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