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Weiche Materie Vortrag: Do., 10:00–10:20 D-V29
Swelling kinetics and structural changes of polyelectrolyte multilayers in
contact with aqueous solution and water vapor
Roland Steitz 1 , John E. Wong 2 , Regine v. Klitzing 3
1 Hahn-Meitner-Institut, SF1, Glienicker Str. 100, D-14109 Berlin – 2 TU Berlin,
Stranski-Laboratorium, Straße des 17. Juni 112, D-10623 Berlin – 3 Christian-
Albrechts-Universität Kiel, Ludewig-Meyn-Strasse 8, D-24118 Kiel
The sequential layer-by-layer adsorption of polyanions and polycations to build polyelectrolyte
multilayers has triggered enormous interest in their potential uses in a wide
range of fields, from photonic to pharmaceutical applications. This is due to the ease
of preparation, the possibility to control film thickness with Angstrom precision and
because the macroscopic properties can be influenced by the chemical composition of
the polymers [1]. The detailed mechanism of film formation and the manipulation of
the films by external means are current topics of active research. Experimental studies
have shown that the main driving force for the assembly of multilayer films is the
electrostatic attraction between the oppositely charged polyelectrolyte chains and the
concomitant release of counter ions. We have found that a minimum charge density
of ca. 60 % of the fully charged chains is necessary for obtaining stable films [2]. We
will show that the conformation of the solvent swollen films - prior to drying - is determined
by the initial adsorption conditions [3], but can be altered ex-situ by exposure
to a liquid phase of very high ionic strength. Recently, it has been observed that the
swelling depends on outermost layer [4, 5]. The water uptake of the outer layers is
more pronounced, which leads to the assumption, that they are more loosely packed
than the inner layers near the template [5]. A neutron reflectivity study of this effect
in addition indicated the existence of two kinds of water, bound with different strength
within the films. Beside unexpected two-step kinetics of swelling, the reflectivity curves
of the layers against vacuum before and after re-hydration in D2O vapor did not agree.
It was only after subsequent re-hydration in saturated H2O vapor that the initial and
final reflectivity curves against vacuum superimposed. We will discuss our findings in
the context of polyion complex formation, interdigitation and film imperfections.
[1] G. Decher, Science 277, 1232 (1997)
[2] R. Steitz, W. Jaeger, R. v. Klitzing, Langmuir 17, 4471 (2001)
[3] R. Steitz, V. Leiner, R. Siebrecht, R. v. Klitzing, Colloids Surfaces A 163, 63 (2000)
[4] B. Schwarz, M. Schönhoff, Langmuir 18, 2964 (2002)
[5] J. E. Wong, F. Rehfeldt, P. Hänni, M. Tanaka, and R. v. Klitzing, Macromolecules,
37, 7285 (2004)