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Abstract To simultaneously improve the impact strength and dielectric properties of cured epoxy (EP), herein we explore liquid rubber toughened EP based on a nonpolar epoxidized hydroxyl-terminated polybutadiene (EHTPB), where [...]

Surface modification of core-shell structured Al (Al@[Al.sub.2][O.sub.3]) nanoparticles was performed using [gamma]-(Aminopropyl)-triethoxysilane (APS) and dopamine (DA), respectively, and the microstructures, dielectric properties and thermal conductivities of the Al/poly(vinylidene fluoride) (PVDF) nanocomposites were investigated. Both DA and APS enhance the interfacial bonding strength between the fillers and the matrix, leading to homogeneous dispersion of Al nanoparticles in PVDF matrix. Compared with raw Al nanoparticles, surface-treated Al/PVDF exhibit much higher dielectric permittivity due to the enhanced interfacial interactions between the two components, whereas, the dielectric loss and electric conductivity of the nanocomposites still remain at rather low levels owing to the insulating alumina shell preventing effectively core Al from direct contact. The dynamic dielectric properties results reveal that dielectric constant and loss increase with temperature due to the gradually enhanced mobility of molecular chain segments of PVDF for the raw Al/PVDF and treated Al/PVDF nanocomposites. Additionally, the PVDF nanocomposites with Al treated with APS and DA show enhanced thermal conductivities compared with raw Al/PVDF under the same filler loading because of reduced thermal interfacial resistance promoting phonon transfer across the interfaces. POLYM. ENG. SCI., 59:103111, 2019., INTRODUCTION With the increasing development of microelectronic integration technology, the microelectronic device system is developing towards high integration, miniaturization, and light weight [1-3]. When compared with discrete capacitors occupying most [...]

Flexible dielectrics with large dielectric constant (ε′) coupled with low loss are highly pursued in many applications. To bolster the ε′ of raw Zn (zinc)/poly(vinylidene fluoride, PVDF) while maintaining pimping dielectric loss, in this study, the core@double–shell structured Zn@zinc carbonate (ZnCH)@polystyrene (PS) particles are first synthesized through a suspension polymerization of styrene, and then composited with PVDF to elevate the ε′ and keep low loss of the composites. By optimizing the PS shells' thickness and tailoring the electrical resistivity of Zn@ZnCH@PS particles, both the slow inter‐particle polarization and fast intra‐particle polarization in the composites can be decoupled and synergistically tuned, thus, the Zn@ZnCH@PS/PVDF achieves a much higher ε′ and lower dielectric loss, simultaneously, which far exceed the unmodified Zn/PVDF. Both experiment and theoretic calculation reveal that the double‐shell ZnCH@PS not only induces and promotes multiple polarizations enhancing the composites' ε′, especially at the optimized PS's thickness, but also maintains suppressed loss and conductivity thanks to their obvious barrier effect on long‐range charge migration. The core@double–shell filler design strategy facilitates the development of polymer composites with desirable dielectric properties for applications in electronic and electrical power systems. [ABSTRACT FROM AUTHOR]

Polymer dielectrics with synergistically large dielectric permittivity (ε') and breakdown strength (Eb) but prohibited loss is of crucial applications in the electronic devices and power equipment. In this study, we aim to elevate the integrated dielectric performances of molybdenum (Mo)/polyvinylidene fluoride (PVDF) by constructing a semiconducting molybdenum oxide (MoO3) shell and insulating polystyrene (PS) shell on the Mo surface through high‐temperature oxidation followed by suspension polymerization. The resulting core@double‐shell Mo@MoO3@PS particles were compounded with PVDF to achieve high ε' and Eb while minimizing the loss. The results reveal that the Mo@MoO3@PS/PVDF composites indicate simultaneously ameliorative ε' and Eb along with restrained loss owing to the existence of the MoO3@PS double‐shell, which not only prominently enhances the interfacial compatibility and interactions between fillers and PVDF, but significantly inhibits the conductivity and loss through impeding the long‐distance motion of carrier charges. The dielectric capabilities could be improved by adjusting the thickness of the PS interlayer. The Havriliak‐Negami equation was used to fit the experimental results, which showed the impact of the PS shell on the polarization mechanism and how it inhibits carrier migration. The Mo@MoO3@PS/PVDF with high ε' and Eb yet exceptionally low loss exhibit potential applications in microelectronics and electrical industries. [ABSTRACT FROM AUTHOR]

Polymers with high thermal conductivity (TC) and dielectric constant (ε) but low dielectric loss show enormously potential applications in electrical power systems. To enhance the ε and TC while significantly suppressing the loss of β‐silicon carbide whisker (β‐SiCw)/polyvinylidene fluoride (PVDF), in this study, SiO2 shells with different morphologies were constructed on the superficies of β‐SiCw via a facile oxidation method in air atmosphere. The SiO2 shell' morphology on the TC and dielectric performances of the β‐SiCw@SiO2/PVDF are systematically explored as a function of the frequency and filler loading. The β‐SiCw@SiO2/PVDF demonstrate astonishingly restricted loss and meliorative TC when compared to the β‐SiCw/PVDF because the SiO2 shell not only suppresses the β‐SiCw from direct contact with one another and impedes the long‐distance charges migration thereby resulting in rather low loss and leakage conductivity, but also restrains the thermal interfacial resistance via increased interfacial compatibility and interactions. The concurrent enhancement effect in the ε and TC but low loss of the composites is more evident in the crystalline SiO2 interlayer with a high TC compared with amorphous one. These results provide insight into the exploration of composite nanodielectrics with large TC and ε but low loss for applications in electrical power systems. Highlights: Core@shell structured β‐SiCw@SiO2/PVDF were obtained by a facile oxidation.The great reduction in both loss and conductivity is attributed to the SiO2 shell.Crystalline SiO2 shell can improve the composites' thermal conductivity.The SiO2 shell prevents long‐range carrier migration. [ABSTRACT FROM AUTHOR]

Exploring polymer composites with a high dielectric constant (ε′) and breakdown strength (Eb), low dissipation factor (tanδ), as well as a high thermal conductivity (TC) is of crucially important thanks to their potential applications in modern electronics. Herein, in this paper, two kinds of core–shell-structured Si particles, i.e., Si@SiO2, Si@SiO2@PS, were prepared by high temperature oxidation and polystyrene (PS) coating and incorporated into PVDF (poly(vinylidene fluoride)). The results indicate that both the fillers' kinds and loading have obvious influences on dielectric and thermal properties of the composites. The SiO2 interlayer between the Si and PVDF matrix remarkably suppresses the loss and reduces leakage conductivity, whereas encapsulation of Si@SiO2 with a PS shell further inhibits the loss and conductivity, and the organic PS interlayer enhances the interfacial compatibility and promotes the fillers' homogeneous dispersion in PVDF, therefore improving the Eb of the composites. More importantly, the PVDF composites with 50 wt.% of Si@SiO2@PS show good comprehensive performances: ε′ of 66.6 but tanδ of 0.04 at 100 Hz, Eb of 2.48 kV/mm as well as a high TC of 1.0 W/m K. The prepared Si@SiO2@PS/PVDF composites show promising potential applications in microelectronics and electrical industries. [ABSTRACT FROM AUTHOR]

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 conductivity (TC) but low dielectric loss polymer composites. The results confirm the formation of a layer PS shell outside of the f-Cu, and indicate that the PVDF composites with f-Cu@PS particles exhibit superior dielectric properties compared with pristine f-Cu/PVDF. The improved dielectric performance can be attributed to the insulating PS interlayer preventing the f-Cu from direct contact with each other and meanwhile hindering the long-range electron migration. The dielectric properties of composites can be tuned through finely tailoring the PS shell' thickness. Additionally, the f-Cu@PS/PVDF composites display slightly higher TC than the raw f-Cu/PVDF, owing to the suppressed thermal interfacial resistance and improved interfacial compatibility between the fillers and matrix. The obtained f-Cu@PS/PVDF composites with enhanced high-k and TC but low loss are promising materials for potential applications in microelectronic and electrical industries. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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, loading, and its reaction time on the dielectric properties of the nanocomposites. Compared with the pristine GO/PVDF, the GO@PVP/PVDF nanocomposites show an improvement of the filler dispersion, and significantly suppressed conductivity and loss. Activation energies of GO/PVDF and GO@PVP/PVDF nanocomposites are calculated as 1.247 eV and 0.435 eV, respectively, indicating that the presence of PVP layer on the GO surface reduces the relaxation activation energy and makes the relaxation occurrence at low temperatures. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Epoxy composites incorporated with three kinds of hybrid aluminum (Al) particles with binary size distribution, that is, [1 μm/45 μm], [1 μm/18 μm], and [18 μm/45 μm], respectively, were prepared, and the mechanical and dielectric properties of the hybrid Al/epoxy composites were investigated as a function of relative weight fraction of smaller-size Al (Ws) of hybrid Al particles at a total filler content of 50 wt%. The mechanical and electrical properties of the hybrid Al/epoxy composites are found to mainly depend on the type of hybrid filler and the Ws and can be tuned by changing the Ws. The maximum tensile strength and elongation at break of the composites appear at an optimal Ws. Furthermore, the dielectric permittivity, dielectric breakdown strength, and volume resistivity of the hybrid Al/epoxy composites also exhibit the similar variations as the mechanical properties with the Ws. The obvious enhancements in the physical properties can be ascribed to the synergistic effect of hybrid particles in the matrix at the optimal Ws, which endows the composites with better mechanical and dielectric properties. So, the results give a facile strategy to enhance the dielectric and mechanical properties of the composites by choosing a proper Ws at a fixed total filler loading. [ABSTRACT FROM AUTHOR]

This article reviewed the latest research progress in thermally conductive polymers/ graphene composites and emphatically discussed the influence factors on thermal conductivity of reinforced polymers, which included the structure and surface functionalization of graphene, the core-shell structural composites or hybrids with graphene as well as their synergistic effect, graphene foams and their processing technologies. Moreover, the current problems in the industrialization of thermally conductive polymers/graphene composites were summarized and their development direction in future was prospected. [ABSTRACT FROM AUTHOR]

Epoxy (EP) resin based nanocomposites with aluminum (Al) nanoparticles were prepared by solution method, with ultrasonic assisted dispersion followed by hot‐pressing methods. The dielectric permittivity, loss tangent, conductivity, and electric modulus of the nanocomposites were investigated by dielectric spectroscopy measurements in a wide frequency range from 1 to 107 Hz at temperatures from −20°C to 200°C. For all samples, the dielectric permittivity, dissipation factor, and electric conductivity increase with increasing temperature due to enhanced chain mobility above glass transition temperature (Tg). Broadband dielectric spectroscopy shows the multiple dielectric processes in the Al/epoxy nanocomposites corresponding to interfacial polarization (IP), α‐relaxation, and ionic conductivity, respectively. IP is detected at low frequencies and high temperatures. A primary α‐relaxation process is found at near Tg at the middle frequencies and the intermediate dipolar effect (IDE) is presented at high frequencies. The mechanisms responsible for dielectric relaxation, conductivity process, and electric modulus response have been discussed in detail. POLYM. COMPOS., 39:887–894, 2018. © 2016 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Epoxy (Ep) resin modified with carboxyl-terminated polybutadiene (CTPB) liquid rubber was investigated in this study. Fourier transform infrared verified the chemical reactions between oxirane ring of Ep and carboxyl groups of CTPB using benzyldimethylamine as a catalyst. The decrease of the thermal stability could be due to the lower thermal stability of CTPB compared with that of pure Ep. The mechanical results showed that CTPB-modified Ep was superior to that of the pure Ep, and the best overall mechanical properties were normally achieved with 20 phr of CTPB content. The impact strength of the system containing 20 phr CTPB increased by 193% due to the two-phase nature of the system. The dielectric constant and dissipation factor of the modified Ep obviously declined with the CTPB content compared with pure Ep, for instance, the dissipation factor remained less than 0.02 in wide frequency range. [ABSTRACT FROM AUTHOR]

The broadband dielectric spectroscopy was carried out in the frequency range of 1–107 Hz at the −20–200°C range to investigate the effect of temperature on the dynamic thermal–dielectric behavior of the aluminum (Al)/epoxy composite. The epoxy composites with core-shell–structured Al particles were prepared by solution method. The results show that the dielectric permittivity of the composites increased smoothly with a rise of filler content and reduced with an increase in frequency at room temperature. While the dielectric loss and conductivity still remained at low level owing to the nanoscale alumina insulating shell serving as a barrier layer to control the dielectric loss. The dielectric permittivity, dissipation factor, and conductivity of the composites increased with temperature and exhibited an abrupt rise around the glass transition temperature (Tg). A large increase in the dissipation factor and conductivity with temperature is attributed to the direct current conduction of thermal-activated charge carriers resulting from pure epoxy above Tg. The observed temperature-dependent dielectric relaxations of the composites indicated a thermally activated behavior of the relaxation time of epoxy chain segments. [ABSTRACT FROM AUTHOR]

Four energetic salts (including two ionic liquids) based on 2-(dimethylamino)-N,N,N-trimethylethanaminium and N,N′-dialkyl-N,N,N′,N′-tetramethylethane-1,2-diaminium was prepared and characterized by1H- and13C-NMR, infrared and Raman spectroscopies, and elemental analysis. Their physicochemical properties such as melting and decomposition temperatures, density, viscosity, heat of formation, detonation performance, and specific impulse were measured or calculated. With thermal stability up to 200°C, the resulting ionic liquids show densities from 1.02 to 1.19 g cm−3and heats of formation from 85.1 to 154.4 kJ mol−1. Moreover, 2-(dimethylamino)-N,N,N-trimethylethanaminium dicyanamide is hypergolic with the oxidizer (100% HNO3) and exhibits potential as a green fuel for bipropellants. [ABSTRACT FROM AUTHOR]

Cu(C10H11O2N2)2(1) and [Zn(C10H12O2N2)2(H2O)2](NO3)2(2) were synthesized and characterized by elemental analysis, FT-IR spectra, UV-Vis absorption spectroscopy, and X-ray single-crystal diffraction. Both complexes show distorted octahedral geometry. In1, Cu(II) is coordinated by four oxygen atoms from four ligands and two nitrogen atoms from two ligands. In2, Zn(II) is coordinated by two oxygen atoms and two nitrogen atoms from two ligands, and two water molecules. The crystal structures suggest that original ligand o-carboxybenzaldehyde salicyloylhydrazone (C15H12O4N2) changed into acetone salicyloylhydrazone (C10H12O2N2). The TG-DTG curves of these complexes indicate two different decomposition processes.1and2display catalytic activities to decomposition of hydrogen peroxide. Interaction between the complexes and DNA studied by UV-Vis titration shows the insert interaction. [ABSTRACT FROM PUBLISHER]

Flaky Cu ( f -Cu) particles coated with various thickness of silica (SiO 2 ) were incorporated into poly(vinylidene fluoride) (PVDF) to investigate the effects of SiO 2 coating layer and its thickness on dielectric properties of the composites. The morphological and dielectric properties of the composites were characterized. The results indicate that the SiO 2 coating layer significantly affects the electrical properties of f -Cu@SiO 2 and f -Cu@SiO 2 /PVDF, and that the PVDF composites with f -Cu@SiO 2 particles exhibit superior dielectric properties compared with raw f -Cu. Dissipation factors (tanδ) of the f -Cu@SiO 2 /PVDF are remarkably suppressed and reduced to rather low level owing to the presence of SiO 2 shell which serves as an interlayer between the f -Cu particles preventing them from contacting with each other. Furthermore, the effect of suppression on tanδ tends to be more prominent as the thickness of SiO 2 coating layer increases. The as-prepared composites possess high dielectric constant and low tanδ, making them promising for the industrial application as embedded capacitors. [ABSTRACT FROM AUTHOR]

Hierarchical structural design has been verified as a feasible strategy to fabricate effective electromagnetic wave (EMW) absorbers, so we designed hierarchical core-sheath composites with magnetic particles and dielectric layers. In this work, a hierarchical structure of carbon fiber (CF)@Fe 3 O 4 @MoS 2 (CPDF7-M) was prepared by introducing Fe 3 O 4 and depositing MoS 2 layers on the surface of fibers. Due to the synergistic effects from the CF@Fe 3 O 4 increasing the conductive and magnetic loss and the outer MoS 2 layers improving the impedance matching, the optimal reflection loss ( R L ) value was -63.1 dB at 2.7 mm and the effective absorption bandwidth (EAB) was 9.1 GHz covering the X and Ku band. Moreover, the EAB values were adjusted with a specific MoS 2 loading at different thicknesses, which provided the necessary reference for the construction of efficient and flexible absorbers in the EMW absorption fields.