new phase merge into larger and more stable domains, and then the difference in the
morphology of new phase between spinodal decomposition and nucleation and
growth becomes negligible. In the next chapter, we will introduce more detailed
knowledge about the nucleation kinetics.
The later stage of the phase separation is dominated by the coalescence of the
new phase domains into larger ones to minimize the total interfacial area. Since
diffusion of the polymers is extremely slow, phase separation cannot reach the
equilibrium phase structure predicted by the phase diagram. Instead, one conven-
tionally obtains a metastable structure interweaving concentrated and diluted
phases of polymer chains. Such a metastable multi-componenttexturecan be
solidified due to glass transition, crystallization or cross-linking in the subsequent
cooling process, which displays unique properties beyond the stable state of pure
components. One typical example is the commercialized high-impact polystyrene.
The interwoven texture of rubber-enhanced polystyrene has been prepared from the
mixture of liquid polybutadiene and polystyrene via a process of two-step phase
separation: the first step is cooling for phase separation to form the concentrated and
diluted phases with specific sizes, and the second step is further cooling for phase
separation to form the interwoven texture in the domains of concentrated and
Fig. 9.8 Illustration of free
energy change upon the
nucleation process
Fig. 9.9 Different morphologies of new phase generated at the early stage of (a) nucleation and
growth; (b) spinodal decomposition (Strobl et al. 1986 ) (Reprint with permission)
178 9 Polymer Phase Separation