Heeley, Ellen L.; Fernyhough, Christine M.; Graham, Richard S.; Olmsted, Peter D.; Inkson, Nathanael J.; Embery, John; Groves, David J.; McLeish, Tom C.B.; Morgovan, Ariana C.; Meneau, Florian; Bras, Wim and Ryan, Anthony J.
Shear-Induced Crystallization in blends of Model Linear and Long-Chain Branched Hydrogenated Polybutadienes.
Macromolecules, 39(15) pp. 5058–5071.
Quiescent and shear-induced crystallizations were performed on several well-defined linear
monodisperse hydrogenated polybutadiene blends with a high-molecular-weight long-chain branched (LCB) combshaped
additive. The connection between microscopic molecular motion and crystallization kinetics has been
quantitatively studied with respect to the formation of either isotropic or oriented shish kebab crystal morphology
using time-resolved X-ray scattering techniques. Using a constant preshear rate, the addition of small amounts of
LCB combs to the sample blends, at concentrations below and just above the overlap concentration c*, has
significantly increased the crystallization rates compared to quiescent conditions. However, only one blend showed
the formation of an oriented shish kebab morphology. Also, for these model blends, the transition between isotropic
and oriented crystals occurs quite sharply between 5 and 10%, which is around c*. We explain these data by
using a shish formation mechanism in which, to form shish kebabs, the combs must be mutually overlapping and
the comb Weissenberg number must be in the strong stretch regime.
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