Biomedical Engineering Reference
In-Depth Information
tion length, which offers a new way for fine tuning photonic and electro-
optical properties of conjugated polymers through a molecular engineering
approach.
Template methods have been widely used to fabricate three-dimensional
nano- and microstructured patterns. The breath figure process is an elegant
yet simple way to generate large arrays of patterned assemblies [143]. When
moist air is blown over a polymer solution in an organic solvent, evaporative
cooling generates water droplets on the liquid surface. The uniform droplets
arrange into a hexagonal array and sink into the polymer solution. Removal
of the volatiles (solvent and water) leaves an imprint of the water droplets as
a hollow, air-filled, hexagonally ordered, polymeric bubble array. It has been
reported that star-shaped polymers and block copolymers form honeycomb
morphologies through the evaporation-induced assembly process [144-146].
Other researchers including us have shown that neither star-shaped nor block
structure is necessarily needed for the formation of well-defined assembling
morphologies [147-151].
We tried to generate assembling structures of
hb
-PYs by employing the
breath figure process. Figure 14 shows the photographs of the patterned
structures of
hb
-P
20
formed by blowing a stream of moist air over its CS
2
solutions. Hexagonally ordered hollow bubble arrays with void sizes of ca.
10
m were obtained over a large area. Similar to the patterns generated
by UV irradiation through a copper negative mask, the honeycomb patterns
obtained from the breath figure process were light-emitting when observed
under a fluorescence microscope and can thus potentially be used as an active
layer in optical and photonic devices.
As described above, the fabrication of micro- and nano-sized patterns
from the hyperbranched polymers as thin layers on defined matrix surfaces
has been nicely accomplished. We went one step further and tried to gener-
ate free-standing three-dimensional structures. Since
hb
-PAAs can be readily
ยต
Fig. 14
Optical micrographs of breath figures of
hb
-P
20
obtained from its CS
2
solutions
by blow drying in a stream of moist air
