Content Hotkeys
Professur Chemische Physik
Chemische Physik

Microstructure of a cylinder forming block copoylmer. From: R. Magerle, Phys. Rev. Lett. 85, 2749 (2000); Copyright © 2000 American Physical Society.

Structure and properties of polymeric materials on the nanometer scale are main research topic. We study the often very complex spatial structure of these materials with imaging methods such as scanning force microscopy, Nanotomography, and scientific image processing. Nanotomography is comparable to an excavation on the nanometer scale: With suitable etching or polishing techniques (for instance wet chemical etching, plasma etching or chemo-mechanical polishing) the specimen is eroded step by step and the chemical composition of each freshly exposed surface is imaged with scanning probe microscopy. Hereby we map with high spatial resolution the shape as well as local material properties of the surface. From the resulting series of images, separated in depth by only a few nanometers, the specimen’s three-dimensional microstructure can be reconstructed with 10 nm resolution. Our current research focus is on semicrystalline polymeres, block copolymers, and biological materials.

Screw dislocation in a crystalline lamella of elastomeric polypropylene. From: M. Franke, N. Rehse, Macromolecules 41, 163 (2008); Copyright © 2008 American Chemical Society.

Semicrystalline polymers, like polyethylene and polypropylene, are the most used polymeric materials. Their properties can be controlled through synthesis and processing conditions. The material's microstructure is an important parameter. Elastomeric polypropylene has a very low degree of crystallinity. The spatial arrangement of crystalline regions can be imaged with Nanotomography based on scanning probe microscopy. A recent example is the structure of a screw dislocation in a crystalline lamella (see image). Before imaging, the formation of the dislocation has been observered using scanning force microscopy. With a micro-tensile test setup we track with scanning probe microscopy the deformations of individual crystals during deformation of the material. The data provide a detailed view on the micromechanics of the material on the scale of 10 – 1000 nm. It might serve as starting point for more realistic finite element models of the micromechanics and the mechanical properties of semicrystalline polymers.

Tapping mode scanning force microscopy movie of the microdomain dynamics in a fluid film of block copolymers. From: A. Knoll et al., Nature Materials 3, 886 (2004).

Mesoscale Dynamics of Block Copolymers. With in-situ tapping mode scanning force microscopy we observe how microdomain patterns rearrange at the surface of a fluid block copolymer film. We study the processes during long-range ordering, terrace formation, and formation of surface reconstructions. Our scanning force microscopy time-laps movies show with 10 nm spatial resolution the mesoscale dynamics and fluctuations during structural phase transitions and phase boundaries between differently ordered phases. Computer simulations based on dynamic density functional theory (MesoDyn) capture the experimental observations in stunning detail. more...

Microstructure of human bone imaged with bimodal amplitude modulation scanning force microscopy.

Biological materials have a complex hierarchical structure ranging from the molecular scale over the nano- and micrometer scale up to the macroscopic length scale. From the materials science point of view, bone can be considered as a composite material of anorganic hydroxyl apatite particles embedded in an organic collagen matrix. We study the structure of human bone and aim establishing routine imaging of native human bone based on Nanotomography. The imaging of mechanical properties with scanning force microscopy is of particular interest for understanding the structure property relationship of bone. For this purpose we develop suitable preparation, etching, and imaging techniques based on scanning probe microscopy.