Shipeng Wen

Fabrication of highly oriented hexagonal boron nitride nanosheet/elastomer nanocomposites with high thermal conductivity.

A homogeneous dispersion of hexagonal boron nitride nanosheets (BNNSs) in elastomers is obtained by solution compounding methods, and a high orientation of BNNSs is achieved by strong shearing. The composites show high thermal conductivities, especially when BNNS loading exceeds 17.5 vol%, indicating that the material is promising for thermal-management applications which need high thermal conductivity, low dielectric constant, and adequate softness.

Preparation and characterization of polystyrene/Ag core-shell microspheres--a bio-inspired poly(dopamine) approach.

A facile and versatile method using a biopolymer as a chelating agent for silver ions and as a reducing agent for the formation of catalytic sites is proposed to prepare polystyrene (PS)/Ag core-shell microspheres. More specifically, the core-shell microspheres were fabricated by electroless plating after the formation of poly(dopamine) (PDA) on the surface of PS microspheres through insitu spontaneous oxidative polymerization of dopamine. The PS-PDA microspheres were characterized by SEM, XPS, and TGA. The results showed that a uniform PDA layer was formed on the PS microsphere surface and the thickness of the PDA layer could be well controlled by varying the concentration of dopamine solution. The PDA layer was used as a chelating agent for silver ions, as a reducing agent for the formation of catalytic sites by reducing the silver ions into silver nanoparticles, and as an adhesion layer between the PS microspheres and silver layer. SEM and XRD results indicate that the diameter of the silver nanoparticles decreased with the increase in the thickness of the PDA layer. The silver nanoparticles could form a continuous and compact silver layer on the surface of the PS microspheres. Furthermore, the PS-PDA/Ag core-shell microspheres showed a good conductivity of 10S/cm and a low effective density of 1.8 g/cm(3), much lower than the corresponding values for block silver. Finally, hollow silver microspheres could be prepared by removing the PS core through calcination. SEM images showed that the hollow Ag microspheres remained unbroken and retained the spherical shape.

Fluorescence and Judd-Ofelt analysis of rare earth complexes with maleic anhydride and acrylic acid

Abstract Two kinds of Eu-complexes, Eu(TTA)2(Phen)(AA) and Eu(TTA)2(Phen)(MA) (HTTA=2-Thenoyltrifluoroacetone, Phen=1,10- phenanthroline, AA=acrylic acid, MA=Maleic anhydride), which combined the excellent fluorescence properties of Eu(TTA)2(Phen)(H2O) and the reactivity of acrylic acid and maleic anhydride with radicals, were synthesized. The two complexes were characterized by elemental analysis, infrared (IR) spectra, and X-ray photoelectron spectroscopy (XPS). Based on the data shown from the fluorescent spectra of the Eu-MA and Eu-AA complexes, the Ωλ (λ=2 and 4) experimental intensity parameters were calculated. The results demonstrated that the Ω2 intensity parameters for the two complexes were smaller than those for the Eu(TTA)2(Phen)(H2O) complex, indicating that a less symmetrical chemical environment existed in the complexes. It implied that the radiative efficiency of the 5D0 of these two complexes could be enhanced by ligand of MA and AA, respectively. The luminescent lifetime of the Eu-AA (τ=7.26×10−4 s) or Eu-MA complex (τ=8.12×10−4 s) was higher than that of the Eu(TTA)2(Phen)(H2O) complex, which was attributed to the substitution of the water molecule (H2O) in Eu(TTA)2(Phen)(H2O) by the MA or AA ligand.

Electrospinning preparation and luminescence properties of Eu(TTA)3phen/polystyrene composite nanofibers

Abstract Efficient luminescent composite nanofibers, composed of polystyrene (PS, M w =250000) and europium complex Eu(TTA) 3 phen (TTA=2-thenoyltrifluoroacetone, phen=1,10-phenanthroline) with diameters ranging from 350 nm to 700 nm, were prepared by electrospinning and characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), fluorescence spectroscopy, and thermogravimetric analysis (TG). The room-temperature fluorescence spectra of the composite nanofibers were composed of the typical Eu 3+ ion red emission, assigned to the transitions between the first excited state ( 5 D 0 ) and the multiplet ( 7 F 0–4 ). Owing to the incorporation of the europium complex into the PS fiber matrix and the subsequent distortion of the symmetry around the lanthanide ions by the capping PS, the polarization of the Eu 3+ ions was enhanced, which increased the probability for electronic dipole allowed transitions. The monochromaticity ( 5 D 0 → 7 F 2 / 5 D 0 → 7 F 1 ) around the Eu 3+ ions was also efficiently improved. Judd-Ofelt intensity parameters (Ω 2 and Ω 4 ) were determined from the emission spectra based on the 5 D 0 → 7 F 2 and 5 D 0 → 7 F 4 electronic transitions, respectively. The results showed that the Ω 2 values of the composite nanofibers were apparently higher than that of the pure complex, indicating an increased covalency degree in the europium first coordination shell due to the modification of PS matrix. The modification of the polymer matrix also resulted in much higher thermal stability of the composite fibers than that of the pure complex.

Network evolutions in both pure and silica-filled natural rubbers during cyclic shear loading

Evolutions of chemical cross-linking and filler networks during sinusoidal small-strain (10%) shear loading (fatigue) process were studied in pure (unfilled) and silica-filled natural rubbers. The experimental results of dynamic mechanical analysis (DMA) and nuclear magnetic resonance (NMR) of pure natural rubber (PNR) indicated that the fatigued PNR has a more homogeneous cross-linking network than that of the virgin one, which can lead to a slight increase of the storage modulus; however, the change of cross-linking density and its effect on the viscoelastic properties of PNR are very limited. By analyzing the variation of storage and loss moduli and the transmission electron microscopy (TEM) images of silica-filled natural rubber (SFNR) during the cyclic loading process, we found that the loosely packed agglomerates were first disrupted, and then the closed ones could also be gradually broken down. Such a filler network evolution process also can be seen from our non-equilibrium molecular dynamics (NEMD) simulation results.

Electrospinning of palladium/silica nanofibers for catalyst applications

Supported catalysts are an increasingly popular research area because supported catalysts are highly efficient and the catalyst particles can be recovered. In this study, a new silica-supported palladium (Pd/SiO2) nanofiber catalyst was developed. Pd/SiO2 nanofibers were prepared by the electrospinning of a solution mixture of poly(vinyl pyrrolidone) (PVP), TEOS gel, and PdCl2 nanoparticles, followed by the calcination of PdCl2/PVP/TEOS nanofibers at a high temperature and the reduction of PdO/SiO2 nanofibers in a H2 atmosphere. The results showed that the prepared Pd/SiO2 nanofibers had an average diameter of 500 nm. Pd nanoparticles with a diameter of 20–30 nm were uniformly dispersed on the surface of SiO2 nanofibers. The composite nanofibers had high Brunauer–Emmett–Teller (BET) specific surface area. The hydrogenation reaction for acrylic acid showed that the hydrogenation efficiency was 93.48% in the presence of 0.1 g of Pd/SiO2 nanofibers. These nanofibers could be easily recycled. These features make the Pd/SiO2 nanofibers promising in a wide range of applications in the catalyst industry.

Luminescence studies of electrospun core–sheath fibers with the core component being a rubber nanocomposite containing a Eu(III) complex

Core–sheath fibers with the core component being a luminescent nanocomposite and the sheath component being poly(vinyl pyrrolidone) were prepared via the method of co-axial electrospinning; the luminescent nanocomposite consisted of a silicone rubber matrix with the complex Eu(TTA)3phen (TTA: 2-thenoyltrifluoroacetone, phen: 1,10-phenanthroline) as the filler. The fluorescence spectra, fluorescence lifetimes, and Judd–Ofelt parameters of the prepared core–sheath fibers were investigated. The results indicated that the Eu(TTA)3phen complex was uniformly dispersed in the silicone rubber as molecular clusters and/or nanoparticles, leading to a high luminescence intensity and efficiency. Additionally, unlike the neat Eu(TTA)3phen complex and electrospun fibers of thermoplastic-based nanocomposites that had no appreciable difference in the fluorescence lifetime and luminescent quantum efficiency at 73 and 293 K, the prepared electrospun core–sheath fibers had a longer fluorescence lifetime and a higher luminescence quantum efficiency at 73 K due to the contribution of the silicone rubber matrix.

Physical dispersion state and fluorescent property of Eu-complex in the Eu-complex/silicon rubber composites

Abstract The fluorescent complex Eu(TTA) 2 (Phen)(MA) (HTTA=2-Thenoyltrifluoroacetone, Phen=1,10-phenanthroline, MA=Maleic anhydrider) was synthesized and characterized with elemental analysis, infrared spectrum (IR), scanning electron microscope (SEM), X-ray Diffraction(XRD), differential scanning calorimetry(DSC), and fluorescent measurement. To explore the effect of different physical dispersion state of Eu-complex on the fluorescent property of the Eu-complex/silicon rubber composites, various quantities of Eu(TTA) 2 (phen) (MA) were mixed with silicon rubber (SiR) and peroxide to form uncured composites. These composites were vulcanized to obtain cured Eu-complex/SiR composites at 250 °C, which was higher than the melting-point of Eu-complex. The SEM, XRD, DSC, and the fluorescent measurement of these composites showed that both the complex molecules dispersed in the silicon rubber during the melting process and the parent Eu-complex particles had positive effects on fluorescent property, whereas the re-crystallized Eu-complex particles and the aggregating complexes formed during the melting-process had negative effects on fluorescent property. For the uncured composites, their fluorescent intensities almost did not change with the increasing amount of Eu-complex. Furthermore, for the composites with small content of Eu-complex, their fluorescent intensities decreased significantly after curing, and this difference in fluorescent intensity became smaller as the content of Eu-complex increases.

Preparation of Rh–SiO2 fiber catalyst with superior activity and reusability by electrospinning

A rhodium (Rh)–SiO2 fiber catalyst was prepared by electrospinning, calcination, and reduction in that order. The as-prepared Rh–SiO2 fiber catalyst was applied in the catalytic hydrogenation of alkenes. This catalyst allowed the hydrogenation reaction to be carried out at room temperature with excellent catalytic activity and could be reused nine times without obvious loss of catalytic activity. The excellent mechanical strength, thermal stability, and chemical stability of SiO2 and the uniform dispersion of the Rh nanoparticles in the fibers are the reasons for the superior activity and reusability of the catalyst.

Self-polymerization of Eu(TTA)3AA in rubber and their fluorescence effect

Abstract A simple europium complex, Eu(TTA)3AA (TTA=4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione, AA=acrylic acid) was synthesized by a simple solution method. Then, two kinds of rubber matrix, nitrile-butadiene rubber (NBR) and silicone rubber (SiR) were used as the substrate for Eu(TTA)3AA to prepare fluorescence composites. The neat Eu(TTA)3AA complex showed the ability of self-polymerization when it was heated at 145 °C. It was found that the fluorescence intensity of the neat Eu(TTA)3AA decreased over 70% when the polymerization time was over 25 min at 145 °C. The results also revealed that the polymerizated Eu(TTA)3AA could be dispersed in nano-scale in two matrices and the luminescent intensities decreased 52% in NBR matrix, and 95% in SiR matrix compared with two relative compounds without crosslinking. To optimize the luminescence intensity of the composites, the Eu(TTA)3AA polymerization kinetic process in matrix was investigated in detail by controlling the temperature, the crosslinking agent, etc. The results showed that the peroxide could accelerate Eu(TTA)3AA self-polymerization in the rubber matrix, and therefore improved the dispersion, but not be helpful for the luminescence intensity enhancement. In addition, the relatively higher luminescence intensity in Eu(TTA)3AA/NBR in comparison to that of Eu(TTA)3AA/SiR might contribute to the interaction between nitrile group (–CN) in NBR and Eu-complexes, suggesting that the luminescence intensity of the composites also depended on the matrix characteristics.