dispersed nanocomposite almost approaches to 1.0 ×10−11 S/m, which is almost four-fold over that of 1%N/LDPE/1%N (i.e, 2.5 ×10−12 S/m). It was concluded that the excellent electrical insulating properties of the sandwich-structured nanocomposites were attributed to the traps existing on the interfaces, which could effectively inhibit the charge injection.

High voltage direct current (HVDC) cable is attracting more attention during power transmission due to its many advantages. However, the accumulation of space charge, poor breakdown strength and low thermal conductivity of cable insulation layer have been a long-standing obstacle to utilize the HVDC cable applications. Because boron nitride nanosheets (BNNSs) are increasingly demanded in high thermal conductivity insulation materials, herein we report a facile and easy way to prepare styrene-(ethylene-co-butylene)-styrene tri-block copolymer/polypropylene (SEBS/PP) blends filled with BNNSs based on the construction of thermal conductive networks with double-percolation process. The morphology, thermal, and electrical properties of the BNNSs/SEBS/PP nanocomposites were investigated. Scanning electron microscopy showed that the BNNSs were well dispersed in the SEBS phase at low loading of 3 phr. The analysis results on electrical properties illustrated that the direct current (DC) breakdown strength and space charge suppression were remarkably improved by the introduction of BNNSs. In addition, the thermal conductivity of SEBS/PP blends (0.42 W m−1 K−1) was increased to 1.38 W m−1 K−1 when doped with 3 phr BNNSs. This nanocomposites with enhanced thermal conductivity and electrical properties have great potential to be used as recyclable insulating materials for HVDC.

Solid polymer electrolytes (SPEs) have great potential to address the safety issues of lithium (Li)-ion batteries when compared with conventional liquid electrolytes, which makes them a promising alternative for next-generation high-energy batteries. In this work, poly(ethylene oxide)-lithium perchlorate (PEO–LiClO(4)) polymer electrolytes for Li-ion batteries were prepared using electrospinning. The crystallinity, ionic conductivity as well as mechanical properties were investigated. Ionic conductivities and mechanical properties of PEO–LiClO(4) based SPE have been obviously increased by incorporating modified TiO(2) nanofibres (TNFs) than TiO(2) nanoparticles (TNPs), due to that both TNFs and TNPs can decrease the crystalline phase concentration of PEO and increase segmental flexibility of PEO. The SPE with 3 wt% TNFs exhibits the highest conductivity of 5.308 × 10^−5 S cm^−1 at 20°C and higher tensile strength of 13.8 MPa. These results highlight the potential of utilising the electrospinning method to improve the ionic conductivity of SPEs.

Polymer blending has been shown to improve the electrical insulation properties of materials, which has good processing performance in practice. In this work, low-density polyethylene (LDPE) was selected as the matrix, and two ethylene-butyl acrylate copolymers (EBA) with similar polarities (BA content) and different molecular weights were selected as fillers. The LDPE/EBA blends with 1 wt% EBA were prepared by melt blending. The crystallization behavior of LDPE/EBA blends was studied by polarizing microscope (PLM) and differential scanning calorimetry. It was observed by PLM that two fillers with different molecular weight promoted the heterogeneous nucleation process of LDPE and produced a mass of uniform small spherulites. The trap characteristics of LDPE/EBA blends were studied by thermal stimulation current (TSC) method, which indicates the introduction of deeper traps in the blends. The space charge behavior of the blends was also studied by pulsed electroacoustic method. The addition of the EBA 1400HN significantly suppress the injection of the homocharge, which reduces the distortion electric field.

A facile route to prepare high−performance dielectric nanocomposites of poly(methyl methacrylate) (PMMA)/poly(vinylidene fluoride) (PVDF)/multi−walled carbon nanotubes (MWNTs) is systematically studied. A 30 wt % solution of PMMA/PVDF/MWNTs mixture in a solvent of N,N−dimethylformamide (DMF) is dried isothermally at ca. 20 °C below the upper critical solution temperature. Cocontinuous structure is formed through spinodal phase separation during the solvent evaporation and the MWNTs are found to be exclusively localized in the PVDF phase of the blends. The experiment results show that phase-separation and selection of CNTs occur quickly, while the conductive network needs more time to be formed. The domain size of such cocontinuous structure is in the sub−micrometer range, which is much lower than that produced by melt processing. When the volume fraction of MWNTs is 2 vol %, the dielectric constant of the composites is about 100 (at 100 Hz) and independent of frequency (102−105 Hz). The thermodynamics and kinetics of the polymer blends and composites are also studied by DSC and DMA. The composites have excellent ductility, their elongation at break is above 150%. Compared with the melt−mixing process, this approach provides a general pathway to prepare high−performance dielectric polymer materials containing cocontinuous microscale and nanoscale structures.

Here a novel photo, pH, and redox triple-responsive nanogel of poly(acrylic acid-co-spiropyran methacrylate) crosslinked by disulfide-containing N,N-bis(acryloyl)cystamine was prepared. Upon UV light irradiation or at low pH, the hydrophobic spiropyran (SP) isomerized to the hydrophilic merocyanine (MC) and the nanogels swelled-up. Upon the addition of reductant agents, the nanogels were disrupted due to the oxidative scission of the disulfide crosslinkers. The anticancer drug doxorubicin (Dox) could be loaded into the nanogels based on electrostatic interactions with the acrylic acids on the NGs, which would be released upon the stimulation of light, pH and DTT. The in vitro cytotoxicity study indicates that the nanogels loaded with anticancer drugs could kill the cancer cells effectively and the effect would be enhanced when irradiated by UV light. Interestingly, the isomerized MC in nanogels could emit intensive green light even endocytosed into the nucleus of the cancer cells, which afforded great potential in fluorescence cell imaging.

Positive temperature coefficient (PTC) materials usually suffer from the low intensity and poor reproducibility, which will limit their service time under harsh thermal control conditions. In this paper, both the functionalized carbon black (CB) and multi-walled carbon nanotubes (MWNT) were introduced into the high-density polyethylene (HDPE) matrix to achieve the improved PTC behaviors. The CB/MWNT/HDPE and CB/HDPE composites were respectively prepared through solution-melt mixing method, and their PTC behaviors were investigated. The results show that the HDPE composites filled with the modified CB exhibit better PTC effect than those filled with raw CB due to the anti-oxidation action of coupling agent. Moreover, it was found that the addition of a small amount of MWNT (0.7 wt%) into the HDPE composites with CB (18 wt%) could make larger intensity (∼6.5) and better reproducibility of PTC behavior. The synergistic effect of the modified CB and MWNT on improving the service time of PTC effect was further explored. The use of multi-dimensional carbon fillers was expected to provide a new route to fabricate high-performance polymeric PTC materials with a potential application as flexible temperature–resistivity sensor.

Herein we report the highly improved electromechanical actuation of thermoplastic polyurethane (TPU) by blending with polydimethylsiloxane (PDMS) to construct a bicontinuous structure. TPU/PDMS blend films with various PDMS loadings were fabricated through a simple solution-assisted casting method. Infrared spectroscopy measurements confirmed that TPU and PDMS are thermodynamically incompatible with each other. For TPU80 with 80 parts of PDMS, a bicontinuous phase structure was achieved. The TPU80 film showed greatly decreased elastic modulus and improved elongation at break compared to pristine TPU. It also showed the highest dielectric constant among the TPU/PDMS blend films with various contents of PDMS due to strong interfacial polarization. Most importantly, the TPU80 film exhibited a maximum areal strain of 2.3% under an electric field of 40 V μm−1, which is about 60 times higher than that of pristine TPU. The results described in this work demonstrate that the construction of a bicontinuous interface structure at the micrometer scale is very effective to develop elastomers with superior electromechanical actuation performance.

An efficient strategy is developed for the fabrication of graphene-filled polypropylene (PP) nanocomposites with graphene nanosheets orderly oriented in the in-plane direction. The nanocomposites with an anisotropic coefficient as high as 35 000 in electrical resistivity were fabricated by a sequential biaxial stretching process. Polymethylmethacrylate (PMMA) was employed to bridge graphene to the non-polar PP matrix, which facilitates the homogeneous dispersion and the orientation of the chemically converted graphene nanosheets. A PMMA/graphene masterbatch was firstly prepared and blended into the PP matrix. During the biaxial stretching, the PMMA/graphene phase was transformed from beads to sheets, which induced the in-plane orientation of the graphene nanosheets. As a consequence, the storage modulus and the conductivity of the nanocomposites were improved in the in-plane direction. The effects of graphene content and draw ratio on the anisotropy of the PP/PMMA/graphene nanocomposites were discussed in detail. This strategy of orientation-effectiveness and cost-effectiveness can be potentially integrated with commercialized biaxial stretching processes to produce high-quality anisotropic polyolefin/graphene composite films.

In the recent decades, the phenomena of space charge accumulation in the high voltage direct current (HVDC) insulation have attracted more and more attention. In this paper, the gradient-distribution multi-layered Al2O3/low density polyethylene (LDPE) nanocomposites were prepared via layer-by-layer melting blending and hot pressing method. Morphologies and electrical properties of these gradient-distribution structured composites were discussed. Results showed that this unique structure could largely enhance the breakdown strength of LDPE. The breakdown strength of the LDPE nanocomposites varied with nano-Al2O3 concentrations, and it could reach to 200 kV/mm for the LDPE nanocomposites. Besides, space charge of the LDPE nanocomposites was measured by pulsed electro-acoustic (PEA) method. The charge profiles indicated that space charge suppression of the gradient-distribution multi-layered composites was better than that of the monolayer ones with general mean-distribution structure. Their excellent insulating properties were attributed to the trap which exists in the surface, and that could well inhibit the charge injecting into the materials.

High-performance polypropylene (PP) plays an important role in electrical/electronic engineering fields. Especially in high voltage direct current (HVDC) cables it compares well to cross linked polyethylene (XLPE) for its potential application as an eco-friendly material without cross-linking. The space charge injection under high electric stress is main obstacle for the development of HVDC cables. Here we adopted chemical modification on PP with polar functional group to improve the electrical properties, whereby the molecular structure has been designed to obtain excellent insulating material. The space charge suppression, dielectric properties and crystal characteristics of PP with and without grafting with maleic anhydride (MAH) were investigated. Results demonstrated that the MAH was successfully grafted onto PP macromolecular chain. Compared to pure PP, the grafting with 2 wt% MAH can effectively suppress space charge injection and provide better stability in volume resistivity as temperature increases. Besides, their dielectric properties were studied, and the mechanism of space charge suppression was proposed. This provides a useful method to prepare the HVDC cable insulating materials.

This paper reports a facile method of fabricating high conductivity and good mechanical properties of ployvinylidene fluoride/multi-walled carbon nanotubes (PVDF/MWNTs) nanofibrous composites by an ultrasonication anchoring technique. Microstructures, electrical conductivity, mechanical and thermal properties of the PVDF/MWNTs nanofibrous composites were studied. Scanning electron microscopy images revealed that the MWNTs were uniformly anchored onto the surface and interspace of PVDF nanofibrous composites and the conductive network structures were easily formed. The PVDF/MWNTs nanofibrous composites exhibited excellent conductivity of 10−2 S m−1 with 3.91 wt% MWNTs anchored. This work opens a new path to optimize the conductivity of thermoplastic polymer nanocomposites with a wide range of application in the field of electronic and electrical engineering.

For present ceramic particles/polymer dielectric composite materials, their dielectric properties and thermal conductivity haven't met the application requirement at the same time. In this research, to achieve this goal, barium titanate@super short MWCNTs (BT@SSCNT) core-shell particle was prepared in a confinement reactive space built by water phase and oil phase. Polyvinylidene fluoride (PVDF) based composite flexible films reinforced by the BT@SSCNT particles possessed desired dielectric and excellent thermal behaviors. Especially for the composite film with 60 wt% (containing less than 17 wt% SSCNT) loading, at 102 Hz and in the wide temperature range of −40–140 °C, dielectric constant and dielectric loss varied from 476 to 764 and from 2.74 to 4.58, respectively. Meanwhile the thermal conductivity of this film reaches 25.43 W/(m K). The promising dielectric properties and high thermal conductivity of the films are attributed to multiple roles of SSCNT shell layer including external electric field applying on BT particles, tremendous interfacial polarization area, restricted electron motion and electron efficient in transporting heat. The BT@SSCNT/PVDF composite films can be a promising candidate for the modern electronic industry.

Optimizing the combination of dielectric and magnetic properties has become an important issue for electrical and electronic devices. Compared to single-function materials, multifunctional materials have the advantages of increasing device response speed, reducing costs, and increasing stability while reducing the device size. In this work, Janus structure polyvinylidene fluoride (PVDF) composites filled with barium titanate (BT) and cobalt ferrite (CFO), respectively, were prepared by electrospinning and hot pressing techniques. The Janus structural composites (J-type) have higher magnetic and dielectric properties than the conventional blended fibrous composites (H-type). When the PVDF matrix was replaced by polystyrene, the effect of Janus structure on dielectric and magnetic properties was even more pronounced. An optimum dielectric constant up to 25.1 and a saturation magnetization of 7.12 emu/g were obtained, which can be attributed to the modification and Janus structure of m-BT/PVDF+m-CFO/PVDF multifunctional composite materials.

Dielectric elastomers are functional materials that can produce significant changes in size and shape under the influence of electric field, enabling the conversion of electrical energy to mechanical energy. In recent decades, they have been widely used in electronically driven devices. The acrylates of VHB series (3M company) are currently the most widely used dielectric elastomer. However, the drawbacks, such as mechanical hysteresis, slow response speed, the need for large pre-strain, and the need for high driving voltage limit their application range. In this work, from the perspective of designing molecular structure, n-butyl acrylate and acrylic acid were polymerized by atom transfer radical polymerization method, and calcium ion was used to coordinate with carboxyl to obtain a new type of acrylic dielectric elastomer with high dielectric constant, low dielectric loss, and excellent mechanical properties.

The cross-linked polyethylene (XLPE) extruded cables have become one of the important equipments in the high-voltage direct current (HVDC) power transmission. Recently, the semiconductive layers as the crucial materials in the XLPE cables developed rapidly. In this study, the semiconductive composites used for high-voltage cables were fabricated by melting blending method via a reciprocating single-screw extruder. The protrusions on the surface of semiconductive layer were scanned through an optical control system (OCS). The influence of carbon black and matrix characteristic as well as the extruding process on the smoothness and electrical properties of the semiconductive materials was discussed. It was found that the addition of lower concentration of carbon black particles with larger oil absorption and higher structure could easily make the formation of excellent conductive networks, which gave rise to the super-smooth surface and better electrical properties. The proper extruding process parameters including the screw configuration and speed as well as the feeding ratio played an important role on reducing the surface impurities of the materials. The prepared semiconductive materials have no protrusions larger than 50 μm and the number of protrusions $( 30 \sim 50 \, \mu \text{m}$) is less than 10 Num/m2. Besides, the space charge behavior of the XLPE insulation and semiconductive materials were investigated. The results show that the prepared semiconductive materials could effectively suppress the injection and accumulation of hetero-charges in the XLPE.

In recent years, liquid silicone rubber (LSR) has been widely used in the external insulation field due to their excellent insulation properties and mechanical performance. LSR is a kind of addition silicon rubber, which has no by-products with vulcanization process and has very low line shrinkage. In this work, LSR based composites filled with boron nitride (BN) particles were prepared by mechanical blending. The surface of BN was functionalized with a coupling agent to increase the compatibility of BN and LSR. The scanning electron microscopy (SEM) was used to characterized the morphologies of the LSR composites, and their electrical properties were also studied. From the SEM images, there are no obvious interfaces between BN and LSR. The breakdown strength of the LSR composites is higher than that of pure LSR. When the content of BN is 40 wt%, the breakdown strength of LSR composite is 45 kv/mm. The outstanding insulation performance of the LSR composites were ascribed to the good dispersion of BN. The highest value of thermal conductivity was obtained for the LSR composite containing 40 wt% BN, and the thermal conductivity is 0.96 $\mathrm{W}\cdot \mathrm{m}^{-} 1\mathrm{K}^{-1}$. Compared to 0.18 $\mathrm{W}\cdot \mathrm{m}^{-1}\cdot \mathrm{K}^{-1}$ of pure LSR, which means a 557% increment. The LSR composite with high thermal conductivity and good insulation properties was very important for electrical power engineering.

Epoxy resin is one of the most widely used thermosetting polymers and commonly applied in electrical power engineering. The intrinsic properties of epoxy can be improved by the introduction of inorganic filler, thus fabricating a composite material. Boron nitride is a ceramic dielectric material with high electric breakdown strength and high thermal conductivity, while exhibiting a low relative permittivity. In this study we investigate the influence of the filler size and its concentration on the electrical properties and thermal conductivity of epoxy. Two types of composites were prepared with an average particle size of 1 μm and 10 μm and a filler concentration of 20, 30, 40, and 50 percent by weight. The surface of the particles was functionalized with a coupling agent in order to increase the compatibility of boron nitride and epoxy resin. The results show that the relative permittivity of the composite decreases more when introducing particles. The breakdown strength of epoxy resin added 30 wt% boron nitrides with size is 1 μm is higher than that of epoxy resin. The highest value of thermal conductivity was obtained for the composite containing 50 wt.% boron nitrides with average particle size of 10 μm, and the thermal conductivity is 1.52 W/m·k.