Dresden 2009 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 37: Biopolymers (joint session CPP/BP)

CPP 37.5: Vortrag

Donnerstag, 26. März 2009, 15:30–15:45, ZEU 114

Silkworm silk under tensile stress as a function of humidity investigated by neutron spectroscopy — •Wiebke Knoll¹, Tilo Seydel², Malte Ogurreck¹, Imke Diddens³, Cedric Dicko³, and Martin Müller⁴ — ¹IEAP, Universität Kiel — ²ILL, Grenoble — ³Department of Zoology, Oxford — ⁴GKSS, Geesthacht

Natural silk fibres exhibit extraordinary mechanical properties, combining high tensile strength with a high elongation at failure. The mesoscopic structure with crystalline regions embedded in a softer disordered matrix is the key to these properties. We measured the molecular vibrational response of Bombyx mori silkworm silk fibres in situ upon externally applied tensile stress using cold neutron time-of-flight spectroscopy. Adding to a previous study on dry silk fibers we recently investigated humid silk fibers. The aligned silk fibres are therefore exposed to a tensile force along the fiber axis generated by a stretching machine in a humidity chamber. The applied force was sufficient to reach the yield point of plastic deformation. It is already known from X-ray studies that most of the deformation upon extension of the fibres is due to the amorphous regions of the silk. The neutron results on dry fibers indicate that the externally applied force is not reflected by any noticeable effect on the molecular vibrational or diffusional/reorientational properties of the amorphous silk protein . However, on humid fibers we observed a quasielastic broadening of the scattering function, which is due to polymer chain mobility enhanced by the adsorbed water. This effect increases with stretching the humid silk fibers.