ABSTRACT
We analyze the wide-angle X-ray scattering from oriented spider silk fibers in terms of a quantitative scattering model, including both structural and statistical parameters of the beta-sheet crystallites of spider silk in the amorphous matrix. The model is based on kinematic scattering theory and allows for rather general correlations of the positional and orientational degrees of freedom, including the crystallite's size, composition and dimension of the unit cell. The model is evaluated numerically and compared to experimental scattering intensities allowing us to extract the geometric and statistical parameters. We show explicitly that for the experimentally found mosaicity (width of the orientational distribution) intercrystallite effects are negligible and the data can be analyzed in terms of single-crystallite scattering, as is usually assumed in the literature.
Subject(s)
Models, Molecular , Silk/chemistry , Spiders/chemistry , Animals , Protein Structure, Secondary , X-Ray DiffractionABSTRACT
Spider silk is well-known for its outstanding mechanical properties. However, there is a significant variation of these properties in literature and studies analyzing large numbers of silk samples to explain these variations are still lacking. To fill this gap, the following work examines the mechanical properties of major ampullate silk based on a large ensemble of threads from Nephila clavipes and Nephila senegalensis. In addition, the effect of relative humidity (RH) on the mechanical properties was quantified. The large effect of RH on the mechanical properties makes it plausible that the variation in the literature values can to a large extent be attributed to changes in RH. Spider silk's most remarkable property-its high tenacity-remains unchanged. In addition, this work also includes hysteresis as well as relaxation measurements. It is found that the relaxation process is well described by a stretched exponential decay.
