The program division “Structure Formation” investigates how molecules, polymers and colloidal particles join to form materials. It studies fundamental processes of structure formation and applies them to prepare new materials from liquid precursors.
We study how the properties of composite and hybrid materials depend on their microstructures and how to change them. To this end, we systematically vary size, geometry, chemical composition, and arrangement of the materials’ constituents. We observe how microstructure and interfaces form and affect material properties to create transparent conductive layers of metal nanoparticles for electronics, composites of conductive polymers with optically active particles for sensors and supraparticles that contain optically active nanoparticles, for example. We see particles as the basis of future “active nanocomposites” that can interface with electronics and change their properties whenever required.
- Gonzalez-Garcia et al., Procedia Eng.2016, 141, 152-156. DOI: 10.1016/j.proeng.2015.08.1120
- Reiser et al., Chem. Sci., 2016, 7, 4190-4196. DOI: 10.1039/C6SC00142D
- Reiser et al., Phys. Chem. Chem. Phys., 2016,18, 27165-27169. DOI: 10.1039/C6CP05181B
- Reiser et al., ACS nano, 2017, 11, 4934-4942. DOI: 10.1021/acsnano.7b01551
- Maurer et al., ACS Appl. Mater. Interfaces, 2015, 7, 7838. DOI: 10.1021/acsami.5b02088
- Maurer et al. Nano Lett., 2016, 16, 2921–2925. DOI: 10.1021/acs.nanolett.5b04319
- Maurer et al., Phys. Status Solidi A, 2016, 213, 2336–2340. DOI 10.1002/pssa.201532874
- Maurer et al., Adv. Mater. Technol., 2017, 482, 1700034. DOI: 10.1002/admt.201700034
- Maurer et al., ACS Appl. Mater. Interfaces, 2018, 10, 7, 6079-6083. DOI: 10.1021/acsami.7b18579
I-Seed unites bioinspired soft robotics, material science, and environmental science, with the aim of developing a new generation of self-deployable and biodegradable soft miniaturized robots that mimic the behavior of plant seeds. These robots, composed of artificial plant structures and sensor materials, are designed to monitor in-situ environmental parameters in air and topsoil, such as the presence of pollutants, moisture, CO2 levels, temperature and water quality. Within this project, we are engineering fluorescent sensor materials whose optical properties are dependent on environmental factors. All these fluorescent materials will be chosen for their degradability and environmental compatibility.
Flexible and printed electronics require new materials. Here, we focus on optically transparent materials for the electronics of the future. This BMBF-funded research project, a part of the NanoMatFutur initiative, uses nanoparticles with defined shapes and arrangements inside polymers to make transparent electrodes for touch-screen display or solar cells, for example. Chemists, material scientists and an engineer collaborate very closely to create new materials that can be processed with well-established wet coating and printing techniques.
Modern methods of “self-arrangement” allow us to produce larger structures from nanoparticles whose geometry is defined to a certain degree. This is very interesting for materials: for example, electrically conductive metal nanoparticles can be arranged in an insulating matrix to maximize or minimize conductivity, depending on whether a dielectric is required or a conductor.
Unfortunately, gravity gets in the way here: larger arrangements of metal particles are very filigree but heavy enough to be torn by their own weight so that, for example, connectivity and thus conductivity is lost. In the ARNIM project, supported by the German Aerospace Center (DLR), we are investigating whether this can be prevented by switching off gravity. To do this, we first use a drop tower (ZARM in Bremen) and “throw” agglomeration experiments in such a way that gravity is eliminated for a few seconds. In the future, experiments on board rockets or the international space station are also planned, which will allow longer agglomeration experiments.
If it turns out that the agglomerates are actually destroyed by their weight, we have to strengthen them – for example by using nanowires. But it could also be that it is not gravity at all, but details of the agglomeration process. These questions are therefore at the heart of the project.
In the NanoSpekt project, we developed sinter-free hybrid inks to apply electrical conductors to sensitive surfaces without sintering – including paper and cardboard. In this project, in cooperation with the Papiertechnische Stiftung (PTS), we are investigating how this material can be used to print RFID antennas for contactless identification of packaging directly on carton.
Paper and cardboard are very important, but also difficult substrates: their surface is porous, and during printing the ink penetrates, making the electrical conduction more difficult. Furthermore, paper begins to curl when heated too much and cartons are folded, which can easily damage conductive structures. Therefore, in this AiF-funded cooperation, we are investigating how to make the connection between the cardboard and the ink strong enough – and how to incorporate additional functions into cartons, preferably directly at the manufacturer.
Normally, composites of elastomers and conductive carbon particles are used if the material is to be and remain conductive. This is, for example, how antistatic shoe soles or gaskets are produced. In the DFG-funded AggloSense project, we want to achieve the opposite: maximum change in electrical conductivity during deformation.
In cooperation with Professor Tanja Schilling from the University of Freiburg, we are investigating what the conductivity of such composites depends on. Carbon particles (so-called “carbon black”) are in fact not spheres, but very complex agglomerates with often fractal structures. In the material they touch each other in a way that is difficult to predict. By comparing the structure of specifically produced materials with simulated arrangements and measurements of conductivity with and without deformation, we hope to find out how the change in conductivity can be made large.
Connecting biological objects with electronics requires soft electrical contacts. To that end, we explore the fabrication of micro-fibrillar adhesion devices from electrically conductive materials. Detailed characterization of these devices reveals the relationship between adhesion properties and electrical resistivity. Their application as electrically tunable devices is also explored.
Embedded nanoparticles lend today’s nanocomposites useful properties such as color, strength, or a high refractive index. Their arrangement affects these properties but does not usually change after material synthesis because the particles are bound too strongly in the matrix. We investigate nanocomposites in which metal nanoparticles can move and reorganize in reponse to a stimulus. Thus, the color or other properties of the composite change. In this project, we synthesize model particles and study how they can be embedded such that they retain a certain mobility.
This interdisciplinary project aims at the scalable growth of mesenchymal stem cells using new carrier materials for proliferation. In collaboration with cell biologists, biochemists, chemists and material scientists, we modify surfaces of microspheres so as to increase cell adhesion, help cell proliferation and allow for their easy detachment from these microbeads. The materials-oriented part of the project involves surface characterization of beads which are about 100 µm in size followed by their surface modification such as by polymer graft, plasma activation, and changing surface roughness and surface charges. The project is a part of “European territorial cooperation” INTERREG.
In addition to conductive layers, dielectric layers are also required for printed electronics, e.g. for capacitor elements. Pure polymer layers show a limited polarization in the electric field and hence a relatively low dielectric constant. We investigate hybrid layers of gold nanoparticles separated by insulating ligands. On the one hand, the polarization capability of the hybrid material and the dielectric constant of the layer are to be increased by the metallic particles. On the other hand, a charge transport between the nanoparticles and the failure of the dielectric layer is to be prevented.
- Hegetschweiler et al., J. Mater. Sci., 2019, 54, 5813-5824. DOI: 10.1007/s10853-018-03263-0
- Hegetschweiler et al., Anal. Chem., 2019, 91, 943-950. DOI: 10.1021/acs.analchem.8b04012
- Hegetschweiler et al., Part. Part. Syst. Charact., 2021, 38, 2000236. DOI: 10.1002/ppsc.202000236
- Meili-Borovinskaya et al., J. Chromatogr. A, 2021, 1641, 461981. DOI: 10.1016/j.chroma.2021.461981
- Webel et al., Ultramicroscopy, 2021, 223, 113219. DOI: 10.1016/j.ultramic.2021.113219
Microalloyed steels contain carbonitride nanoparticles which are responsible for their compelling mechanical properties and good weldability.
In cooperation with the Dillinger Hütte, a steel mill in Saarland, we are investigating the size distribution, chemical composition and morphology of the particles contained in the provided steels. Particle analysis is performed using methods that we developed for colloidal particles and that are not usually employed in metallography.
Mixtures of nanoparticles and proteins tend to form hybrid agglomerates. We are interested in the agglomeration mechanisms and the structure of such agglomerates to better understand their role in medicine, ecology, and biomaterials.
Formation Mechanism for Stable Hybrid Clusters of Proteins and Nanoparticles (ACS)
ACS NANO, DOI: 10.1021/acsnano.5b01043
Field-flow fractionation can fractionate particles after size, but it is often plagued by losses of particles due to adsorption and agglomeration. This AiF-ZIMM-project (supported by the BMWi) aims to reduce such losses and make FFF suitable as a standard technique for nanoparticle detection in products, the environment, and food.
Digital imagers for medical X-ray are based on ceramic layers. This project is a BMBF-funded effort, coordinated by Siemens, to build X-ray imagers based on a new material that contains conductive polymers and inorganic particles. The particles absorb and convert X-ray photons, the polymer transports the charges to electrodes. The Structure Formation Group is mainly concerned with the analysis of the particle-polymer composites’ structures, its origins in fabrication, and its effect on detector performance.
Interactions drives particles to agglomerate, mobility allows them to follow this drive. We use flow setups and synchrotron Small-Angle X-ray Scattering (SAXS) to study early stages of agglomeration. The results help us to better understand the formation of composites, crystallization mechanisms, and biomineralization phenomena.
Nanoparticles that are trapped in emulsion droplets react to their confinement depending on the surfactant. Some of them form beautifully ordered “supraparticles”, fully defined structures that remind of noble gas condensates or small metal clusters. We study how nanoparticles interact with each other and liquid-liquid interfaces in this DFG-funded project. Tanja Schilling at the University of Luxembourg use simulations to predict and understand structure formation, we explore it experimentally.