Wanquan Jiang

A facile method to fabricate carbon-encapsulated Fe3O4 core/shell composites

One-step synthesis of carbon-encapsulated Fe(3)O(4) core/shell composites is reported. The Fe(3)O(4) cores were formed via the reduction of Fe(3+) by glucose under alkaline conditions obtained by the decomposition of urea. The amorphous carbon shells were carbonized from glucose. A possible formation mechanism for the Fe(3)O(4)@C composite was discussed. In order to characterize these Fe(3)O(4)@C core-shell composites, high-resolution transmission electron microscopy (HR-TEM), x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), x-ray photoelectron spectroscopy (XPS) and a superconducting quantum interference device (SQUID) magnetometer were employed to characterize the sample obtained using the above method.

Study of the knife stab and puncture-resistant performance for shear thickening fluid enhanced fabric

This work developed a shear thickening fluid enhanced fabrics and the influence of the shear thickening fluid types on the knife stab and puncture resistance performance were investigated. The rheological properties of the shear thickening fluids were tunable by varying both the dispersing particles (silica, polymethylmethacrylate and polystyrene-ethylacrylate) and the mediums (ethylene glycol, polyethylene glycol 200 and polyethylene glycol 600). The mechanical properties of the shear thickening fluid reinforced fabrics were evaluated by the knife and spike drop tower testing, respectively. The hardness of the particles was the dominant factor for the knife stab resistance, while the inter-yarn friction played as the critical role for improving the puncture resistance. In comparison to neat fabric, the knife stab and puncture resistance of the shear thickening fluid-fabrics exhibited significant enhancement, which can be proven by the results of yarn pull-out testing and optical microscope images investigation. The enhancing effect was systematically discussed and the improving mechanism was analyzed. Because the influencing factors for the knife stab resistance and puncture resistance were different, the enhancing effect of the dispersing particles and the mediums for the shear thickening fluid-fabrics should be also different.

Superparamagnetic Ag@Fe3O4 core-shell nanospheres: fabrication, characterization and application as reusable nanocatalysts.

Superparamagnetic Ag@Fe(3)O(4) nanospheres with core-shell nanostructures have been prepared by a facile one-pot method. The diameter of the as-synthesized nanospheres was about 200 nm and the core sizes were between 50 and 100 nm. By varying the concentrations, particles with tunable core size and total size are successfully achieved. Time dependent experiments were constructed to investigate the synthesis mechanism, which indicated that the present method corresponded to an Ostwald ripening progress. The BET area of the core-shell nanospheres is about 22.6 m(2)/g and this result indicates that the product shows a porous character. The saturated magnetization of the superparamagnetic Ag@Fe(3)O(4) nanospheres is 27.4 emu g(-1) at room temperature, which enables them to be recycled from the solution by simply applying a small magnet. Due to the unique nanostructure, these particles show high performance in catalytic reduction of 4-nitrophenol and can be used as reusable nanocatalysts.

The investigation on the nonlinearity of plasticine-like magnetorheological material under oscillatory shear rheometry

To fully understand the structure dependent mechanical property, the harmonic strain loadings were applied to the magnetorheological plastomer (MRP) to study their dynamic properties. Under different test conditions, nonlinearity which was induced by strain amplitude and driving frequency was generated. In order to investigate the mechanism of nonlinearity, a facile and effective strategy by analyzing the response stress and actuating strain within an oscillatory cycle was introduced. In addition, the microstructures of isotropic and anisotropic MRP were observed and the time dependence of dynamic properties for MRP (from isotropic to anisotropic) under an 800 mT magnetic field was also investigated, which were helpful to further understand the structure dependent dynamic properties depending on actuating strain amplitude.

Enhancement in Magnetorheological Effect of Magnetorheological Elastomers by Surface Modification of Iron Particles

In order to obtain magnetorheological (MR) elastomers with high magnetorheological effect, a family of anisotropic rubber-based MR elastomers was developed using a new form of chemical modification. Three different kinds of surfactants, i.e. anionic, nonionic and compound surfactants, were employed separately to modify iron particles. The MR effect was evaluated by measuring the dynamic shear modulus of MR elastomer with a magneto-combined dynamic mechanical analyzer. Results show that the relative MR effect can be up to 188% when the iron particles are modified with 15% Span 80. Besides the surface activity of Span 80, however, such high modifying effect is partly due to the plasticizing effect of Span 80. Compared with the single surfactant, the superior surface activity of compound surfactant makes the relative MR effect reach 77% at a low content of 0.4%. Scanning electron microscope observation shows that the modification of compound surfactant results in perfect compatibility between particles and rubber matrix and special self-assembled structure of particles. Such special structure has been proved beneficial to the improvement of the relative MR effect.

Creep and recovery behaviors of magnetorheological plastomer and its magnetic-dependent properties

The creep and recovery behaviors of magnetorheological plastomer (MRP) were systematically investigated to further understand its deformation mechanism under constant stress. The experimental results suggested that the time-dependent mechanical properties of MRP were highly dependent on the magnetic field and the magnetic-controllable mechanism was discussed. The influences of iron particle distribution and temperature on the creep and recovery behaviors in the absence and presence of a magnetic field were investigated, respectively. A great discrepancy was presented in creep curves for the isotropic and anisotropic MRP under an external magnetic field, which must be induced by the different particle assemblies. In addition, the creep strain of MRP tended to decrease with increasing temperature under a 930 mT magnetic field and this phenomenon was opposite to the results obtained without a magnetic field. Finally, a hypothesis was proposed to explain the temperature effect on the creep behaviors of MRP.

Shear Thickening Fluids Based on Additives with Different Concentrations and Molecular Chain Lengths

Shear thickening fluids (STFs) based on additives with different concentrations and molecular chain lengths were investigated. STF samples were prepared with silica and additive dispersed in polyethylene glycol (PEG) 400, where three types of additives with different molecular chain lengths of PEG4000, PEG6000, and PEG10000 were used. For PEG10000, different concentrations, including 0, 1%, 3%, and 5%, were selected to study the influences of additive concentrations. Rheological properties of the samples were measured with a rheometer. The results show that the shear thickening effect was significantly enhanced with the increase of the concentration and the molecular chain length of additives. The mechanism of enhancement was quantitatively explained with the formation of large particles clusters.

One step method to encapsulate nanocatalysts within Fe3O4 nanoreactors

Here reported a facile approach to synthesize rattle type magnetic nanocomposite with a permeable Fe3O4 shell and noble metallic core. The core of yolk materials are controlled by varying the metallic ion precursor (such as K2PdCl4, AgNO3, KAuCl4, and Cu(NO3)2). The content of the metallic cores increases by increasing of the amount of the metallic salt. This one step method is based on an in situreduction and Ostwald ripening process. As-obtained particles show porous nature and superparamagnetic characteristic. Moreover, the as-prepared magnetic recyclable nanocatalyst manifests high activity when evaluated for their catalytic properties and they can be separated from the reaction system by using a magnet.

Effect of maleic anhydride on the damping property of magnetorheological elastomers

In this study, maleic anhydride (MA) was selected as the compatibilizer to modify the interfaces of magnetorheological elastomers (MREs) for improving the damping property. Several samples of MREs with different contents of MA were prepared. The content of bound-rubber was measured by the extraction method. The microstructures were observed by using an environmental scanning electron microscope (SEM). The dynamic performances of these samples, including shear storage modulus, loss factor and MR effect were measured with a modified dynamic mechanical analyzer (DMA). The tensile strength was tested by using an electronic tensile machine. The experimental results indicate that both the content of bound-rubber and the compatibility between the magnetic particles and rubber matrix were enhanced with the increase of MA. The enhancement of the bond between the two phases resulted in different mechanical properties: the increase of shear storage modulus; the reduction of the loss factor; the stability improvement of the loss factor; the enhancement of the tensile strength; and the reduction of the MR effect.

The effect of pre-structure process on magnetorheological elastomer performance

Abstract On fabricating magnetorheolgoical elastomer, the mixture of iron particles and un-vulcanized rubber is placed under a curing magnetic field for some time so that iron particles are driven by the magnetic force to form a columnar structure; this process is called the pre-structure process. The microstructure of a magnetorheological elastomer sample is influenced by the pre-structure process, however, few reports address this problem in detail. This paper aims to study the effect of the pre-structure process on the magnetorheological elastomer performance. The pre-structure process is dominated by three influencing factors: magnetic field, curing time and temperature. A variety of magnetorheological elastomer samples were fabricated under different pre-structure conditions and their shear moduli were measured by using a dynamic mechanics analyzer machine. Scanning electron microscope images of these samples were also taken. The results demonstrated the magnetic field-induced modulus shows an increasing trend with magnetic strength before the magnetorheological elastomer samples reach magnetic saturation. The relative magnetorheological effect has an optimal value when the pre-structure field is 110 mT. The effects of the pre-structure time and temperature on the magnetorheological effect were also addressed by using the optimal pre-structure field. These three pre-structure conditions also affect each other. Thus, to fabricate higher-performance magnetorheological elastomer, these pre-structure conditions should be optimized. These results were also explained by study of the particle motion within the matrix.