Formation Of Core-shell Structure Research Articles

Shell phase selection and layer numbers of core–shell structure in monotectic alloys with stable miscibility gap

Shell phase selection in the core–shell structure formation was investigated in the systems with stable miscibility gaps, and the shell phase selection and the formation mechanism of different layers structure are examined. It is found that the shell phase is always composed of L2 phase owing to its lower surface energy compared with that of L1 phase. This surface/interfacial energy dependent shell phase selection was confirmed by the phase separation of SCN–H2O transparent system with glass/Teflon wall which has different wetting ability to SCN and H2O. On the basis of the surface energy dependent shell phase selection, the formation mechanism of the double- and triple-layer core–shell structure is elucidated.

Simulation of self-assembled compositional core-shell structures in InxGa1−xN nanowires

We report the simulation of compositional core-shell structure formation in epitaxial InGaN nanowires (NWs) and its dependence on kinetic growth mode and epitaxial relation to substrate, based on atomistic-strain-model Monte Carlo simulations. On a lattice mismatched substrate, the layer-by-layer growth results in self-assembled core-shell structures with the core rich in the unstrained component (relative to the substrate), while the faceted growth mode leads to the strained core component, and both are distinctively different from the equilibrium composition profiles. Our simulation results explain the reason that all the existing core-shell alloy NWs grown by vapor-liquid-solid experiments have cores rich in the unstrained (or less strained) components is because they have been grown via the layer-by-layer mode and, more importantly, suggest a possible route towards controlling the NW core-shell composition by altering growth mode and/or selecting substrate.

The Preparation of Core-Shell Type Acrylic-Polyurethane Composite Emulsions for Pigment Printing

Vinyl-endblocked polyurethanes were prepared from polyether diols(N210), isophorone diisocyanate (IPDI), dimethylol propionic acid (DMPA) and 2-hydroxyethyl acrylate (HEA). The core-shell structure acrylic-polyurethane composite emulsion was prepared by seeded emulsion polymerization of methyl methacrylate (MMA) and butyl acrylate (BA) using the polyurethanes emulsions as seeded emulsions. The core and shell regions were occupied by acrylic polymer and polyurethane, respectively. Because polyurethanes were vinyl-endblocked, acrylic monomers could graft partially to them. The formation of core-shell structure was observed by transmission electron microscopy (TEM). The structure and properties of dried film were studied by Fourier-transform infrared spectroscopy (FT-IR) and TGA.

Predicting microstructures in polymer blends under two-step quench in two-dimensional space

The formation of nanostructures during two-step quench in binary polymer systems having various types of liquid miscibility gaps are investigated systematically via computer simulations using the phase field method. Coupled liquid spinodal decomposition and fluid flow processes are considered by solving simultaneously the Cahn-Hilliard and Navier-Stokes equations. Various interesting phenomena and morphological patterns are predicted. It is found that the primary microstructures developed at the first quench and isothermal holding temperature greatly affect the secondary microstructures developed during the second quench and isothermal holding. Depending on the morphology and scale of the primary microstructure, either multicore and multishell or unicore and unishell structures are predicted. The breakup of annuluses in a core-shell structure in two dimensions is analyzed. The effects of viscosity on the formation of core-shell structure and on the growth and coarsening behaviors of bimodal droplets produced by the two-step quench in systems are also investigated.

Fabrication and optical study of Ag@SnO2 core-shell structure nanoparticle thin films

Ag@SnO2 core-shell nanoparticles dispersed in poly-(vinyl) alcohol films were fabricated on glass substrate by employing a dip-coating technique. Synthesis of Ag@SnO2 nanoparticles with core-shell morphology is carried out by a soft-chemical technique in aqueous phase at 60°C. Formation of core-shell structure is monitored by the red-shift of the surface plasmon band of Ag nanoparticles (from 390 to 410 nm) in the UV-visible spectrum. These nanoparticles are deposited on the glass substrate. The structure and morphology of these films were investigated by X-ray diffraction technique and field-emission transmission electron microscopy, respectively. Optical properties of these pseudo-solids were studied by UV-visible spectroscopy. Surface plasmon spectrum of the core-shell nanoparticles film remained unaltered with increase in the number of layers. However, silver nanoparticles films have shown peak broadening and development of additional peaks with increase in the number of layers. Our investigations showed that the surface plasmon band of the silver nanoparticles could be preserved by controlled deposition of the tin dioxide shell.

Composition, surface segregation, and electrochemical properties of binary PtM/C (M = Co, Ni, Cr) catalysts

The effect of the nature of transient metal and chemical treatment of binary cathodic PtM/C (M = Co, Ni, Cr) catalysts, which were prepared by high-temperature synthesis, on their structure, surface segregation, and characteristic properties (activity and stability) is studied. It is shown that, in the course of treatment in 0.5 M H2SO4 at the elevated temperature (60°C), the surface of nanoparticles becomes enriched in platinum with the formation of core-shell structures. The PtCo/C catalyst is the most efficient one. In this case, a compromise between the corrosion resistance and electrocatalytic activity is reached due to a higher, as compared with PtNi/C and PtCr/C, degree of alloy formation and enriching of surface in platinum in the course of corrosive attack. Thereby, the properties of platinum on the core surface change as a result of a pronounced ligand effect of the core. Thus, depending on the nature of transient metal, the binary cathodic PtM/C catalysts differ in their activity and stability, which depend on the degree of alloy formation and a possibility of formation of core-shell structure as a result of surface segregation in the course of synthesis and chemical treatment.

Formation of core-shell structured silicon nanoparticles during pulsed laser ablation

We performed pulsed laser ablation of Si target in nitrogen background gas and found that core-shell structured nanoparticles can be prepared without postsurface treatment. The predominant ejected species from the target at free expansion region is Si, and N related species appears at the point blast region. The core-shell structure and plume expansion dynamics suggest that nuclei of the Si nanodroplets are formed in early stage followed by growth of nanodroplets and nitraidation at the surfaces region of the nanodroplets. Formation of core shell structure is a result of nonequilibrium high energy pulsed ejection of Si species.

Direct Observation of a Surface Induced Disordering Process in Magnetic Nanoparticles

We present experimental evidence of surface induced disordering at magnetic FeCoPd nanoparticles during the L1(0)-A1 phase transition using high-resolution aberration-corrected electron microscopy and strain mapping. In situ electron diffraction studies show a narrow temperature range of fully ordered L1(0) structure. The order-disorder transition is size dependent and induces strong lattice deformation in outer part of the nanocrystals. The formation of unusually large strain of 20% is discussed in terms of core-shell structure formation with surface disordered layer and ordered core.

Co 3O 4 coated Al composites as anode materials for lithium ion batteries

The Co 3O 4 coated Al composites with different Co 3O 4 content were synthesized by a rheological phase reaction in combination with a following heat-treatment process. The composites were characterized by X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, galvanostatic cycling and ac impedance spectroscopy. Results revealed that Al matrix is coated by Co 3O 4 nanoparticles to form a core-shell structure. The composites exhibit improved cycle performance than pure Al particles. After ten cycles, the capacity retentions of Al-1 wt.% Co 3O 4, Al-3 wt.% Co 3O 4 and Al-5 wt.% Co 3O 4 are 66.8, 69.9 and 70.1% respectively, which are much higher than that of pure aluminum (42%). The improvement of cycle performance is related to the formation of core-shell structure, which plays important roles in the enhancement of mechanical stability and the reinforcement of electronic contact.

Formation of Core-Shell Structure in BaTiO3Grains

To understand the formation of core-shell structure in BaTiO₃ (BT) grains in multilayer ceramic capacitors, specimens were prepared with BT powders mixed with Y and Mg, and their microstructures were investigated with scanning electron microscopy, x-ray diffractometry, and transmission electron microscopy. Microstructural investigation showed that Y dissolved easily in BT lattice to a certain depth inside of the grain, whereas Mg tended to stay at grain boundaries rather than become incorporated into BT. It was considered that in case of Y and Mg addition in a proper ratio, Y could play a dominant role in the formation of shell leading to a slight dissolution of Mg in the shell. Next, the effects of ball-milling conditions on the core-shell formation were studied. As the ball-milling time increased, the milled powders did not show a significant change in size distribution but rather an increase of residual strain, which was attributed to the milling damage. The increase in milling damage facilitated the shell formation, leading to the increased shell portion in the core-shell grain.

Imidazolium cation mediated synthesis of polystyrene–polyaniline core–shell structures

Herein we report a novel strategy to fabricate polystyrene–polyaniline (PS–PANi) core–shell structures using cationic PS latex particles without any further surface modification. Imidazolium cation functionalized monodispersed PS particles with diameter ranging from 100 to 700 nm were first prepared via precipitation polymerization and emulsion polymerization processes with the aid of ionic liquids containing imidazolium cations. Subsequently, AuCl4− was immobilized on the surface of PS particles via the imidazolium cations and acted as the oxidant for aniline polymerization, thus directing the core–shell structure formation as aniline hydrochloride was added into the system. PS–PANi core–shell spheres with uniform PANi shells were obtained. Furthermore, a seeded growth method was successfully applied in controlling the thickness of PANi shell. This is the first example in which the oxidant was immobilized on the surface of PS particles to direct the PS–PANi core–shell structure formation.

Role of yttrium and magnesium in the formation of core-shell structure of BaTiO 3 grains in MLCC

To understand the contribution of additive elements to the formation of core-shell structure in BaTiO 3 (BT) grains in multilayer ceramic capacitors, specimens were prepared with BT powders mixed with Y and Mg, and their microstructures were investigated in terms of scanning electron microscopy, X-ray diffractometry, and transmission electron microscopy. The additives inhibited growth of the BT grains, particularly leading to a much reduced sinterability for Y addition. Microstructural investigation showed that Y dissolved easily in BT lattice to a certain depth inside of the grain whereas Mg tended to stay at grain boundaries rather than to be incorporated into BT. It was considered that, added in a proper ratio, Y could play a dominant role in the formation of shell, leading to a slight dissolution of Mg in the shell.

Detecting Core-Shell Structure Formation Using near Infrared Spectroscopy

It is well known that the final end-use properties of polymer resins depend on several variables. Among them, the morphological aspects of the polymer resin have received considerable attention over the last few years. Particularly, efforts have been devoted towards the study and production of core-shell polymer particles, which find many applications as supports; chromatographic packing among others. Recently, Lenzi et al.1 developed a new process, that combines typical suspension and emulsion polymerisation recipes, to produce polystyrene core-shell particles. In this work, it is shown that NIR spectroscopy can be used as an alternative tool as an in-line system (for in situ detection) of the formation of the core-shell structure in polystyrene core-shell polymer particles produced during simultaneous suspension/emulsion polymerisations.

Preparation and properties of amorphous titania-coated zinc oxide nanoparticles

Amorphous TiO 2-coated ZnO nanoparticles were prepared by the solvothermal synthesis of ZnO nanoparticles in ethanol and the followed by sol–gel coating of TiO 2 nanolayer. The analyses of X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that the resultant ZnO nanoparticles were hexagonal with a wurtzite structure and a mean diameter of about 60 nm. Also, after TiO 2 coating, the TEM images clearly indicated the darker ZnO nanoparticles being surrounded by the lighter amorphous TiO 2 layers. The zeta potential analysis revealed the pH dependence of zeta potentials for ZnO nanoparticles shifted completely to that for TiO 2 nanoparticles after TiO 2 coating, confirming the formation of core-shell structure and suggesting the coating of TiO 2 was achieved via the adhesion of the hydrolyzed species Ti–O − to the positively charged surface of ZnO nanoparticles. Furthermore, the analyses of Fourier transform infrared (FTIR) and Raman spectra were also conducted to confirm that amorphous TiO 2 were indeed coated on the surface of ZnO nanoparticles. In addition, the analyses of ultraviolet–visible (UV–VIS) and photoluminescence (PL) spectra revealed that the absorbance of amorphous TiO 2-coated ZnO nanoparticles at 375 nm gradually decreased with an increase in the Ti/Zn molar ratio and the time for TiO 2 coating, and the emission intensity of ZnO cores could be significantly enhanced by the amorphous TiO 2 shell.

Redox−Transmetalation Process as a Generalized Synthetic Strategy for Core−Shell Magnetic Nanoparticles

Although multicomponent core-shell type nanomaterials are one of the highly desired structural motifs due to their simultaneous multifunctionalities, the fabrication strategy for such nanostructures is still in a primitive stage. Here, we present a redox-transmetalation process that is effective as a general protocol for the fabrication of high quality and well-defined core-shell type bimetallic nanoparticles on the sub-10 nm scale. Various core-shell type nanomaterials including Co@Au, Co@Pd, Co@Pt, and Co@Cu nanoparticles are fabricated via transmetalation reactions. Compared to conventional sequential reduction strategies, this transmetalation process has several advantages for the fabrication of core-shell type nanoparticles: (i) no additional reducing agent is needed and (ii) spontaneous shell layer deposition occurs on top of the core nanoparticle surface and thus prevents self-nucleation of secondarily added metals. We also demonstrate the versatility of these core-shell structures by transferring Co@Au nanoparticles from an organic phase to an aqueous phase via a surface modification process. The nanostructures, magnetic properties, and reaction byproducts of these core-shell nanoparticles are spectroscopically characterized and identified, in part, to confirm the chemical process that promotes the core-shell structure formation.

Synthesis and Characterization of N,N-Dimethyldodecylamine-Capped Aucore-Pdshell Nanoparticles in Toluene

In this paper a convenient route for synthesizing Au(core)-Pd(shell) bimetallic nanoparticles in toluene has been reported as a result of co-reduction of gold(III) and palladium(II) precursors in toluene. N,N-Dimethyldodecylamine was used as a capping agent for the core-shell particles, which not only imparts stability to the organosol but also controls morphology of the evolved particles. The particles were characterized using UV-visible, transmission electron microscopy, and X-ray diffraction measurements. All results substantiate the formation of core-shell structure of the synthesized particles.

A facile liquid foam based synthesis of nickel nanoparticles and their subsequent conversion to NicoreAgshell particles: structural characterization and investigation of magnetic properties

A facile route for the synthesis of nickel nanoparticles in stable aqueous foams is reported. The Ni nanoparticles were roughly 12–15 nm in size and were stable as aqueous suspensions or powders when oleic acid was used as a capping agent. These Ni nanoparticles were subsequently coated with a silver shell in view of the extra stability and the enhanced manipulative ability afforded by the silver nanocoating. This was accomplished by a simple transmetallation reaction wherein the nanoparticle surface nickel atoms act as localized reducing agents for the silver ions in solution. As the silver shell is formed through the surface reaction a reduction in the average size of the Nicore occurs. After the core–shell structure formation, the Nicore has an average diameter of 10–20 nm while the Agshell has a thickness of 2–4 nm. The pristine oleic acid coated Ni and NicoreAgshell nanoparticles were probed for their magnetic characteristics by a vibrating sample magnetometer. The nascent, oleic acid coated Ni nanoparticles display a low superparamagnetic blocking temperature, TB, of 20 K. The field dependent magnetic behaviour above and below TB displays the standard features corresponding to superparamagnetism, as expected for very small Ni crystallites suggesting again that each 12 nm particle is polycrystalline. The magnetic contribution in the NicoreAgshell system comes from only the Ni core and predictably, the blocking temperature of this system is below 12 K due to the smaller size of the Ni core.

Effect of Ho/Mg Ratio on Formation of Core-shell Structure in BaTiO3 and on Dielectric Properties of BaTiO3 Ceramics

Ceramics were prepared from hydrothermally-synthesized BaTiO3 (100 mol%), BaSiO3 (1.5 mol%), MnO (0.1 mol%) with Ho2O3 (0.5 mol%) and MgO (0.25–1 mol%). The compositions with Ho/Mg molar ratios of 4:4, 4:2, 4:1 were selected for examination. The ceramic samples were sintered at 1340°C (PO2<10-9 Pa) and, then, annealed at 1000°C (PO2<30 Pa). The distribution of Ho and Mg in the samples was examined by transmission electron microscope (TEM) equipped with an element analyzer (EDS). Measurements of temperature dependence of dielectric permittivity over -55–155°C showed that the sample with a Ho/Mg ratio of 4/4 showed the least change of dielectric permittivity with temperature compared to the sample with a high Ho/Mg ratio of 4/1. The material with a Ho/Mg ratio of 4/1 is characterized by the deepest Ho diffusion into BaTiO3 and the slowest decrease of Ho concentration that is considered to result in a formation of a shell with considerable amounts of low-concentrated Ho-containing solid solutions.

Synthesis and Characterization of Core-Shell Silica-Phosphor Nanoparticles &amp;lt;italic&amp;gt;via&amp;lt;/italic&amp;gt; Sol-Gel Process

&lt;p&gt;Cost-effective functional phosphor nanoparticles are prepared by introducing low-cost SiO&lt;sub&gt;2&lt;/sub&gt; spheres to rareearth phosphor (YVO&lt;sub&gt;4&lt;/sub&gt;:Eu&lt;sup&gt;3+&lt;/sup&gt;, YVO&lt;sub&gt;4&lt;/sub&gt;:Er&lt;sup&gt;3+&lt;/sup&gt;, and YVO&lt;sub&gt;4&lt;/sub&gt;:Nd&lt;sup&gt;3+&lt;/sup&gt;) shells using a sol-gel synthetic method. These functional nanoparticles are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and general photoluminescence spectra. The SiO&lt;sub&gt;2&lt;/sub&gt; sphere occupying the interior of the conventional phosphor is advantageous in significantly reducing the cost of expensive rare-earth phosphor nanoparticles. The sol-gel process facilitates the core–shell structure formation; the rare-earth shell phosphor has strong interactions with chelating agents on the surfaces of SiO&lt;sub&gt;2&lt;/sub&gt; nanoparticles and thus forms layers of several nanometers in thickness. The photoluminescence wavelength is simply tuned by replacing the active materials of Eu&lt;sup&gt;3+&lt;/sup&gt;, Er&lt;sup&gt;3+&lt;/sup&gt;, and Nd&lt;sup&gt;3+&lt;/sup&gt;. Moreover, the photoluminescent properties of the core–shell nanoparticles can be optimized by manipulating the specific contents of active materials in the phosphors. Our simple approach substitutes low-cost SiO&lt;sub&gt;2&lt;/sub&gt; for expensive rare-earth-based phosphor materials to realize cost-effective phosphor nanoparticles for various applications.&lt;/p&gt;