2
Nanomaterials and Nanocomposites
2.1
Introduction
Nanomaterials may be zero-dimensional (e.g., nanoparticles), one-dimensional
(e.g., nanorods or nanotubes), or two-dimensional (usually realized as thin films
or stacks of thin films). As a typical example, an electron micrograph of zirconia
powder (a zero-dimensional object) is shown in Figure 2.1.
The particles depicted in Figure 2.1 show a size of about 7 nm, characterized by a
very narrow distribution of sizes. This is an important point, as many of the
properties of nanomaterials are size-dependent. In contrast, many applications do
not require such sophistication and therefore cheaper materials with a broader
particle size distribution (see Figure 2.2a) would be sufficient. The material depicted
in Figure 2.2a, which contains particles ranging in size from 5 to more than 50 nm,
would be perfectly suited for applications such as pigments or ultraviolet (UV)
absorbers.
A further interesting class of particles may be described as fractal clusters of
extreme small particles. Typical examples of this type of material are most of the
amorphous silica particles (known as “white soot”) and amorphous Fe 2 O 3 particles,
the latter being used as catalysts (see Figure 2.2b).
Apart from properties related to grain boundaries, the special properties of
nanomaterials are those of single isolated particles that are altered, or even lost,
in the case of particle interaction. Therefore, most of the basic considerations are
related to isolated nanoparticles as the interaction of two or more particles may cause
significant changes in the properties. For technical applications, this proved to be
negative and, consequently, nanocomposites of the core/shell type with a second
phase acting as a distance holder were developed. The necessary distance depends
on the phenomenon to be suppressed; it may be smaller in the case of the tunneling
of electrons between particles, but larger in the case of dipole–dipole interaction. In
this context, most important are bifunctional particles exhibiting a ferromagnetic
core and a luminescent coating, as they are used medical applications [2]. Nanocomposites – as described in this chapter – are composite materials with at least one
phase exhibiting the special properties of a nanomaterial. In general, random
arrangements of nanoparticles in the composite are assumed.
Nanomaterials: An Introduction to Synthesis, Properties and Applications, Second Edition. Dieter Vollath.
Ó 2013 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2013 by Wiley-VCH Verlag GmbH & Co. KGaA.
j5
Nanomaterials and Nanocomposites
2.1
Introduction
Nanomaterials may be zero-dimensional (e.g., nanoparticles), one-dimensional
(e.g., nanorods or nanotubes), or two-dimensional (usually realized as thin films
or stacks of thin films). As a typical example, an electron micrograph of zirconia
powder (a zero-dimensional object) is shown in Figure 2.1.
The particles depicted in Figure 2.1 show a size of about 7 nm, characterized by a
very narrow distribution of sizes. This is an important point, as many of the
properties of nanomaterials are size-dependent. In contrast, many applications do
not require such sophistication and therefore cheaper materials with a broader
particle size distribution (see Figure 2.2a) would be sufficient. The material depicted
in Figure 2.2a, which contains particles ranging in size from 5 to more than 50 nm,
would be perfectly suited for applications such as pigments or ultraviolet (UV)
absorbers.
A further interesting class of particles may be described as fractal clusters of
extreme small particles. Typical examples of this type of material are most of the
amorphous silica particles (known as “white soot”) and amorphous Fe 2 O 3 particles,
the latter being used as catalysts (see Figure 2.2b).
Apart from properties related to grain boundaries, the special properties of
nanomaterials are those of single isolated particles that are altered, or even lost,
in the case of particle interaction. Therefore, most of the basic considerations are
related to isolated nanoparticles as the interaction of two or more particles may cause
significant changes in the properties. For technical applications, this proved to be
negative and, consequently, nanocomposites of the core/shell type with a second
phase acting as a distance holder were developed. The necessary distance depends
on the phenomenon to be suppressed; it may be smaller in the case of the tunneling
of electrons between particles, but larger in the case of dipole–dipole interaction. In
this context, most important are bifunctional particles exhibiting a ferromagnetic
core and a luminescent coating, as they are used medical applications [2]. Nanocomposites – as described in this chapter – are composite materials with at least one
phase exhibiting the special properties of a nanomaterial. In general, random
arrangements of nanoparticles in the composite are assumed.
Nanomaterials: An Introduction to Synthesis, Properties and Applications, Second Edition. Dieter Vollath.
Ó 2013 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2013 by Wiley-VCH Verlag GmbH & Co. KGaA.
j5