Page 449 - Book Hosokawa Nanoparticle Technology Handbook

APPLICATION 1

1 DISPERSION OF FINE SILICA PARTICLES USING ALKOXYSILANE AND
INDUSTRIALIZATION

1. Sol–gel hybrid method for developing a molecular hybrid dispersed
with silica particles smaller than polymer chain length.
Development of composite materials that have the For the sol–gel hybrid, the kinds of applicable poly-
properties of rigid light plastics and hard heat-resistant mers are restricted to those soluble to alcohol or water
ceramics is a key objective of R&D in nanotechnology having strong interaction with the generated silica. In
together with the preparation of nanocomposites by the forming process of the sol–gel hybrid, the sol–gel
the layer intercalation method and nanofiller disper- hardening reaction takes place at competitive speed
sion method [1–3]. considering the evaporation of the solvent and the
A recent technology called the sol–gel hybrid hardening of the polymer, the relative speed of which
method enables the mixing of plastics and ceramics in is affected by environmental changes in the kind of
the nanosized range. The sol–gel method is used to solvent. The hardening conditions and thickness of
produce a metal oxide thin layer by hardening metal hybrid material etc. determines the quality of the
alkoxide represented by alkoxysilane [TMOS (tetra- hybrid materials, namely the dispersion state of silica.
methoxysilane) or TEOS (tetraethoxysilane)] as For this reason, it is difficult to utilize the sol–gel
shown in Fig. 1.1. When this sol–gel hardening reac- hybrid for various industrial applications with constant
tion takes place in a selected melted polymer or poly- quality [1, 4]. Therefore we aimed at developing a
mer solution, the growth of the siloxane bond by the hybrid method by which anyone can easily obtain
sol–gel hardening is hindered by the polymer and con- good dispersion of silica for diverse sorts of polymers.
sequently the hardened composite material with the Plastic materials become harder and were brittle
nanosized silica particles dispersed in the polymer is but gain in heat resistance when ceramic materials
obtained, which is called a sol–gel hybrid. Principally, like glass are mixed into them. By mixing these dif-
it utilizes the interaction between the silanol group ferent kinds of materials, the advantages and disad-
(Si-OH) generated in the process of sol–gel hardening vantages of each material can be reflected in the
and the hydrogen bond in the polymer [1, 2]. The com- properties of the composite material. Our research
posite material made by the sol–gel method is com- target was not the preparation of composite material
pletely transparent and does not look like a mixture of of polymer and silica having arithmetically averaged
different kinds of materials. Therefore the terminology properties but the creation of new material with the
“hybrid” is applied for this material rather than advantages of both the materials in consideration of
“composite”. individual applications.
The site selective molecular hybrid method devel-
2. Molecular design oped was a hybrid method, which overcomes each of
the above-mentioned problems of conventional com-
The finer the ceramic particles dispersed in the matrix posite materials. As shown in Fig. 1.2, by a site selec-
polymer in the composite materials, the greater the tive molecular hybrid method, an alkoxysilane
interface between both the materials inversely propor- compound is polymerized to produce polyalkoxysilox-
tional to the particle size and the more significant its ane with a functional group like a glycidyl group.
effects on the properties of the composite materials. Using this functional group, polyalkoxysiloxane is
For this reason, we examined the hybrid by sol–gel introduced to a certain position of a polymer, produc-
ing an alkoxysilane-denatured polymer [5].
At the site of polyalkoxysiloxane, a sol–gel harden-
ing reaction takes place like the monomer to generate
silica. By covalent bonding of the alkoxysiloxane with
Hydrolysis
the polymer by their prior reaction, the hybrid technol-
Si(OR) + H O (RO) SiOH + ROH ogy can be applied to various kinds of polymers and
3
2
4
realize good stable dispersion of silica, which is barely
affected by environmental parameters such as the film
Condensation
thickness and the hardening conditions.
≡ SiOH + HOSi ≡ ≡ SiOSi ≡ + H O The most important advantage of the site selective
2
molecular hybrid method developed here, is that the
Figure 1.1 structure can be designed to suit the applications
Sol–gel curing reaction. (Fig. 1.3). In a similar manner used by polymer
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