Enhancing electromagnetic wave absorption with core‐shell structured SiO_(2)@MXene@MoS_(2) nanospheres

Material composition and structural design are important factors influencing the electromagnetic wave(EMW)absorption performance of materials.To alleviate the impedance mismatch attributed to the high dielectric constant of Ti_(3)C_(2)T_(x)MXene,we have successfully synthesized core‐shell structured SiO_(2)@MXene@MoS_(2)nanospheres.This architecture,comprising SiO_(2) as the core,MXene as the intermediate layer,and MoS_(2) as the outer shell,is achieved through an electrostatic self‐assembly method combined with a hydrothermal process.This complex core‐shell structure not only provides a variety of loss mechanisms that effectively dissipate electromagnetic energy but also prevents self‐aggregation of MXene and MoS_(2) nanosheets.Notably,the synergistic combination of SiO_(2) and MoS_(2) with highly conductive MXene enables the suitable dielectric constant of the composites,ensuring optimal impedance matching.Therefore,the core‐shell structured SiO_(2)@MXene@MoS_(2) nanospheres exhibit excellent EMW absorption performance,featuring a remarkable minimum reflection loss(RL_(min))of−52.11 dB(2.4 mm).It is noteworthy that these nanospheres achieve an ultra‐wide effective absorption bandwidth(EAB)of 6.72 GHz.This work provides a novel approach for designing and synthesizing high‐performance EMW absorbers characterized by“wide bandwidth and strong reflection loss.”

Photochemical synthesis of bimetallic Au-Ag nanoparticles with “core-shell” type structure by seed mediated catalytic growth

The colloidal Au core/Ag shell structure composite nanoparticles were synthesized in PEG-acetone solution by photochemical route. The monodispersed Au nanoparticles with average diameter of 3.9 nm were used as growth seeds. The optical property of colloids and the sizes of composite nanoparticles were characterized when the molar ratio of Au to Ag ranges from 4∶1 to 1∶4. The results show that a composite nanoparticle structure similar to strawberry shape is formed at the molar ratio of Au to Ag from 4∶1 to 1∶1; the composite nanoparticles consisting of a core of Au and shell of Ag were generated at the 1∶4 molar ratio, having a striking feature of forming (interconnected) network structure.

Synthesis of Ag@Al_2O_3 Core-shell Structure Nanoparticles and Their Enhancement Effect on Dielectric Properties for Ag@Al_2O_3/Polyimide Nanocomposites

A novel core-shell structure Ag@Al2O3 nano-particles were synthesized and doped into polyimide as conductive fillers to prepare the composite films with high dielectric properties and low dielectric loss. The morphology and structures of the Ag@Al2O3 nano-particles were characterized by transmission electron microscopy （TEM）, X-ray diffraction （XRD）, and UV-visible spectroscopy. All the results proved that the Ag@Al2O3 nano-parficles had a typical core-shell structure, for the Ag particles were coated by Al2O3 shell and the average sizes ofAg@Al2O3 particles were between 30 to 150 nm. The as-prepared Ag@Al2O3 nanoparticles were doped into the polyimide with different mass fractions to fabricate the Ag@Al2O3/PI composite films via in-situ polymerization process. SEM analysis of composite films showed that the Ag@Al2O3 nano- particles homogeneously dispersed in polyimide matrix with nanoseale. As dielectric materials for electronic packaging systems, the Ag@Al2O3/PI composites exhibited appropriate mechanical properties and erthaneed dielectric properties, including greatly enhanced dielectric constant and just a slight increase in dielectric loss. These improvements were attributed to the core-shell structure of fillers and their fine dispersion in the PI matrix.

Shell-driven Fine Structure Transition of Core Materials in Co@Au Core-shell Nanoparticles

Co@Au core shell nanoparticles(NPs) of different shell thicknesses were fabricated by a combination of the displacement process and the reduction-deposition process in a microfluidic reactor. The effect of the shell thickness on the fine structures(local atom arrangement) of core materials was investigated by X-ray Absorption Near Edge Structure(XANES) and Extended X-ray Absorption Fine Structure(EXAFS).The results indicate that the shell thickness affects the fine structure of the core materials by causing atomic re-arrangement between the hexagonal close pack(hcp) and the face centered cubic(fcc) structure, and forming Co-Au bonds in the core-shell interface.

Reduced-temperature ordering of FePt nanoparticle assembled films by Fe30Pt70/Fe3O4 core/shell structure

In this paper, Fe30Pt70/Fe3O4 core/shell nanoparticles were synthesized by chemical routine and the layered polyethylenimine （PEI）-Fe30Pt70/Fe3O4 structure was constructed by molecule-mediated self-assembly technique. The dimension of core/shell structured nanoparticles was that of 4nm core and 2 nm shell. After annealing under a flow of forming gas （50%Ar2＋30%H2） for 1 h at or above 400℃, the iron oxide shell was reduced to Fe and diffused to Pt-rieh core, which leaded to the formation of L1. phase FePt at low temperature. The x-ray diffraction results and magnetic properties measurement showed that the chemical ordering temperature of Fe30Pt70/Fe3O4 core/shell nanoparticles assembly can be reduced to as low as 400℃. The sample annealed at 400℃ showed the eoereivity of 4KOe with the applied field of 1.5T. The core/shell structure was suggested to be an effective way to reduce the ordering temperature obviously.

Preparation of Core-shell Structured Particles and Their Nucleation in Polyester:I. Preparation of Monodisperse SiO_2/PS Core-shell Composite Particles

To enhance the nucleation and crystallization properties of polyester (e.g., polyethylene terephthalate, PET), core-shell structured particles are used to improve these properties by controlling the inorganic dispersion properties in the polymers. In the paper, monodisperse particles of silica/polystyrene (PS) are prepared with both dispersion and emulsion polymerization techniques. The monodisperse silicon dioxide particles are first prepared with the seed growth method and modified by the coupling agents. Silica is properly modified with KH-570, and its size deviation is 3.0% or so. The modified silica then reacts with the mixture of ethanol, water medium, and monomer of styrene under dispersion polymerization. Results show that the dispersion polymerization technique is more suitable for monodisperse core-shell SiO2/PS particles than that of the emulsion. The morphology and molecular structure of the core-shell particles are investigated with the transmission electron microscope (TEM), and fourier transform infra-red spectroscopy (FTIR). The results show that the modified silica particles are successfully encapsulated with polystyrene. The average number of silica particles encapsulated into each polystyrene sphere decreases when the size of silica particles increases from 50 nm to 600 nm, and will approach one when the silica is greater than 380nm in size. The mass ratio for silica/PS particles in emulsion polymerization is 4.7/1, lower than that of 6.8/1 for dispersion polymerization, which is the first reported optimized data for preparing the similar monodisperse composite particles. Thus, the PS shell in the former is thinner than that in the latter.

Raman scattering in In/InOx core-shell structured nanoparticles

The properties of Raman phonons are very important due to the fact that they can availably reflect some important physical information. An abnormal Raman peak is observed at about 558 cm-1 in In film composed of In/InOx core-shell structured nanoparticles, and the phonon mode stays very stable when the temperature changes. Our results indicate that this Raman scattering is attributed to the existence of incomplete indium oxide in the oxide shell.

A Comparative Study on the Selected Area Electron Diffraction Pattern of Fe Oxide/Au Core-shell Structured Nanoparticles

The selected area electron diffraction （SAED） pattern of magnetic iron oxide core/gold shell nanoparticles has been studied. For the composite particles with mean size less than 10 nm, their SAED pattern is found to be different from either the pattern of pure Fe oxide nanoparticles or that of pure Au particles. Based on the fact that the ring diameters of these composite particles fit the characteristic relation for the fcc structure, the Au atoms on surfaces of the concerned particles are supposed to pack in a way more tightly than they usually do in pure Au nanoparticles. The driving force for this is the coherency strain which enables the shell material at the heterostructured interface to adapt the lattice parameters of the core.

Structural response of aluminum core–shell particles in detonation environment

Natural aluminum particles have the core-shell structure.The structure response refers to the mechanical behavior of the aluminum particle structure caused by external influences.The dynamic behavior of the structural response of aluminum core-shell particles before combustion is of great importance for the aluminum powder burning mechanism and its applications.In this paper,an aluminum particle combustion experiment in a detonation environment is conducted and analyzed;the breakage factors of aluminum particles shell in detonation environment are analyzed.The experiment results show that the aluminum particle burns in a gaseous state and condenses into a sub-micron particle cluster.The calculation and simulation demonstrate that the rupture of aluminum particle shell in the detonation environment is mainly caused by the impact of the detonation wave.The detonation wave impacts the aluminum particles,resulting in shell cracking,and due to the shrinkage-expansion of the aluminum core and stripping of the detonation product,the cracked shell is fractured and peeled with the aluminum reacting with the detonation product.

Preparation of a p-n heterojunction BiFeO_3@TiO_2 photocatalyst with a core–shell structure for visible-light photocatalytic degradation

Magnetically separable bismuth ferrite(BiFeO3)nanoparticles were fabricated by a citrate self‐combustion method and coated with titanium dioxide(TiO2)by hydrolysis of titanium butoxide(Ti(OBu)4)to form BiFeO3@TiO2core-shell nanocomposites with different mass ratios of TiO2to BiFeO3.The photocatalytic performance of the catalysts was comprehensively investigated via photocatalytic oxidation of methyl violet(MV)under both ultraviolet and visible‐light irradiation.The BiFeO3@TiO2samples exhibited better photocatalytic performance than either BiFeO3or TiO2alone,and a BiFeO3@TiO2sample with a mass ratio of1:1and TiO2shell thickness of50-100nm showed the highest photo‐oxidation activity of the catalysts.The enhanced photocatalytic activity was ascribed to the formation of a p‐n junction of BiFeO3and TiO2with high charge separation efficiency as well as strong light absorption ability.Photoelectrochemical Mott-Schottky(MS)measurements revealed that both the charge carrier transportation and donor density of BiFeO3were markedly enhanced after introduction of TiO2.The mechanism of MV degradation is mainly attributed to hydroxyl radicals and photogenerated electrons based on energy band theory and the formation of an internal electrostatic field.In addition,the unique core-shell structure of BiFeO3@TiO2also promotes charge transfer at the BiFeO3/TiO2interface by increasing the contact area between BiFeO3and TiO2.Finally,the photocatalytic activity of BiFeO3@TiO2was further confirmed by degradation of other industrial dyes under visible‐light irradiation.

One-dimensional ZnS-based Hetero-,Core/shell and Hierarchical Nanostructures

A focus of the current nanotechnology has shifted from routine fabrication of nanostructures to designing functional electronic devices and realizing their immense potentials for applications. Due to infusion of multi-functionality into a single system, the utilization of hetero-, core/shell and hierarchical nanostructures has become the key issue for building such devices. ZnS, due to its direct wide bandgap, high index of refraction, high transparency in the visible range and intrinsic polarity, is one of the most useful semiconductors for a wide range of electronics applications. This article provides a dense review of the state-of-the-art research activities in one-dimensional （1D） ZnS-based hetero-, core/shell and hierarchical nanostructures. The particular emphasis is put on their syntheses and applications.

Hierarchical Carbon Microtube@Nanotube Core-Shell Structure for High-Performance Oxygen Electrocatalysis and Zn-Air Battery

Zinc-air batteries(ZABs)hold tremendous promise for clean and efficient energy storage with the merits of high theoretical energy density and environmental friendliness.However,the performance of practical ZABs is still unsatisfactory because of the inevitably decreased activity of electrocatalysts when assembly into a thick electrode with high mass loading.Herein,we report a hierarchical electrocatalyst based on carbon microtube@nanotube core-shell nanostructure(CMT@CNT),which demonstrates superior electrocatalytic activity for oxygen reduction reaction and oxygen evolution reaction with a small potential gap of 0.678 V.Remarkably,when being employed as air-cathode in ZAB,the CMT@CNT presents an excellent performance with a high power density(160.6 mW cm^−2),specific capacity(781.7 mAhgZn^−1)as well as long cycle stability(117 h,351 cycles).Moreover,the ZAB performance of CMT@CNT is maintained well even under high mass loading(3 mg cm−2,three times as much as traditional usage),which could afford high power density and energy density for advanced electronic equipment.We believe that this work is promising for the rational design of hierarchical structured electrocatalysts for advanced metal-air batteries.

TOUGHENING OF POLYCARBONATE WITH PBA-PMMA CORE-SHELL PARTICLES

The miscibility,mechanical properties,morphology and toughening mechanism of PC/PBA-PMMA blends wereinvestigated.The dynamic mechanical results show that PC/PBA-PMMA blend has good miscibility and strong interfacialadhesion.The Izod impact strength of blend PC/PBA-PMMA with 4%(volume fraction)PBA-PMMA core-shell modifier is16 times higher than that of pure PC.The core-shell volume fraction and thickness of the PMMA shell have effect on thetoughness of PC/PBA-PMMA blends.As PMMA volume fraction increases,the toughness of PC/PBA-PMMA blendincreases,and reaches a maximum value at 30% volume fraction of PMMA or so.The tensile properties of PC/PBA-PMMAblend with a minimum amount of PBA-PMMA modifier show that brittle-tough transition has no significant variance incomparison with that of pure PC.The scanning electron microscopic(SEM)observation indicates that the tougheningmechanism of the blend with the pseudo-ductile matrix modified by small core-shell latex polymer particles is the synergeticeffect of cavitation and shear yielding of the matrix.

THE PREPARATION AND CHARACTERIZATION OF SBR/PS CORE-SHELL PARTICLES BY GAMMA IRRADIATION

A kind of core(SBR)-shell(PS)particles was synthesized by using SBR latex and grafting with St under gammairradiation.The influences of absorbed dose and dose rate on the grafting yield of PS on SBR seed latex have beeninvestigated.Results show there was a transition layer which contained the SBR/PS graft copolymer between the SBR coreand PS shell.Dynamic laser scattering(DLS)and differential scanning calorimetry(DSC)results confirm the existence ofgrafted polystyrene,and transmission electron microscope(TEM)observation verifies the core-shell structure of SBR-g-PSlatex.Such SBR/PS core-shell latex could be processed easily to ultrafine rubber powders by using spray drying andexpected to be used as an impact modifier for PS.

Polybutylacrylate/poly (methyl methacrylate) Core-Shell Elastic Particles as Epoxy Resin Toughener: Part Ⅱ Toughness on DGEBA/DDM system

Mechanlcal properties of epoxy resin were investigated by adding core-shell elastic particles (CSEP). The results indicated that optimized core-shell ratio was 60/40 and the loading volume of CSEP was 10 phr (per hundred parts of epoxy resin by weight). The impact strength of modified systems increased apparently with the decrease of core sizes. However, the shearing strength changed gently with the particle sizes. CSEP with lightly crosslinked rubbery core showed more effectiveness on toughness than others. With solution blending, CSEP could be dispersed in epoxy matrix well, and the morphologies of dispersed rubber domains were controlled perfectly by CSEP whose structure was predesigned. A cavitation-shearing band toughness mechanism was observed from the SEM micrographs of fracture surface. It also was found that the deforming temperature (DT) of modified epoxy did not decline apparently.

Review:Progress in Core-shell Rubber Particles for Efficiently Toughening Resins

Core-shell toughening particles are structured composite particles consisting of generally two different components, one at the center as a rubbery elastic core and surrounding by the second as a glassy inelastic shell. The design, preparation, and application of core-shell polymer particles have been briefly reviewed. Morphological characteristics of the core-shell particles by transmission electron microscopy(TEM) and scanning electron microscopy(SEM) are focused. The vital factors that are useful to control core-shell morphology and toughening properties including core-shell monomer species, polymerization conditions, cross-linking reagents, synthetic method, and post-processing techniques are analyzed. Distinguished properties are mainly considered as the most desirable features that endow core-shell polymer particles with various applicabilities, particularly as effectively toughening components in brittle epoxy resin and polylactide that are substrate of copper clad laminate widely used in the modern electronic world and environmentally friendly materials that are useful as packaging films, disposable tableware, biomedical equipment, and new energy vehicles.

Effect of milling process on the core-shell structures and dielectric properties of fine-grained BaTiO_3-based X7R ceramic materials

Fine-grained BaTiO3-based X7R ceramic materials were prepared and the effects of milling process on the core-shell structures and dielectric properties were investigated using scanning electron microscope, transmission electron microscope, and energy dispersive spectroscopy （EDS）. As the milling time extends, the dielectric constant of the ceramics increases, whereas the temperature coefficient of capacitance at 125℃ drops quickly. The changes in dielectric properties are considered relevant to the microstructure evolution caused by the milling process. Defects on the surface of BaTiO3 particles increase because of the effects of milling process, which will make it easier for additives to diffuse into the interior grains. As the milling time increases, the shell region gets thicker and the core region gets smaller; however, EDS results show that the chemical inhomogeneity between grain core and grain shell becomes weaker.

Core@shell sulfur@polypyrrole nanoparticles sandwiched in graphene sheets as cathode for lithium–sulfur batteries

A nano sulfur-based composite cathode material featured by uniform core@shell-structured sulfur@polypyrrole nanoparticles sandwiched in three-dimensional graphene sheets conductive network（S@PPy/GS） is fabricated via a facile solution-based method. The S@PPy nanoparticles are synthesized by in situ chemical oxidative polymerization of pyrrole on the surface of sulfur particles,and then graphene sheets are covered outside the S@PPy nanoparticles,forming a three-dimensional conductive network. When evaluating the electrochemical performance of S@PPy/GS in a lithium–sulfur battery,it delivers large discharge capacity,excellent cycle stability,and good rate capability. The initial discharge capacity is up to 1040 m Ah/g at 0.1 C,the capacity can remain 537.8 m Ah/g at 0.2 C after 200 cycles,even at a higher rate of 1 C,the specific capacity still reaches 566.5 m Ah/g. The good electrochemical performance is attributed to the unique structure of S@PPy/GS,which can not only provide an excellent transport of lithium and electron ions within the electrodes,but also retard the shuttle effect of soluble lithium polysulfides effectively,thus plays a positive role in building better lithium-sulfur batteries.

Core-shell structured 1,4-benzoquinone@TiO_2 cathode for lithium batteries

Organic carbonyl compounds are considered as promising candidates for lithium batteries due to theirhigh capacity and environmental friendliness, However, they suffer from serious dissolution in the elec-trolyte, leading to fast capacity decay. Here we report core-shell structured 1,4-benzoquinone@titaniumdioxide （BQ@TiO2） composite as cathode for lithium batteries. The composite cathode can deliver a highdischarge capacity of 441.2 mA h/g at 50 mA/g and a high capacity retention of 80.7% after 100 cycles. Thegood cycling performance of BQ@TiO2 composite can be attributed to the suppressed dissolution of BQ,which results from the physical confinement effect of Ti02 shell and the strong interactions between BQand Ti02. Moreover, the combination of ex situ infrared spectra and density functional theory calculationsreveals that the active redox sites of BQ are carbonyl groups. This work provides an alternative way tomitigate the dissolution of small carbonyl compounds and thus enhance their cycling stability.

Controlling Shell Thickness of PS/SiO_2 Core-Shell Particles and Their Crystallization into 3-D Ordered Thin Film

PS/SiO2 particles with core-shell structure were synthesized by coating silica on surface of polystyrene(PS) colloidal particles.The reaction parameters,such as initial tetraethyl orthosilicate(TEOS) concentration,water concentration and reaction temperature,have been investigated to control the thickness of silica shells.The shell thickness was prepositional to the square root of the initial concentration of TEOS and first increased with increasing water concentration,reached a maximum at about 2.0 mol/L and then started decreasing beyond that concentration.It was also found that the shell thickness decreased firstly with the reaction temperature added,then tended to a constant.The so-synthesized PS/SiO2 core-shell particles were directly crystallized into 3-D ordered thin film,then sintered at 570℃ into the ordered macroporous thin film.Compared with the conditional method,the present approach avoids repeatedly filling the precursor in the templetes and save time more.