The role of long chains in extension
flow-induced crystallization
was studied with a combination of extension rheological and in situ small-angle X-ray scattering (SAXS) measurements
at 52 °C. To elucidate the effects of long chains, bidisperse
blends of poly(ethylene oxide) (PEO) with the long-chain concentration
above the overlap concentration were prepared, constructing long-chain
entanglement network in short-chain matrix. Rheological data of step
extension on PEO melt are divided into two regions with fracture strain
of pure short-chain sample as a boundary. Distinctly different features
of crystallization kinetics and crystal morphologies are observed
in these two regions, exactly corresponding to rheological behavior.
A new mechanism based on entanglement network perspective is proposed,
in which the second entanglement network constructed by long chains
has three effects: (i) helping flow to change the free energy of polymer
melt more effectively; (ii) ensuring the specific work can impose
on the system; (iii) favoring the formation of precursors. This mechanism
captures both rheological observation and crystallization behavior
successfully and offers a new viewpoint for FIC study.