Core-shell Particles Research Articles

Liquid-liquid phase separation reduces radiative absorption by aged black carbon aerosols

Black carbon aerosols absorb radiation and their absorptive strength is influenced by particle mixing structures and coating compositions. Liquid-liquid phase separation can move black carbon to organic particle coatings which affects absorptive capacity, but it is unclear which conditions favour this redistribution. Here we combine field observations, laboratory experiments, and transmission electron microscopy to demonstrate that liquid-liquid phase separation redistributes black carbon from inorganic particle cores to organic coatings under a wide range of relative humidity. We find that the ratio of organic coating thickness to black carbon size influences the redistribution. When the ratio is lower than 0.12, over 90% of black carbon is inside inorganic salt cores. However, when the ratio exceeds 0.24, most black carbon is redistributed to organic coatings, due to a change in its affinity for inorganic and organic phases. Using an optical calculation model, we estimate that black carbon redistribution reduces the absorption enhancement effect by 28–34%. We suggest that climate models assuming a core-shell particle structure probably overestimate radiative absorption of black carbon aerosols by approximately 18%.

Effects of fabrication parameters and post-processing treatments on the mechanical and tribological behavior of surface-enhanced copper based materials by selective laser melting

Selective laser melting (SLM), which is an advanced manufacturing method developed in recent years, produces parts with complex shapes and critical dimensions using metallic powder and laser beam. In this study, copper based conductive materials with silver networks were fabricated by electroless silver coating and SLM. The effects of laser power, scanning speed, hatch spacing, build orientation and post treatments on the mechanical and tribological properties of SLM compacts manufactured from core-shell particles were investigated. After the mechanical tests, higher stress and elongation values were obtained in the sample positioned horizontally on the build platform with a laser power of 100 W, scanning speed of 250 mm/s and hatch spacing value of 45%. After that SLM process, the post-processes were applied to the samples and the physical and mechanical properties improved significantly. The highest density value was obtained by the rolling process at 900 °C, and an increase of approximately 35.6% was obtained compared to the sample without post-processing. The lowest wear rate among all samples was obtained in the hot-pressing process at 750 °C. • Silver coating of copper particles by electroless silver plating method. • Production of copper-based compacts by SLM using core-shell particles. • Investigation of critical SLM parameters on the properties of SLMed parts. • Investigate the effect of post treatments on SLMed parts. • Obtaining the improved properties by electroless coating, SLM, post treatments.

Tailoring microstructure and mechanical properties of aluminum matrix composites reinforced with novel Al/CuFe multi-layered core-shell particles

Aluminum matrix composites (AMCs), reinforced with novel pre-synthesized Al/CuFe multi-layered core- shell particles, were fabricated by different consolidation techniques to investigate their effect on microstructure and mechanical properties. To synthesize multi-layered Al/CuFe core-shell particles, Cu and Fe layers were deposited on Al powder particles by galvanic replacement and electroless plating method, respectively. The core-shell powder and sintered compacts were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDX), pycnometer, microhardness and compression tests. The results revealed that a higher extent of interfacial reactions, due to the transformation of the deposited layer into intermetallic phases in spark plasma sintered composite, resulted in high relative density (99.26%), microhardness (165 HV0.3) and strength (572 MPa). Further, the presence of un-transformed Cu in the shell structure of hot-pressed composite resulted in the highest fracture strain (20.4%). The obtained results provide stronger implications for tailoring the microstructure of AMCs through selecting appropriate sintering paths to control mechanical properties.

On mode-I and mode-II interlaminar crack migration and R-curves in carbon/epoxy laminates with hybrid toughening via core-shell rubber particles and thermoplastic micro-fibre veils

This study investigates the influence of hybrid toughening—via core-shell rubber (CSR) particles and non-woven thermoplastic veils—on the delamination resistance, crack migration and R-curve behaviour in carbon fibre/epoxy laminates under mode-I and mode-II conditions. Core-shell rubber particles, varying in size from 100 nm to 3 μm, with 0–10 wt% content, are dispersed within the epoxy resin, and thermoplastic micro-fibre veils with polyphenylene sulfide (PPS) fibres, with 5–20 g/m 2 areal weight, are introduced at the interlaminar region to achieve hybrid toughening. Carbon fibre/epoxy laminates are manufactured with a two-part resin using vacuum infusion and out-of-autoclave curing. Double cantilever beam (DCB) and four-point end-notch-flexure (4ENF) specimens are used to obtain mode-I and mode-II fracture energies and R-curves. Damage mechanisms and crack paths are characterised using fractography that provide understanding of energy dissipation. The results show that the hybrid toughening significantly improves fracture initiation and propagation energies ( i.e . mode I initiation by ∼245% and propagation by ∼275%, and mode-II initiation by ∼64% and propagation ∼215%) by extrinsic and intrinsic toughening mechanisms. Moreover, it is shown that rising R-curves can be achieved with hybrid toughening when compared with falling R-curves obtained with just thermoplastic veil toughening. Fractography revealed that the hybrid toughening constrained the crack predominantly within the veil region, making it harder to grow and absorb more energy.

Immobilization of boronic acid derivative onto the magnetic Gd-containing composites

Aiming to develop new magnetic materials for neutron shielding applications, B- and Gd-containing magnetic nanoparticles were synthesized. Following bottom-up synthetic approach, core-shell Fe 3 O 4/Gd 2 O 3 nanocomposite particles were synthesized at the first stage. In the next stage, magnetic core-shell particles were modified with amino groups followed by grafting onto their surface of the boronic acid derivative. Such a multifunctional material, containing both boron (B) and gadolinium (Gd) atoms is a promising candidate for developing films and membranes, strongly interacting with neutrons. Due to the presence of boronic acids and bound to the indicator (Alizarin Red S), the material can induce color changes while immersed in sugar-containing solutions. Such a feature enables a possibility to estimate the number of boron atoms left after interaction with neutrons, thus allowing to check composite neutron-capture recourse.

Boosting the enantioresolution of zwitterionic-teicoplanin chiral stationary phases by moving to wide-pore core-shell particles

A novel zwitterionic-teicoplanin chiral stationary phase (CSP), based on superficially porous particles (SPPs) of 2.7 µm particle diameter and 160 Å pore size, has been prepared and evaluated towards the enantioseparation of important classes of compounds, including chiral drugs, pesticides, and N-derivatized amino acids. The comparison with two analogous CSPs prepared on SPPs with 2.7 and 2.0 µm particle diameter and 90 Å pore size has revealed that the use of large-pore particles allows to dramatically improve both the enantioselectivity and the resolution-per-analysis-time, at the point that the column prepared with the new CSP outperformed the one packed with the finest particles. On the novel wide-pore CSP, the separation of fifteen racemates of pratical importance was significantly improved in terms of both enantioselectivity and resolution-per-analysis time-compared to the CSPs based on SPPs with smaller pores (90 Å). Such a CSP would be suitable for very fast enantioseparations allowing the saving of solvent for greener high-efficiency/high-throughput applications.

Microsized aluminum/ammonium dinitramide core-shell particles to improve the combustion performance of aluminum powders

Microcomposite particles of aluminum (Al) dotted by ammonium dinitramide (ADN) ([email protected]) are successfully prepared by an in-situ crystallization growth method. The morphologies, structures and thermal behavior of [email protected] are characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and simultaneous thermogravimetry and differential scanning calorimetry. The compositions and morphologies of [email protected] after heating are characterized by X-ray photoelectron spectroscopy (XPS) and SEM. A high-speed camera is used to record the combustion performances of [email protected] in a transparent quartz tube. Furthermore, the morphologies and structures of the residues are analyzed by SEM and XRD. The results show that ADN is deposited on the surface of Al to form [email protected] The decomposition of ADN increases the total oxidation degree of the Al particles. Under heating, the acids decomposed by ADN corrode the surficial alumina layer and the internal aluminum react with HNO3 to form Al(NO3)3, which makes the combustion of Al easier. Under an oxygen atmosphere, the pure Al could not be ignited. In contrast, [email protected] could be ignited and [email protected] 5:1 has a shorter ignition and burning time compared with [email protected] 10:1. After burning, the [email protected] composites are completely converted to α- and γ-Al2O3. For [email protected] 10:1, the residues show a cube-like stacking, while a ribbon-like stacking is presented for [email protected] 5:1.

Elastic Deformations of Spherical Core-Shell Systems Under an Equatorial Load

Macroscopic elastic core-shell systems can be generated as toy models to be deformed and haptically studied by hand. On the mesoscale, colloidal core-shell particles and microgels are fabricated and investigated by different types of microscopy. We analyse, using linear elasticity theory, the response of spherical core-shell systems under the influence of a line density of force that is oriented radially and acts along the equator of the outer surface. Interestingly, deformational coupling of the shell to the core can determine the resulting overall appearance in response to the forces. We address various combinations of radii, stiffness, and Poisson ratio of core and shell and illustrate the resulting deformations. Macroscopically, the situation could be realized by wrapping a cord around the equator of a macroscopic model system and pulling it tight. On the mesoscale, colloidal microgel particles symmetrically confined to the interface between two immiscible fluids are pulled radially outward by surface tension.

New out-performing structured pigments for anticorrosive practical applications

PurposeLong time ago, multistructured materials showed great interest being considered as the bridge between bulk and atomic materials. Core-shell particles are kind of composite materials that refer to multilayered structures with a core totally surrounded by shell(s) (onion-like structure). These new structures can offer an advantage of applying new adjustable parameters like shape, stoichiometry and chemical ordering, in addition to the opportunity of tailoring more complexed structures for different applications. Recently it was found that these structures can be tuned and taken for more advanced path with novel structures formed of core surrounded by multishells. The purpose of this study is to study the effect of the new anticorrosive pigments with its mutual shells and how each shell affects the performance of the pigment in protecting the metal and which shell will be more relevant in its effect.Design/methodology/approachThe prepared pigments were characterized using X-ray fluorescence, X-ray diffraction, TEM and SEM/EDX to prove their core-shell structure, and then they were integrated in coating formulations to evaluate their anticorrosive activity using immersion test and electrochemical impedance spectroscopy (EIS).FindingsThe results showed that the prepared core-shell pigments possess a lot of unique characteristics and can offer improved anticorrosive performance in the generated coatings.Originality/valueCore-mutual shells structured pigments were prepared for improving the corrosion resistivity of the organic coatings as a new trend in anticorrosive pigments.

Core-shell structure nanoprecipitates in Fe-xCu-3.0Mn-1.5Ni-1.5Al alloys: A phase field study

The core-shell structure precipitatates of Fe-xCu-3.0Mn-1.5Ni-1.5Al alloys under internal and external strain was investigated by using a multicomponent continuous phase field model based on Gibbs free energy of sub regular solution. Results show that the early cluster nuclei are not pure Cu, and Mn/Ni/Al also gather in the same position of Cu rich nuclei, resulting in four core-shell structures in precipitation. In the absence of external strain, the morphology of precipitates is mainly determined by interfacial energy, intrinsic elastic anisotropy and lattice distortion between new phase and parent phase. Intrinsic elastic strain energy can inhibit precipitation, while has no obvious effect on particle morphology. In coarsening, the elastic energy decreases due to the combination of particles. The loading direction and magnitude of the applied elastic strain field can control the morphology of precipitates. The external strain and the interaction between Mn, Ni and Al promote the joining and merging of adjacent core-shell particles. This work has guiding significance for the design of Fe-xCu-3.0Mn-1.5Ni-1.5Al alloys and other core-shell precipitates materials.

Morphology of multilayer core-shell emulsion: Influence of crosslinking agent

We describe a new method for synthesis of phase-separated multilayer core–shell emulsion particles with different morphologies, such as multilayer inverse core–shell (MLICS) particles and multilayer sea-island core–shell (MLSICS) particles. These emulsion particles were prepared by three-stage semicontinuous polymerization with changing addition methods of divinylbenzene (DVB) as a crosslinking agent. The multilayer core–shell morphologies of the various particles were clearly shown in transmission electron microscopy (TEM), as well as average diameters and distributions of particles during multistage polymerization were characterized by dynamic laser scattering (DLS) method. Furthermore, the effect of DVB on particle morphology was discussed in more detail. Considering the inhibitory effect of polymer networks on chain migration, multilayer core–shell particles with various defined morphologies and different functional groups can be synthesized in shell layer by introducing crosslinking structure during emulsion polymerization.

Bi2O3 in-situ oxidizing effect upon the core-shell structure design for the Fe-Si directional alloyed soft magnetic material (DASMM)

High performance soft magnetic composites (SMCs) materials require the particles surface coating shell have a high electric resistivity and strong adhesion to the substrate ferromagnetic core. However, it’s very challenging to meet those property demands at the same time. In this research work we proposed a new type of Fe-Si directional alloyed soft magnetic material (DASMM), this core-shell structured Fe-Si DASMM powder particle surface insulating SiO2 shell both have high resistivity and strong metallurgical bonding to the substrate Fe core. The influence of 0–2 wt% doped Bi2O3 upon the microstructure and magnetic properties of sintered Fe-Si DASMM were systematically studied. The meltedBi2O3in-situ reacted with the surface Si shell in Fe-Si directional alloyed soft magnetic powder (DASMP) and formed high resistive SiO2shell and Bi metal through a reduction reaction. Consequently, the doped Bi2O3promoted the Fe-SiO2core-shell structure formation for the Fe-Si DASMM.As the doped Bi2O3content increased, the insulating SiO2 shell network structure intensity, continuity and uniformity progressively improved; the resistivity increased first and then decreased. While due to the effective inter-particle eddy current insulating effect by the in-situ reduction formed SiO2shell, both the core loss (Pcv) and coercivity (Hc) of Fe-Si DASMM decreased gradually.

Morphological and Structural Transformations of Fe-Pd Powder Alloys Formed by Galvanic Replacement, Annealing and Acid Treatment.

In this article, we report the preparation and structural features of Fe-Pd powder alloys formed by galvanic replacement, annealing and selective dissolution of iron via acid treatment. The alloys were studied by the X-ray diffraction phase analysis, Mössbauer spectroscopy, scanning electron microscopy, and energy-dispersive spectroscopy. The Fe@Pd core–shell particles were obtained by a galvanic replacement reaction occurring upon treatment of a body-centered cubic (bcc) iron powder by a solution containing PdCl42− ions. It was found that the shells are a face-centered cubic (fcc) Pd(Fe) solid solution. HCl acid treatment of the Fe@Pd core–shell particles resulted in the formation of hollow Pd-based particles, as the bcc phase was selectively dissolved from the cores. Annealing of the Fe@Pd core–shell particles at 800 °C led to the formation of fcc Fe-Pd solid solution. Acid treatment of the Fe-Pd alloys formed by annealing of the core–shell particles allowed selectively dissolving iron from the bcc Fe-based phase (Fe(Pd) solid solution), while the fcc Fe-rich Fe-Pd solid solution remained stable (resistant to acid corrosion). It was demonstrated that the phase composition and the Fe/Pd ratio in the alloys (phases) can be tailored by applying annealing and/or acid treatment to the as-synthesized Fe@Pd core–shell particles.

A Novel Numerical Treatment of Nonlinear and Nonequilibrium Model of Gradient Elution Chromatography considering Core-Shell Particles in the Column

An extended method of semidiscrete high-resolution finite volume is used in this paper to obtain numerical solutions for a formulated nonlinear lumped kinetic model of liquid chromatographic process to examine the effect of chromatographic column overloading gradient elution considering core-shell particles. The model constitutes linear solvent strength (LSS), Henry’s constant, coefficient of nonlinearity, and coefficient of axial dispersion. The effects of modulator concentration changes for the elution of single and two components are analyzed. The advantages of introducing gradient elution against isocratic elution in terms of core radius fraction are investigated intensively. Numerical temporal moments are generated from the solutions obtained for a more in-depth examination of the considered model. Moreover, multiple forms of a single- and two-component mixture are generated to analyze the influences of core radius fractions on gradient elution. For example, the obtained results are utilized to investigate the effects of the slope of gradient, concentration of modulator, solvent strength parameter, coefficient of nonlinearity, coefficient of mass transfer, and coefficient of axial dispersion on the profiles of concentration in order to improve the process performance using optimal core radius fraction parameter values.

The closer the better? Theoretical assessment of the impact of catalytic site separation for bifunctional core–shell catalyst particles

One-pot heterogeneous catalysis with different active centers offers great potential for increasing yield and selectivity. In this field, the distance between the different catalytically active centers starts playing a role and its influence as well as its control is an open question. Here, porous core–shell particles provide the opportunity to control the distance on a mesoscopic scale, where the centers are placed on different shells and are separated by an inert porous matrix. We present a continuum-mechanical model of such particles and exploit symmetry to arrive at a computationally efficient reduced model. Using methanol synthesis from CO2 on the first kind of center followed by a dimethylether synthesis on a second kind of center as an example, we investigate the influence of the distance between these two centers. In particular, we consider three simple backcoupling mechanisms and address the question whether it is best to place the centers as close as possible or at a non-zero optimal distance. We find that this question cannot a priori be answered but the answer depends largely on the employed backcoupling mechanism.

Construction of insulating layers on conductive nickel-plated core particles by thermal fusion of heterocoagulated polymer shell particles

In this study, we developed a method for fabricating conductive particles with an insulating layer on the surface, which can be applied to anisotropic conductive films. Core-shell particles were prepared from conductive nickel-plated core particles and positively charged polystyrene (PSt) shell particles carrying phosphonium groups on their surface by the heterocoagulation technique. The effect of alkyl chain lengths (ethyl, n-butyl, and n-octyl) of (4-vinylbenzyl)trialkylphosphonium chloride on the interfacial properties was investigated by surface tension measurement. Monodisperse PSt shell particles with a controlled particle size were successfully synthesized by emulsifier-free emulsion polymerization of styrene, (4-vinylbenzyl)triethylphosphonium chloride, and n-butyl acrylate. The effects of stirring time, temperature, NaCl concentration, and PSt shell particle concentration on heterocoagulation between the nickel-plated core particles and PSt shell particles were investigated. Uniform core-shell particles with a coverage of 60% could be prepared even though the heterocoagulation temperature was below the glass transition temperature and the NaCl concentration was below the critical coagulation concentration of the PSt shell particles. When the core-shell particles obtained through the heterocoagulation process were heated above the glass transition temperature of the shell particles for 6 h, a smooth polymeric insulating layer with melted shell particles was successfully formed on the surface of the nickel-plated core particles.

Enhanced mechanical and electrical properties of CuCrZr-WC alloy prepared by mechanical alloying and spark plasma sintering

In current work, CuCrZr alloy with 3 wt.% WC were prepared by MA-SPS method. SEM, TEM, XRD, electrical and mechanical testing were used to characterize the microstructure and performance of composite materials. The interfaces between WC nanoparticles and Cu matrix were systematically studied. The results show that the addition of WC lead to a great improvement on yield and ultimate tensile strength, with the cost of slightly decreased of plasticity and conductivity. The particles with ZrC-W2C-WC core-shell particles were observed in the Cu matrix, which improve the interface between the matrix and the WC particles. The formation of ZrC-W2C-WC core-shell structure was explained using Kirkendall effect and the effects of this core-shell structure on mechanical and electrical conductivity were discussed.

Quercetin loading on mesoporous magnetic MnFe2O4@ hydroxyapatite core-shell nanoparticles for treating cancer cells

Despite the availability of various nanostructure for cancer cells therapeutic, caring hydrophobic drugs to the target site is still one of the great challenges in chemotherapy. In this study, quercetin (QC), a poorly water-soluble natural anticancer agent, was used as a model drug to evaluate the efficiency of mesoporous magnetic MnFe2O4 core-shell nanocomposite particles. A simple co-precipitation method was employed to synthesis MnFe2O4 as core of nanostructure. Then, the obtained MnFe2O4 nanoparticles were coated with mesoporous hydroxyapatite (HA) shell as a new perspective for drug loading. The magnetic mesoporous nanostructure had specific surface area and mean pore size of 165.44 m2/g and 11.561 nm, respectively. In QC loading process, the MnFe2O4@HA nanostructure demonstrated loading capacity of 123 µg/mg with pH-depended release manner. In compare with free QC, loaded QC on MnFe2O4 core-shell nanocomposite particles exhibited 55% higher antioxidant activities against free 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals. Moreover, comparative in-vitro anticancer studies on Michigan cancer foundation (MCF)-7 cells, breast cancer cell line, demonstrated more reduction in number of viable cells (35.6%) using loaded QC than that of free QC (50.76%), suggesting improvement in the solubility of QC by loading onto mesoporous magnetic nanocomposite particles compared to free QC.

Synthesis of hollow Fe, Co, and N-doped carbon catalysts from conducting polymer-metal-organic-frameworks core-shell particles for their application in an oxygen reduction reaction

Oxygen reduction reaction (ORR), one of the key reactions for fuel cells and zinc-air batteries, should be improved for higher performance. Herein, we fabricated hollow Fe, Co, and nitrogen co-doped carbon (H-FeCo-NC) catalyst, which was prepared by carbonization of core-shell particles made of polypyrrole (PPy)-coated polystyrene (PS) spheres as cores and (Zn, Co) bimetallic-zeolitic imidazolate frameworks (ZnCoBZIFs) as shells. PPy was used as a nitrogen and a carbon source. The H-FeCo-NC catalyst had a high surface area of 324.08 m2 g−1 with uniformly distributed Fe and Co species, and excellent ORR performance with the half-wave potential of 0.888 V vs. reversible hydrogen electrode in alkaline media. Furthermore, the H-FeCo-NC catalyst demonstrated exceptional stability, durability, and tolerance to methanol crossover.

Titania coated silica core-shell spheres with dual grain size as efficient photocatalysts

The TiO2 nanoclusters were modified into the pores of silica core-shell particles (SiO2@dSiO2) by the sol-gel method, and the loading amount reached 47%. Based on the Ostwald ripening theory, by simply extending the reaction time, a part of the TiO2 in the pores of the shell was dissolved and then re-deposited on the outer surface of the shell to form a TiO2 layer. Using this method, TiO2 crystalline grains of different sizes were obtained simultaneously inside and outside the shell of silica core-shell spheres. Small-sized crystalline grains were located in the pores of the shell, and they had a strong quantum size effect. The large crystalline grains were located in the TiO2 layer on the outer surface of the shell of SiO2@dSiO2. Due to the formation of larger-sized crystalline grains, the recombination probability of photogenerated electron-hole pairs was reduced. When used as photocatalysts for the degradation of Rhodamine B under UV irradiation, the catalytic activity of SiO2@dSiO2@TiO2 was 5.4 times higher than that of the commercial P25 TiO2 photocatalyst.