2.2 Elementary Consequences of Small Particle Size 13
However, as gold can be dissolved in the glass matrix, a diffusion barrier is necessary. In the case of gold-ruby glass the diffusion barrier consists of tin oxide. In
colloid chemistry, this principle of stabilization is well known as “colloid stabilization”. This material was produced for the first time by the Sumerians in the
seventh century BC and re-invented by Kunkel in Leipzig in the seventeenth
century. It is interesting to note that the composition used by the Sumerians was
practically identical to the one reinvented by Kunkel and that is used nowadays.
Furthermore, the properties of a bulk solid made of coated nanoparticles
may be adjusted gradually with the thickness of the coating. Depending on the
requirements of the application, the coating material may be ceramic or polymer.
Coating nanoparticles with a second and third layer leads to the following
improvements:
• The distribution of the two phases is homogenous on a nanometer scale.
• The kernels are arranged in a well-defined distance. Therefore, the interaction
of the particles is controlled.
• The kernel and one or more different coatings may have different properties.
This allows the combination of properties in one particle that are never found
together in nature. Additionally, by selecting a proper polymer for the outermost coating, it is possible to adjust the interaction with the surrounding
medium.
• During densification, i.e. sintering, the growth of the kernels is thwarted,
provided core and coating show no mutual solubility. An example for this is
depicted in Figure 2.7.
These arguments demonstrate that the most advanced type of nanocomposites are
coated nanoparticles. They allow not only the combination of different properties
in one particle, but also in bulk materials.
In addition to the composites displayed in Figures 2.6 and 2.7, one observes
nanocomposites with regular well-ordered structure, as displayed in Figure 2.9.
In general, self-organization processes in the case of spherical filler particles
or mechanical stretching are appropriate mechanisms to create this type of composite, if the filler particles are one- or two-dimensional. Successful realization
of self-organization processes, leading to structures as depicted in Figure 2.9a,
requires particles nearly identical in size.
2.2
Elementary Consequences of Small Particle Size
2.2.1
Surface of Nanoparticles
The first and most important consequence of the small particle size is the
huge surface area. To get an impression of the importance of this geometric
However, as gold can be dissolved in the glass matrix, a diffusion barrier is necessary. In the case of gold-ruby glass the diffusion barrier consists of tin oxide. In
colloid chemistry, this principle of stabilization is well known as “colloid stabilization”. This material was produced for the first time by the Sumerians in the
seventh century BC and re-invented by Kunkel in Leipzig in the seventeenth
century. It is interesting to note that the composition used by the Sumerians was
practically identical to the one reinvented by Kunkel and that is used nowadays.
Furthermore, the properties of a bulk solid made of coated nanoparticles
may be adjusted gradually with the thickness of the coating. Depending on the
requirements of the application, the coating material may be ceramic or polymer.
Coating nanoparticles with a second and third layer leads to the following
improvements:
• The distribution of the two phases is homogenous on a nanometer scale.
• The kernels are arranged in a well-defined distance. Therefore, the interaction
of the particles is controlled.
• The kernel and one or more different coatings may have different properties.
This allows the combination of properties in one particle that are never found
together in nature. Additionally, by selecting a proper polymer for the outermost coating, it is possible to adjust the interaction with the surrounding
medium.
• During densification, i.e. sintering, the growth of the kernels is thwarted,
provided core and coating show no mutual solubility. An example for this is
depicted in Figure 2.7.
These arguments demonstrate that the most advanced type of nanocomposites are
coated nanoparticles. They allow not only the combination of different properties
in one particle, but also in bulk materials.
In addition to the composites displayed in Figures 2.6 and 2.7, one observes
nanocomposites with regular well-ordered structure, as displayed in Figure 2.9.
In general, self-organization processes in the case of spherical filler particles
or mechanical stretching are appropriate mechanisms to create this type of composite, if the filler particles are one- or two-dimensional. Successful realization
of self-organization processes, leading to structures as depicted in Figure 2.9a,
requires particles nearly identical in size.
2.2
Elementary Consequences of Small Particle Size
2.2.1
Surface of Nanoparticles
The first and most important consequence of the small particle size is the
huge surface area. To get an impression of the importance of this geometric