diss_SCHWAIGER.pdf - OPUS Bayreuth - Universität Bayreuth

7 Summary
own measurements for the concentration and temperature dependence, allows for
the numerical integration of the stationary extended diffusion equation. It is physically
well motivated, as it captures the essential features in some limiting cases
as the scaling relation of the hydrodynamic radius in the diluted regime and the
loss of any molar mass dependence in the high concentration regime are correctly
described. Due to the complex concentration, molar mass and temperature dependence,
self-amplification and attenuation of the concentration shift compete with
each other.
The Soret coefficient of the system pullulan/water has a thermally induced sign
change which results in complex structure formations. The concentration field has
been calculated numerically and visualized. Contrary to PS/toluene mixtures, it
is no longer a monotonic function but shows a depletion in the vicinity of the heat
source and an enrichment of pullulan at intermediate distances. This is a consequence
of the sign change of the Soret coefficient. The position of the maximum
can directly be calculated from the parameterization of the Soret coefficient.
Two scenarios have been discussed regarding the dynamics of embedded gold colloids
in mixtures of polystyrene and and toluene which is determined by the local
viscosity. The first one deals with solutions at high polymer concentrations, where
it approaches the glass transition. Both the polymer depletion and the temperature
increase act towards a lowering of the viscosity. Especially the latter one is only
found in systems with a high contrast in the glass transition temperatures of the
two components. Due to the relatively small Soret coefficient and its decrease with
increasing temperature, this effect in self-attenuated and the polymer depletion is
limited to some finite value which is independent of the molar mass in the high
polymer regime. The second scenario considers the viscosity change in case of very
long polymer chains. The dramatically increase of the viscosity in the semidilute
solution, which is reached at very low concentrations, is linked to the regime of
self-amplification, where dilution of the polymer leads to a continuous increase of
the Soret coefficient, which in turn fuels the polymer depletion. In these systems,
the polymer can entirely be removed from the colloid with a rather moderate temperature
increase.
Additionally, it has been shown, that gold nanoparticles can be used as tracers
for a polymer network deformation as long as their dimensions exceed the size of the
network meshes. Then, every thermophoretic flux is encoded in the motion of the
particles, which can be determined using standard video single particle tracking
techniques. It has been shown, that the displacement field of a high molecular
polymer solution in an infinite medium is of long range. It becomes asymptotically
constant and is independent of the distance from the heat source. In finite systems,
the displacement is still far reaching, but it decays on length scales of the system
size. Numerical evaluations are in good agreement with the experiments.
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