Chemistry Reference
In-Depth Information
immersion and transonication in the solution. During the dissolution, the resist layer
was lifted off, resulting in removing the LBL film on top of the photoresist at the
selected area.
Crespo-Biel and coworkers developed various patterning strategies to create
polymer-mediated nanoparticle films on active cyclodextrin (CD) SAMs through
host-guest CD-adamante (Ad) interactions (Crespo-Biel, Dordi, et al. 2006;
Crespo-Biel, Ravoo, et al. 2006). They utilized CD modified gold nanoparticles
(CD-Au nanoparticles) and admantyl-terminated poly(propylene imine) dendrimers
(Ad-PPI) as the basis for a supramolecular LBL assembly process. The first approach
is based on nanotransfer printing introduced by Park and Hammond (2004). Initially,
the poly(dimethylsiloxane) (PDMS) stamps were pretreated by a UV/ozone treat-
ment, resulting in a slightly negatively charged surface (Fig. 6.12). This weakly oxi-
dized surface was employed as the substrate for the formation of the LBL
supramolecular assembly, which was composed of alternative CD-Au nanoparticles
and Ad-PPIs. Because of the stronger interaction of Ad-PPI and CD-SAM, adsorbed
LBL assemblies on the PDMS stamps were completely transferred onto a full CD-
SAM by the microcontact printing method. Moreover, the thickness of the patterned
thin films could be manipulated by an LBL sorption process. Integration of nano-
imprinting lithography and the lift-off approach led to a similar patterned LBL assem-
bly templated on the surface. The prepatterned PMMA structure obtained through
nanoimprinting lithography served as a physical barrier for the formation of
CD-SAMs. The CD-SAMs were placed on the native silicon oxide areas through
three steps of functionalization. The LBL assemblies of CD-Au nanoparticles and
Ad-PPIs were performed on the entire area, followed by the lift-off process in the
acetone that led to patterned LBL films on the silicon substrate.
6.3.3. Control of 3-D Hierarchical Organization in the Solution
Highly structured, 3-D nanoparticle-polymer nanocomposites possess unique mag-
netic, electronic, and optical properties that differ from individual entities, providing
new systems for the creation of nanodevices and biosensors (Murray et al. 2000;
Shipway et al. 2000). The choice of assembly interactions is a key issue in order
to obtain complete control over the thermodynamics of the assembled system.
The introduction of reversible hydrogen bonding and flexible linear polymers
into the bricks and mortar concept gave rise to system formation in near-equilibrium
conditions, providing well-defined structures.
A random diaminotriazine-immobilized PS (Triaz-PS) was employed as the
mortar, whereas a complementary thymine-functionalized gold nanoparticle (Thy-
Au) functioned as bricks (Fig. 6.13; Boal et al. 2000, 2002). A black solid was
formed immediately after fixing of Triaz-PS and Thy-Au. In contrast, no precipitate
was observed when gold nanoparticles functionalized with structurally analogous
N-methyl thymine ligands (Me-Thy-Au) were used. This strongly indicated the
essentiality of the assembly process by three-point hydrogen bonding. The diameter
of these resulting spherical nanoparticle aggregates was strongly dependent on the
temperature at which the assembly was performed. Sizes of 100 nm to 0.5-1 mm
