posted on 2022-07-26, 14:36authored byKun Song, Lin-Feng Wu, Dong Liu, Li-Zhao Huang, Xia-Ran Miao, Zhe Wang
Shish appears under certain conditions in flow-induced crystallization
of polymers. The morphology of shish is determined by experimental
conditions, such as strain and polymer properties. Moreover, shish
distribution significantly affects the morphology and arrangement
of subsequent epitaxial kebabs. Therefore, quantitatively clarifying
the chain relation of experimental conditions–shish nucleation–final
shish–kebab structure is of scientific and practical importance.
We investigate this problem by measuring lightly crosslinked high-density
polyethylene samples with small-angle X-ray scattering and an extensional
rheometer. It is found that the critical strain for shish formation
(ε1) is the one fully extending the crosslinked strand
in the network. The shish radius (Rs)
is determined by the spacing (S||) between
adjacent parallel stretched strands. Based on these observations,
the mechanism for shish nucleation in the stretched network is discussed.
As the strain further increases and exceeds the one fully stretching
the whole chain (ε2), the limit on the growth of
shish is suppressed by overstretching, resulting in a further increase
of the shish radius. The packing of shish also undergoes a transition
at the strain of ε2 from an ordered state to a sparse
and disordered state. The lateral ordering of shish induces the interlocked
shish–kebab structure, which is a candidate for polymeric materials
with ultrahigh moduli.