two properties have utilized a multishell design of the particles. In the design
depicted in Figure 2.10, the coupling layer may consist of an appropriate polymer or
a type of glucose, although in many cases hydroxylated silica is also effective.
Biological molecules such as proteins or enzymes may then be attached at the
surface of the coupling layer.
2.2
Elementary Consequences of Small Particle Size
Before discussing the properties of nanomaterials, it may be advantageous to
describe some examples demonstrating the elementary consequences of the small
size of nanoparticles.
2.2.1
Surface of Nanoparticles
The first and most important consequence of a small particle size its huge surface
area; in order to obtain an impression of the importance of this geometric variable,
the surface over volume ratio should be discussed. So, assuming spherical particles,
the surface a of one particle with diameter d is a ¼ pd
2 and the corresponding
volume v is v ¼ d
3 p=6. (Within this book, in all thermodynamic considerations
quantities related to one particle are written in lower case characters, whereas
for molar quantities upper case letters are used.) Therefore, one obtains for the
surface/volume ratio:
R
0 ¼
a
v
¼
6
d
ð2:1Þ
Figure 2.10 Nanocomposite particle for
application in biology or medicine. The ceramic
core may be magnetic or luminescent. The cellor tumor-specific proteins at the surface, which
are necessary for application, require a coupling
layer, as typically they cannot be attached
directly to the ceramic surface.
12j 2 Nanomaterials and Nanocomposites