Contributions to the Yearbook of the Max Planck Society

The separation of different substances requires a large proportion of the world's energy. In an innovative approach, my research group is trying to realize highly energy-efficient possibilities by using quantum effects. The discovery of "quantum friction" between liquids and the walls of channels enables the precise control of liquid flows on a nanoscale by influencing the electrons in the channel walls. This mechanism could significantly improve separation processes in the future.

Drugs undergo a complex testing procedure before they are used. This process often involves tests on animals. Among other things, it is important to know how drugs can pass through the cell walls of the intestine into the blood. In order to be able to simulate this process in laboratory experiments, we have developed a transistor based on organic materials. With this transistor, the permeability of cell layers can be measured by measuring ionic currents in our experimental setup.

The production of hydrogen or the generation of energy from molecular hydrogen could be important processes in future energy storage systems, such as those already used in hydrogen-powered cars. At the Max Planck Institute for Polymer Research we have taken a closer look at the processes taking place on molecular length scales and thus gained fundamental insights into the chemical reactions at electrodes.

Injuries resulting from severed nerve tracts are difficult to treat sometimes requiring complex operations. We have asked ourselves: Would it be possible to stimulate nerve cells to grow using tailor-made materials? This would help the cells to close a gap in theinjured nerve. In the laboratory, we have produced an artificial material that may solve this problem and provide an alternative to surgery in the future.

The fungal disease Esca affects vines and leads to the dying of the plants. The infection may also happen years before the first external indications are observed, therefore an early treatment is nearly impossible. This causes a yearly damage of over one billion Euros worldwide. During our research we developed a treatment method based on nanotechnology that fights the fungus in the inside of the vine.

The movement of water drops on surfaces is an actual research topic. An understanding of the physical processes on such solid-liquid interfaces helps us to produce long-living, clean surfaces. In our division we focus on getting insights into the sliding of drops with the help of modern microscopical methods. These results lead to new concepts for modern self-cleaning surfaces.

The synthesis of very small diamond particles, so-called nanodiamonds, with precisely localized lattice defects and controlled morphologies, remains of great challenge in synthetic chemistry and materials design. However, mastering these challenges represents an exciting and prospective endeavor. Functionalized nanodiamonds offer great potential as unique quantum sensors and they promise mastering the far-reaching goal of structure and dynamic analysis of single biomolecules in their cellular environments and serve as efficient transport and improved contrast agents for in vivo drug delivery.

1993, twelve years after the discovery of photonics, was the birth of phononic materials for the controlled propagation of mechanical/acoustic waves. The first experimental realization followed in soon after at sonic and later at hypersonic frequencies using macromachinery and soft matter self-assembly. Two examples, artificial and natural hierarchical structures, will highlight the new emerging field of high frequency phononics aiming at tunable strong, deaf, cool and interactive materials.

The sun is a well-known source of energy that has been heavily used in recent years. After long-term research and optimization, solar cells which convert solar energy into electrical energy, make it possible for many households and municipalities to use energy in an environmentally friendly manner by installing them on roofs and fields. However, this generation of energy is dependent on weather and daylight. The energy requirement, on the other hand, is usually not proportional to energy production. For this reason, the development of energy storage is becoming a major factor.

By means of two examples, graphene nanoribbons and dimensionally stable dendrimers, I describe complex polymer syntheses and their great benefits for electronics on the one hand and gene therapy on the other. The first message I want to convey is that for ambitious goals in materials research, synthesis cannot only be "simple and practical," and the second message is that innovation needs the right people and partners.

Conjugated polymers can be processed from solution; this attractive feature opens up the realization of roll-to-roll based production processes. Yet commercial success has been hindered. The MPI-P recently demonstrated that the intrinsic properties of conjugated polymers have been masked by defects and therefore have not been fully exploited so far. Our aim is to uncover and characterize these intrinsic properties and improve them further. Using polymer blends, novel properties and nanostructures are realized by controlling the phase separation between various functional polymers.

The economic losses due to corrosion in industrialized countries can represent up to 6% of gross national product. This explains the emphasis placed on the research dealing with corrosion protection. As part of a collaboration with the Max Planck Institute for Iron Research in Düsseldorf, we have produced new coatings for an adequate corrosion protection. We studied corrosion attacks and clarified the fundamental aspects of self-healing and anti-corrosion mechanisms.

Self-cleaning surfaces have existed in nature for a long time. Microstructures on lotus leaves lead to a strong water repellency and ensure that water drops roll off while dragging down dirt with them. This effect is much more difficult to achieve with oily substances. Lately, new surfaces have been developed which not only repel water, but also oil and even human blood. New applications, such as a solvent-free synthesis of polymeric particles or the production of more efficient gas membranes, may become possible.

Macromolecular structures and functionality, ranging from biology to photovoltaics, are the result of non-equilibrium processes. Though crucially important, a basic understanding of the underlying processes on a molecular level is missing. Thanks to recent developments it is now possible to observe such processes over numerous time and length scales. MolProComp takes up these advances and will develop computer simulations methods aiming at the understanding, control and manipulation of such processes.

Two phenomena will be crucial for our future society: Energy supply and data processing. The quality of our problem-solving approach depends on the materials. Graphene, a monolayer segment of graphite, is being dealt with as a wonder material. Which demands have to be fulfilled to ensure solid, promising technologies on a graphene basis?

Organic electronics has established itself as a new technology for widespread microelectronic applications, e.g. flexible monitors, electronic newspapers, non-contact acquisition of data through transponders and smart labels. Most of these applications require memory functions, preferably the kind that save data when the electricity is switched off and which can furthermore be programmed electronically, deleted and read.

Controlled management of thermal energy by material design is an important step in the quest of clean and renewable energies. Predictive atomistic simulations unravel the details of heat transport in nanostructures and pave the way to engineer materials at the nanoscale. Here we illustrate applications of atomistic simulation tools to the study of heat transport in silicon-based thermoelectric materials and nano-devices and in carbon nanostructures.

Glasses, windscreens and windows have one thing in common: They become dirty. In the field of photovoltaic we are fighting against dirt adhering to solar cells as well. Meanwhile, there are coatings on which water drops hardly adhere. However, this does not apply to organic liquids. Coatings are rather seldom repelling oils, water, soapy and protein solutions at the same time. Not only oils but red wine would roll off these surfaces without leaving stains. An almost fractal structure consisting of silica spheres unveils new opportunities in this area.

By using a modular approach the miniemulsion process allows for the formation of complex functionalized polymer nanoparticles and the encapsulation of solid or liquid, inorganic or organic, hydrophobic or hydrophilic materials in a polymer shell. Here, different materials from organic and inorganic pigments, magnetite or other solid materials to hydrophilic or hydrophobic liquids like perfumes, vitamins, drugs, or photoinitiators can be encapsulated and deliberated in a well-defined manner. The functionalization of the nanoparticles can be easily controlled.

It has been a long-standing dream to watch molecules as they rotate, translate, interact and react to form new chemicals with temporal and spatial resolution that matches the molecular scale, i.e. on femtosecond time scales and nanometer length scales. Several new laser-based vibrational spectroscopic approaches are presented here, aimed towards the realization of this dream, with a specific emphasis of watching molecules at work on surface and interfaces.

Electronic devices made of organic materials have certain advantages that other, inorganic devices miss. The materials that have been developed so far are however not efficient enough and are thus unfit for an area-wide application. This is due to fundamental processes on the molecular and nuclear scale which determine the storage and transportation of the charge. These processes are determined by a complex interplay of material compositions and their interactions. The Max Planck Institute for Polymer Research uses numeric simulations in order to examine and understand these processes.

Measurement methods which are based on magnetic resonance have become very important in the fields of modern research and medical diagnostics these days. Magnetic resonance spectroscopy and magnetic resonance tomography (MRT) use the quantum mechanical properties of the spin as a spy to gain a very detailed insight into the morphology of materials and tissues. Thus, new hyperpolarized contrast agents used in MRT now make it possible to visualize processes in the human body and provide a whole new range of possible applications in the medical diagnostics of tomorrow.

Strategies to control phenomena at the interface between artificial materials and biological systems are relevant for many fields ranging from biosensing to tissue engineering. The inertness and static character of artificial surfaces contrasts with the dynamic, reversible and evolutionary character of biological processes. This gap can be filled with novel strategies that allow precise and active change of the surface properties by application of ready-available and biological friendly external fields.

The formation of dew, i.e., condensation of water on cold substrates involves the formation of complex patterns, breath figures. Growth and merging of droplets and the overall volume of condensed liquid depend sensitively on the local environment of the droplets and the mechanical properties of the substrate. The softer the substrate, the more drops condense onto it, and the more strongly the drops interact with the substrate.

Conducting organic materials aim to compete with traditional silicon-based technology for optoelectronic applications, for instance light-emitting diodes, solar cells and transistors. To further develop these materials for commercial applications, a profound understanding of the relation between chemical structure and optical / electronic properties is required. Recent advances in optical spectroscopy with pulsed lasers allow studying the photophysical processes down to a timescale of femtoseconds.

Organic semiconductors allow the preparation of low-cost, flexible and large-area processable devices such as light-emitting diodes (LEDs), field-effect transistors (FETs), photovoltaic cells (PVs), and sensor materials. Thereby a lot of basic science is involved, since besides of technical optimizations there is also a strong need for new synthetic building blocks. Thus actual research focuses on the development of tailored functional organic materials and their processing as films of suitable morphology for the individual applications.

Biological membranes, flexible bilayers composed of lipid molecules, form the outer envelope of every living cell. Many of its important properties rest on principles that can be understood using methods from soft matter physics. For instance, adhering proteins can interact with each other after imprinting a local membrane curvature, as has recently been demonstrated in computer simulations.

Quantum mechanical molecular dynamics simulations and solid state NMR spectroscopy reveal structural and dynamical properties of polymeric membrane materials of modern fuel cells. The atomistic resolution allows to model the proton transport along the fluctuating hydrogen bond network. The results support the design of improved materials for proton conducting polymers, yielding significant efficiency improvements in future generations of fuel cells.

At the MPI for Polymer Research, the combination of chemistry and biology resulted in the development of novel experimental strategies for investigation of membrane proteins. Employing the well-known strategy of in-vitro transcription and translation, proteins with subtle sensing capabilities, such as olfactory receptors, are generated and characterized. To obtain such proteins, an artificial membrane system is generated and a cell extract containing the genetic information of the receptor species of interest is added on the membrane surface. The protein synthesis machinery in the cell extract is still functional and inserts the olfactory receptor molecules into the lipid membrane. Finally, we can investigate the resulting proteins by optical and biochemical methods.

Three novel techniques for micro- and nanostructuring soft and delicate materials, such as polymers are presented. Compared with conventional processes they have the advantage of being low-cost, fast, and straightforward. They are based on simple physical and chemical effects: polymers can be crosslinked with plasma or UV-irradiation, and they can be locally solved or swollen with solvents.

The first experimental results for up-conversion photoluminescence excited by using ultra low (~10 W/cm²) intensity non-coherent light in solution of diphenylanthracene blended with platinum octaethyl porphyrin are presented. The crucial advantage of this bi-molecular up-conversion process is the inherent independence from the coherence properties of the excitation light.

The smallest functional units of organisms and soft materials have dimensions between 1 and 10 nm and are not usually repeated periodically in space. By site-directed spin labelling and modern electron spin resonance experiments it is possible to elucidate functionally important aspects of such complex structures.

Our images of organized soft matter, e.g. polymers, colloids, are dominated by static structures that provide only snapshots of the possible conformations. Since the typical energies are of the order of the thermal energy, soft matter is amenable to large fluctuations. Structural dynamics are essential for material function. The study of molecular motions over broad time and spatial ranges challenges both experimentalists and theoreticians. Three selected topics from ongoing projects should exemplify such challenges.

By supporting metallocenes on µm-sized aggregated organic nanoparticles, prepared by emulsion polymerization, highly active catalysts for the olefin polymerization can be obtained. The influence of the support is studied by scanning confocal optical microscopy and videomicroscopy.

For the first time images of gases can be acquired my magnetic resonance techniques due to recent developments in optical polarization methods. This can be used to investigate the lung with unrivalled spatial resolution. The morphology and function of the lung down to microscopic levels can be characterized by the combination of these methods with further physical information.

We present three different fields of research in which analytic theory and computer simulation of polymers play an important role. First the relationship between the specific adsorption of single chemical groups in a polymer onto a metal surface as well as the influence on the global chain conformations are studied. The second example establishes a relation between the chain conformations and the so-called entanglement length that determines the rheology of melts respectively the module of elastomers. The third example shows that based on a relatively simple DNA model ("semi flexible worm-like chain") basic phenomena of the DNA repositioning alongside the chromatin can be understood.