Biomedical Engineering Reference
In-Depth Information
Fig. 7.3
(
a
) Dependence of the interfacial correlation function
f
(
m,R
0
)on
m
and
R
0
. (b) Mea-
sured
f
(
m,R
0
) in ice nucleation [
55
-
57
]. (
b
) Dependence of the interfacial correlation function
f
(
m,R
0
)
f
(
m
)on
m
at
R
0
10. (
c
) Schematic illustration of
the shadow effect
of the substrate in
heterogeneous nucleation. The presence of the substrate blocks the collision of growth units onto
the surface of the nucleus. Reprinted with permission from Ref. [
9
] ©2004 Springer
D
Although many theories have been put forward, the “atomic” process has never
been visualized and treated in a quantitative way until recently when a 2D nucleation
process was monitored in the system of charged PS spheres driven by the alternating
field with a fixed field strength and a frequency (i.e., Fig.
7.1
)[
13
,
57
]. A typical
process of nucleation has been presented in Fig.
7.4
. On the electrode surfaces,
the concentration of particles was supersaturated and the particles started to form
the nuclei (Fig.
7.4
a, b, where we represented crystal-like particles as blue spheres).
The nucleus in red circle kept growing whatever its state was pre- or post-nucleation;
the nucleus in green circle shrank far more frequently than they grow (Fig.
7.4
c-e).
In Fig.
7.4
f, the plots reflected the evolution of size of two adjacent nuclei during
the process of pre-nucleation. One nucleus was growing larger and larger when
its size is larger than the critical size. Moreover, the other nucleus was shrinking
before reaching the critical size. This implies that nucleation is a number of
simultaneous fluctuating assembly-disassembly events. A successful nucleation
process corresponds to one of such events that can survive till the nucleus reaches
critical size [
53
].
