2.1 Nanoparticles 9
may change the properties significantly. Certainly, this is senseless in view of the
technical applications.
The two problems described above and to exploit these very special properties
of nanoparticles, composite particles of the core–shell type, with a second phase
acting as distance holder were developed. The necessary distance depends on the
phenomenon to be suppressed; it may be smaller, in the case of tunneling of
electrons between particles, and is larger in the case of dipole–dipole interaction.
Furthermore, such composite particles can be designed in a way to combine different “incompatible” properties, such as magnetism and luminescence. The
typical design of these particles is depicted in Figure 2.3.
The core–shell composite design, as depicted in Figure 2.3 is typical for advanced
applications, for example, in medicine or biotech. Such a core–shell nanocomposite consists of a core, carrying the property, which demand the largest volume, for
example, magnetism. The property of Coating 1, is the case of a bifunctional
particle, for example, luminescence. The outermost layer, Coating 2 in Figure 2.3
has to mediate with the surrounding medium. Therefore, in most cases, it is either
hydrophilic or hydrophobic. In many medical applications, the outermost layer
may consist of a protein or enzyme, which is characteristic for a specific type
of cells.
Typical examples for coated particles are shown in Figures 2.4a–c. In Figure
2.4a, a ceramic core (ZrO 2 ), which is coated with a ceramic layer (Al 2 O 3 ), an amorphous one, is displayed. In Figure 2.4b, the ceramic core (Fe 2 O 3 ) is coated with a
polymer (PMMA). This type of composite is often used as a special magnetic
material. As a third variety, a ceramic particle (TiO 2 ) decorated with a metal (Pt)
is displayed in Figure 2.4c. Coating of ceramic particles with thin metallic layers
is, because of the relation in the surface energy, in most cases impossible. Instead
of a coating, one obtains a decoration of the core with metallic clusters. This type
of composite is often used as a catalyst.
Most interesting are the particles displayed in Figure 2.4a, as they show an
important phenomenon, characteristic of nanomaterials. This figure shows three
coated ceramic particles. The particle in the center of the figure originates from
Figure 2.3 Typical design of a core–shell
nanocomposite particle. The properties of
the core and coating 1 are, in most cases,
selected to the demand of the physics (e.g.,
magnetic and luminescence); the second
coating is selected in view of the interaction
with the surrounding medium (e.g.,
hydrophilic or hydrophobic) [2].
Core
Property I
CoaƟng 1
Property II
CoaƟng 2
Property III
may change the properties significantly. Certainly, this is senseless in view of the
technical applications.
The two problems described above and to exploit these very special properties
of nanoparticles, composite particles of the core–shell type, with a second phase
acting as distance holder were developed. The necessary distance depends on the
phenomenon to be suppressed; it may be smaller, in the case of tunneling of
electrons between particles, and is larger in the case of dipole–dipole interaction.
Furthermore, such composite particles can be designed in a way to combine different “incompatible” properties, such as magnetism and luminescence. The
typical design of these particles is depicted in Figure 2.3.
The core–shell composite design, as depicted in Figure 2.3 is typical for advanced
applications, for example, in medicine or biotech. Such a core–shell nanocomposite consists of a core, carrying the property, which demand the largest volume, for
example, magnetism. The property of Coating 1, is the case of a bifunctional
particle, for example, luminescence. The outermost layer, Coating 2 in Figure 2.3
has to mediate with the surrounding medium. Therefore, in most cases, it is either
hydrophilic or hydrophobic. In many medical applications, the outermost layer
may consist of a protein or enzyme, which is characteristic for a specific type
of cells.
Typical examples for coated particles are shown in Figures 2.4a–c. In Figure
2.4a, a ceramic core (ZrO 2 ), which is coated with a ceramic layer (Al 2 O 3 ), an amorphous one, is displayed. In Figure 2.4b, the ceramic core (Fe 2 O 3 ) is coated with a
polymer (PMMA). This type of composite is often used as a special magnetic
material. As a third variety, a ceramic particle (TiO 2 ) decorated with a metal (Pt)
is displayed in Figure 2.4c. Coating of ceramic particles with thin metallic layers
is, because of the relation in the surface energy, in most cases impossible. Instead
of a coating, one obtains a decoration of the core with metallic clusters. This type
of composite is often used as a catalyst.
Most interesting are the particles displayed in Figure 2.4a, as they show an
important phenomenon, characteristic of nanomaterials. This figure shows three
coated ceramic particles. The particle in the center of the figure originates from
Figure 2.3 Typical design of a core–shell
nanocomposite particle. The properties of
the core and coating 1 are, in most cases,
selected to the demand of the physics (e.g.,
magnetic and luminescence); the second
coating is selected in view of the interaction
with the surrounding medium (e.g.,
hydrophilic or hydrophobic) [2].
Core
Property I
CoaƟng 1
Property II
CoaƟng 2
Property III