Confined nucleation and growth of poly(ethylene oxide) on the different crystalline morphology of poly(butylene succinate) from a miscible blend

The confined and fractional crystallization behavior of poly(ethylene oxide)(PEO) in miscible poly(butylene succinate)(PBS)/PEO blends has been investigated. Both nucleation and growth of PEO crystals through the two-step crystallization process were significantly influenced by the morphology of pre-existed PBS spherulites. At the first crystallization step, the PEO component as diluents was segregated into different regions (interlamellar, interfibrillar and interspherulitic) of PBS crystals, which was dependent on the crystal growth rate of PBS and the diffusion coefficient of PEO. With the increase of crystallization temperatures of PBS (T_c,PBS), more and more PEO molecules were excluded out of the lamella stacks of PBS, and the segregations of PEO became larger and larger. Meantime, the connectivity between the adjacent PEO domains was reduced dramatically. At the second crystallization step, PEO crystallized subsequently within the existed frameworks of PBS spherulites formed at various T_c,PBS. On the one hand, the nucleation rate of PEO was determined by the total solid-liquid interfacial area between PBS crystals and PEO domains, which could significantly reduce the free energy barrier of nucleation embryos. As T_c,PBS increased, the nucleation rate of PEO decreased with the decrease of PBS crystal surfaces which were around PEO domains. The fractional crystallization of PEO occurred when the nuclei formed at various supercoolings. On the other hand, the crystal growth rate of PEO was mostly influenced by the connectedness between the PEO domains. With the increase of T_c,PBS, the continuous phases of PEO were transformed into isolated domains. The crystal growth of PEO decreased gradually, due to the restrictions to the diffusion of PEO chains. PEO could only nucleate and grow inside each isolated domains, just forming tiny PEO crystals. It was found that the crystallization of PEO was dependent not only on the diffusion length of PEO, but also on the intrinsic morphological features of PBS spherulites.