Shaohua Chen

Preparation and characterization of monodisperse solvent-free silica nanofluids

ABSTRACT A series of solvent-free ionic silica (SiO2) nanofluids of 12.3–17.3 nm in diameter were synthesized by surface functionalizing nanoscale SiO2 with a charged corona and ionically tethering with oligomeric chains as canopy. The structure and properties of the nanofluids were systematically characterized by Fourier transform infrared (FTIR), differential scanning calorimeter (DSC), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and rheology tests. The resultant nanofluids with low-molecular-weight oligomeric as canopy are homogeneous, stable yellow-like fluids with no evidence of phase separation at room temperature, while other nanofluids containing high-molecular-weight as canopy behave like a soft glassy, and they exhibit fluidity with still high modulus and viscosity above 60°C. For deeper understanding of the nature of SiO2 nanofluids, the rheological behavior, thermal stability, as well as morphology of SiO2 nanofluids were investigated in details. The flow properties of nanofluids could be easily regulated from soft glassy to free flowing liquids by varying the molecule weight of canopy. Most importantly, the thermal stability, rheological behavior, as well as morphology can be also regulated through varying molecule weight and thickness of canopy, which will guide our future work on synthesis of nanofluids with controllable physical properties. GRAPHICAL ABSTRACT

Effects of ultrasound on the conformational and crystallization behavior of isotactic polypropylene polymerized with different Ziegler—Natta catalyst

Using different Ziegler—Natta catalysts, we have prepared two samples of isotactic polypropylene with similar molecular weight and average isotacticity, but different stereo-defect distributions. The influence of ultrasonic irradiation on the conformation and crystallization behavior of those samples were investigated by differential scanning calorimetry, wide-angle X-ray diffraction and Fourier transform infrared spectroscopy. The ultrasonic treatment induced a decrease in the degree of crystalline perfection and a wider distribution range of the crystalline perfection of polypropylene. Meanwhile, the crystal particles pack looser and the crystallite size decreased under the influence of ultrasonic irradiation. On the conformation aspect, the molecular movement in polypropylene became more intensive, the molecular entanglement was reduced when ultrasound was applied. Moreover, it was found that the uniformity of stereo-defect distribution also played important role in determining the conformation and crystallization behavior of polypropylene samples irradiated by ultrasound.

Effects of stereo-defect distribution on the crystalline morphology and tensile behavior of isotactic polypropylene prepared by compression molding process

ABSTRACT In this study, the aggregation morphology, tensile behavior, and morphology evolution during the tensile test of two isotactic polypropylene (iPP) samples with similar molecular weight and average isotacticity but different uniformities of stereo-defect distribution are investigated by differential scanning calorimetry (DSC), two-dimensional wide angle X-ray diffraction (2D-WAXD), and scanning electronic microscopy (SEM). The results revealed that the uniformity of stereo-defect distribution of iPP determines the crystalline structure and aggregation morphology, and further influences the tensile behavior and morphology evolution during the tensile test. For PP-A with less uniform stereo-defect distribution, its ability of crystallization is stronger compared with PP-B, resulting in smaller spherulite sizes, higher melting point and degree of crystallinity, and narrower distribution of lamellar thickness of the compression molding specimens. During the tensile test, mainly the inter-spherulite deformation takes place at the early stage for deformation, which further results in drastic deformation of lamellar and high degree of reorientation at the strain increases, exhibiting higher yield strength and elastic modulus, and lower elongation at break compared with PP-B; for PP-B with more uniform stereo-defect distribution, larger spherulite sizes, lower melting point and degree of crystallinity in its compression molding sample are observed. During the tensile test, intra-spherulite deformation mainly takes place, which can disperse the tensile stress more uniformly. As the strain increases, lower degree of crystalline destruction and reorientation of the crystallites take place. The yield strength and elastic modulus of PP-B is lower than PP-A, and its elongation at break is higher.

Non-Isothermal Crystallization Behavior of β-Nucleated Isotactic Polypropylene/Multi-Walled Carbon Nanotube Composites with Different Melt Structures

In this study, the melt structure status of isotactic polypropylene/multi-walled carbon nanotubes composites (iPP/MWCNTs) nucleated with β-NA was tuned by changing the fusion temperature Tn fn . The non-isothermal crystallization behavior and subsequent melting behavior of the sample were studied in detail. The results showed that under different cooling rates (2, 5, 10, 20 and 40 deg/min), the crystallization temperature increased gradually with the decrease of Tn fn , meanwhile, when Tn fn was in the temperature range of 166–174°C where ordered structures survived in the melt (named Region II), the crystallization activation energy was significantly lower compared with the case Tn fn > 174°C or Tn fn < 166°C. On the subsequent melting curves, the occurrence of the melt structure can be observed at all the cooling rates studied; the location of the Region II was constant, which did not show dependency on the cooling rates; low cooling rate and relative low Tn fn within 166–174°C encouraged the formation of more β-phase triggered by melt structure.

Polyphenylene sulfide microfiber membrane with superhydrophobicity and superoleophilicity for oil/water separation

To dispose the increasing oil pollution, tremendous effective ways have been proposed to deal with the oil/water mixture. In this study, polyphenylene sulfide (PPS) microfiber membrane was firstly employed as the substrate for separation. Polyethylene wax (PEW) powder and polytetrafluoroethylene (PTFE) ultrafine powder were simply and effectively introduced on the PPS membrane by employing one-step spray-coating method. The as-prepared membrane displayed excellent oil affinity and water-repellent behaviors. Significantly, the obtained membrane showed long-term stability under various extreme conditions such as strong acid, alkali, salt solutions and high temperature. Moreover, this membrane could maintain high oil flux (above 3500xa0L/m2xa0h) and separation efficiency (above 98%) even after 20 cycles of oil/water separation and isolate a wide range of oil/water mixture effectively. The fabrication of superhydrophobic and superoleophilic PPS microfiber membrane presented here can be easily scaled up on a large scale, which will provide attractive potential in practical oil/water separation.

Load of Ag3PO4 Particles on Sulfonated Polyphenylene Sulfide Superfine Fibre with High Visible-light Photocatalytic Activity

Ag3PO4 was loaded on sulfonated polyphenylene sulfide (SPPS) superfine fibre by a facile precipitation method. Both the structure and properties of the as-synthesized Ag3PO4/SPPS composites were characterized via XRD, SEM, EDS, XPS, FTIR, and UV-vis. The photocatalytic performance of Ag3PO4/SPPS composites was investigated via degradation of Methylene blue(MB) solution under visible light irradiation. The degradation results revealed that the photocatalytic activity of Ag3PO4/SPPS composites was greatly enhanced by the incorporation of Ag3PO4 with SPPS superfine fibre. For concentrations of AgNO3 and Na2HPO4 solutions of 0.3 M and 0.06 M in the preparation process, the Ag3PO4/SPPS composite showed higher photocatalytic activity under visible light irradiation.

Immobilization of Ag 3 PO 4 nanoparticles on chitosan fiber for photocatalytic degradation of methyl orange

Ag3PO4 and chitosan fiber (CF) composites were successfully fabricated using an in situ growth technique. The structure and properties of the obtained Ag3PO4/CF composites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy, and UV–visible diffuse reflectance spectroscopy. SEM results suggested that the 50–500xa0nm Ag3PO4 particles grew on the CF surface into a spherical or dentate shape. Photocatalytic degradation of methyl orange (MO) solution was used as a typical reaction to evaluate the visible-light photocatalytic performance of the Ag3PO4/CF composites. The reaction results indicated that the Ag3PO4/CF composites-3 exhibited excellent photodegradation efficiency, with 93.8% removal of the MO solution. The effects of MO concentrations and cycling runs on the photocatalytic performance of the Ag3PO4/CF composites were evaluated as well.