Time-resolved observation by transmission electron microscopy (TEM), viz, in situ TEM, of "same regions" in an oriented amorphous and in an unoriented amporphous i-PS thin films during isothermal cyrsallization was carried out to elucidate its oriented-cystallization and unoriented-crystallization mechanisms, respectively. In situ TEM of an oriented i-PS thin film showed that dege-on lanellane grew perpendicularly to the flowing direction to which the c-axis is parallel, but the number of lamellae stacked in the flowing direction did not increase with increasing crysllization time. On the other hadn,in situ TEM of an unoriented i-Ps thin film showed that a small- sheaf-like structure, which consists of several edge-on lamellae, appeared and then these edge-on lamellae grew to make a binocularly developed two-dimensional spherulite. These results indicate that "central entities"(which have been named by us in this study) in the stacked lamellae form at a first stage of iosthermal crystallization , and the length orientation of the "central entities"have an effect on the resulting crystalline morphology after isothermal cyrstallization . In addition, by real-time in situ TEM of an unoriented i-PS thin film, de growth of i-PS adge-on lamellae were continuously observed for the first time though image quality at the present stage was not sufficient to clearly identify individual lamellae
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