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Robert Magerle - he will change the location in the near future
from Bayreuth to Chemnitz
(Information Office University Bayreuth)
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Though, when seen from a distance, the individual dancers are
indistinguishable and only the resulting average color can be seen. Then a
regular pattern is discerned: there are regions on the dance floor where there
are more black dancers than white and vice versa. What is fascinating about this
phenomenon is that it results form a very simple rule: "like attracts like". In
the case of block copolymers, the regions where like dancers cluster together
are called microdomains and they can have different shapes including spheres,
rods, lamella, and more complex structures, depending on the type and the
architecture of the molecule.
In our recent work to be published in the December issue of Nature Materials (published
online on 28 November 2004, 18.00 GMT) we have used scanning probe microscopy to
record images of the pattern formation process in a thin film of block
copolymers. In our analogy, the thin film would correspond to a situation where
the dancers are confined to a narrow, corridor-like dance floor. Here new
patterns appear that are very different from those that formed on an
indefinitely wide dance floor. We observe how rods reorient and transform into a
new pattern known as a perforated lamella. The underlying physical principles of
this pro-cess correspond to the choreography of the molecular pattern dance. A
computer simu-lation reveals this choreography by reproducing all of the
elementary steps of the pattern trans-formation dance in great detail.
Remarkably, the choreography is rather simple and based only on local rules: the
width of the corridor and the amount of preferential attraction of one kind of
dancers to the walls are the two parameters which select which pattern forms.
When one of these external parameters is changed, a pattern transformation
occurs where each individual dancer follows a local rule. It tries to move to a
region where there are more of its kind while firmly holding its dislike partner.
Our results are expected to have implications in different areas since block
copolymers and nanostructured fluids are very common in both nature and
technology. They are the physico-chemical basis for morphogenesis in biological
cells and are very common in pharmaceutical products, plastic materials, and
numerous other applications. The methods and the computer model presented in our
work can be used to study and predict pattern formation processes in these
materials. We expect a large impact on nanotechnology where block copolymers can
be used as self-organised templates for the synthesis of inorganic
nanostructured materials. For instance, block copolymer templated patterned
magnetic media will be used in the next generation of computer hard disks to
increase the storage density and overall capacity. |
