Page 237 - Book Hosokawa Nanoparticle Technology Handbook

4.4 NANOCOMPOSITE STRUCTURE FUNDAMENTALS
synthetic methods [12, 13] have been developed to [7] K. Masenelli-Varlot, E. Reynaud, G. Vigier and
prepare unbundled or not highly entangled SWNTs. J. Varlet: J. Polymer Sci. Part B Polymer Phys., 40,
Another plausible method is to apply a high shear on 272–283 (2002).
the blend of SWNTs and polymer when they are [8] H.R. Dennis, D.L. Hunter, D. Chang, S. Kim, J.L.
kneaded. With the application of high shear, however, White, J.W. Chao and D.R. Paul: Plastics Eng., 56–60
there exists a fair chance for the destruction of (2001).
SWNT structure and the breakage of SWNT tubes. [9] Y. Kojima, A. Usuki, M. Kawasumi, A. Okada,
This may result in obtaining composites with prop-
erty levels much lower than those expected originally T. Kurauchi, O. Kamigaito and K. Kai: J. Polymer Sci.
especially for mechanical strength and electrical con- Part B Polymer Phys., 33, 1039–1045 (1995).
ductivity. Barrera [14] summarized various methods [10] M. Okamoto, P.H. Nam, P. Maiti, T. Kotaka,
applicable to improve the orientation of SWNTs in N. Hasegawa and A. Usuki: Nano Letts., 1, 295–298
polymer matrix. Here, we briefly describe three fea- (2001).
sible methods selected from his article. First, a [11] H. Fong, W. Liu, C.-S. Wang and R.A. Vaia: Polymer,
monomer is polymerized to the corresponding poly- 43, 775–780 (2002).
mer in the presence of SWNTs, which are aligned [12] L. Huang, X. Cui, B. White and S.P.O’Brien: J. Phys.
beforehand in a desired direction. Second, SWNTs Chem. B, 108, 16451–16456 (2004).
are oriented in a direction under a simultaneous [13] K. Hata, D.N. Futaba, K. Mizuno, T. Namai, M.Yumura
application of high shear and magnetic field. Third,
molten composites are strongly elongated under heat- and S. Iijima: Science, 306, 1362–1364 (2004).
ing to allow fillers to align in a direction of elonga- [14] E.V. Barrera: JOM-J. Mater. Metals & Mater. Soc., 52,
tion. Note that a Japanese patent [15] was requested A38–A42 (2000).
for a method similar to the second method. [15] Japanese Publication of Unexamined Patent
Composite materials presented in Sections (2) and Applications: Tokukai 2002-273741.
(3) are expected to be commercialized in the near [16] M.D. Elkovitch, L.J. Lee and D.L. Tomosako: Polymer
future. In industrial-scale productions of composites Eng. Sci., 41, 2108–2125 (2001).
one will face the same problems as those encountered
in the laboratory-scale productions. They are the dis-
persion and orientation of filler. Simply speaking, 4.4.4 In situ particle polymerization
desirable results will be obtained if the motion of the
filler is not restricted in matrix. This may be attained In this section, two techniques are described for
by decreasing the viscosity of filler-polymer mixture. preparing composite materials by polymerization in
For this purpose an attempt [16] was made to inject the presence of particles or precursors of particles.
supercritical carbon dioxide into the mixture during Also information on these techniques is presented.
the course of kneading. Needless to say caution
should be exercised in regard to the property changes (1) Polymerization in the presence of particles
of products, which may be caused by the injection of This technique along with the mixing and kneading
carbon dioxide. Yet, the attempt should be considered technique of particles with polymers by a 2-screw
one of the promising techniques for obtaining com- extruder is a typical method of obtaining composite
posites with well-dispersed and designed orientation materials. Many patents have been published using
of filler in matrix. various polymers.
Well-known nanocomposites include nylon, poly-
ester, and epoxy resin in which layered particles such
References as clay are dispersed. Many of them are produced by
“in situ particle polymerization”; that is, layered par-
[1] L.L. Brott, R.R. Naik, D.J. Pikas, S.M. Kikpatrick, ticles such as clay are first dispersed in monomers or
D.W. Tomlin, P.W. Whitiock, S.J. Clarson and M.O. oligomers and then the mixture is polymerized.
Stone: Nature, 413, 291–293 (2001). Typical layered particles are clay minerals of several
[2] F. Grohn, G. Kim, B.J. Bauer and E.J. Amis: micrometers such as montmorillonite or originally
Macromolecules, 34, 2179–2185 (2001). large kaolin. These particles are formed by many lam-
inated layers several nanometers in size. How to
[3] E. Kumacheva, O. Kalinina and L. Lilgel: Adv. Mater.,
delaminate and disperse them in the polymer is a key
11, 231–234 (1999).
point. As an example, a schematic depiction of the
[4] M. Okamoto: Seikei Kakou (J. Jpn. Soc. Polymer
structure of montmorillonite is shown in Fig. 4. 4. 15.
Process.), 16, 574–578 (2004).
Generally, as pretreatment, interlayer metal cations
[5] N. Ogata, G. Jimenez, H. Kawai and T. Ogihara: J. Poly. in layered particles are replaced with cationic organic
Sci. Part B Poly. Phys., 35, 389–396 (1997). compounds or monomers modified with organic
[6] M. Alexandre and P. Dubois: Mater. Sci. Eng., 28, 1–63 cations to widen the interlayer space and make it
(2001). hydrophobic (intercalation). The modified particles
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