C. Wang et al., MORPHOLOGY OF BANDED SPHERULITES IN POLY(EPSILON-CAPROLACTONE) POLY(STYRENE-RAN-ACRYLONITRILE) BLENDS/, Acta polymerica, 48(9), 1997, pp. 354-362
The occurrence of banded spherulites in blends of poly(epsilon-caprola
ctone) with poly(styrene-ran-acrylonitrile) is studied by means of opt
ical-, scanning electron-, environmental scanning electron-, and atomi
c force-microscopy as well as small-angle X-ray scattering. The measur
ements reveal that lamellae are confined in fibrils that bend periodic
ally from the center of spherulites in a radial direction. The fibrils
show also a regular spacing in the lateral direction. Single bent lam
ellae can be observed by atomic force microscopy after permanganic etc
hing. The enrichment of amorphous material near to the growth front of
the spherulites can be directly observed by polarized light microscop
y after temperature jump experiments. The excluded amorphous material
on the surface of the growing spherulites has the shape of droplets. T
his might be the main reason for the initiation of the bending process
because the result is a non-uniform stress distribution acting on the
growing lamellae at the interface between spherulites and the surroun
ding melt. The amorphous material of the blends can be found in three
areas as observed by small-angle X-ray scattering experiments and micr
oscopical methods: i) between the lamellae, ii) excluded from the inte
rlamellar region but within the spherulite, and iii) for high contents
of non-crystallizable material, it can be excluded from the spherulit
e. The banding periodicity of spherulites as a function of the crystal
lization temperature can be described in terms of two models, based ei
ther i) on the inherent twisting of lamellae perpendicular to the axis
of a screw dislocation or ii) on the dependence of the diffusion of a
morphous material away from the growth front of lamellae and the tempe
rature dependence of the rate of crystallization Both models fail at v
ery low supercoolings near to temperatures where the banding disappear
s completely.