Mobility, flow properties and the structural behavior of
complex liquids Max Planck Institute for
Dynamics and Self-Organization
Ralf Seemann is a group leader at
the Max-Planck-Institute for Dynamics and Self-Organization in
Göttingen (Germany). His research interests are wetting
physics, microfluidics, wet granular materials, and thin polymer
melt films. Our projects include:
By scanning force (AFM) and
optical microscopy, we study the variety of liquid morphologies
forming on topographically structured substrates. Using the
electrowetting effect, we explore the transport of liquids on
substrates bearing appropriate steps and grooves, by switching
between various equilibrium morphologies of the free liquid
surface ('open microfluidics').. Insert droplet figure here.
Wet granulates can be regarded as
a particular situation for wetting of topographic surfaces:
Liquid bridges between sand grains enable us to build a sand
castle. The mechanical properties are strongly depending on
liquid content and surface tension of the liquid. We study
mechanical properties of wet granular matter like shear stiffness
and fluidization due to vertical agitation as a function of
liquid content. We try to relate the distribution of the liquid
bridges and clusters within granulates to its mechanical
properties using optical index matching techniques and X-ray
tomography. Insert wet granular matter figure here.
Above right: X-ray tomograph of wet granulates
consisting of wet glass spheres and an aqueous wetting fluid.
top: liquid content 10% bottom: liquid content
3%. The width of the images is about 6 mm.
We explore possibilities of
"digital microfluids" using a compartmented liquid consisting of
an emulsion of water in oil, where the oily phase has a very
small volume fraction. This emulsion is then geometrically
analogous to foam, which exhibits a variety of transitions in its
topology upon interaction with an externally provided geometric
constraint. The vision is to exploit the manipulation of the
emulsion droplets by the channel geometry and external fields in
order to position, sort, exchange, compile, and redistribute
liquid compartments with different chemical contents. Insert
digital microfluidics figure here.
Above right: Laser scanning confocal micrograph of
a reverse emulsion confined in a channel. The aqueous and the
oily phase are colored with fluorescence dyes.
The mobility of polymer chains
close to an interface differs from its mobility in the bulk. As a
result the glass transition temperature can be lowered or raised
depending on the particular polymer and its interaction with the
interface offered. We study the glass transition temperature of
confined polymers using optical dilatometrie (ellipsometry) and
probing relaxation behaviour by nuclear magnetic resonance
(NMR).
Within PolyFilm we intend to
study the mobility, flow properties and the structural behavior
of complex liquids in confined geometries.
Above right: Scanning force micrograph (AFM) of a
polystyrene droplet sitting on top of a groove. The droplet is
not confined to the groove due to the large contact angle of
polystyrene on the hydrophobized silicon substrate.
