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Structure and dynamics of silkworm silk and spider silk

Mercredi 13 mars 10:00 - Duree : 1 heure
Lieu : Science Building Room 036 - EPN campus - 71 avenue des Martyrs - Grenoble

Orateur : Martin MÜLLER Institute of Experimental and Applied Physics, Kiel University & Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Germany)

Silk combines high extensibility with high mechanical strength. The key to those unique mechanical properties lies in the hierarchically organised micro- and nanostructure with nanocrystals embedded in a softer, disordered matrix in the fashion of a composite material. Scattering techniques using synchrotron radiation and neutrons are ideal tools for the investigation of nature’s engineering materials as they cover the relevant length and time scales. They are sensitive to the most relevant structural parameters, e. g. lattice constants (including internal stress), orientation distributions and molecular disorder. In the case of silkworm silk, new models were developed to explain how the yield mechanisms of both the fibroin nanocrystals and the disordered matrix contribute to the mechanical properties. We used a combination of high-resolution mechanical relaxation experiments, in situ neutron small-angle scattering [1,2] and spectroscopy [3], in situ X-ray microdiffraction and high-pressure experiments [4]. Based on our findings, native silk fibres were functionalised with chromophores in order to make them optically switchable ; again, the mechanical switching effect is readily visible in X-ray diffraction experiments [5]. Structural relaxations in humid silkworm silk fibres exposed to tensile stress have been observed to take place on a very wide range of time scales from a few milliseconds to several hours. The time-dependence of the measured tensile force following a quasi-instantaneously applied external strain on the fibres can be understood in terms of a fractional viscoelastic relaxation function introducing memory effects by which the mechanical state of a fibre depends on its tensile history. An analogous fractional relaxation also gives rise to the subdiffusion observed on picosecond time scales as measured in situ using quasielastic neutron scattering (QENS) combined with tensile tests. It describes the mobility of the amorphous polymer chains in silkworm silk and of the adsorbed water on the molecular level in an excellent way. The reduction of the subdiffusive memory effect in stretched fibres compared to native fibres is consistent with the higher order of the polymers in the stretched state [3]. The different morphology leading to the unique mechanical properties of spider silk is reflected in the strain dependence of the fractional dynamics parameters from QENS [6].

References :

[1] M. Müller, I. Krasnov, M. Ogurreck, M. Blankenburg, T. Pazera, T. Seydel, Adv. Eng. Mat., 9, 767 (2011).

[2] J. A. Wagner, S. P. Patil, I. Greving, M. Lämmel, K. Gkagkas, T. Seydel, M. Müller, B. Markert, F. Gräter, Scientific Reports 7, 15273 (2017).

[3] I. Krasnov, T. Seydel, M. Müller, Phys. Rev. E, 91, 042716 (2015).

[4] C. Krywka, I. Krasnov, R. Figuli, M. Burghammer, M. Müller, Macromolecules, 47, 7187 (2014).

[5] I. Krasnov, N. R. Krekiehn, C. Krywka, U. Jung, A. U. Zillohu, T. Strunskus, M. Elbahri, O. Magnussen, M. Müller, Appl. Phys. Lett., 106, 093702 (2015).

[6] I. Krasnov, T. Seydel, I. Greving, M. Blankenburg, F. Vollrath, M. Müller, J. R. Soc. Interface, 13, 20160506 (2016)

Contact : mader@ill.fr

Discipline évènement : (Physique)
Entité organisatrice : (ILL)
Nature évènement : (Séminaire)
Evènement répétitif : (General ILL Seminar - College 8)
Site de l'évènement : Polygone scientifique

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