Crystalline Morphology of Polymer Blends

The crystallization of homopolymers in binary blends is more complicated as compared with that of neat homopolymers. This is because the second homopolymer, usually amorphous homopolymer, may accelerate the crystallization by working as a diluent or decelerate it by disturbing the diffusion of 

In miscible binary blends, amorphous homopolymers are completely accommodated within amorphous layers of the lamellar morphology formed after the crystallization of crystalline homopolymers. Stein et al. [51], for example, observed the lamellar morphology formed in a miscible blend of PCL and poly(vinyl chloride) (PVC) using SAXS as a function of composition. They found that PVC existed in amorphous layers of the lamellar morphology to yield a linear increase in the amorphous layer thickness with increasing PVC composition, whereas the crystalline layer thickness remained constant irrespective of composition. Wenig et al. [52] obtained similar results for a miscible blend of poly(2,6-dimethylphenylene oxide) (PPO) and isotactic polystyrene (iPS). However, a different result was reported for a miscible blend of iPS and atactic polystyrene [53], where the amorphous layer thickness was almost constant irrespective of composition. Stein et al. [51] explained this difference in 

The lamellar morphology formed in miscible blends is usually observed using SAXS as described in Section 10.2.2, because its typical repeating distance is in the order of 10nm. In addition, a combination of SAXS and differential scanning calorimetry (DSC) results straightforwardly provides the crystalline layer thickness and amorphous layer thickness if we assume a perfect lamellar morphology with no transition zone between both layers. 

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