Silk films cast from an aqueous solution onto oriented poly(tetrafluor
oethylene) substrates and characterized by external reflection infrare
d spectroscopy showed that the oriented poly(tetrafluoroethylene) subs
trate bath promoted crystallization of the silk II in a beta-pleated s
heet structure and induced orientation in the silk films, even for sil
k films cast from dilute silk solutions and salt solutions. Possible n
ucleation mechanisms are discussed.