Guannan Sun

Zhengzhou University, Cheng, Henan Sheng, China

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Publications (4)4.95 Total impact

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    ABSTRACT: Using emulsifier-free emulsion polymerization method, monodispersed crosslinked poly(styrene-co-methacrylic acid-co-ethylene glycol dimethacrylate) colloid microspheres were synthesized. The microspheres were treated in supercritical carbon dioxide (SCCO2) after they have self-assembled into ordered three-dimensional (3D) colloid arrays. The CO2 absorbed into the polymer microspheres enhances chain segments mobility and reduces the glass transition temperature (Tg) of polymer, which induce the microspheres coalesce at the relatively low temperature. The coalescence degree of microspheres was studied by varying the experimental temperature, pressure, and exposure time in SCCO2. The results were shown by scanning electron microscopy (SEM). Further, the lattice spacing of the assembled 3D colloid microspheres was calculated from the SEM images. It was illustrated that the coalescence degree enhanced with the increase of CO2 pressure; however, this tendency became weak when CO2 pressure reached a certain value. Extending exposure time in SCCO2 or elevating temperature can also increase coalescence degree, and the effect of temperature is more significant. It is believed that these results will make sense when the polymer microspheres are considered to be used as templates in SCCO2; meanwhile, it raises a new method about tuning the final morphology of the stabilized colloidal crystals and porous materials via controlling the coalescence degree with the assistance of SCCO2. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
    Journal of Applied Polymer Science 02/2011; 119(4). · 1.40 Impact Factor
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    ABSTRACT: This article presents a novel route to prepare hollow silica microspheres with well-defined wall thickness by using cross-linked polystyrene (PS) microspheres as templates with the assistance of supercritical carbon dioxide (SC-CO2). In this approach, the cross-linked PS templates can be firstly prepared via emulsifier-free polymerization method by using ethylene glycol dimethacrylate or divinylbenzene as cross-linkers. Then, the silica shell from the sol–gel process of tetraethyl orthosilicate (TEOS) which was penetrated into the PS template with the assistance of SC-CO2 was obtained. Finally, the hollow silica spheres were generated after calcinations at 600°C for 4h. The shell thickness of the hollow silica spheres could be finely tuned not only by adjusting the TEOS/PS ratio, which is the most frequently used method, but also by changing the pressure and aging time of the SC-CO2 treatment. Fourier transform infrared spectroscopy, transmission electron microscopy, and scanning electron microscope were used to characterize these hollow silica spheres. KeywordsMorphology–Supercritical carbon dioxide–Hollow silica microsphere–Controlled wall thickness
    Colloid and Polymer Science 01/2011; 289(12):1397-1406. · 2.16 Impact Factor
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    ABSTRACT: Using emulsifier‐free emulsion polymerization method, monodispersed crosslinked poly(styrene‐co‐methacrylic acid‐co‐ethylene glycol dimethacrylate) colloid microspheres were synthesized. The microspheres were treated in supercritical carbon dioxide (SCCO2) after they have self‐assembled into ordered three‐dimensional (3D) colloid arrays. The CO2 absorbed into the polymer microspheres enhances chain segments mobility and reduces the glass transition temperature (T g ) of polymer, which induce the microspheres coalesce at the relatively low temperature. The coalescence degree of microspheres was studied by varying the experimental temperature, pressure, and exposure time in SCCO2. The results were shown by scanning electron microscopy (SEM). Further, the lattice spacing of the assembled 3D colloid microspheres was calculated from the SEM images. It was illustrated that the coalescence degree enhanced with the increase of CO2 pressure; however, this tendency became weak when CO2 pressure reached a certain value. Extending exposure time in SCCO2 or elevating temperature can also increase coalescence degree, and the effect of temperature is more significant. It is believed that these results will make sense when the polymer microspheres are considered to be used as templates in SCCO2; meanwhile, it raises a new method about tuning the final morphology of the stabilized colloidal crystals and porous materials via controlling the coalescence degree with the assistance of SCCO2. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
    Journal of Applied Polymer Science 01/2011; 119(4). · 1.40 Impact Factor
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    ABSTRACT: Using the excellent transport properties of supercritical carbon dioxide, tetraethyl orthosilicate (TEOS) could be easily carried into the template of the cross-linked polystyrene (PS) microspheres. Through the sol–gel procedure, the TEOS penetrated into the PS microspheres was transferred into silica. After sintering these composite particles, hollow silica microspheres were obtained. Through the above method, the hollow titanium dioxide microspheres also could be synthesized. The formation mechanism of the hollow particles was discussed and the morphology of the hollow microspheres was characterized by transmission electron microscopy (TEM) and scanning electronic microscope (SEM).
    Colloids and Surfaces A: Physicochemical and Engineering Aspects. 01/2010;