Fig. 18 presents a series of TEM images showing
the details of deformation structures in macrophaseseparated
blend (ST2C20% PS082) that possesses
hPS particles in a ST2 matrix. Morphological changes
around the hPS particles during deformation are very
helpful in understanding the micromechanical
processes.
The growth of microvoids at the poles (i.e. along
the direction of applied stress) of the particles is well
known for particle filled polymers [11,19]. In the
present case, the hPS inclusions act as stiff particles
embedded in the soft ST2 matrix. Due to the
maximum stress concentration at particles poles,
microvoid-formation takes place, as shown in
Fig. 18a. Fig. 18b indicates that the high stress
concentration at the particle poles makes both PS and
PB lamellae turn to fibrillar structures just before the
formation of microvoids [96]. Each lamella appears to
consist of a parallel array of ‘fibrils’ lying normal to
the lamellar axis (details in Fig. 18c). The fibrillar
nanostructures represent the deformation stage prior
to the debonding between the block copolymer matrix
and hPS particles. The growth of these microvoids
into cracks and subsequent propagation of these
cracks cause specimen-failure.