Liquid Crystalline Characteristics of Natural Silk Secretions

Abstract

We have used transmitted polarized light microscopy to examine the fluid contents of silk glands taken from Bombyx mori silkworms and Nephila clavipes orb-weaving spiders. In the absence of shear, the secretions are optically isotropic. As the concentration is allowed to increase by evaporation, microstructures typical of the nematic liquid crystalline state are observed. Thus it appears that naturally spun silk becomes liquid crystalline en route to solidifying into fiber - which is advantageous to introducing and retaining global molecular alignment. This will facilitate the formation of strong, stiff fibers without the need for a significant post-spinning draw. We have also found that natural silk does not exhibit the defects in molecular alignment that are typical of synthetic polymer fibers spun from liquid crystalline solutions or melts.

Silk

“…The process forms a lyotropic nematic liquid crystalline phase prior to spinning in both the spider and the silkworm, and in many of the different glands of the spider responsible for the different silks (Kerkam et al, 1991). The formation of the nematic liquid crystalline phase is characterized by axial alignment and interaction of polymer chains in various stages of registry with each other while remaining soluble in aqueous medium.…”