Distinct Core-shell Structure Research Articles

Grinding Characteristics and Removal Mechanisms of LaPO<sub>4</sub>/Al<sub>2</sub>O<sub>3</sub> Micro-Nano Composite Ceramics

In this paper, the prepared LaPO4/Al2O3composite ceramics were ground by the surface grinding machine. The phase composition and morphology of the coated powders as well as the microstructure of grinding surface of the ceramics were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Scanning electron microscope (SEM), respectively. The results show that the coated powders have a distinct core-shell structure which has a great effect on material’s removal approaches. The main fracture mode is caused by intragranular fracture of layered LaPO4rather than the weak interface. Besides, the primary grinding removal mechanism of LaPO4/Al2O3composite ceramics mainly rise from cracks propagating along the interlayer of LaPO4.

One-Step Synthesis of Fe@SiO<sub>2</sub> and Its Application in Cr(VI) Removal

Without using aqueous ammonia and a surface modifier, a facile one-step method was developed to fabricate Fe nanoparticles coated with a SiO2 shell (Fe@SiO2) by a modified Stober method combined with an aqueous reduction method. The Fe@SiO2, was prepared by directly adding potassium borohydride to a mixed solution of tetraethylorthosilicate (TEOS) and anhydrous ferric chloride. The structure and morphology of the as-synthesized powders were investigated by X-ray powder diffraction (XRD), energy dispersion analysis of X-ray (EDAX), transmission electron microscopy (TEM), ultraviolet-visible (UV-Vis) absorption spectroscopy, Fourier-transform infrared (FTIR) spectrometry and X-ray photoelectron spectroscopy (XPS). The feasibility of using the prepared Fe@SiO2 for the reductive immobilization of Cr(VI) in water was studied. The influence of TEOS addition on Cr(VI) removal by Fe@SiO2 was investigated. The results showed that the prepared Fe@SiO2 had a distinct core-shell structure. One or two Fe nanoparticles (20-30 nm in diameter) were homogeneously coated by a porous SiO2 shell. With an increase in the amount of added TEOS the Fe nanoparticles had better dispersion and the thickness of the SiO2 coating increased gradually. Compared with uncoated Fe nanoparticles, Cr(VI) removal by Fe@SiO2 increased greatly. At a TEOS dosage of 0.1 mL the removal ability of the prepared Fe@SiO2 was the highest. The highest removal ability of Fe@SiO2 was 466.67 mg . g(-1) and it was only 76.35 mg . g(-1) for uncoated Fe nanoparticles.

Self-assembly and drug delivery behaviors of a novel thermo-sensitive block glycopolymer

A novel thermo-sensitive block glycopolymer based on peracetylated maltoheptaose (AcMH) and poly(2-ethyl-2-oxazoline) (PEtOz) was synthesized for the first time and characterized by hydrogen nuclear magnetic resonance (1H NMR) spectroscopy and gel permeation chromatograph (GPC) analyses. To obtain such a block polymer, the dihydroxyl poly(2-ethyl-2-oxazoline) homopolymer (OH-PEtOz-OH) was first synthesized by cationic ring-opening polymerization of 2-ethyl-2-oxazoline (EtOz), and then coupled with the peracetylated maltoheptaose having a free hydroxyl group at the reducing end (AcMH-OH) prepared from β-cyclodextrin. It was found that the obtained block polymer could self-assemble into nanosize spherical micelles with a distinct core-shell structure in aqueous solution triggered by its amphiphilic character without any organic solvent. The model drug indomethacin (IND) was efficiently loaded into the resultant polymeric micelles, which was confirmed by 1H NMR spectra, transmission electron microscope (TEM) and dynamic light scattering (DLS) techniques. The release behavior of IND loaded micelles was well in response to the environmental temperature change. It is suggested that the resulting micelles might be a potential targeted carrier for drug delivery.

Synthesis and characterization of poly ( n-butyl acrylate)-poly (methyl methacrylate) latex interpenetrating polymer networks by radiation-induced seeded emulsion polymerization

A series of latex interpenetrating polymer networks (LIPNs) were prepared via a two-stage emulsion polymerization of methyl methacrylate (MMA) or mixture of MMA and n-butyl acrylate ( n-BA) on crosslinked poly( n-butyl acrylate)(PBA) seed latex using 60Co γ-ray radiation. The particles of resultant latex were produced with diameters between 150 and 250 nm. FTIR spectra identified the formation of crosslinked copolymers of PMMA or P(MMA- co-BA). Dynamic light scattering (DLS) showed that with increasing n-BA concentration in second-stage monomers, the particle size of LIPN increased. Transmission electron microscope(TEM) photographs showed that the morphology of resultant acrylate interpenetrating polymer network (IPN) latex varied from the distinct core-shell structure to homogenous particle structure with the increase of n-BA concentration, and the morphology was mainly controlled by the miscibility between crosslinked PBA seed and second-stage copolymers and polarity of P(MMA- co-BA)copolymers. In addition, differential scanning calorimeter (DSC) measurements indicated the existence of reinforced miscibility between PBA seed and P(MMA- co-BA)copolymer in prepared LIPNs.

EXAFS studies of bimetallic Ag-Pt and Ag-Pd nanorods

Nanoparticles of Ag-Pt and Ag-Pd with high aspect ratios were synthesized using a radiolysis method. Gamma rays at dose rates below 0.5 kGy/h were used for irradiation. The nanoparticles were characterized by transmission electron microscopy (TEM), optical absorption spectroscopy and x-ray Absorption Fine Structure (XAFS) spectroscopy. Bright field micrographs show that Ag-Pt nanowires are composed of large particles with diameters ranging from 20–30 nm and joined by filaments of diameter between 2–5 nm. The Ag-Pd nanowires have diameters of 20–25 nm and lengths of 1.5 μm. For XAFS measurements, the Pt L3 edge (11.564 keV), Ag K-edge (25.514 keV) and Pd K-edge (24.350 keV) were excited to determine the local structure around the respective atoms in the cluster. The Ag-Pt particles were found to possess a distinct core-shell structure with Pt in the core surrounded by Ag shell, with no indication of alloy formation. However, nanorods of Ag-Pd have formed an alloy for all the alloy compositions.

In situ formation of SiC–Si2ON2 micro-composite materials from preceramic polymers

Si-filler-loaded poly(methylsilsesquioxane) was pyrolyzed in nitrogen atmosphere between 1250 and 1600°C to fabricate Si–O–C–N micro-composite materials. The evolution of the microstructure and the resulting nanocomposition were studied by X-ray diffraction, scanning electron microscopy (SEM), high-voltage electron microscopy, high-resolution electron microscopy, electron energy-loss spectroscopy (esp. energy-loss near-edge structures), and porosity analysis. At pyrolysis temperatures below the melting point of Si (1414°C) the silicon oxynitride (Si2ON2) formation proceeds via a vapor phase reaction between SiO and N2 in the pores and results in fiber-like aggregates with distinct core–shell structures containing nanocrystalline regions. At higher temperatures the molten Si filler is involved in the silicon oxynitride formation reactions, and above 1500°C a complete conversion of the Si filler and the Si–C–O matrix into Si2ON2 takes place with a significant reduction of the porosity in comparison to the gas phase reaction regime.

Liquid-phase sintering and chemical inhomogeneity in the BaTiO3–BaCO3–LiF system

An ongoing goal of multilayer capacitor research is to lower the firing temperature of the dielectric. This paper gives a detailed study of sintering BaTiO3 with LiF flux, which lowers the firing temperature through liquid-phase sintering. A detailed set of experiments is discussed concerning microstructural evolution and corresponding dielectric properties under a number of processing variables, including amount of LiF, sintering temperature, and particle size. Different scales of chemical inhomogeneity were observed in this system, which reflect two underlying mechanisms: solution reprecipitation with limited grain growth at low temperatures, which resulted in distinct core–shell structures, and flux volatility, which gave rise to microscopic chemical inhomogeneity at higher sintering temperatures.

A transmission electron microscope study of commercial X7R-type multilayer ceramic capacitors

X7R-type multilayer ceramic capacitors produced by three commercial manufacturers (A, B and C) have been investigated by transmission electron microscopy. All the specimens contained grains with distinct core-shell structures; the cores were almost pure BaTiO 3 and exhibited domain structures at room temperature. Specimens of type A had a grain size of 1–2μm, with ‘wide’ shells containing Pb, Bi, Nb, Ba and Ti. A bonding phase, rich in Si, Al, Ba and Ti was detected between the dielectric grains and Ag-Pd electrodes. Heating the samples to temperatures above 130 °C caused the ferroelectric domain structure to be lost and replaced by a dislocation network. Specimens of type B and C had a grain size of 0.5–1.0 μm; the ferroelectric cores were surrounded by ‘narrow’ shells rich in Nb, Co, Ba and Ti. The Ag-Pd internal electrodes were twinned. Type I and type II core-shell structures were found in all three sets of multilayer ceramic capacitors.

Measurement of mutation frequency at the HPRT locus in peripheral lymphocytes; Is this a good method to evaluate a cancer risk in pediatric patients?

A novel approach based on surface molecularly imprinted technique is demonstrated for the synthesis of surface molecularly imprinted silica nanoparticles (MI-SiNPs) in aqueous media, using l-tryptophan (l-Trp) as template molecule. The MI-SiNPs were fully characterized by transmission electron microscopy (TEM), thermo gravimetric analysis (TGA) and atomic force microscopy (AFM), and the results showed MI-SiNPs thus prepared were uniform in particle size (∼87 nm) with a distinct core–shell structure with shell thickness of ∼7 nm. The terminal carboxyl groups endowed the MI-SiNPs with good water-compatibility, and so good suspension stability for MI-SiNPs in water-rich buffer solutions can be easily achieved without the addition of any other reagents. When MI-SiNPs were used as pseudostationary phases (PSPs) in electrokinetic chromatography (EKC) for the enantioseparation of Trp, a resolution of 2.73 can be achieved in less than 10 min with symmetric peaks. These excellent separation features are mainly attributed to the fast mass transfer and good accessibility of the interaction sites locating at the surface of the MI-SiNPs. The effects of some important separation factors, e.g., pH and concentration of buffer solution, content of MI-SiNPs added, content of organic modifier in buffer solution, on the enantioseparation of Trp were studied, and an optimum separation condition of 30% (v/v) acetonitrile in 20 mmol L−1 phosphate buffer (pH 7.0), with 0.50 mg mL−1 MI-SiNPs added was ultimately selected.

Competitive adsorption of an anionic and a nonionic surfactant on polystyrene latex particles as monitored by small x-ray scattering

Adsorption of the anionic surfactant sodium dodecylsulfate (SDS) as well as competitive adsorption of SDS with the nonionic surfactant Triton X-405 on a polystyrene latex has been examined by the use of small-angle x-ray scattering (SAXS). Since the latex particles only have a low contrast towards water whereas the electron densities of the added surfactants are rather high, their gradual adsorption can be monitored with good sensitivity. The particles covered with SDS have been investigated by the contrast variation method. A distinct core-shell structure has been observed. After maximum coverage of the surface is reached, the additional surfactant forms free micelles. The analysis presented here allows the simultaneous investigation of the covered particles and the free micelles. This is due to their respective characteristic scattering contributions in different angular ranges. Information on the competitive adsorption could be obtained by analyzing the structure of the coated particles and the composition of the free mixed micelles. The adsorption is shown to be an equilibrium process where adsorption of the nonionic component is found to be much stronger than of the SDS molecules.