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.