Core-shell Filler Research Articles

Core-Shell Engineered Fillers Overcome the Electrical-Thermal Conductance Trade-Off.

The rapid development of modern electronic devices increasingly requires thermal management materials with controllable electrical properties, ranging from conductive and dielectric to insulating, to meet the needs of diverse applications. However, highly thermally conductive materials usually have a high electrical conductivity. Intrinsically highly thermally conductive, but electrically insulating materials are still limited to a few kinds of materials. To overcome the electrical-thermal conductance trade-off, here, we report a facile Pechini-based method to prepare multiple core (metal)/shell (metal oxide) engineered fillers, such as aluminum-oxide-coated and beryllium-oxide-coated Ag microspheres. In contrast to the previous in situ growth method which mainly focused on small-sized spheres with specific coating materials, our method combined with ultrafast joule heating treatment is more versatile and robust for varied-sized, especially large-sized core-shell fillers. Through size compounding, the as-synthesized core-shell-filled epoxy composites exhibit high isotropic thermal conductivity (∼3.8 W m-1 K-1) while maintaining high electrical resistivity (∼1012 Ω cm) and good flowability, showing better heat dissipation properties than commercial thermally conductive packaging materials. The successful preparation of these core-shell fillers endows thermally conductive composites with controlled electrical properties for emerging electronic package applications, as demonstrated in circuit board and battery thermal management.

CoFe2O4-BaTiO3 core-shell-embedded flexible polymer composite as an efficient magnetoelectric energy harvester

Flexible magnetoelectric (ME) generators gained immense interest due to the broad applications in wearable and Internet of Things (IoT)-based devices. The key to achieving high energy conversion performance of 0–3 type ME composite films is the prevention of filler aggregation in the polymer matrix and accessing the full potential of intrinsic properties of filler. To achieve high performance, a flexible ME composite film was fabricated by homogeneous distribution of magnetostrictive CoFe2O4-BaTiO3 core-shell (CBCS) fillers into piezoelectric polyvinylidene fluoride (PVDF) polymer. The ME composite film generates an enhanced energy conversion efficiency by optimizing the shell thickness of CBCS and maximizing the electroactive β-phase at the BaTiO3 shell-PVDF interfacial region. The observed ME coefficient of the film reached up to 710 mV/cm∙Oe. Multiphysics simulations based on the finite element analysis were adopted to investigate the role of BaTiO3 shell thickness on the performance of ME film. This study paves the way to achieve higher filler loading content in the ME composite films to develop an efficient, flexible ME generator for eco-friendly permanent power sources.

Experimental studies of absorption properties of polymer composites based on core–shell fillers with hybrid shells

Microwave absorbing properties of polymer composites based on core-shell fillers with ultra-high molecular weight polyethylene core and GNP-carbonyl iron, GNP-cobalt oxide Co3O4, GNP-micro-sized MoS2, and GNP-barium hexaferrite BaFe12O19 hybrid shells were investigated in the frequency range of 40–60 GHz. Scanning electron microscopy sizing of the constituent particles in the composites showed the characteristic dimension of micron for Fe particles while Co3O4 and BaFe12O19 particles are found to be much smaller (nanometer-sized); MoS2 particles mostly form agglomerates and have diverse shapes and varying from 70 nm to 3–4 μm sizes. The shielding properties of composite materials (CMs) with 30 wt % Fe (Co3O4,MoS2, BaFe12O19) + C wt. % GNP/PEwith the GNP concentration c in the range of 1–5 wt% of nanocarbon are weakly frequency dependent. But the analyzed composites interaction with the electromagnetic radiation reveals significant influence of both the nanocarbon content and the additional dielectric or magnetic component type in the shell materials on the shielding parameters. The calculated values of the effective absorption coefficients Aeff for the investigated composites with different hybrid shells have shown that at 3 wt % GNP in the composite with 30 % Co3O4Aeff increases greatly and reaches 0.75, exceeding the correspondent values for the 30%BaFe12O19+GNP system. The primary contribution of absorption to the shielding characteristics of the investigated polymer CMs based on core-shell fillers with hybrid shells constitutes good prospects of applications.

Sandwich-structured relaxor ferroelectric nanocomposite incorporated with core-shell fillers for outstanding-energy-storage capacitor application

Significance reduction in characteristic dimension and weight of energy conversion system is urgently needed for developing outstanding-energy-density dielectric materials. For conventional single-layer configuration, huge enhancments in dielectric constant (K) was achieved in polymer nanocomposite system by the introduction of high-K fillers at the expense of the breakdown strength (Eb). Herein, we reported that the crafting of core-shell structured BT@TP NPs and BN@TP NSs was used as the nanofillers to achieve a sandwich-structured nanocomposite that one high-K layer of BT@TP-TP was sandwiched by two high-Eb layers of BN@TP-TP. In comparison to unmodified BT NPs and BN NSs, the crafting of core-shell BT@TP NPs and BN@TP NSs is beneficial for improving dispersion quality and thus endure high-Eb in the matrix P(VDF-TrFE-CTFE) (TP). The newly designed sandwich-structured polymer nanocomposites are capable of balancing the contradict factors of high-K and high-Eb. In addition, the enhanced interfacial polarization was directly detected by piezoelectric force microscopy, and the formation of electric trees was well displaced by FEA simulation. Outstandingly, the sandwich-structured nanocomposite 3BN@TP-TP/4BT@TP-TP/3BN@TP-TP exhibits a discharged energy density of 10.3 J/cm3 and dicharged-charged efficiency of 71.2 % at a field of 270 MV m−1, which is 5-fold higher than that of commercial BOPP.

Vertically-aligned Zn2SnO4–Fe3O4 core-shell microsphere-based thermal interface material with high thermal conductivity

In this study, we successfully fabricated vertically aligned Zn2SnO4 (ZTO)-Fe3O4 core-shell microsphere (MS)-based thermal interface material (TIM) formed by an external magnetic field. The thermal conductivity of the randomly distributed ZTO-Fe3O4 core-shell/PDMS-based TIMs was enhanced with increasing loading fraction of fillers and TIM with 25 vol % fillers 2.5 times effectively reduced GPU temperature compared to bare PDMS sample. Moreover, the vertically-aligned 25 vol% ZTO-Fe3O4 core-shell filler embedded TIM additionally reduced temperature by 5.1 % and 24.1 % compared to randomly dispersed ZTO-Fe3O4 MS TIMs and bare PDMS, respectively. Experimental results showed that the ZTO-Fe3O4 TIMs can be used as high thermal conductivity TIM filler, and vertically aligned core-shell filler can maximize thermal conductivity by forming an effective thermal path from bottom to top. The theoretical analysis results obtained using COMSOL Multiphysics 5.6 simulation corresponded well with experimental ones. Our suggested vertically aligned ZTO-Fe3O4 core-shell-based TIM can provide an effective heat dissipation path for advanced semiconductor devices with a wide range of applications.

Thermal conductivity and dielectric properties of EP composites filled by one-dimensional core-shell structured h-BN@SiO2 fibers

With the miniaturization and integration of modern high-power electronic devices, heat accumulation has become a key issue affecting their performance and reliability, which puts forward higher requirements for the thermal conductivity of polymer materials. In this study, boron nitride (h-BN) was dispersed into silica sol, and high aspect ratio core-shell fillers (h-BN@SiO2) were prepared by electrospinning. Then h-BN@SiO2/epoxy resin (EP) composites were prepared by hot pressing. Owing to the macroscopic and microscopic “double network” conduction paths constructed by h-BN@SiO2 fillers, the in-plane thermal conductivity (λ||) of h-BN@SiO2-Ⅲ/EP composites is 6.719 Wm−1K−1, which is 27 times that of EP, and the out-of-plane thermal conductivity (λ⊥) is 0.698 Wm−1K−1, which is 4 times that of EP. The simulation and the classical thermal conductivity model verify that the new designed filler in this paper has advantages over the traditional filler in terms of heat transfer. More importantly, the prepared composites also maintain excellent electrical insulation and dielectric properties, which provides a new idea for the preparation of high thermal conductivity electrical insulation composites.

A novel three-layer woven fabric composite reinforced by (polyaniline + carbonyl iron) core-shell/carbonyl iron/polyaniline fillers for high-performance broadband radar absorbing structure

One of the most important applications of electromagnetic wave absorption is in stealth aircrafts and electromagnetic protection of avionic systems. The main limitations in the design of these structures are aerodynamics, thickness or weight, mechanical strength, manufacturing process, and reasonable cost. In this study, a novel three-layer woven fabric composite laminate (with a total thickness of about 3 mm) is proposed which each layer is reinforced by individual polyaniline, carbonyl iron, or (PANI + CI) core-shell fillers. The developed Non-dominated Sorting Genetic Algorithm II optimization algorithm suggests the stacking sequence of layers, the appropriate thickness of each layer, and the filler weight fraction in each layer to achieve a broadband absorption. Due to using both dielectric and magnetic absorbing fillers, this structure shows well-impedance matching and approximately absorbs 80% of the X-band (8-12 GHz) electromagnetic waves. The maximum reflection loss is about −14dB. Finally, the effect of the addition of absorbent particles on the mechanical properties has been investigated. Experimental results showed that the tensile modulus and strength decrease by about 21.5% and 20.6%, respectively, and the flexural modulus and strength reduce by 21.7% and 19.7%, respectively. However, the (PANI + CI) core-shell filler can be introduced as a high performance absorber filler because it suggests maximum reflection loss with low weight fraction compared to other fillers and consequently the minimum reduction in mechanical properties.

Excellent dielectric and actuated strain properties in CCTOx@BT(1−x)@KH560/NR system via a tunable BaTiO3 interfacial buffer layer

AbstractDielectric elastomers (DEs) require high drive voltages to obtain large actuated strain, which limits their application in the biological field. In this work, we enhanced the dielectric properties of natural rubber (NR) composites by using core–shell structured (CaCu3Ti4O12)x@(BaTiO3)(1−x) (CCTOx@BT(1−x)) high‐dielectric particles with an buffer layer, and adjusted the thickness of the BT buffer layer by adjusting the addition of titanate during the preparation process, and then observed the relationship between the dielectric properties of NR composites and the thickness of the BT buffer layer. In addition, we modified the CCTO0.75@BT0.25 fillers surface with silane coupling agent KH560 to enhance the interfacial interaction between the inorganic fillers and polymeric matrix to obtain better dispersion and greater dielectric properties. As a result of the optimization of the CCTO0.75@BT0.25@KH560 structure, the actuated strain performance is greatly improved. The actuated strain of 5 per hundred rubber (phr) CCTO0.75@BT0.25@KH560/NR is 16.3% at 74.03 kV/mm, which is 6.52 times higher than the actuated strain obtained by NR (2.5%) at 50.28 kV/mm. This work presents a method to optimize the structure of core–shell fillers by modulating the buffer layer, and provides a new idea for further preparation of dielectric elastomer materials with large actuated strain at low voltage.

Excellent energy storage and discharge performances realized in polymer nanocomposites by introducing core-shell antiferroelectric fillers and constructing bilayer interfaces

Polymer composites filled with one or two-dimensional ferroelectrics possess large discharged energy density (Ue), but deliver low efficiency (η) by reason of their high remnant electric displacement (Dr), and require demanding process conditions. To solve these issues, we have proposed Pb,La(Zr,Sn,Ti)O3 (PLZST)@Al2O3 nanoparticles (NPs)/polyimide (PI)-PLZST@Al2O3 NPs/poly(vinylidene fluoride-hexafluoropropylene) P(VDF-HFP) bilayer nanocomposites. PLZST antiferroelectrics exhibit small Dr and high maximum electric displacement (Dmax), and the Al2O3 shell possesses near dielectric constant with P(VDF-HFP) and PI, which can improve the Dmax, increase the breakdown strength (Eb), and refine D-E loops, and simple preparation method of the NPs is beneficial for the industrial production. The bilayer structure combines advantages of PLZST@Al2O3 NPs/PI with slim D-E loops and small Dr, and PLZST@Al2O3/P(VDF-HFP) possessing high Dmax. Besides, large dielectric differences between adjacent layers inhibit electrical tree growth, thus further causing improved Eb, which is confirmed by electrical tree evolving simulations. Consequently, the bilayer nanocomposites display an ultrahigh Ue of 21.89 J/cm3, which surpasses those of currently reported polymer nanocomposites filled with NPs, and large η of 78.2%. More encouragingly, it manifests ultrafast discharge time of 18.8 ns and ultrahigh power density of 28.3 MW/cm3, meaning its great application prospect in pulse power systems.

Al@SiO2 Core-Shell Fillers Enhance Dielectric Properties of Silicone Composites.

Over the past decade, there has been significant interest in polysiloxane-based dielectric elastomers as promising soft electroactive materials. Nevertheless, the natural low permittivity of polydimethylsiloxane has limited its practical applications. In this study, we have developed silicone rubber/Al@SiO2 composites with a high dielectric constant, low dielectric loss, and high electrical breakdown strength by controlling the shell layer thickness and the content of the core-shell filler. We also investigated the dielectric behavior of the composites. The use of core-shell fillers has increased the Maxwell-Wagner-Sillars (MWS) relaxation process while reducing the dielectric loss of direct current conductance in silicone rubber composites. Moreover, the temperature dependence of the MWS relaxation time in the composites follows the Arrhenius equation. This strategy of increasing the permittivity of silicone composites through core-shell structural fillers can inspire the preparation of other high dielectric constant composites.

Features of the Microstructure and Thermoelectric Properties of Bi2Te2.7Se0.3 + Fe Composites with Core–Shell Filler Inclusions

Features of the Microstructure and Thermoelectric Properties of Bi2Te2.7Se0.3 + Fe Composites with Core–Shell Filler Inclusions

Patterns of effect of spark plasma sintering temperature on microstructure of thermoelectric composites based on Bi<sub>2</sub>Te<sub>2.1</sub>Se<sub>0.9</sub>Bi<sub>2 </sub>matrix with cobalt inclusions

Effect of spark plasma sintering temperature on the formation of Co filler particles in the Bi2Te2.1Se0.9 matrix has been examined. Owing to high-temperature diffusion redistribution of atoms in the matrix and filler materials and chemical interaction between these materials, in the Bi2Te2.1Se0.9 + 0.33 wt % Co, core–shell filler particles (Co@CoTe2) are formed. With increasing the sintering temperature, fraction of the “CoTe2 shell” in the particles increases, while fraction of the “Co core” decreases. This behavior is due to an increasing in the diffusion coefficient of Co in the Bi2Te2.1Se0.9 matrix with increasing in the sintering temperature. The concentration profiles of the Co distribution of in the Bi2Te2.1Se0.9 matrix, governed by diffusion, are well described using Fick’s second law for diffusion from a limited source of a diffusing substance. The diffusion coefficient of Co increases with increasing un the sintering temperature in accordance with the Arrhenius law and with an activation energy of ~0.61 eV.

Dendritic Structure-Inspired Coating Strategy for Stable and Efficient Solar Evaporation of Salinity Brine

Solar thermal evaporation has been widely used to tackle the problem of freshwater shortage. The strategy to improve the evaporative performance of solar thermal evaporation by simple and effective methods is still a challenge. Herein, a dendritic structure-inspired coating strategy based on the dendritic structure of polyvinyl alcohol (PVA) colloids firmly grabbing titanium trioxide (Ti2O3) on the outer surface as a light-absorbing core–shell filler was prepared using the non-solvo-induced precipitation method. Such a core–shell structure was then coated on the PVA sponge to prepare the solar photothermal composite Ti2O3/PVA@PVA, which gave full play to the photothermal advantage of the filler itself and can be long-term stable. Meanwhile, a three-dimensional Ti2O3/PVA@PVA evaporator with an embossment-sawtooth structure was prepared, which enhances light absorption to 98% in the whole solar spectrum through folds. Under 1.0 solar irradiation, the evaporation rate reaches as high as 2.66 kg m–2 h–1 and the evaporator illustrates good stability in simulated seawater for 7 consecutive days. Such a design showed good salt resistance and self-cleaning ability and could be reliably used for seawater desalination. In addition, the evaporator illustrates good adsorption capacity for dye molecules and heavy metal ions. This work provides new insights into the development of simple, efficient, environmentally friendly, sustainable, and salt-resistant solar evaporators.

Effect of flake silver-plated copper particles on the property enhancement of electrically conductive adhesives.

To impart conductivity and improve the shear performance of epoxy resin-based adhesives, a simple, environmentally friendly, and stable method was used to deposit silver on the surface of 5 μm flake copper particles as a conductive filler. The core-shell metal fillers were prepared by utilizing the autocatalytic properties of Cu without adding any reducing agent during the reaction. An epoxy curing agent (MeTHPA) was used as a curing agent for the crosslinking reaction with epoxy resin to form a supporting skeleton of conductive components. The structure of flake plated Cu@Ag particles was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). It was verified that a layer of compact and crystalline silver with a concave-convex characteristic was deposited on the surface of copper particles. This feature has a positive effect on improving the performance of silver-plated copper particles. The results show that the optimal curing condition of flake plated Cu@Ag particle-epoxy composite electrically conductive adhesives (ECAs) was 200 °C for 1 h, the resistivity of flake plated Cu@Ag particle-epoxy composite ECAs with a content of flake plated Cu@Ag particles above 55 wt% was less than 6 × 10-5 Ω m, and the maximum shear strength was 8 MPa. The flake plated Cu@Ag particle-epoxy composite ECAs prepared by this method have excellent properties and have very important application value for advanced electronic devices.

Core-Shell Engineering of Conductive Fillers toward Enhanced Dielectric Properties: A Universal Polarization Mechanism in Polymer Conductor Composites.

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.

SiC@BaTiO3 core-shell fillers improved high temperature energy storage density of P(VDF-HFP) based nanocomposites

The emerging industry has put forward stricter requirements for the operating temperature of electrostatic capacitors. Improving the high temperature breakdown strength is the key issue to enhance the thermal stability of polymer-based nanocomposites. In this study, the nanoparticles which is composed of high heat conductivity coefficient core (SiC) and high dielectric constant shell (BaTiO3) were prepared and used as fillers, with the purpose of improving breakdown strength (Eb) and discharged energy storage density (Udis) of P(VDF-HFP)-based nanocomposites at high temperature. Compared with the pure polymer, the composite films, especially the films with 7.5 wt% fillers, showed great enhancements in breakdown strength and discharged energy storage density at high temperature. The average Eb reached 1524.6 kV/cm at 120 °C, which was 1.84 times of the contrast. The Udis at 120 °C was 2.05 J/cm3 (1700 kV/cm), which increased by 569.4% than that of pure polymer (at 700 kV/cm, 0.36 J/cm3). The improvement of thermal performance and Young's modulus of materials was contributing to the enhancements of thermal breakdown strength and electromechanical breakdown strength at high temperature. This study provides an effective way to prepare dielectric composites for high-temperature environment application.

Polarization Structural Design in Core–Shell Fillers: An Approach to Significantly Enhance the Energy Storage Properties of BST/PVDF Composite Films

Polarization Structural Design in Core–Shell Fillers: An Approach to Significantly Enhance the Energy Storage Properties of BST/PVDF Composite Films

Biomimetic brain-like nanostructures for solid polymer electrolytes with fast ion transport

The intrinsic drawbacks of electrolytes and the growth of lithium dendrites limit the development of commercial lithium batteries. To address the aforementioned challenges, a novel biomimetic brain-like nanostructure (BBLN) solid polymer electrolyte was created by manipulating the shape of the incorporated nanoparticles. Our designed BBLN solid polymer electrolyte was created by incorporating spherical core-shell (UIO-66@67) fillers into polymer electrolyte, which is significantly different from traditional polymer-based composite electrolytes. UIO-66@67 spherical nanoparticles are highly favorable to eliminating polymer electrolyte stress and deformation during solidification, indicating a great potential for fabricating highly uniform BBLN solid polymer electrolytes with a substantial number of continuous convolutions. Furthermore, spherical nanoparticles can significantly reduce the crystalline structure of polymer electrolytes, improving polymer chain segmental movement and providing continuous pathways for rapid ion transfer. As a result, BBLN solid polymer electrolyte shows excellent ionic conductivity (9.2 × 10−4 S cm−1), a high lithium transference number (0.74), and outstanding cycle stability against lithium electrodes over 6500 h at room temperature. The concept of biomimetic brain-like nanostructures in this work demonstrates a novel strategy to enhance ion transport in polymer-based electrolytes for solid-state batteries.

High energy density of BaTiO3@TiO2 nanosheet/polymer composites via ping-pong-like electron area scattering and interface engineering

Dielectric substances exhibit great potential for high-power capacitors due to their high stability and fast charge–discharge; however, a long-term challenge is to enhance energy density. Here, we propose a poly(vinylidene fluoride) (PVDF) composite utilizing BaTiO3 nanoparticle@TiO2 nanosheet (BT@TO ns) 2D nanohybrids as fillers, aiming at combining the interfacial strategy of using a core–shell filler and the electron scattering of a 2D filler to improve the energy density. With 4 wt% filler, the composite possesses the largest breakdown strength (Eb) of 561.2 MV m−1, which is significantly enhanced from the 407.6 MV m−1 of PVDF, and permittivity of 12.6 at 1 kHz, which is a 23% increase from that of PVDF. A superhigh energy density of 21.3 J cm−3 with an efficiency of 61% is obtained at 550 MV m−1. The 2D BT@TO ns-filled composite exhibits a higher energy density than composites filled with core–shell 1D BT@TO nws or non-core–shell 0D BT, 1D TO, or 2D TO particles. The Eb and energy density improvements are attributed to the buffer layer-based interface engineering and enhanced area scattering of electrons caused by the 2D hybrids, an effect similar to that of a ping-pong paddle to scatter electric field-induced charge migrations in composites. Thus, an effective hybrid strategy is presented for achieving high-performance polymer composites that can be used in energy storage devices.

Investigation of microstructure evolution and strength mechanism of the Cu coated BNi-7 core-shell structure filler metal

In this paper, a novel method of using the Cu coated BNi-7 core-shell structured composite filler metals to braze was adopted to alleviate the residual thermal stress in the joints of Inconel 718. A pure Cu layer coated with the BNi-7 powders was successfully prepared by electroless plating to fabricate ductile filler metal with excellent mechanical properties. The obtained BNi-7 powders with 2 μm thick Cu coating exhibit dense and uniform structure through the elemental mapping analysis of the composite filler metal. The thickness and the content of the Cu layer could be determined by electroless plating time and the pH value of the plating solution. Meanwhile, the thermal physical parameters of the obtained composite filler were characterized by DSC analytical method, and the result indicated that the melting point was higher than the BNi-7 filler metal. The Inconel 718 were brazed without any defects using the composite filler metal in a vacuum. Compared to the BNi-7 filler metal, the Cu coated BNi-7 composite filler metal could form plenty of uniform reticular solid solutions during the high-temperature brazing process instead of acicular eutectic compounds. When adding the Cu powders mechanically into the original BNi-7 filler metals, voids and cracks could be found through the joints due to the uneven distribution of the Cu. The typical interfacial sequence of the joints was Inconel 718/Ni(Cu)ss+ σ-FeCr/Ni5P2 + Ni3P + Ni(Cr)ss + Ni2Cr + Ni(Cu)ss + σ-FeCr + Ni(Cu, Cr, Fe)ss/Ni(Cu)ss+ σ-FeCr/Inconel 718. The formation of the reticular Ni(Cu, Cr, Fe)ss phase released the stress in the brittle phase adjacent leading to the increasing ductility of the joints. The addition of the Cu-coated layer significantly enhanced the strength of the joint at room temperature, and the strengthening mechanisms were proposed.