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Thin block copolymer films have
awakened a lot of interest in recent years, because
they form spontaneously structures on submicrometer
length scales leading to structured film surfaces.
The stability of these films and their response
to changes of the environment are of fundamental
interest and of key importance for applications.
Heat treatment of the films or their exposure
to solvent vapor is often used for creating long-range
order. However, most studies are carried out ex-situ,
and astonishingly little is known on the structural
changes on the mesoscopic length scale and their
molecular origin.
Grazing-incidence small-angle X-ray scattering
(GISAXS) offers the possibility to study in-situ
and in real time the mesoscopic structure of thin
polymer films with high a time resolution of a
few seconds. GISAXS reveals the inner film structure,
which is complementary to microscopical methods
monitoring the surface texture.
We study the response of lamellar diblock copolymer
thin films to heat treatment and to solvent vapor.
We focus on poly(styrene-b-butadiene) which, in
the dry state, forms the parallel or the perpendicular
lamellar orientation, depending on molar mass
[1]. Thus, the changes of both lamellar orientations
can be studied in the chemically identical system.
Varying the film thickness, the block copolymer
molar mass, the annealing temperature [2], the
vapor pressure and the selectivity of the solvent
towards the two blocks, we have observed that
both destruction and healing may take place (Fig.
1). Moreover, in solvent vapor, the films not
only swell but under certain conditions, the lamellar
structure breaks up and reforms. These processes
can be related to a change in conformation of
the blocks in the solvent-swollen state which
require different interfacial areas.
- P. Busch, D. Posselt, D.-M. Smilgies, M. Rauscher,
C.M. Papadakis (2007). Macromolecules 40,
630.
- C.M. Papadakis, Z. Di, C. Darko, D. Posselt,
D.-M. Smilgies, M.A. Singh, Lecture Notes: Applications
of Synchrotron Light to Non-crystalline Diffraction
in Materials and Life Sciences, in print.
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