Research in interacting fermion models using a diagrammatic approach:
In this project I investigate
the possibility of using Feynman diagramms to calculate the self-energy
of an interacting fermion system.
i.e. the Anderson impurity model and the Hubbard model.
Granular material
Segregation and mixing are two very interesting phenomena appearing in granular material.
The interplay of different sizes, densities, shapes etc. can lead to a variety of effects.
Research of band formation and segregation in a rotating drum
containing glass beads of two sizes: After mixing two types of glass beads in a rotating drum
a number of bands appear which over time change in shape and thickness. Bands merge
and sometimes complete segregtion occurs. The time of segregation and merging as well as the shape of
the bands depends for example significantly on the speed of rotation. A large number of experiments
is performed to study this behavior. Numerical investigations of the band forming behavior
are carried out. The experiments include optical observation, NMR scans of the
internal bead distribution as well as PIV (particle image velocimetry) measurements
of the particle flow on the surface.
Axial and radial segregation is observed and compared to
existing models. A new model based on a simple random walk behavior is used
to intepret the experimental data.
Talk at DPG Frühjahrstagung, Dresden March 2006.
Microemulsion A ternary mixture of oil, water and surfactant can at a given mass relation between the constituents build a so called microemulsion. This is a thermodynamically stable transparent solution where aqueous nanodroplets of 5 - 25 nm are surrounded by a surfactant layer. The droplets can be loaded with reactants and via an exchange between the droplets a chemical reaction of different reactants can take place. This can lead to a particle precipitation where very small particles of nanometer range are produced. Research of the phase diagram of ternary and quartenary systems of oil, water, surfactant and reactants: A Metropolis Monte-Carlo method is applied on a lattice model of the system in order to study the phase behavior for a variety of different systems. The influence of a head-tail distribution of the surfactant is studied as well as the influence of reactant ions on the phase behavior.
Particle precipitation in microemulsion droplets:
The exchange, reaction, nucleation and growth phenomena and their interplay on different time scales
are the important processes to model the particle precipitaion in microemulsion.
A kinetic Monte-Carlo method is applied to this problem. It is used to investigate the dynamics of particle
precipitation as well as to indentify suitable process control parameters for an upscale approach
of this technology.
Nanoparticles
Nanoparticles of different size, shape and constitution are building blocks of different technical systems and applications.
The large-scale technical production of such particles is challenging and full of surprises.
Self-made nanoparticles of gold (left) or barium sulfate (right) show a variety in size and shape.
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©Andreas Voigt Last modified: 12/22/2004