Friederike Schmid: Research

We study the statistical mechanics of systems out of equilibrium. For more information, see the Group Research page.

Selected Projects

Lipid Membranes

All living things depend on membranes. Their basic structure is provided by lipid bilayers, which self-assemble spontaneously in water due to the amphiphilic character of lipid molecules - they contain both hydrophilic and hydrophobic units. In our group, we are interested in generic properties of such amphiphilic bilayers.

We have established a coarse-grained lipid model, which reproduces the main phases and phase transitions of phospholipid membranes at temperatures close to room temperature. As particular highlights, we have (i) recovered and investigated the mysterious modulated "ripple phase" in one-component membranes, which had intrigued researchers for many decades, and (ii) discovered and investigated nanoscale structures, so-called "lipid rafts" in multicomponent membranes. Rafts are small structural entities in biomembranes which are believed to play an important role for many cellular functions. The question whether they can exist in pure lipid membranes had been discussed controversially in the past. We found that ripple states and rafts seem to be stabilized by very similar mechanisms: A propensity for global phase separation, which is suppressed by elastic interactions in the membrane. This is analyzed by computer simulations and elastic theories.

The same approach is used to study  lipid-mediated interaction mechanisms membrane proteins. In the past, we have focused on  a comparison between analytical predictions and simulation data for "proteins" that can be represented by simple cylindrical inclusions (see Figure). In the future, we also plan to investigate flexible proteins and their interaction with rafts. For more information, please contact Friederike Schmid.

Interplay of Electrostatic and Hydrodynamic Interactions in Complex Fluids

The project aims at the development of new efficient simulation methods for investigating electrostatic and hydrodynamic effects in complex fluids. Examples are the dynamics of charged macromolecules in solution under the influence of external fields and/or in confined geometry, as well as the (hydro)dynamics of interfaces in phase separating fluids. Examples of physical problems of interest are (i) the electrophoresis of charged polyelectrolytes or colloids in microchannels with different geometries and different wall properties, (ii) the dielectrophoresis of polyelectrolytes or colloids in an alternating electric fields, and (iii) multiphase flow. We collaborate with C. Holm (Uni Stuttgart) and B. Dünweg (MPI-P Mainz), and we are funded in part by the VW foundation. For more information, please contact Friederike Schmid.

Self-Assembling Block Copolymers

Melts of one or more kinds of polymers have been demonstrated over the last few decades to 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 structure formation in rod-coil block copolymers, which have possible applications, e.g., for photovoltaics. This work is funded by the DFG. Moreover, we are interested in the effect of crosslinking for the stabilization of ordered structures. 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. The projects are funded by the VW foundation and by the DFG, and carried out in collaboration with Agur Sevink (Leiden, the Netherlands), Andrei Zvelindovsky (Preston, UK), and Alexander Boeker (Aachen), as well as with Wolfgang Paul (Halle). For more information, please contact Friederike Schmid.

Statistical physics of molecular recognition

Selective interactions between biomolecules play an essential role in biological systems. Without selective recognition of antigens by corresponding antibodies, for example, the immune system could not work efficiently. One of the most salient features of molecular recognition is the fact that biomolecules often discriminate very accurately between many different but structurally similar interaction partners which are also present in a heterogeneous biological system.

Our studies aim at an understanding of the basic and universal mechanisms of recognition processes between biomolecules in an heterogeneous environment. In order to identify and investigate these basics mechanisms we develop idealised coarse-grained models. These models neglect those details which are particular for a specific system and are thus constructed to represent generic types of recognition processes. The thermostatic and dynamical properties of the models are then analysed with numerical and analytical methods from statistical physics. For more information, please contact  Friederike Schmid.