Page 124 - Book Hosokawa Nanoparticle Technology Handbook

FUNDAMENTALS CH. 2 STRUCTURAL CONTROL OF NANOPARTICLES
method using two different types of sol precursors is enzymes or proteins [5]. Optical properties due to the
currently the most effective method. large difference in refractive index of core and shell
materials are also unique. Hollow particles are
applied to photoelectric devices and coating materials
References because of their optical properties [6, 7].
As described above, hollow particles have more
[1] H.J. Fan, R. Scholz, F.M. Kolb, M. Zacharias and U.
potentialities of application based on their unique
Goesele: Sol. State Commun., 130, 517—521 (2004).
properties compared with solid particles that have been
[2] K. Oshima, K. Tsuto, K. Okuyama and N. Tohge:
widely used so far. In the following, organic bead tem-
Kagaku Kogaku Ronbunsyu, 18(3), 288–295 (1992). plate method will be described as one of the most
[3] N. Tohge, S. Tamaki and K. Okuyama: Jpn. J. Appl. famous ways to prepare hollow nanoparticles.
Phys., 34, L207–L209 (1995). The feature of this organic bead template method is
[4] S. Tamaki, N. Tohge and K. Okuyama: J. Mater. Sci. usage of organic bead as a template. Poly(stylene)
Lett., 14, 1388–1390 (1995). (PS) is most frequently used in this method, but basi-
[5] M. Abdullah, F. Iskandar, S. Shibamoto, T. Ogi and K. cally, any template can be applied to this method if it
can be removed.
Okuyama: Acta Materialia, 52(17), 5151–5156 (2004).
Preparation of hollow particles of silica [4, 5, 8], tita-
[6] F. Iskandar, L. Gradon and K. Okuyama: J. Colloid
nia, zinc sulfide [6], and cadmium sulfide [9] by using
Interface Sci., 265, 296–303 (2003).
the organic beads template method have been reported.
[7] F. Iskandar, I.W.Lenggoro, B. Xia and K. Okuyama:
These hollow particles are prepared via core–shell
J. Nanoparticle Res., 3, 263–270 (2001). (coated) particles that are formed by coating a shell
[8] F. Iskandar, H. Chang and K. Okuyama: Adv. Powder material around the core organic beads by using selec-
Technol., 14(3), 349–367 (2003). tive precipitation on the charged surface of the core
[9] F. Iskandar Mikrajuddin, K. Okuyama: Nano Lett., particles [10]. The hollow particles are prepared by
2(4), 389–392 (2002). removing the organic core particles after filtration and
[10] L. Gradon´, S. Janeczko, M. Abdullah, F. Iskandar and drying. The thermal (pyrolytic) and the chemical
decomposition are known as the way to remove the
K. Okuyama: AIChE J., 50(10), 2583–2593 (2004).
organic core. A schematic illustration of the organic
bead template method is given in Fig. 2.5.11.
2.5.2 Liquid-phase synthesis The hollow particles that were prepared by using
this organic beads template method are introduced
2.5.2.1 Hollow particles below.
Synthesis and application of hollow particles with their Caruso et al. [5] have reported about the hollow sil-
diameter ranging from nano to micrometer are attract- ica and silica-polymer core–shell particles synthesized
ing much attention these days. Because hollow parti- by this method. At first, PS latex particles are coated
cles have unique properties which are different from with polymer in order to control the surface charge of
solid particles, for example low density, high-specific the core. This coating layer provides positively
surface area, and ability to incorporate a material. charged surface that promotes adsorption of negatively
Owing to these properties, hollow particles are charged SiO as well as it provides smooth surface.
2
applied for various materials such as lightweight A multi-layer of SiO /PDADMAC (poly(diallyl-
2
filler, an insulator [1], composite materials [2], and dimethylammonium)chloride) is formed by alterna-
color materials [3]. Meso- and macroporous hollow tive adsorption of SiO 2 and PDADMAC. The
particles with controlled shell thickness are used as template PS latex polymer is removed by calcination
analytical isolation and encapsulating materials [4]. at 500 C. Then, hollow particles with the shape of
Especially, encapsulating materials are used for drug internal cavity templated by core particles were
delivery and inhibition of hypersensitiveness of obtained.

Tuning of Removal of
surface charge Coating organic core

Organic Hollow particle
template
particle Adsorption or Inorganic reagents Calcination or
surface modification or particles dissolution in solvent

Figure 2.5.11
Organic beads template method.

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