| Popis: |
The combination of micro-Raman spectroscopy and an advanced universal fibre tester (UFT) made it possible to probe at the nanoscale (through monitoring the modification of chemical bonds) the change in conformation (a-helix, b-sheet, etc.), macromolecular fibroin chain orientation and coupling during the application of stress, quantitatively. Different single fibres of silkworms (Bombyx mori, Gonometa rufobrunea, Gonometa postica) and a spider (Nephila madagascariensis) were tested in a dry environment and compared with the behaviour of keratin fibre. As observed previously for single keratin fibres, a direct relationship is observed between nano- and micro-mechanical tensile behaviour. The phase transition plateau, well defined for some pristine B. mori fibres, disappears in degummed fibres, which indicates a structural modification and increasing disorder with chemical treatments. Stress-controlled micro-Raman analysis shows that a few modes involving CH2 and/or amide groups of b-conformation chains undergo a wavenumber softening during the elastic behaviour (∼0‐3%), although most of the modes are not affected. A different behaviour is observed for modes associated with ‘ordered’ and ‘disordered’ b-sheets and helical chains. Larger softening is observed for lattice modes with increasing stress/strain, as expected. Structural changes and relationships with mechanical behaviour are discussed. Copyright 2008 John Wiley & Sons, Ltd. Supplementary electronic material for this paper is available in Wiley InterScience at http://www.interscience.wiley.com/ jpages/0377-0486/suppmat/ |
Plný text