diluted phases, as illustrated in Fig.9.10. Such a hierarchical interweaving texture
in the matrix of polystyrene can induce a significant amount of crazes to absorb the
impact energy, which greatly raises the impact strength and harvests the advanta-
geous properties of both components.
9.3 Microphase Separation of Diblock Copolymers
Diblock copolymers can form only molecular-scale small domains ofmicrophase
separationrather than macroscopic phase separation, because of the constraint of
the covalent bond between the two components. According to compositions, the
major component forms the continuous matrix, while the minor component forms
the microphase domains. The most common equilibrium geometric shapes of
microdomains can be lamellae, gyroids, cylinders and spheres, as illustrated in
Fig.9.11, which pack orderly into a nano-scale periodic pattern and be used as
nano-scale templates for the fabrication of functional nano-materials (Bates and
Fredrickson 1990 ; 1999 ).
The long period of the regularly packed microdomains, as illustrated in
Fig.9.12, can be determined by the small-angle X-ray scattering. One may make
a scaling analysis on the equilibrium domain sizes from the calculation of free
energy changes as follows. In comparison to the macrophase-separated polymer
blends, the microphase-separated diblock copolymer system contains mainly two
Fig. 9.10 AFM image for the composite texture formed by polybutadiene well-distributed in
polystyrene matrix via two steps of phase separation (Liu 2003 ) (Courtesy of Jiang Liu)
9.3 Microphase Separation of Diblock Copolymers 179