Page 203 - Book Hosokawa Nanoparticle Technology Handbook

CHAPTER 4 CONTROL OF NANOSTRUCTURE OF MATERIALS

4.1 Assembly of nanoparticles and ceramics, aerosol deposition, colloid chemical
processes, self-organization phenomena of nanoparti-
functionalization
cles in liquid phase, assembly patterning technologies
and organic/inorganic mesoporous materials.
Implementation of excellent functional materials or
devices using nanoparticles requires to not only iden-
tify nanostructures with desirable functions, but also 4.2 Nanoparticles arranged structures
assemble those nanostructures up to a practical size
maintaining the nanostructure arrangement. This
process is similar to the biological technique of 4.2.1 Photonic fractal
assembling small structural blocks of the atomic or
molecular level up to a large structure, or the bottom- A fractal is defined as a rough and irregular structure
up technology. The bottom-up assembling and com- with self-similarity. In other words, the local configu-
pounding of plural different materials and nanospace ration or substructure is similar to the whole configu-
will enable the creation of nanoparticle structures ration [1, 2]. The characteristic feature of fractal is
with more versatile functionality. found in complex forms of nature such as thunder-
In the field of the wet process of fine particles, for head, complex coastline, forest, and wrinkled wall of
example, many reports have been published recently intestine. These forms have statistical self-similarity
on self-organization and self-assembling technologies because the enlarged local configuration does not
to construct structures by utilizing the laws of nature. coincide with the whole, but resemble it.
In these technologies, the phenomenon of convective The geometric dimension D is defined by equation
assembling is used, which accompanies meniscus (4.2.1), where N is the number of self-similar units
(liquid surface) movement. In this process, a field is newly created when the size of the initial unit
formed changing from a dispersed to an assembled decreases to 1/S. It is called self-similar dimension or
state of particles so that the free energy of the system fractal dimension.
is reduced. In the future, understanding and system-
atization will be increasingly required of these new N S D (4.2.1)
process technologies from the perspective of both
basic research and application. For example, when each edge of a cube is divided into
In this chapter, process technologies are summa- three equivalent segments, the initial cube consists of
rized for nanostructural controls using mainly fine 27 smaller identical cubes as seen in Fig. 4.2.1(a), and
particles including nanoparticles as a starting mate- the equation (4.2.1) will be 27 3 . This result coin-
3
rial. In Section 4.2, the assembly structures of cides with our recognition of three-dimensions. In
nanoparticles are discussed, introducing nanobiotech- case of Fig. 4.2.1(b), seven smaller cubes are
nologies and colloid processes. In addition, there is an extracted from the body-and face-centers. The equa-
explanation of fractal structures, rather than periodic tion is 20 3 . Therefore, the fractal dimension is
D
or random structures, and optical properties. Section about 2.73. When this division and extraction process
4.3 looks at nanoporous structures and their control is repeated three times, it is called the stage 3 Menger
technologies, including zeolite, creation technologies sponge as shown in Fig. 4.2.1(d). The fractal dimen-
of nanoporous structures by dry processes, control sion is non-integer number. Menger sponge structure
technologies of nanoporous structures, and the con- can be imaged as an intermediate structure between
trol of tubular porous structures. two- and three-dimensions when the stage number is
In Section 4.4, the relation between nanocomposite increased.
structures used in catalysts and fuel cell electrodes A lot of research has been carried out [3, 4],
and their functions is explained together with polymer because it is interesting to investigate what will hap-
nanocomposite technologies. In addition, plastic pen when electromagnetic waves or light travels
deformation technologies are discussed for control- through a fractal structure. However, all the fractal
ling the nanostructures of metal and alloy. The structures investigated were one- or two-dimensional
distinctive process technologies of sintering and bond- ones because of difficulty in fabrication of complex
ing of nanoparticle assembly and self-organization of 3D structures. Japanese researchers have first fabri-
nanoparticles are covered in Sections 4.5 and 4.6, cated cube fractals of Menger sponge structure with
respectively. The latest information is also introduced dielectric materials and found the localization of elec-
on various technologies useful for forming nanostruc- tromagnetic waves in 2003 [5–7]. They named such a
tures, including sintering technologies of nanoparti- fractal having localization function of electromag-
cles, low temperature sintering technologies of netic waves or light as photonic fractal.

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