Template synthesis of nanostructured silica with hollow core and mesoporous shell structures

Silica capsules with hollow macroporous core–mesoporous shell (HCMS) were synthesized through template-assisted replication of submicrometer-size polystyrene spheres as templates. The silica mesoporous shell exhibited highly ordered hexagonal structure as confirmed by X-ray diffraction pattern and TEM image. The pore diameter and BET surface area of this sample were found to be 2.1 nm and 1387 m²/g, respectively.     

A novel approach to fabrication of superparamagnetite hollow silica/magnetic composite spheres

We described a method for synthesizing hollow silica/magnetic composite spheres using sulfonic acid functionalized hollow silica spheres (SAFHSS) as templates. The Fe₃O₄ nanoparticles were deposited on or imbedded in the hollow silica shell by a precipitation reaction. The morphologies, composition and properties of the hollow composite spheres were characterized by transmission electron microscopy, Fourier transform infrared analysis, X-ray diffraction measurement and vibrating-sample magnetometry measurement. The results indicated crystal sizes and amount of the Fe₃O₄ nanoparticles on the SAFHSS. The magnetic properties of the hollow composite spheres were controlled by adjusting the proportion between Fe²⁺ and Fe³⁺ and iron ion total concentration. When appropriate loading species were added into the system, superparamagnetite hollow composite spheres were obtained. The method also could be applicable to prepare other superparamagnetite hollow silica/ferrite composite spheres.     

Preparation and characterization of core/shell particles with siloxane in the shell

The core/shell particles consisting of polystyrene core and 3-(methacryloxypropyl)-trimethoxysilane (MPS) shell were prepared in the present study by successive seeding polymerization under kinetically controlled conditions and were characterized by particle size analyser, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The TEM image indicated that the particles containing organic siloxane presented an evident core/shell structure. Additionally, the study of XPS also revealed that MPS could be grafted onto the surface of polystyrene microspheres and the atomic ratio of C/Si on the surface of the core/shell particles (MPS-40) was very close to the ratio of C/Si in the molecule of MPS. The surface properties of the films produced from the core/shell particles were also investigated by the static contact angle method. Compared with the homopolymer of PS, the core/shell particles were more effective to create hydrophobic surface, so, the introduction of MPS was capable of obvious increase in water repellency.     

A novel approach for the preparation of PMMA-PDMS core-shell particles with PDMS in the shell

The core/shell particles consisting of polymethyl methacrylate (PMMA) core and polydimethylsiloxane (PDMS) shell via 3-(methacryloxypropyl)-trimethoxysilane (MPS) as the medium to link the core and shell were prepared in our present study by successive seeding polymerization under kinetically controlled conditions and were characterized by FT-IR, particle size analyzer, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS).The picture of optical microscope showed the clear form of PDMS-0 and PDMS-40 (the content of PDMS in the particles), which approached to monodispersed distribution. Compared with the PMMA microspheres, PDMS-40 presented an evident core/shell structure through the observation of TEM. Additionally, the study of XPS revealed that PDMS could be grafted onto the surface of PMMA particles and the atomic ratio of C/Si on the surface of PDMS-40 was very close to the ratio of C/Si in the molecule of PDMS. The surface properties of the films produced from the core/shell microspheres also were investigated by contact angle method, contrast with the homopolymer of PMMA, the core/shell particles were more effective to form hydrophobic surface and the water repellency on the surface would be better than that of PMMA.     

Synthesis of magnetic and lightweight hollow microspheres/polyaniline/Fe3O4 composite in one-step method

After hollow microspheres (HM) were surface modified, a layer of electromagnetic polyaniline/Fe₃O₄ composite (PAN/Fe₃O₄) was successfully grafted onto the surface of the self-assembled monolayer coated HM, resulting in HM/PAN/Fe₃O₄ composites. In this approach, γ-aminopropyltriethoxy silane was adopted to form a well-coating monolayer with amino groups for the graft polymerization of aniline, which played an important role in fabricating the core-shell structure. FeCl₃ was used as the oxidant not only for aniline to form PAN, but also for FeCl₂ to prepare the magnets. The structure, morphologies, and magnetic properties of the as-prepared samples were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and vibrating sample magnetometer. The results indicated that the HM/PAN/Fe₃O₄ composites possess low density (ρ < 1.0 g/cm³), controllable morphology, and good magnetic properties at room temperature (saturation magnetization Ms = 8.32 emu g⁻¹ and coercive force Hc ≈ 0).     

Effects of crystalline grain size and packing ratio of self-forming core/shell nanoparticles on magnetic properties at up to GHz bands

Self-forming core/shell nanoparticles of magnetic metal/oxide with crystalline grain size of less than 40 nm were synthesized. The nanoparticles were highly concentrated in an insulating matrix to fabricate a nanocomposite, whose magnetic properties were investigated. The crystalline grain size of the nanoparticles strongly influenced the magnetic anisotropy field, magnetic coercivity, relative permeability, and loss factor (tan δ=μ″/μ′) at high frequency. The packing ratio of the magnetic metallic phase in the nanocomposite also influenced those properties. High permeability with low tan δ of less than 1.5% at up to 1 GHz was obtained in the case of the nanoparticles with crystalline grain size of around 15 nm with large packing ratio of the nanoparticles.     

Ultrasonic-assisted ultra-rapid synthesis of monodisperse meso-SiO2@Fe3O4 microspheres with enhanced mesoporous structure

A core–shell-type of meso-SiO₂@Fe₃O₄ microsphere was synthesized via an ultrasonic-assisted surfactant-templating process using solvothermal synthesized Fe₃O₄ as core, tetraethoxysilane (TEOS) as silica source, and cetyltrimethyl ammonium bromide (CTAB) as templates. The samples were characterized by FT-IR, XRD, TEM, N₂ adsorption–desorption technology, and vibrating sample magnetometer (VSM). The results show that as-prepared meso-SiO₂@Fe₃O₄(E) and meso-SiO₂@Fe₃O₄(C) microspheres, treated by acetone extraction and high temperature calcination, respectively, still maintain uniform core–shell structure with desirable mesoporous silica shell. Therein, the meso-SiO₂@Fe₃O₄(E) microspheres possess a distinct pore size distribution in 1.8–3.0 nm with large specific surface area (468.6 m²/g) and pore volume (0.35 cm³/g). Noteworthily, the coating period of this ultrasonic-assisted method (40 min) is much shorter than that of the conventional method (12–24 h). The morphology of microspheres and the mesoporous structure of silica shell are significantly influenced by initial concentration of CTAB (C_CTAB), ultrasonic irradiation power (P) and ultrasonic irradiation time (t). The acceleration roles of ultrasonic irradiation take effect during the whole coating process of mesoporous silica shell, including hydrolysis-condensation process of TEOS, co-assembly of hydrolyzed precursors and CTAB, and deposition of silica oligomers. In addition, the use of ultrasonic irradiation is favorable for improving the homogeneity of silica shell and the monodispersity of meso-SiO₂@Fe₃O₄ microspheres.     

Facile synthesis and characterization of glass/cobalt core/shell composite spheres with tunable shell morphologies

Polyhedral cobalt microcrystals assembled on hollow glass spheres are successfully synthesized by a facile and easy-control hydrothermal reduction process, and thus hierarchical glass/cobalt core/shell composite hollow spheres are fabricated with low-density (0.96 g cm⁻³). By properly tuning the process conditions and the component of the reaction solution, a series of composite spheres with gradient in morphologies of the shell layer can be prepared. Based on a series of contrast experiments, the probable formation mechanism of the core/shell hierarchical structures is proposed. The magnetic properties of the products are studied and the results demonstrate that the composite spheres present ferromagnetic properties related to the special shell morphologies. The composite hollow spheres thus obtained may have some promising applications in the fields of low-density magnetic materials, conduction, and catalysis, etc. This work provides an additional strategy to prepared core/shell composite spheres with tailored shell morphology and magnetic properties.     

Novel magnetic Fe onion-like fullerene micrometer-sized particles of narrow size distribution

Magnetic polydivinylbenzene (PDVB)/magnetite micrometer-sized particles of narrow size distribution were prepared by entrapping Fe(CO)₅ within the pores of uniform porous PDVB particles, followed by the thermal decomposition of the encapsulated Fe(CO)₅ at 300 °C in a sealed cell under inert atmosphere. Magnetic Fe onion-like fullerene micrometer-sized particles of narrow size distribution have been prepared by the thermal decomposition of the PDVB/magnetite magnetic microspheres at 1100 °C under inert atmosphere. The graphitic coating protects the elemental iron particles from oxidation and thereby preserves their very high magnetic moment for at least a year. Characterization of these unique magnetic carbon graphitic particles was also performed.     

Effects of pressure on maghemite nanoparticles with a core/shell structure

The magnetic property and intraparticle structure of the γ phase of Fe₂O₃ (maghemite) nanoparticles with a diameter (D) of 5.1±0.5 nm were investigated through AC and DC magnetic measurements and powder X-ray diffraction (XRD) measurements at pressures (P) up to 27.7 kbar. Maghemite originally exhibits ferrimagnetic ordering below 918 K, and has an inverse-spinel structure with vacancies. Maghemite nanoparticles studied here consist of a core with structural periodicity and a disordered shell without the periodicity, and core shows superparamagnetism. The DC and AC susceptibilities reveal that the anisotropy energy barrier (ΔE/k_B) and the effective value of the core moment decrease against the initial pressure (P≤3.8 kbar), recovering at P≥3.8 kbar. The change of ΔE/k_B with P is qualitatively identical with that of the core moment, suggesting a down-and-up fluctuation of the number of Fe³⁺ ions constituting the core at the pressure threshold of about 4 kbar. This phenomenon was confirmed by the analysis of the XRD measurement using Scherrer’s formula. The core volume decreased for P≤2.5 kbar, whereas at higher pressure the core was restructured. For 2.5≤P≤10.7 kbar, the volume shrinkage of particle hardly occurs. There, ΔE/k_B is approximately proportional to the volume associated to the ordered fraction of the nanoparticles as seen from XRD, V_core. From this dependence it is possible to separate the core/shell contribution to ΔE/k_B and estimate core and surface anisotropy constants. As for the structural experiments, similar experimental data have been obtained for D=12.8±3.2 nm as well.     

Hard magnetic properties of anisotropic Sm-Fe-N magnets produced by compression shearing method

Anisotropic Sm-Fe-N bulk magnets were produced by the compression shearing method using a hardened steel plate and a tungsten-carbide (WC) plate. It was found that the magnets retained the original Sm₂Fe₁₇N₃ phase structure without any appreciable decomposition of the Sm₂Fe₁₇N₃ phase. The anisotropic Sm-Fe-N bulk magnet produced using a WC plate had a higher density and higher crystallographic alignment of the Sm₂Fe₁₇N₃ phase than that produced using a hardened steel plate, and exhibited high maximum energy products of 228 kJ/m³ with a high coercivity of 0.88 MA/m.     

壳核型磁性纳米纤维素微球的超声制备及表征

以纳米级的Fe3 O4液体作为磁核 ,在非水体系的纤维素DMAc(N N二甲基乙酰胺 ) /LiCl溶液中 ,使用包埋法 ,在超声波的辅助下制备得到了纳米尺度的壳核型磁性纤维素微球 .利用FT IR、XRD及AFM/MFM (原子力显微镜 /磁场力显微镜 )对得到的磁性微球进行了表征 ,证实该微球由磁性的核与纤维素的壳组成 ,微球大小为 30～ 5 0nm ,且具有良好的分散性 .并研究了超声条件对磁性微球尺寸的影响 .     

Synthesis and rheological investigation of a magnetic fluid using olivary silica-coated iron particles as a precursor

A new type of magnetic fluid was prepared by dispersing monodispersed iron–silica (Fe–SiO₂) composite particles in polyethylene glycol (PEG) 400. The composite particles Fe–SiO₂ were synthesized by hydrogen reduction from α-Fe₂O₃–SiO₂ spheres. Their microstructures were observed by a high-resolution transmission electron microscope (HRTEM) and the magnetism was characterized with a superconducting quantum interference device (SQUID) magnetometer. Both steady-state and dynamic rheological properties of the magnetic fluid under different magnetic fields were studied by using a rheometer. Experimental results show that this magnetic fluid has a relatively high magnetoviscous effect at low shear rates. The yield stress of this material shows an increasing trend with a magnetic flux density. Also, viscoealstic properties of such materials are different from conventional ones.     

A one-pot method to prepare N-doped titania hollow spheres with high photocatalytic activity under visible light

N-doped titania hollow spheres (NTHS) were prepared by a one-pot hydrothermal method using urea as precursor of nitrogen. The prepared hollow spheres were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectrum (DRS). The photocatalytic activity of as-prepared titania hollow spheres was determined by degradation of Reactive Brilliant Red dye X-3B (C.I. reactive red 2) under visible light irradiation, and was compared to non-doped titania hollow spheres and commercial P25 titania. Results indicated that the as-prepared NTHS showed highest photocatalytic activity.     

液滴法制备空心玻璃微球的模拟计算

 通过对液滴法制备空心玻璃微球的成球过程进行分析,建立了成球过程数学模型,定量描述了液滴的形成、液滴的封装、凝胶球壳的形成与干燥,发泡剂的分解,球壳的预热与熔炼、冷却与收集等过程中,液滴/球壳的大小、速率、壁厚、气压等随操作条件的变化,计算了抽气速率、发泡剂浓度、玻璃溶液浓度和初始液滴大小等的改变对成球过程的影响,并进行了初步验证实验。     

A novel approach to preparing magnetic protein microspheres with core-shell structure

Magnetic protein microspheres with core-shell structure were prepared through a novel approach based on the sonochemical method and the emulsion solvent evaporation method. The microspheres are composed of the oleic acid and undecylenic acid modified Fe₃O₄ cores and coated with globular bovine serum albumin (BSA). Under an optimized condition, up to 57.8 wt% of approximately 10 nm superparamagnetic Fe₃O₄ nanoparticles could be uniformly encapsulated into the BSA microspheres with the diameter of approximately 160 nm and the high saturation magnetization of 38.5 emu/g, besides of the abundant functional groups. The possible formation mechanism of magnetic microspheres was discussed in detail.     

A simple method to estimate the magnetic moment of magnetic micro-particles

Micro-particles in suspension in a fluid are an example of a very low Reynolds number problem. In this case, no inertial effects are observed. Magnetic micro-particles with magnetic moment m, suspended in a fluid orient to applied external magnetic fields B due to the interaction between the field and the magnetic moment. In this work, we present a simple method to estimate the total magnetic moment of magnetic micro-organisms. The method is based on the application of an external oscillating magnetic field in the sites where the micro-organisms are. In this case, it is possible to obtain theoretically the solution of the equation of motion (rotation of the organism and its trajectory). The solution is a transcendental equation relating the orientation angle and m and can be solved by numerical methods. Changing the frequency and/or the field intensity, it is possible to obtain a situation in which the crystal rotates uninterruptedly (a resonance regime). This condition is related to the applied field intensity, to the frequency, to the medium viscosity, to the crystal dimension, and to the micro-crystal magnetic moment m. The method can be used to estimate the total cellular magnetic moment of magnetic micro-particles.     

Fabrication and characterization of Pd/Ag alloy hollow spheres by the solvothermal method

Pd/Ag alloy hollow spheres have been synthesized in ethylene glycol solution by the solvothermal method and have been characterized extensively. TEM results have revealed the formation of Pd/Ag hollow spheres. Moreover, HRTEM results confirmed the formation of Pd/Ag alloy spheres, where the lattice fringe spacing is 0.229 nm corresponding to the (111) plane of Pd/Ag alloy. SEM, XRD and UV–vis results have further suggested the formation of alloy hollow spheres. The preliminary results showed the reaction time may be an importance factor influencing the formation of Pd/Ag alloy hollow spheres.     

Novel structure for magnetic rotation bands in Ni

The self-consistent tilted axis cranking relativistic mean-field theory based on a point-coupling interaction has been established and applied to investigate systematically the newly observed shears bands in ⁶⁰Ni. The tilted angles, deformation parameters, energy spectra, and reduced M1 and E2 transition probabilities have been studied in a fully microscopic and self-consistent way for various configurations and rotational frequencies. It is found the competition between the configurations and the transitions from the magnetic to the electric rotations have to be considered in order to reproduce the energy spectra as well as the band crossing phenomena. The tendency of the experimental electromagnetic transition ratios B(M1)/B(E2)$B(\mathrm{M}1)/B(\mathrm{E}2)$ is in a good agreement with the data, in particular, the B(M1)$B(\mathrm{M}1)$ values decrease with increasing spin as expected for the shears mechanism, whose characteristics are discussed in detail by investigating the various contributions to the total angular momentum as well.     

Low-density core-shell composite hollow microspheres with tunable magnetic properties

Low-density (about 0.9 g/cm³) composite core-shell hollow microspheres with tunable magnetic properties were fabricated by Ni-Fe-P deposition on hollow glass microspheres (HGM) with modified electroless plating process. The effects of mole ratio of Fe²⁺/Ni²⁺, concentration of the reducer and pH value of the solution on the magnetic properties of the products were investigated. In conclusion, the increase in the mole ratio of Fe²⁺/Ni²⁺ and pH value of the solution could improve the soft magnetic properties of composite microspheres remarkably, while the increase in the concentration of NaH₂PO₂ had the opposite effect. The as-obtained metallic shells were amorphous and the crystallization got better with increased annealing temperature after plating. In addition, the saturation intensity of the composite microspheres was enhanced monotonically by increasing the annealing temperature. This work provided a facile and effective strategy to fabricate core-shell composite hollow microspheres with tailored magnetic properties.