Abstract
The influence of longitudinal stress on the microstructure of bivoltine silk fibers has been investigated by the Positron Lifetime Technique (PLT). The variation of o–Ps (ortho–positronium atom) pick-off lifetime and intensity as a function of stress (0–240 kPa) reveals that the free volume size and its number density remains unchanged within the elastic limit (60 kPa). Thereafter, the free volume size decreases from 67 to 57 Å 3. Owing to the loose helix structure, the chain alignment in the crystalline regions starts prior to that in the amorphous regions, leading to a more ordered silk-II type. The estimated low activation energy in the disordered regions suggests a folded chain conformation for the more ordered silk-II type.
Published Version
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