Xufeng Dong

Catalytic pyrogenation synthesis of C/Ni composite nanoparticles: controllable carbon structures and high permittivities

Catalytic pyrogenation of methane gas in the presence of Ni nanoparticles was employed to synthesize C/Ni composite nanoparticles at various reaction temperatures. The Ni nanoparticles prepared by the arc-discharge method served as a catalyst to decompose the hydrocarbon molecules and also provided isolated templates for the formation of carbon nanocapsules at 400 and 500 °C or multi-walled carbon nanotubes at 600 and 650 °C. The generation and growth mechanism of the carbon shells are discussed on the basis of structure evolution. By dispersing the nanoparticles homogeneously into a paraffin matrix, the electromagnetic parameters of the nanoparticles have been investigated in the frequency range 2–18 GHz. The samples exhibit high permittivities varying with the microstructures of the nanoparticles. The relationship between the dielectric properties and diverse carbon structures is indicated. The high permittivities of the nanoparticles are attributed to the better conductivity of the carbon shells and the charge polarizations at the defects or interfaces between metal cores and carbon shells.

Morphology, crystallization and mechanical properties of poly(ɛ-caprolactone)/graphene oxide nanocomposites

A series of nanocomposites based on poly(ɛ-caprolactone) (PCL) and graphene oxide (GO) were prepared by in situ polymerization. Scanning electron microscopy observation revealed not only a well dispersion of GO but also a strong interfacial interaction between GO and the PCL matrix, as evidenced by the presence of some GO nanosheets embedded in the matrix. Effects of GO nanofillers on the crystal structure, crystallization behavior and spherulitic morphology of the PCL matrix were investigated in detail. The results showed that the crystallization temperature of PCL enhanced significantly due to the presence of GO in the nanocomposites, however, the addition of GO did not affect the crystal structure greatly. Thermal stability of PCL remarkably increased with the addition of GO nanosheets, compared with that of pure PCL. Incorporation of GO greatly improved the tensile strength and Young’s modulus of PCL without a significant loss of the elongation at break.

Synthesis, characterization and magnetorheological study of 3-aminopropyltriethoxysilane-modified Fe3O4 nanoparticles

In this study, monodisperse Fe3O4 nanoparticles were synthesized successfully using a sonochemical method in the presence of 3-aminopropyltriethoxysilane (APTES). The morphology, microstructure and magnetic properties of the bare Fe3O4 and APTES-coated Fe3O4 were investigated in detail by TEM, XRD, FTIR and SQUID. It was found that APTES-coated Fe3O4 showed relatively good dispersion with a narrow size distribution of 8.4 ± 2.1 nm diameter. The functionalization of Fe3O4 was proved to be covalent linking between Fe3O4 and APTES. The field-dependent magnetization curve indicated superparamagnetic behavior of Fe3O4-APTES with a saturation magnetization (M s) of 70.5 emu g−1 at room temperature. A magnetorheological (MR) fluid was prepared using the obtained Fe3O4-APTES nanoparticles with 25 wt% particles, and its MR properties were tested using a Physica MCR301 rheometer fitted with an MRmodule. The results showed that the as-prepared APTES-coated Fe3O4 nanoparticle-based MR fluid exhibited typical MR effects, with increasing viscosity, shear stress and yield stress depending on the applied magnetic field strength.

Facile preparation of poly(ε-caprolactone)/Fe3O4@graphene oxide superparamagnetic nanocomposites

The main goal in this work was to prepare and characterize a kind of novel superparamagnetic poly(ε-caprolactone)/Fe3O4@graphene oxide (PCL/Fe3O4@GO) nanocomposites via facile in situ polymerization. Fabrication procedure included two steps: (1) GO nanosheets were decorated with Fe3O4 nanoparticles by an inverse co-precipitation method, which resulted in the production of the magnetite/GO hybrid nanoparticles (Fe3O4@GO); (2) incorporation of Fe3O4@GO into PCL matrix through in situ polymerization afforded the magnetic nanocomposites (PCL/Fe3O4@GO). The microstructure, morphology, crystallization properties, thermal stability and magnetization properties of nanocomposites were investigated with various techniques in detail. Results of wide-angle X-ray diffraction showed that the incorporation of the Fe3O4@GO nanoparticles did not affect the crystal structure of PCL. Images of field emission scanning electron microscope and transmission electron microscopy showed Fe3O4@GO nanoparticles evenly spread over PCL/Fe3O4@GO nanocomposites. Differential scanning calorimeter and polar optical microscopy showed that the crystallization temperature increased and the spherulites size decreased by the presence of Fe3O4@GO nanoparticles in the nanocomposites due to the heterogeneous nucleation effect. Thermogravimetric analysis indicated that the addition of Fe3O4@GO nanoparticles reduced the thermal stability of PCL in the nanocomposites. The superparamagnetic behavior of the PCL/Fe3O4@GO nanocomposites was testified by the superconducting quantum interference device magnetometer analysis. The obtained superparamagnetic nanocomposites present potential applications in tissue engineering and targeted drug delivery.

Properties of aniline-modified strontium titanyl oxalate-based electrorheological suspension

Aniline-modified strontium titanyl oxalate (STO) particles were fabricated with a precipitation method. The structures of the particles were analyzed by x-ray diffraction analyses, Fourier transform infrared spectrometry and thermogravimetric analysis. Scanning electron microscopy was used to analyze the morphology of the particles. The results indicate chemical bonds are formed between STO and aniline. By tuning the molar ratio of aniline to Ti, the morphology of the aniline-modified STO particles can be sphere, polyhedron and a mixture composed of clusters of nano particles and micro rod-like particles. Electrorheological (ER) properties, temperature effect, thixotropy and sedimentation stability of the ER fluids based on the pure STO and the aniline-modified STO were tested. The results indicate all the properties strongly depend on the content of the aniline during the fabrication process of the particles. The ER fluid with a molar ratio of aniline/Ti of 2 presents the highest shear stress, yield stress, leak current density and the most stable ER behavior at changing temperatures. The reason is the particles have polyhedron morphology and absorbed polar aniline molecules. Because of the stable space grid structure formed by the particles with a molar ratio of aniline/Ti of 3, the ER fluid exhibits better thixotropy and sedimentation stability than the others.

Properties of cobalt nanofiber-based magnetorheological fluids

Co nanofibers were synthesized by a surfactant-assisted solvothermal method. They were characterized by XRD, EDS, SEM, TEM and SQUID. The results indicated that the obtained products were hexagonal close-packed cobalt nanofibers with high purity. They presented large length to diameter ratio, and a high saturation magnetization of 142 emu g−1. Two magnetorheological (MR) fluids were prepared by the Co nanofibers and carbonyl iron particles with 12% particles volume fraction, respectively. Their magnetorheological properties and sedimentation stability were tested and compared. The results indicated that the Co nanofiber-based MR fluid presented higher yield stress than the carbonyl iron particles-based one at low field levels (0–150 kA m−1). The strong chains or column structure caused by the specific morphology and high magnetization of the Co nanofibers is responsible for their significant MR properties. In 15 days setting, the Co nanofibers-based MR fluid presented little sedimentation, while the sedimentation ratio of the carbonyl iron particles-based MR fluid was 50%. The Co nanofibers are ideal candidates to prepare MR fluids with good sedimentation stability as well as good magnetorheological properties.

Solvothermal synthesis, characterization, and magnetorheological study of zinc ferrite nanocrystal clusters

In this study, zinc ferrite (ZnFe2O4) nanocrystal clusters were synthesized successfully with a surfactant-assistant solvothermal method and investigated as a potential magnetorheological material. The morphology, structure, and magnetic properties of the obtained ZnFe2O4 nanocrystal clusters were investigated in detail using a scanning electron microscope, transmission electron microscope, X-ray diffraction, and superconducting quantum interference device. It was found that the ZnFe2O4 nanocrystal clusters showed well-defined shape and homogeneous dispersion with narrow size distribution of 276 nm in diameter. The field-dependent magnetization curve indicated superparamagnetic properties of as-prepared ZnFe2O4 nanocrystal clusters with saturation magnetization (Ms) of 86.6 emu/g at room temperature. The magnetorheological fluid with 25% particle mass fraction was prepared by ZnFe2O4 nanocrystal clusters, and the corresponding magnetorheological properties were also tested using a Physica MCR301 rheometer fitted with a magnetorheological module. The prepared magnetorheological fluid changed from a liquid-like to a solid-like state under an external magnetic field, suggesting typical Bingham plastic behavior. Compared with conventional carbonyl iron particles, ZnFe2O4 nanocrystal clusters–based magnetorheological fluid showed enhanced sedimentation stability. The obtained ZnFe2O4 nanocrystal clusters are considered as an ideal candidate for magnetorheological fluid with typical magnetorheological effect as well as improved sedimentation stability.

The contribution of friction to electrorheological properties of a chrysanthemum-like particle suspension

Several studies have proved that a significant electrorheological (ER) effect can be obtained by using particles with hierarchic structures as the dispersing phase. The inter-particle friction and fluid friction caused by the rough surface of the particles plays an important role for their enhanced ER effect. However, the detailed contribution of friction to ER properties remains unclear. We prepare two different ER fluids with chrysanthemum-like particles and spherical particles, respectively. We carry out a low shear velocity oscillation test to separate the friction-induced shear stress from the electrostatic attraction-induced shear stress. The chrysanthemum-like particle-based ER suspension presents much better ER performance than the ER fluid with spherical particles. The larger friction force caused by the rougher surface of the chrysanthemum-like particles is a major reason for the improvement. The contribution of friction to the ER effect depends on the electric field strength. The contribution has a maximum value at a critical electric field.

Predicating magnetorheological effect of magnetorheological elastomers under normal pressure

Magnetorheological elastomers (MREs) present reversible change in shear modulus in an applied magnetic field. For applications and tests of MREs, a normal pressure must be applied on the materials. However, little research paid attention on the effect of the normal pressure on properties of MREs. In this study, a theoretical model is established based on the effective permeability rule and the consideration of the normal pressure. The results indicate that the normal pressure have great influence on magnetic field-induced shear modulus. The shear modulus of MREs increases with increasing normal pressure, such dependence is more significant at high magnetic field levels.

Titanium glycerolate-based electrorheological fluids with stable properties

Titanium glycerolate (TiGly) particles were prepared with different molar ratios of glycerol to tetrabutyltitanate (TBOT) (glycerol/TBOT = 2, 2.5, and 3) by a simple precipitation method. For comparison, titanium propanediol (TiPro) particles were prepared with 1,3-propanediol and TBOT (propanediol/TBOT = 2) by the same route. The composition and morphology of the four kinds of particles were characterized by Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM), respectively. The results indicate that the secondary hydroxyl groups originating from glycerolate are doped into the TiGly particles, and the four kinds of particles present different morphology. The suspensions prepared with TiGly particles by 60% weight fraction and silicone oil show significant electrorheological (ER) performance, while the TiPro particles-based fluid with the same particles fraction present weak ER properties. Constant shear rate and step-function electric field pulses were applied to investigate the stability of the ER fluids. The TiGly particles synthesized with the molar ratio of glycerol to TBOT equaling 2.5 exhibit significant (~40 kPa at 5 kV mm−1) and stable ER activity.