Shouhu Xuan

Preparation, Characterization, and Catalytic Activity of Core/Shell Fe3O4@Polyaniline@Au Nanocomposites

We report a new method to synthesize magnetically responsive Fe3O4@polyaniline@Au nanocomposites. The superparamagnetic Fe3O4@polyaniline with well-defined core/shell nanostructure has been synthesized via an ultrasound-assisted in situ surface polymerization method. The negatively charged Au nanoparticles with a diameter of about 4 nm have been effectively assembled onto the positively charged surface of the as-synthesized Fe3O4@polyaniline core/shell microspheres via electrostatic attraction. The morphology, phase composition, and crystallinity of the as-prepared nanocomposites have been characterized by transmission electron microscopy (TEM) and powder X-ray diffraction (XRD). The central Fe3O4 cores are superparamagnetic at room temperature with strong magnetic response to externally applied magnetic field, thus providing a convenient means for separating the nanocomposite from solution. As-prepared inorganic/organic nanocomposite can be used as a magnetically recoverable nanocatalyst for the reduction of a selected substrate.

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.

Facile synthesis of size-controllable monodispersed ferrite nanospheres

Monodispersed ferrite nanospheres were synthesized in an ethylene glycol/diethylene glycol (EG/DEG) binary solvent by using poly(vinylpyrrolidone) (PVP) as the surfactant. Particle size control can be attained by careful adjustment of the VEG/VDEG ratio. Different from previous reports, the magnetic studies of our iron ferrite (Fe3O4) nanospheres with various sizes from 20 to 300 nm reveal that they exhibit a similar magnetic saturation (Ms) value. In particular, both the ferromagnetic and superparamagnetic Fe3O4 nanospheres with similar Ms can be selectively obtained by varying the H2O concentration in the reaction system. The magnetic resonance imaging (MRI) characterization indicates that the as-prepared superparamagnetic Fe3O4 and ZnFe2O4 nanospheres possess a T2 relaxivity range that can be used as potential MRI contrast agents.

pH-Controllable Supramolecular Systems

This Focus Review surveys representative examples of pH-controllable supramolecular systems with interesting features and state-of-the-art applications such as 1) conformational changes within individual molecules; 2) folding/unfolding of polymers; 3) simultaneous binding of cations and anions; 4) logic function; 5) ON-OFF switchable colorimetric sensing; 6) translocation of macrocycle-in-rotaxane molecules; 7) large-scale movement within molecules; and 8) regulation of the substrate flow in nanocontainers. In particular, systems will be discussed that involve: pH-induced conformational changes of a resorcinarene cavitand and a bis(iron porphyrin) complex; pH control in assembly and disassembly of supramolecular systems stabilized with different major noncovalent interactions; pH-driven movements of interlocked molecules involving rotaxanes, molecular elevators, and molecular muscles; and, finally, multicomponent supramolecular systems immobilized on solid supports as pH-responsive nanovalves for the controlled release of specific substrates. Recent advances in the understanding of pH-controllable supramolecular systems have led to the construction of meaningful molecular machines for electronic and biological applications that are amenable to control by simple perturbation with acids and bases.

Development of a real-time tunable stiffness and damping vibration isolator based on magnetorheological elastomer

A tunable stiffness and damping vibration isolator based on magnetorheological elastomers (MREs) is developed. In this isolator, four MRE elements are used as the tunable springs, whose stiffness can be controlled by varying the magnetic field. A voice coil motor, which is controlled by the relative velocity feedback of the payload, is used as the tunable damper of the isolator. Under the combined ON–OFF control, the proposed vibration isolator shows satisfying isolation effect. The experimental results indicate that the responses of the payload are suppressed significantly in comparison to the passive system. The transmissibility of the payload around the resonant frequency is decreased by 61.5%. The root mean square (RMS) value and the maximum value of the displacement responses of the payload are decreased by 36.0% and 50.0%, respectively. In addition, the RMS values and maximum values of the velocity responses are decreased by 45.4% and 52.5%, respectively.

A high-performance magnetorheological material: preparation, characterization and magnetic-mechanic coupling properties

A novel high-performance magnetorheological material, named as magnetorheological plastomer (MRP), was developed by dispersing iron particles into a plastic polyurethane (PU) matrix. The dynamic properties (including storage modulus and loss factor) of the MRP material were systematically tested and the influences of the iron particle content and magnetic field were analyzed. It is found that the anisotropic MRP product with 80% iron particle weight fraction (A-MRP-80), shows a high dynamic property: the maximum magneto-induced storage modulus is 6.54 MPa; the relative MR effect reaches as high as 532%; the loss factor can be reduced to 0.03 by adjusting magnetic field. This kind of MRP shows a much higher magnetorheological performance than the previously reported magnetorhelogical elastomer (MRE). The mechanism for its high MR performance was proposed and the influence of the iron particle distribution and temperature on the dynamic properties were discussed.

The design of an active–adaptive tuned vibration absorber based on magnetorheological elastomer and its vibration attenuation performance

This paper presents an active–adaptive tuned vibration absorber (AATVA) which is based on magnetorheological elastomer (MRE). A voice coil motor is attached to a conventional MRE adaptive tuned vibration absorber (ATVA) to improve its performance. In this study, two feedback types of the activation force were analyzed and the stability condition was obtained. In order to eliminate the time delay effect during the signal processing, a phase-lead compensator was incorporated. Based on the analysis, an MRE AATVA prototype was designed and its dynamic properties were experimentally investigated. The experimental results demonstrated that its resonant frequency could vary from 11 to 18 Hz and its damping ratio decreased to roughly 0.05 from 0.19 by adding the activation force. Besides, its vibration reduction abilities at the first two resonant frequencies of the experimental platform could reach 5.9 dB and 7.9 dB respectively. (Some figures in this article are in colour only in the electronic version)

Durable Mesenchymal Stem Cell Labelling by Using Polyhedral Superparamagnetic Iron Oxide Nanoparticles

Small polyhedral superparamagnetic iron oxide (SPIO) nanoparticles (<10 nm) coated with a thin layer of silica were prepared (SPIO@SiO(2) and SPIO@SiO(2)-NH(2)). Surface modification of the small polyhedral silica-coated SPIO nanoparticles with amines led to substantially higher mesenchymal stem cell (MSC) labelling efficiency without the use of additional transfecting agents. Therefore, amine surface-modified nanoparticles (SPIO@ SiO(2)-NH(2)) appeared to be the preferred candidate for MSC labelling. In vitro studies demonstrated that controlled labelling of SPIO@SiO(2) and SPIO@SiO(2)-NH(2) did not cause MSC death or proliferation inhibition. MSCs labelled with SPIO@SiO(2)-NH(2) nanoparticles retained differentiation potential and showed osteogenic, adipogenic and chondrogenic differentiations. The noncytotoxic polyhedral SPIO@SiO(2)-NH(2) nanoparticle-labelled MSCs were successfully implanted in rabbit brain and erector spinae muscle, and demonstrated long-lasting, durable MRI labelling efficacy after 8-12 weeks.

Discrete Functional Gold Nanoparticles: Hydrogen Bond-Assisted Synthesis, Magnetic Purification, Supramolecular Dimer and Trimer Formation

Amine monofunctional gold nanoparticles (1-AuNPs) were synthesized by employing a solid-supported technique and pH-switchable pseudorotaxane formation. Purification was repeatedly facilitated using crown ether peripherally coated superparamagnetic iron oxide microspheres to yield the monofunctional gold nanoparticles in excellent yield. The product and its related intermediate superstructures were characterized by IR and X-ray photoelectron spectroscopies. Novel supramolecular dimers and trimers were prepared by titrating the 1-AuNPs with bisDB24C8 and trisDB24C8 at different ratios. UV/visible absorption spectroscopic analyses of the supramolecular dimer and trimer solutions, which were formed by mixing their separate components in different ratios, indicated the gradual appearance of two distinct plasmonic resonance bands at 620 and approximately 700 nm. Furthermore, TEM images of the dimers revealed a significant amount of dimer pairs on the surface, while the TEM images of the trimers demonstrated the presence of both dimers and trimers. The trimers appeared as triangular or near-linear shapes.

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.