Page 187 - Book Hosokawa Nanoparticle Technology Handbook

3.6 AGGREGATION AND DISPERSION, CHARACTERIZATION AND CONTROL FUNDAMENTALS
[12] Y. Tomita, L. Guo, Y. Zhang, N. Uchida and K. Uematsu: wave with high frequency than several gigahertz for
J. Am. Ceram. Soc., 78, 2153–2156 (1995). mobile phones and precise medical instrument, etc., it
[13] Japan Society for the Promotion of Science 124th is necessary to develop highly concentrated dispersion
Committee on Preparation and Application of Advanced of magnetic nanoparticles less than several 10 nm into
polymer resin.
Ceramics. The Nikkan Kogyo Shimbun, Ltd. (2005).
[14] M. Takahashi, M. Oya, M. Fuji: J. Soc. Powder (2) Dispersion method and process of nanoparticles into resin
Technol., Jpn., 40, 410–417 (2004).
The general process to prepare powder-dispersed
[15] H. Abe, M. Naito, K. Okamoto, T. Hotta, S. Ohara, polymer composites is the kneading of particles into
T. Fukui: J. Soc. Powder Technol., Jpn., 41, 10–14 resin with fluid. However, for nanoparticles, the parti-
(2004). cle aggregation and the rapid increase of polymer vis-
cosity by the addition of nanoparticles inhibits the
highly concentrated filling up to several tens of vol-
3.6.3 Dispersion in organic solvent and polymer resin
ume percent by kneading process. For the preparation
of nanoparticle/polymer composites, it is necessary to
(1) Function and application of nanoparticle composite
develop new preparation processes. The outline of
material two kinds of approach to prepare nanocomposites will
Various types of nanoparticle-dispersed composite be introduced. One is the dispersion of synthesized
materials, whose matrix material is polymer, metal, nanoparticles into organic solvent and resin, and the
glass, or ceramics, have been developed aiming at the other is in-situ synthesis of nanoparticles during poly-
improvement of various functions. The examples are, merization process of monomer [1, 2].
thermal properties such as heat-resistance and thermal
conductivity, mechanical properties such as strength, 1) In-situ synthesis of nanoparticles during polymerization
fracture toughness, and abrasion resistance, electro- process of monomer
magnetic properties such as dielectric property and In this popular process, raw monomer materials and
electromagnetic wave shielding, optical properties organic metal compound such as metal alkoxide are
such as refractive index. For fine inorganic particles mixed uniformly, and during the polymerization
larger than submicronmeter, various polymer compos- process, nanoparticles are generated by nucleation and
ites dispersed with fine powders have been already growth in the polymer matrix material. If the initial
developed and utilized in various applications. mixing condition of monomer and alkoxide is good, the
If the primary size of dispersed particles in polymer uniform distribution of nanometer-sized particulate
is less than several nanometers, the additional function matter in polymer will be obtained in comparison with
and behavior will be given to the composite materials. other methods. Some composite polymers dispersed
In Table 3.6.1, the material of nanoparticles, function, with amorphous silica nanoparticles of high fracture
and application field of composites are summarized. strength and heat resistance has already been devel-
For example, if titanium oxide nanoparticles with high oped and brought out to the market. Lü et al. reported
refractive index larger than 2.5 are uniformly dispersed to have succeeded in dispersion of nanometer-sized
at high concentration into polymer lens material with titanium oxide in polymer with a high concentration of
relatively low refractive index 1.4–1.8, they are more than 60 vol% and increase of reflective index
expected to apply to the new optical lens and optical with the increasing addition of inorganic particles [3].
fiber cable with high refractive index. To obtain a high However, by using this process, if the concentration of
transparency and prevent scattering of the visible light, inorganic nanoparticles increases over a certain critical
it is needed to disperse the nanoparticles to the primary value, the coalescence and growth of dispersed
particles without any aggregation in the polymer. For nanoparticles occur during the in-site synthesis
the application of shield material of electromagnetic process. In order to keep the uniform dispersion of
nanoparticles in the composite, it is necessary to con-
trol the polymerization reaction process precisely.
Table 3.6.1 The inorganic phase generated by this process is
Examples of nanoparticle dispersed polymer composite. generally amorphous. In some cases, the interface
between the inorganic and organic compounds is not
Material of Function Application clear. It is rather difficult to control the crystal phase
nanoparticle of nanoparticles, because the heat resistance of poly-
mer compounds is not so high. If the expected func-
TiO 2 High refractive Lens, optical fiber
index tion of composite does not depend on the crystal
BaTiO 3 High dielectric Capacitor phase of inorganic component such as heat resistance,
constant etc., it is not necessary to control the crystal phase.
Silica-coated High Electromagnetic However, when the function of composite materials
Fe, Co permeability absorber depends on the crystal phase, for example, optical
properties such as refractive index and electromagnetic

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