7
Nanoparticles – Nanocomposites
2
2.1
Nanoparticles
Nanoparticles may be classified as zero-dimensional, these are the nanoparticles
per se, one-dimensional such as nanorods or nanotubes, and two-dimensional that
are, in most cases, plates or stacks of plates. As a typical example of particles,
Figure 2.1 displays an electron micrograph of zirconia (ZrO 2 ) powder, zerodimensional objects.
The particles depicted in Figure 2.1 show a size of ca. 7 nm. It is important to
mention that the particles are in a very narrow range of sizes. This may be important, as many properties of nanomaterials are size dependent. On the other hand,
many applications do not need such sophisticated material or they just need a
broad variation of properties. Therefore, in many cases, cheaper materials with
broader particle size distribution, as is depicted in Figure 2.2a, are necessary or,
at least, sufficient. The material depicted in this figure shows particles in the size
range from 5 to more than 50 nm. Such materials are perfectly suited for applications as pigments, UV-absorbers, etc.
A further interesting class of particles may be described as clusters of extremely
small particles. Typical examples of this type of materials are most of the amorphous silica particles, well known as “white soot”, and amorphous Fe 2 O 3 particles.
Typically, particles of this type, as shown in Figure 2.2b, are applied as catalysts.
In producing bulk nanocomposites, the central problem is to obtain a perfect
distribution of the particulate phase in the matrix. Processes based on mechanical
blending or synthesizing the two phases separately and mixing during the step
of particle formation, never lead to homogeneous products on the nanometer
scale. Provided there are no preferences and the process of blending is random,
the probability that two or more particles are touching each other and form a
cluster is very high. Usually, in such a mixture, one wants to obtain a relatively
high concentration of “active” particles, carrying the physical property of interest.
Assuming, in the simplest case, particles of equal size, the probability p n that a
number of n particles with the volume concentration c are touching each other, is
p n = c
n . The consequences of this simple relation are severe: for example, assuming
a concentration of 0.30, the probability of two touching particles is 0.09 and for
Nanoparticles – Nanocomposites – Nanomaterials: An Introduction for Beginners, First Edition. Dieter Vollath.
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2013 by Wiley-VCH Verlag GmbH & Co. KGaA.
Nanoparticles – Nanocomposites
2
2.1
Nanoparticles
Nanoparticles may be classified as zero-dimensional, these are the nanoparticles
per se, one-dimensional such as nanorods or nanotubes, and two-dimensional that
are, in most cases, plates or stacks of plates. As a typical example of particles,
Figure 2.1 displays an electron micrograph of zirconia (ZrO 2 ) powder, zerodimensional objects.
The particles depicted in Figure 2.1 show a size of ca. 7 nm. It is important to
mention that the particles are in a very narrow range of sizes. This may be important, as many properties of nanomaterials are size dependent. On the other hand,
many applications do not need such sophisticated material or they just need a
broad variation of properties. Therefore, in many cases, cheaper materials with
broader particle size distribution, as is depicted in Figure 2.2a, are necessary or,
at least, sufficient. The material depicted in this figure shows particles in the size
range from 5 to more than 50 nm. Such materials are perfectly suited for applications as pigments, UV-absorbers, etc.
A further interesting class of particles may be described as clusters of extremely
small particles. Typical examples of this type of materials are most of the amorphous silica particles, well known as “white soot”, and amorphous Fe 2 O 3 particles.
Typically, particles of this type, as shown in Figure 2.2b, are applied as catalysts.
In producing bulk nanocomposites, the central problem is to obtain a perfect
distribution of the particulate phase in the matrix. Processes based on mechanical
blending or synthesizing the two phases separately and mixing during the step
of particle formation, never lead to homogeneous products on the nanometer
scale. Provided there are no preferences and the process of blending is random,
the probability that two or more particles are touching each other and form a
cluster is very high. Usually, in such a mixture, one wants to obtain a relatively
high concentration of “active” particles, carrying the physical property of interest.
Assuming, in the simplest case, particles of equal size, the probability p n that a
number of n particles with the volume concentration c are touching each other, is
p n = c
n . The consequences of this simple relation are severe: for example, assuming
a concentration of 0.30, the probability of two touching particles is 0.09 and for
Nanoparticles – Nanocomposites – Nanomaterials: An Introduction for Beginners, First Edition. Dieter Vollath.
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2013 by Wiley-VCH Verlag GmbH & Co. KGaA.