Macromolecular Chemistry and Molecular Materials

Between Chemistry, Physics and Biology on the trail of self-organization

Thomas Fuhrmann-Lieker's research group is part of the Department of Macromolecular Chemistry and Molecular Materials. There, at the interface of the natural sciences, research is carried out on how materials can organize themselves on the nanometer scale in order to be able to use these structures in possible applications. The Kassel location is an ideal working environment for his research, explains Thomas Fuhrmann-Lieker, as the close proximity to the fields of physics and biology as well as to the engineering sciences enables an intensive exchange.

The principles of self-organisation

When one assembles materials into a component, such as a solar cell or a light-emitting diode, the structure is far removed from what physicochemists call equilibrium. There are forces that would deform the structure if the materials yielded to these forces. In this context, components made of "soft matter" are of particular interest because, as the name suggests, these materials are particularly easily deformable. In principle, "soft matter" refers to everything that is not gaseous or a crystalline solid, such as liquids, polymers (plastics), gels, dispersions, large biomolecules and liquid crystals (which LC displays consist of).

The surprising thing is that on the way from a non-equilibrium state to a more stable state, spontaneously ordered structures with fascinating regular patterns can emerge.

Principle of "Wrinkling"

Self-folding oft hin layers

One example being studied in the group is the spontaneous "folding" of thin layers consisting of a "soft" material between a solid substrate and an elastic top layer. Normally, after the layers have been produced using modern coating techniques, the middle material is sufficiently strong so that all interfaces are flat. If, however, the middle material is softened, for example by heating or, with new materials developed by Thomas Fuhrmann-Lieker, by irradiation with light, the existing tensions cause the layers to wave up, astonishingly enough in absolutely regular lamellas. According to Fuhrmann-Lieker, the swelling of plates has long been a problem of mechanics and is also found, for example, in the wrinkling of skin, but the nanoscale is absolutely new territory here, since macroscopic predictions reach clear limits. It is only since the introduction of the atomic force microscope that it has become possible to characterise such structures.

The glass shell of diatoms

Similar processes of self-organisation can also be found in completely different areas, for example in the formation of biological structures, the so-called morphogenesis. A few years ago, the formation of the filigree cell wall of diatoms from silicic acid was explained with the occurrence of instabilities and periodic separations of water- and oil-containing components. The algae are thus able to produce regular pore patterns in their glass cell wall through as little genetic control as possible. Even if this model has its limits, it is nevertheless certain that organic components play a major role in the formation of the structure. Fuhrmann-Lieker goes one step further in this respect: By adding specially functionalised molecules to the algae during cultivation, the algae are stored in the shell so that novel composite materials with self-organised nanostructures are created. "The first step into biology was not easy for a physicochemist and materials scientist," said Fuhrmann-Lieker, "but thanks to the environment of CINSaT and Dr. Kucki as a competent biology colleague, we were able to take this step. This research project has attracted a lot of attention in the media, for example in the WDR magazine Quarks&Co.

Applications in photonics

The fascinating thing about these self-organized structures is that their periodicity is in the range of the wavelengths of visible light. As a result, light can be controlled and the research group is trying to exploit this effect. One of the main targets is photovoltaics, since the capture of light by light-scattering structures can improve the efficiency of solar cells. Through the efficient coupling of light and the effective separation of charges at inner interfaces, self-organizing structures can kill two birds with one stone. "Who knows, perhaps diatoms, which we call biological photonic crystals, also use their structure to optimize photosynthesis," speculates Fuhrmann-Lieker. "It will probably not be possible to finally clarify this, but we can certainly learn a lot from how nature organises its building blocks itself.



Contact

apl Professor Thomas Fuhrmann-Lieker

Address Universität Kassel
Fachbereich 10 - Naturwissenschaften & Mathematik
Institut für Chemie
Heinrich-Plett-Str. 40
34132 Kassel
Room Raum 3163
Telephone +49 561 804-4795
Telefax +49 561 804-4555
Picture of apl Professor Thomas  Fuhrmann-Lieker