Macromolecular Systems: Selected Projects



Dispersions of Polymers and Nanocolloids in Complex Fluids

The structure and dynamics of nano-objects (polymers, colloids) in solution is to a large extent governed by their interaction with the solvent.  We aim at developing efficient methods for simulating nano-objects (polymers, colloids) that are dispersed in complex fluids, at equilibrium and nonequilibrium.

In particular, we are interested in studying electrolyte solvents, where the interplay of electrostatic interactions and hydrodynamic flows gives rise to a wealth of intriguing phenomena on a wide range of time and length scales. Physical problems of interest are the electrophoresis of charged polyelectrolytes or colloids in microchannels with different geometries and wall structurings, or the dielectrophoresis of polyelectrolytes or colloids in alternating electric fields.

A second, more general challenge is to develop coarse-graining strategies for systems where the separation of time scales is incomplete and memory becomes important. We are developing methods to reconstruct memory kernels, so that memory effects can be included in implicit solvent simulations. For more information, please contact Friederike Schmid.

Crystalline or Liquid-Crystalline Order in Polymeric Systems
A single polymer chain in a poor solvent may collapse into a dense fluid globule, but it may instead also crystallize: By extensive simulations with the Wang-Landau algorithm we have shown that the crystal is favorable if the range of the attractive interactions between the monomers exceeds the range of the repulsions only slightly. These findings may be useful to understand scenarios for protein crystallization. The resulting structure is also modified when an attractive substrate surface is present, and/or when one considers a semiflexible rather than a flexible polymer: then liquid-crystal-line ordering comes into play. Single chains then may collapse forming torodial or plate-like strucutures, or lamellae attached to walls. Multichain systems, or semi-flexible polymers, however, are found to undergo isotropic to nematic transitions, similar to systems of hard rods. In the presence of confinement into thin films by hard walls, "capillary normalization" (i.e. wall-induced nematic order) is found. This research is carried out in collaboration with V. A. Ivanov (Moscow State University), J. Luettmer-Strathmann (The University of Akron), M. P. Taylor (Hiram College), and W. Paul (Martin Luther Universität Halle.) For more information, please contact Kurt Binder.

Self-Assembling Block Copolymers and Polymer Brushes

Melts of one or more kinds of polymers exhibit a wealth of diverse phases whose geometric properties make them interesting systems not only for condensed matter research, but for industrial applications, as well. Specifically, block copolymers made of chemically incompatible monomers (say, A and B) exhibit microphase separation, thus forming regular nanoscale patterns of varying complexity. Our current research focusses on the influence of curvature on structure formation in thin films and membranes.  Moreover, we are interested in the effect of crosslinking for the stabilization of ordered structures.

Another important application for polymers is to attach them to surfaces, thus modifying the surface properties. We are interested in the effect of polydispersity on the structure of such ''polymer brushes'', and on strategies to design smart surfaces that can be used as sensors and switches. For more information, please contact Friederike Schmid.

(Hybrid) Field-based Simulation Methods for Polymers

The so-called 'self-consistent field' (SCF) theory is one of the most successful density functional theories fo inhomogeneous polymer systems, which allows to calculate the local structure of dense blends at an almost quantitative level (see review article). We use dynamic self-consistent field theory to study the kinetics of structure formation in solutions containing amphiphilic block copolymers. Furthermore, we develop new hybrid simulation schemes for such systems, combining particle- and field-based representations as well as different kinetic descriptions (diffusive Langevin and hydrodynamic Lattice-Boltzmann fields) in a consistent way. For more information, please contact Friederike Schmid.