Allgemeines Physikalisches Kolloquium im Wintersemester 2012/2013
Ort:     48149 Münster, Wilhelm-Klemm-Str. 10, IG I, HS 2,
Zeit:    Donnerstag, 10.01.2013 16:00 Uhr c.t.
Kolloquiums-Kaffee ab 15:45 Uhr vor dem Hörsaal

Multiple scale interfaces and mechanical adaption of biological materials
Prof. Dr. Peter Fratzl, MPI für Kolloide und Grenzflächen, Potsdam

A large variety of natural materials with outstanding mechanical properties have appeared in the course of
evolution. This includes wood, grasses, bone, sea shells or glass sponges. Biological materials are
generally composites of different types of polymers and – sometimes – mineral. They are built in a
hierarchical fashion, which allows the material to be optimized for its function at many different structural
levels. One of the consequences is that interfaces are joining structural units at all relevant levels of
hierarchy. From a mechanical viewpoint, interfaces may be considered as defects, but with an appropriate
interface design they might also lead to an improvement rather than to a deterioration of the overall
mechanical properties of the composite. Bone, for example, consists in about equal amounts of a collagenrich
matrix and calcium-phosphate nano-particles. These components are joined in a complex hierarchy of
fibres and lamellar structures to a material with exceptional fracture resistance. Similarly, tendon collagen
consists of an assembly of fibrils which partly deform by shearing the interface between them. An example
for molecular-scale interfaces are byssus fibres by which mussels are attached to rocks. They are purely
organic and very extensible but also reach considerable strength and are covered by a hard abrasion
resistant coating. This extraordinary mix of properties seems to be tuned by inhomogeneously distributed
metal-coordination bonds which cross-link the proteins in the filament and in the coating. Finally, plant cell
walls are able to generate considerable stresses and complex movements with changing environmental
humidity. These actuation capabilities are based on intricate cellulose fibre architectures and the water
swelling of hemicelluloses forming the interface between cellulose microfibrils. Unravelling the structural
principles of these unexpected material properties may indicate ways towards composite materials with
adaptive capabilities.

Einladender: Prof. Dr. Helmut Zacharias

Im Auftrag der Hochschullehrer des Fachbereichs Physik

Prof. Dr. Nikos Doltsinis