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.
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Experimentally, we study structure formation in controlled coating equipment — miniaturized and better controlled versions of technologically relevant coating processes. We observe structure formation directly through in situ analytics. A combination of light- and X-ray scattering, electron microscopy, optical spectroscopy and intensive thinking helps us to explain how materials form in the coater. Our well-defined precursors and direct observation provide deeper insights that are usually possible in large-scale processing.
We investigate whether certain formation processes resemble known phase transitions, whether they occur far from equilibrium and what dominates them microscopically. Mass transport is important for structure formation because it governs whether energy minima are reached, a stationary structure forms or disordered regions remain. We investigate the fluid mechanics, solvent effects, and diffusion in interacting dispersions. Our working model considers interactions between material components together with mobility, that is, the capability of components to arrange in assemblies defined by interactions.
Templates and external fields influence structure formation. We use them to impose boundary conditions and energy minima that affect the microstructures of materials and study the reaction of the system.
Certain conditions lead to the formation of ordered structures in soft matter. Such “self-assembly” processes are promising routes to materials that are ordered at length scales below one micron. They can complement conventional high temperature and vacuum processes. Small energy differences are sufficient to bias structure formation processes in a certain direction. Small perturbations can inhibit the formation of the desired structures; careful control of process parameters such as temperature, particle mobility and solvent properties is therefore required. The sensitivity of the ordering process renders such “bottom-up” structuring methods interesting, but also challenging.
Structure formation processes can yield materials that interact strongly with electromagnetic waves, combine properties of constituent particles, and exhibit anisotropic properties or hierarchical geometries. Their possible applications range from functional surface coatings to electronic components.
At the centre of our work are interfaces: the surface of particles that interacts with the solvent; the interfaces between particles that rule electrical conductivity and optical properties; the interface between liquid “paint” and air during coating. We study under which conditions particles and molecules accumulate at this interface and how this can be applied in new materials.