Self-assembly in a polystyrene/montmorillonite nanocomposite
749
polystyrene are strong, resulting in a disordered orienta-
tion of the phenyl ring.
In summary, we have demonstrated that a self-assem-
bly in an extruded polystyrene/montmorillonite nanocom-
posite happened during a temperature increase process. In
the self-assembled structure, the montmorillonite primary
particles align parallel and the phenyl rings lie perpendi-
cular to the montmorillonite primary particles.
Acknowledgement: This work was financially supported by
National Natural Science Foundation of China, the contract
number is 59833310. We acknowledge Professor Jiang Bing-
zheng and Mr. Li Guang for allowing us to use the Philips
PW1700 X-ray diffractometer as well as valuable discussions.
We also wish to thank Leica Microsystems Ltd. for sectioning
the TEM samples.
Fig. 3. FTIR spectra of the extruded polystyrene/montmorillo-
nite sample under conditions similar to Fig. 1. A: room tempera-
ture (1) parallel polarization and (2) perpendicular polarization;
B: after heating at 958C (1) parallel polarization and (2) perpen-
dicular polarization; C: after heating at 1108C (1) parallel polar-
ization and (2) perpendicular polarization
1)
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Tab. 1. The dichroic ratios of the CH2 asymmetric stretch-
ing (mas(CH2)) and symmetric stretching (ms(CH2)) of all
the specimens are essentially equal to unity, indicating
that little orientation occurs for the aliphatic chain of the
polystyrene before and after heating. With respect to
phenyl rings, it is complex. For the film specimen, the
phenyl rings lie parallel to the shear flow direction and
the montmorillonite primary particles. This is because the
dichroic ratios of the phenyl ring out-of-plane vibration
modes, m10 B, m11, and m4, are obviously lower than unity,
and each of the out-of-plane vibration bands has a transi-
tion moment perpendicular to the phenyl ring plane. As
for the film specimen after heating at 958C, the dichroic
ratios of m10B, m11, and m4 are larger than unity, revealing
that the phenyl rings lie perpendicular to the montmoril-
lonite primary particles. However, no apparent orientation
was measured for the specimen after heating at 1108C.
The fact that the polystyrene phenyl ring changes from
parallel to perpendicular orientation with respect to the
silicate primary particle, and then becomes disordered
may be explained as follows. In the extruded sample, the
parallel orientation is induced by shear flow and fixed by
adjacent inorganic planar oriented silicate layers. With
increasing temperature the phenyl rings obtain a certain
degree of mobility. They prefer face-to-face orientation,
i.e., perpendicular to silicate layers, due to the interaction
among the phenyl rings. When the temperature is high
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enough, near the glass transition temperature (Tg
=
19)
1038C, determined by DSC) of the nanocomposite, the
mobilities of both aliphatic chain and phenyl ring of the
20)