title: Strain-dependent fractional molecular diffusion in humid spider silk fibres.
abstract: Spider silk is a material well known for its outstanding mechanical properties, combining elasticity and tensile strength. The molecular mobility within the silk's polymer structure on the nanometre length scale importantly contributes to these macroscopic properties. We have therefore investigated the ensemble-averaged single-particle self-dynamics of the prevailing hydrogen atoms in humid spider dragline silk fibres on picosecond time scales in situ as a function of an externally applied tensile strain. We find that the molecular diffusion in the amorphous fraction of the oriented fibres can be described by a generalized fractional diffusion coefficient Kα that is independent of the observation length scale in the probed range from approximately 0.3-3.5 nm. Kα increases towards a diffusion coefficient of the classical Fickian type with increasing tensile strain consistent with an increasing loss of memory or entropy in the polymer matrix.
authors.affiliation: Institut für Experimentelle und Angewandte Physik, Universität Kiel, 24098 Kiel, Germany Institute of Materials Research, Helmholtz-Zentrum Geesthacht (HZG), 21502 Geesthacht, Germany.
authors.forename: Igor
authors.initials: I
authors.lastname: Krasnov
authors.affiliation: Institut Max von Laue-Paul Langevin (ILL), CS 20156, 38042 Grenoble, France seydel@ill.eu.
authors.forename: Tilo
authors.identifier: 0000-0001-9630-1630
authors.initials: T
authors.lastname: Seydel
authors.affiliation: Institute of Materials Research, Helmholtz-Zentrum Geesthacht (HZG), 21502 Geesthacht, Germany.
authors.forename: Imke
authors.initials: I
authors.lastname: Greving
authors.affiliation: Institut für Experimentelle und Angewandte Physik, Universität Kiel, 24098 Kiel, Germany Institute of Materials Research, Helmholtz-Zentrum Geesthacht (HZG), 21502 Geesthacht, Germany.
authors.forename: Malte
authors.initials: M
authors.lastname: Blankenburg
authors.affiliation: Department of Zoology, University of Oxford, Oxford OX13PS, UK.
authors.forename: Fritz
authors.initials: F
authors.lastname: Vollrath
authors.affiliation: Institut für Experimentelle und Angewandte Physik, Universität Kiel, 24098 Kiel, Germany Institute of Materials Research, Helmholtz-Zentrum Geesthacht (HZG), 21502 Geesthacht, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Müller
mesh_terms: D000818:Animals; D006813:Humidity; D047011:Silk / Q000737:chemistry*; D013112:Spiders; D013314:Stress, Mechanical; D013718:Tensile Strength
chemical_list: D047011:Silk
keywords: fractional dynamics; hydrophobic collapse; nanocomposite polymer fibres; neutron spectroscopy; spider dragline silk; supercontraction