Research

This relatively new term refers to a broad class of systems including rubber, plastic, paper, foams, soap solutions, liquid crystals, blood, biomembranes, biopolymers, and many others. Soft materials share a number of common features: energies are of the order of the thermal energy kT. Therefore, the systems respond strongly to weak external forces, and their properties are predominantly determined by entropic effects. In that sense, they resemble simple fluids. In contrast to simple fluids, however, soft materials display structure not only on the atomic scale, but also on mesoscopic scales (nano- or even micrometers).

Whereas these qualities fascinate statistical physicists, they also make it impossible to describe all aspects of a soft matter system within one single theoretical model. Thus there usually exist several models which operate on different length and time scales, and one of the great current challenges is to develop methods which link the scales with each other (multiscale modelling). Different models often have roots in different scientific disciplines: Soft matter science is a highly interdisciplinary field which brings together materials science, organic chemistry, physical chemistry, statistical physics, condensed matter physics, and biology.

In our group, we are particularly interested in phase transitions and surface and interface phenomena in soft matter, and in nonequilibrium phenomena. Among other, we study

• Macromolecular systems , containing large molecules with many identical repeat units (polymers). Such molecules are usually very "floppy" and many of the properties of the materials are dictated by conformational entropy.
• Amphiphilic systems : If molecules contain chemically incompatible units, i.e., units that tend to demix, this may lead to local phase separation, and to the formation of a variety of complex (locally or globally) ordered structures. Such processes often lie at the heart of self-organization in biological systems.
• Colloidal systems: They can be viewed as model systems for solid matter and glasses, because times scales are slow and dynamics processes can often be studied through the microscope.
• Anisotropic fluids and liquid crystals.
• Biologically motivated problems related to biopolymers (e.g., DNA) or biomembranes

Computational Soft and Biological Physics

This highly interdisciplinary field employs computational models and simulations to investigate phenomena such as polymer self-assembly and topology, membrane dynamics, and the folding of proteins and DNA. These systems share common traits: Their characteristic energies are on the order of thermal energy (kT) and entropy is an indispensable factor. The goal is to uncover fundamental principles governing soft and living matter, with applications spanning from materials science to biomedical research, by combining physics, chemistry, and biology.

Multiscale Modeling

The enormous success of computer simulations can be attributed not only to Moore’s law, but also to the development of increasingly refined models and smart simulation algorithms. One key to success is multiscale modeling, i.e., the art of systematically constructing hierarchies of models operating on different scales. Our work is concentrated on developing such approaches for soft matter, which is particularly challenging because of the dominant role of entropy. This research also gives fundamental insights into the microscopic origins of emerging phenomena such as dissipation and memory.

Nonequilibrium Phenomena

Living and breathing organisms, fluid flows, or driven quantum systems – no matter which system and scale we look at, the world around us is dynamically evolving. The general principles governing the behavior of such nonequilibrium systems are, to a large extent, unknown. Our aim is to uncover how such principles emerge from the microscopic laws governing the individual constituents of the system. This research touches upon a large variety of aspects – from fundamental philosophical issues concerning the flow of time to practical applications in biology and nanotechnology. Methodologically, we employ both pen-and-paper theory and large-scale computer simulations including machine learning.

Specific Current Research Projects

Please see the web sites of our group leaders or contact us directly.