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Weiche Materie Vortrag: Do., 10:20–10:40 D-V30
Dynamics of soft matter surfaces investigated with X-ray photon correlation
spectroscopy
Christian Gutt 1 , Robert Fendt 2 , Simone Streit 2 , Tuana Ghaderi 2,3 , Anders
Madsen 4 , Metin Tolan 2 , Sunil K. Sinha 3
1 Hasylab at Desy, Notkestrasse 85, 22603 Hamburg – 2 Experimentelle Physik Ia,
Universität Dortmund – 3 University of California at San Diego, CA 92039, USA –
4 European Synchrotron Radiation Facility (ESRF), Grenoble, France
X-ray photon correlation spectroscopy is used to study the dynamics of soft matter
surfaces. We present results of capillary wave dynamics on bulk liquid surfaces, thin
wetting films on solid substrates and the 2-dimensional slow dynamics of gold cluster
on polymer surfaces.
We present a formalism for resolution effects in XPCS experiments based on the theory
presented in reference [1]. This formalism enables us to explain experimentally observed
transitions between homodyne and heterodyne correlation functions and to explain the
excess damping usually found for propagating waves.
XPCS experiments from thin vapour deposited wetting films on solid substrates showed
the absence of capillary wave dynamics on length scales even below the thickness
dependent van der Waals cutoff. Instead of capillary wave dynamics we found a static
surface morphology with a peculiar 1/q 3 power law behaviour. The speckle structure
from the diffuse scattering in plane scattering and the reflectivities depend on the
conditions of sample preparation.
The dynamic structure factor of gold particles moving on the surface of thin polymer
films has been measured. Above the glass transition of the polymer we found
the dynamic structure factor of the gold clusters to follow the peculiar form f(q,t) ∼
exp(-(t/τ) α ) with an exponent α= 3/2 that is a faster than exponential decay of the
correlation function. The relaxation times scales 1/q thus pointing to hyperdiffusive
motion. Moreover aging phenomena are observed.
[1] S. K. Sinha, M. Tolan, A. Gibaud, Phys. Rev. B 57, 2740 (1998)