Current Research
The least known state of matter are liquids:
strongly interacting but disordered with
molecules moving around. This postponed area
of condensed matter research gets growing
attention in recent years. The microscopic
unterstanding of properties previously described
by phenomenological thermodynamics shall be
achieved. The ubiquity of liquid phases in
chemical reactions and processes in biology
makes research about liquids an interdisciplinary
field of great importance.
The theme of our present research activity is the
structure of liquids, is origin in the molecular
interactions, is relation to thermodynamic
properties and phase transitions. Especially we
focus on liquid phase boundaries, the free
surface towards the vapour, the interface with a
solid, e.g. between an electrolyte and an
electrode, and the interphase between coexisting
liquid phases.
Our methods of investigation are the calculation
of particle density distributions and correlation
functions from integro-differential-equations,
which are related to free energy density
functionals. The equations are solved
numerically by iteration on a computer. The
liquids are modelled by classical effective
pairwise interactions.
Some recent projects:
The electrolyte-electrode interface
(Vossen, Diaz-Herrera, Kraemer, Buettner)
Production of hydrogen from solar electric
energy, retrieving the energy in fuel cells,
production of aluminium and chlorine, corrosion
and passivation and many other technological
processes function at electrolyte-electrode
interfaces. Therefore, we try to contribute to the
undestanding of this system.
We have studied a dipolar solvent with ionic
solutes. We calculated changes in dielectric
properties due to surface induced structure,
distribution of solvent and solutes and of solvent
orientation under applied electrode fields. We
found a demixing transition in this electrolyte
and sudden "condensation" of ions onto the
electrode related to this concentration instability.
We have employed a central force model of
water, the most important solvent, developed
the integral equation method for this
complicated liquid, and got the result , that
water forms a rather well ordered structure in
front of an electrode, which is rather stable
under applied fields and determines the dielectric
properties and the approach of ions towards the
surface.
The future work requires a development of
models for closer relations of our microscopic
results to measurements of thermodynamic
interface properties. We will also study the free
electrolyte surface.
Phases of dipolar liquids
(Klapp)
Dipole interactions are most important in
solvents.Tey are more complicated than
interactions in magnets, because the favorable
orientation of a neighbour is parallel in the
direction of the dipole and antiparallel vertical to
it. This is obviously the reason, why the phases
of dipolar systems are not yet known. Recent
studies have indicated, that there is no
condensation of a dipole gas. We predicted a
pairing and clustering instead. The theoretical
investigations predict at higher densities a
"ferro-electric" liquid phase with parallel dipoles
and a transition to a solid ferro-electric phase at
very high densities. These transitions have not
yet been seen in experiments with ferro-fluids
and their characteristics and regions are not
yet clear. Therefore this project investigates
these phases.
Interfaces between coexisting liquids
(Iatsevitch, Weich,Antonevych)
Many technologically important processes like
concentration of metals in metallurgy or oil
extraction by detergents depend on the
properties of liquid-liquid interfaces. The
structure of such interfaces is the topic of this
project. We develop methods for this
investigation, again integral equations, and study
model systems. We get information about the
particle distributions within the interface, the
surface tension and other thermodynamic
properties and study the dependencies on
interactions and thermodynamic parameters as
well as on external electric fields in case of
electrolytes. We also aim at modelling of
surface active substances.