Shear-induced ordered structure in polystyrene/clay nanocomposite
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Shear-induced ordered structure in polystyrene/clay nanocomposite Guangming Chen and Zongneng Qia) State Key Laboratory of Engineering Plastics, Center for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, People’s Republic of China
Deyan Shen Polymer Physics Laboratory, Center for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, People’s Republic of China (Received 8 October 1999; accepted 12 November 1999)
A shear-induced ordered structure in an exfoliated polystyrene (PS)/clay nanocomposite is reported. X-ray diffraction (XRD), transmission electron microscopy (TEM), and infrared dichroism techniques have been employed to investigate the shear-induced ordered structure in the exfoliated PS/clay nanocomposite. Compared with the broad amorphous peaks before extrusion, a series of sharp diffraction peaks were observed in XRD pattern for the extruded PS/clay nanocomposite pellet sample, showing that an ordered structure occurred under shear flow. TEM images confirmed directly that the origin of the ordered structure was mainly due to the planar orientation of the primary particles of silicate layers as well as local ordered microstructure of the primary particles, induced by shear flow. The infrared dichroism study indicated that the phenyl group of PS apparently oriented parallel to the film surface, whereas no obvious orientation of the aliphatic chain could be observed. Based on these investigations, a possible mechanism was deduced for the formation of the ordered structure induced by shear flow in the exfoliated PS/clay nanocomposite.
I. INTRODUCTION
The field of organic–inorganic nanocomposites has recently attracted considerable attention due to their unexpected hybrid properties synergistically resulting from their parent components.1–3 One of the most promising organic–inorganic nanocomposites is layered silicatebased polymer nanocomposites. 4–19 The polymerlayered silicate (PLS) nanocomposites were prepared via in situ intercalative polymerization, polymer solution intercalation, or melt intercalation process. The organic polymers used have been reported for a broad range with varying degree of polarity and crystallinity, such as nylon-6, 6–9,15a poly(ethylene terephathalate), 10 PS,5,11 polypropylene,12 epoxy,13,14 silicon rubber15 and poly(ethylene oxide)17a,18 and the inorganic layered silicate used was montmorillonite. These PLS nanocomposites exhibit dramatic increases in mechanical properties as well as gas barrier properties, and the reason is generally attributed to the uniform dispersion of the 1-nmthick clay silicate layers in polymer matrix. It is well known that polymer molecular orientation during melt processing has a significant effect on physia)
Address all correspondence to the author. J. Mater. Res., Vol. 15, No. 2, Feb 2000
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cal properties, especially tensile strength, modulus, and gas barrier properties. Un
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