crystals. Such a shish-kebab-like crystal morphology is often calledshish-kebab
crystals. As illustrated in Fig.10.19, with an increase of strains in bulk polymers,
crystal morphologies ranging from spherulites, shish-kebab crystals to fiber crystals
can be obtained (Phillips 1990 ).
There are still hot ongoing debates about the formation mechanism of shish
structures in the oriented flow field. Recently, Hashimoto and his coworkers
proposed a new scenario for flow-induced phase transitions in polymer solutions
to form the hierarchical structures of shish-kebabs (Hashimoto et al. 2010 ; Murase
et al. 2011 ).
Sometimes, the shish fibers can be so thin that they are invisible under the
present microscopes, leaving an array of parallel-oriented lamellar crystals, called
therow-structure. The molecular simulations demonstrated that even a single pre-
aligned polymer chain can play the role of shish in inducing the growth of kebab
crystals, as demonstrated in Fig.10.20.
Fig. 10.19 Illustration of
crystal morphologies of
polymers influenced by the
different degree of preload
strain rates (percentage in the
figure). Thearrowindicates
the direction of stresses. The
right-handschematic picture
for shish-kebab crystals is
adopted from Pennings et al.
( 1970 )
Fig. 10.20 Molecular simulations obtain the shish-kebab structure induced by single pre-aligned
chain (a) and its local enlargement (b) (Hu et al. 2002 )
10.3 Crystalline Structures of Polymers 207