Core-shell Filler Research Articles

Epoxy composites with ceramic core–shell fillers for thermal management in electrical devices

In this work, a novel core–shell material has been manufactured in order to enhance the thermal conductivity of epoxy‐based composites. The polymer derived ceramics technique has been used to produce fillers whose core is composed of a standard material – silica, and whose outer layer consists of a boron nitride or silicon nitride shell. The synthesized filler was characterized by infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy coupled with an energy dispersive spectroscopy analysis. The successful formation of core–shell structure was proven. Composite samples based on an epoxy resin filled with 31 vol% of synthetized core–shell filler have been investigated in order to determine the effective thermal conductivity of the modified system. The resulting core–shell composite samples exhibited improvements in thermal conductivity of almost 30% in relation to standard systems, making them a promising material for heat management applications. Additionally, the temperature dependence of the thermal conductivity was investigated over a broad temperature range indicating that the thermal behavior of the composite with incorporated core–shell filler is stable. This stability is a crucial factor when considering the potential of using this technology in applications such as electronics and power systems. Copyright © 2017 John Wiley & Sons, Ltd.

Highly foldable PANi@CNTs/PU dielectric composites toward thin-film capacitor application

In this work, we synthesized a core-shell conductive filler of carbon nanotubes covered with polyaniline (PANi@CNTs), which showed good dispersibility to prepare highly flexible and foldable dielectric PMCs (PANi@CNTs/PU). The dielectric, mechanical, and thermal properties of the PANi@CNTs/PU composites were investigated. The mechanical flexible and foldable PANi@CNTs/PU composites could be promising dielectric material for preparing thin film capacitors.

Core–shell SiC/SiO2 whisker reinforced polymer composite with high dielectric permittivity and low dielectric loss

A polymer composite with high dielectric permittivity and low dielectric loss was successfully fabricated by embedding core–shell structure whisker in polymer matrix. The novel core–shell structure of silicon carbide/silicon dioxide whisker (SiC/SiO2-W) filler was prepared via a one-step air-exposure calcination treatment of original SiC whisker (SiC-W). The effects of semiconductor-insulator core–shell filler on morphology structure, mechanical properties, dielectric and electrical properties of poly(vinylidene fluoride) (PVDF) composite were investigated. Compared with SiC-W/PVDF composite, SiC/SiO2-W/PVDF composite shows stronger mechanical properties, and dramatically suppressed dielectric loss and conductivity while remains high dielectric permittivity. Furthermore, the dielectric and electrical properties of the composite can be further optimized by adjusting the shell thickness. Especially, the composite with SiO2 thickness of 6–7nm presents the best integrative dielectric and electrical properties, which exhibits a dielectric permittivity of 2230.3 and a dielectric loss of 0.86 at 100Hz.

Functional composites with core–shell fillers: I. Particle synthesis and thermal conductivity measurements

Filled epoxy composites are broadly used in electronic and power devices as an electrical insulation. It is of importance to achieve efficient heat dissipation in such devices due to fact that thermal properties have a strong influence on their proper operation. For this reason, the modification of standard filler materials, such as silica or alumina, can give a promising solution. In this work, a novel core–shell material has been proposed and manufactured by means of a carbothermal reduction and nitridation process. The obtained fillers are made of a standard material which is covered by the high thermally conductive shell. The synthesized fillers were characterized by means of X-ray diffraction, and scanning electron microscopy coupled with elemental analysis. The composite samples based on epoxy resin filled with the manufactured core–shell fillers have been investigated in order to determine their effective thermal conductivity. The obtained composite samples exhibited a significant improvement in the thermal conductivity, represented by a 63 % relative increase. The obtained results show the potential for the novel core–shell fillers to be applied for the electrical insulation with the enhanced thermal conductivity.

Thermal conductivity prediction of magnetic composite sheet for near-field electromagnetic absorption

The magnetic composite sheets were designed by using core-shell structured magnetic fillers instead of uncoated magnetic fillers to resolve concurrently the electromagnetic interference and thermal radiation problems. To predict the thermal conductivity of composite sheet, we calculated the thermal conductivity of the uncoated magnetic fillers and core-shell structured fillers. And then, the thermal conductivity of the magnetic composites sheet filled with core-shell structured magnetic fillers was calculated and compared with that of the uncoated magnetic fillers filled in composite sheet. The magnetic core and shell material are employed the typical Fe-Al-Si flake (60 μm × 60 μm × 1 μm) and 250 nm-thick AlN with high thermal conductivity, respectively. The longitudinal thermal conductivity of the core-shell structured magnetic composite sheet (2.45 W/m·K) enhanced about 33.4% in comparison with that of uncoated magnetic fillers (1.83 W/m·K) for the 50 vol. % magnetic filler in polymer matrix.

Polymer composite electrolytes having core-shell silica fillers with anion-trapping boron moiety in the shell layer for all-solid-state lithium-ion batteries.

Core-shell silica particles with ion-conducting poly(ethylene glycol) and anion-trapping boron moiety in the shell layer were prepared to be used as fillers for polymer composite electrolytes based on organic/inorganic hybrid branched copolymer as polymer matrix for all-solid-state lithium-ion battery applications. The core-shell silica particles were found to improve mechanical strength and thermal stability of the polymer matrix and poly(ethylene glycol) and boron moiety in the shell layer increase compatibility between filler and polymer matrix. Furthermore, boron moiety in the shell layer increases both ionic conductivity and lithium transference number of the polymer matrix because lithium salt can be more easily dissociated by the anion-trapping boron. Interfacial compatibility with lithium metal anode is also improved because well-dispersed silica particles serve as protective layer against interfacial side reactions. As a result, all-solid-state battery performance was found to be enhanced when the copolymer having core-shell silica particles with the boron moiety was used as solid polymer electrolyte.

Energy storage in ferroelectric polymer nanocomposites filled with core-shell structured polymer@BaTiO3 nanoparticles: understanding the role of polymer shells in the interfacial regions.

The interfacial region plays a critical role in determining the electrical properties and energy storage density of dielectric polymer nanocomposites. However, we still know a little about the effects of electrical properties of the interfacial regions on the electrical properties and energy storage of dielectric polymer nanocomposites. In this work, three types of core-shell structured polymer@BaTiO3 nanoparticles with polymer shells having different electrical properties were used as fillers to prepare ferroelectric polymer nanocomposites. All the polymer@BaTiO3 nanoparticles were prepared by surface-initiated reversible-addition-fragmentation chain transfer (RAFT) polymerization, and the polymer shells were controlled to have the same thickness. The morphology, crystal structure, frequency-dependent dielectric properties, breakdown strength, leakage currents, energy storage capability, and energy storage efficiency of the polymer nanocomposites were investigated. On the other hand, the pure polymers having the same molecular structure as the shells of polymer@BaTiO3 nanoparticles were also prepared by RAFT polymerization, and their electrical properties were provided. Our results show that, to achieve nanocomposites with high discharged energy density, the core-shell nanoparticle filler should simultaneously have high dielectric constant and low electrical conductivity. On the other hand, the breakdown strength of the polymer@BaTiO3-based nanocomposites is highly affected by the electrical properties of the polymer shells. It is believed that the electrical conductivity of the polymer shells should be as low as possible to achieve nanocomposites with high breakdown strength.

Novel Organically Modified Core-Shell Clay for Epoxy Composites-"SOBM Filler 1".

Preparation of a novel organically modified clay from spent oil base drilling mud (SOBM) that could serve as core-shell clay filler for polymers is herein reported. Due to the hydrophilic nature of clay, its compatibility with polymer matrix was made possible through modification of the surface of the core clay sample with 3-aminopropyltriethoxysilane (3-APTES) compound prior to its use. Fourier transform infrared (FT-IR) spectroscopy was used to characterize clay surface modification. Electron dispersive X-ray diffraction (EDX) and scanning electron microscopy (SEM) were used to expose filler chemical composition and morphology, while electrophoresis measurement was used to examine level of filler dispersion. Results show an agglomerated core clay powder after high temperature treatment, while EDX analysis shows that the organically modified clay is composed of chemical inhomogeneities, wherein elemental compositions in weight percent vary from one point to the other in a probe of two points. Micrographs of the 3-APTES coupled SOBM core-shell clay filler clearly show cloudy appearance, while FT-IR indicates 25% and 5% increases in fundamental vibrations band at 1014 cm−1 and 1435 cm−1, respectively. Furthermore, 3-APTES coupled core-shell clay was used to prepare epoxy composites and tested for mechanical properties.

Fabrication, structure, and property of epoxy-based composites with metal–insulator core–shell structure fillers

Abstract

Computational study of dielectric composites with core-shell filler particles

Phase field modeling and computer simulation is employed to study dielectric composites with core-shell filler particles for high-energy-density applications. The model solves electrostatic equations in terms of polarization vector field in reciprocal space using fast Fourier transform technique and parallel computing algorithm. Composites composed of linear constituent phases (matrix, core, and shell materials) of different dielectric constants are considered. Inter-phase boundary conditions are automatically taken into account without explicitly tracking inter-phase interfaces in the composites. The core-shell structures of filler particles are systematically investigated in terms of shell thickness and dielectric constant with respect to core size and matrix dielectric constant, respectively. The effects of filler particle size, shape, and orientation are considered. It is found that core-shell structures of filler particles provide effective means to mitigate local electric field concentration in dielectric composites, improving dielectric breakdown strength and energy density of the composites. Optimal design of core-shell filler particles requires low shell dielectric constant and thick shell coating as compared to core material and core size, respectively.

Filler engineering for papermaking: Comparison with fiber engineering and some important research topics

Fibers and fillers are important raw materials for the preparation of paper products. Similar to fiber engineering, filler engineering for papermaking has become an active research area. There are similarities as well as differences between engineering involving each of these classes of materials. There are differences in such aspects as the nature of materials to be engineered, applicable engineering methods, and engineerablity of the material surfaces. The co-development of fiber engineering and filler engineering can potentially provide many benefits to the papermaking industry. For filler engineering, the relevant research topics broadly can include fibrous filler engineering, hollow/porous filler engineering, acid-stabilization of calcium carbonate fillers, surface encapsulation of naturally occurring polymers or their derivatives, preflocculation, precoagulation, cationic modification, filler/size hybrid formation, organic filler engineering, using combinations of different types of available fillers, multilayer deposition modification, modification with polymer latexes or dispersants, physical modification, mechanical modification, surface functionalization, fines-filler composite/hybrids or fiber-filler composite/ hybrid formation, in-situ polymerization modification, surface grafting, physical treatment in the presence of polymeric additives, filler precipitation, and core-shell composite filler engineering.

Modification of styrene-isoprene-styrene triblock copolymer with a core-shell filler

Mechanical properties of composite materials based on triblock poly(styrene-b-isoprene--b-styrene) copolymers (SIS) and modified with two different grades of core-shell fillers (core -silsesquioxane microgel, shell - grafted polystyrene, particle diameters 15.7 and 17.7 nm, respectively). Significant improvement - almost 60 % increase in tensile strength, relative elongation at break reaching 700 % - was observed in case of a high molecular weight (M w ) copolymer at the maximal filler concentration of about 2 wt. % and longer chains of the polystyrene-shell. The rheological properties of nanocomposites differed with respect to the non-modified copolymer - softening of the material at higher temperatures was noticed.

Study of nanocomposites containing core-shell fillers with rigid nano-SiO2 core in PMMA matrix

Study of nanocomposites containing core-shell fillers with rigid nano-SiO2 core in PMMA matrix

Microwave absorbing materials using Ag–NiZn ferrite core–shell nanopowders as fillers

Silver nanoparticles coated with Ni0.5Zn0.5Fe2O4 spinel ferrites, forming a core–shell structure, were synthesized by utilizing hydrothermal method at different ferrite/silver ratio (ferrite/silver=6/1, 4/1, 2/1, 1/1, 1/6) and introduced into polyurethane matrix to be a microwave absorber. The complex permittivity (ε',ε'') and permeability (μ',μ'') of absorbing composite materials consisted of ferrite/silver core–shell nanopowders and polyurethane were measured in the frequency range of 2–15GHz. The reflection loss and matching frequency were calculated from measured data using theory of the absorbing wall for different ferrite/silver ratios. It was found that the matching frequency for reflection loss exceeded a satisfactory −25dB at 9.0GHz for using NiZn ferrite as a filler shifts to higher frequencies (10.9–13.7GHz) as the ferrite/silver ratio of core–shell nano-filler decreased from 6/1 to 2/1. The present result demonstrates that microwave absorbers using ferrite/silver core-shell filler can be fabricated for the applications over 9GHz, with reflection loss more than−25dB for specific frequencies, by controlling the ferrite/silver ratio of the core–shell nano-fillers in the composites.

Effect of filler size and surface condition of nano-sized silica particles in polysiloxane coatings

Silica nanoparticles with different sizes (from 14 to 60 nm) and different surface modifications (hydrophobic treatment, core–shell structures) are synthesized as colloids and introduced at different concentrations in polysiloxane type coatings in order to perform indentation and scratch experiments. The adding of fillers increases the Young's modulus of the coatings but decreases the 200-μm scratch resistance. The weakness of matrix–filler interactions has no significant effect on the Young's Modulus, but also alter the 200-μm scratch resistance. Core–shell fillers, i.e. silica particles coated with a low modulus polymeric shell, can be equivalent to non modified silica particles as far as the 200-μm scratch test is concerned, but they weakly improve the Young's modulus of the Glymo films, suggesting a poor resistance of filled coatings to small scratches.