Chemistry Reference
In-Depth Information
FIGURE 1.11
Hierarchical control of self-assembly via molecular solid angle [46].
a
0
)
determined in all cases according to (
360/u, where u is the number of dendrons in
a column stratum or supramolecular sphere. Increasing the branching via a change in
sequence or increase in generation number of taper-like dendrons increases the (
¼
a
0
)
and the fraction of the disk occupied in columnar self-assembly. At a certain threshold
only unimolecular disks are formed. Above this threshold, further branching results in
deformation of the disk into a conical segment with diminished (
a
0
). Beyond this
a
0
) and the fraction of a sphere formed.
Ultimately, a unimolecular sphere should result. A wide variety of periodic and
quasiperiodic lattices can be formed by simply tuning the dendron shape parameters
as described in Figure 1.12 [45].
point, increased branching increases (
1.3.3 Quantized Surface Chemistry
More than 1000 different surface reactions have been reported for dendrons/
dendrimers. Essentially, all mechanistic reaction types (i.e., covalent, ionic, radical,
etc.) have been reported. Several examples of these reactions are illustrated in
Figure 1.13. Both subnanoscale, and nanoscale reagents (i.e., proposed nano-elements)
have been used in these surface reactions. The surface valency and stoichiometry are
mathematically quantified by relationships described in Figure 1.8 (i.e., Z
¼
N
c
N
b
G
).
Generally, these valencies and stoichiometric binding ratios are operational for all
generations preceding serious onset of de Gennes-type dense packing congestion.
Surface congested generations (i.e.,
4 for poly(amidoamine) (PAMAM) den-
drimers) usually exhibit lower than theoretical stoichiometries even with small-sized
reagents. Large-sized reagents (i.e.,
>
G
¼
1 nm) may lead to less than ideal stoichiometries
>
