title: Increased molecular mobility in humid silk fibers under tensile stress.
abstract: Silk fibers are semicrystalline nanocomposite protein fibers with an extraordinary mechanical toughness that changes with humidity. Diffusive or overdamped motion on a molecular level is absent in dry silkworm silk, but present in humid silk at ambient temperature. This microscopic diffusion distinctly depends on the externally applied macroscopic tensile force. Quasielastic and inelastic neutron-scattering data as a function of humidity and of tensile strain on humid silk fibers support the model that both the adsorbed water and parts of the amorphous polymers participate in diffusive motion and are affected by the tensile force. It is notable that the quasielastic linewidth of humid silk at 100% relative humidity increases significantly with the applied force. The effect of the tensile force is discussed in terms of an increasing alignment of the polymer chains in the amorphous fraction with increasing tensile stress which changes the geometrical restrictions of the diffusive motions.
authors.affiliation: Institut Laue-Langevin, Boîte Postale 156, F-38042 Grenoble, France. seydel@ill.eu
authors.forename: Tilo
authors.initials: T
authors.lastname: Seydel
authors.forename: Wiebke
authors.initials: W
authors.lastname: Knoll
authors.forename: Imke
authors.initials: I
authors.lastname: Greving
authors.forename: Cedric
authors.initials: C
authors.lastname: Dicko
authors.forename: Michael M
authors.initials: MM
authors.lastname: Koza
authors.forename: Igor
authors.initials: I
authors.lastname: Krasnov
authors.forename: Martin
authors.initials: M
authors.lastname: Müller