Chemistry Reference
In-Depth Information
Figure 6.6 (a) Schematic representation of PEI-mediated assembly of gold nanoparticles.
Transmission electron micrographs of (b) hexagonal and (c) cubic packing arrangements of
nanoparticles. Reprinted with permission from Schmid et al. (2000). Copyright 2000 Wiley
InterScience.
in a polyethyleneimine (PEI) coated surface through electrostatic interactions
(Fig. 6.6). The low molecular weight PEI (M
W
¼ 60 000) permitted the nanoparticles
to have enough mobility to rearrange on the surface. The final well-ordered array
exhibited either hexagonal or cubic packing, depending on the crystalline phase of
the underlying PEI support. This study suggested that the PEI surface acts as a tem-
plate to direct the arrangement of nanoparticles on the substrate.
In addition to electrostatic interaction, multipoint hydrogen bonding has been uti-
lized for selective deposition of nanoparticles on polymer template surfaces to gen-
erate ordered functional arrays (Murray et al. 2000). Incorporation of such
recognition units provides a new direction in the assembly based on the reversible
and specific nature of hydrogen bonds. Binder et al. (2005) reported selective
binding of gold nanoparticles onto a microphase separated diblock copolymer film
(Fig. 6.7). Gold nanoparticles (5.0 nm) were functionalized by ligands containing a
barbituric acid moiety, which features a strong affinity with the Hamilton receptor
through six-point hydrogen bonding (K
a
¼ 1.2
10
5
M
-1
). One block of the copoly-
mer was postfunctionalized with complementary Hamilton receptors through
Huisgen 1,3-dipolar cycloaddition (“click chemistry”), whereas the other block
bore a fluorinated side chain to enhance microseparation. Nanoparticles selectively
deposited on a specific domain with Hamilton receptors of the block copolymer.
This intelligent approach takes advantages of both microseparated block copolymer
film and specific hydrogen bonding to directly create a patterned surface in the micro-
scale range, which has great potential applications in multifunctional biosensors and
novel electronic, mechanical, and photonic devices.
The formation of a patterned surface through selective segregation of nano-
particles onto one domain of a block copolymer film can be used to produce
complex 2-D nanoparticle arrays in a controlled fashion. However, the resulting
