Berlin 2001 – wissenschaftliches Programm
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CPP: Chemische Physik und Polymerphysik
CPP 4: Thin Polymer Films
CPP 4.3: Vortrag
Dienstag, 3. April 2001, 16:25–16:45, 111
Segment density profiles of polyelectrolyte brushes determined by Fourier transform ellipsometry — •Diethelm Johannsmann1, Jürgen Rühe2, and Markus Biesalski3 — 1MPI for Polymer Research, PO Box 3148, 55021 Mainz — 2Institute for Microsystem Technology (IMTEK), Georges-Köhler-Allee 103, D-79085 Freiburg — 3Department of Chem. Engineering, University of California, Santa Barbara, CA 93106
We describe a method for the explicit determination of the segment density profile φ (z) of surface-attached polymer brushes with multiple angle of incidence null-ellipsometry. Because the refractive index contrast between the brush layer and the solvent is weak, multiple reflections are of minor influence and the ellipsometric spectrum is closely related to the Fourier transform of the refractive index profile, thereby allowing for explicit inversion of the ellipsometric data. We chose surface-attached monolayers of poly-methacrylic acid (PMAA), a weak polyelectrolyte, as a model system and determined the segment density profile of this system as a function of the pH of the surrounding medium by the Fourier method. Complementary to the Fourier analysis, fits with error functions are given as well. The brushes were prepared on the bases of high refractive index prisms with the grafting-from technique. In water, the brushes swell by more than a factor of 30. The swelling increases with increasing pH because of a growing fraction of dissociated of acidic groups leading to a larger electrostatic repulsion.