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Polyamide 66 (PA 66) nanofiber bundles were first electrospun and then introduced into isotactic polypropylene (iPP) melts to prepare nanofiber bundle/iPP composites. To reveal the influences of matrix molecular weight (M n ) on the transcrystalline layer, three kinds of iPP with different M n were adopted. Polarized optical microscope was employed to investigate the transcrystallinity. In the presence of PA 66 nanofiber bundle, the heterogeneous nucleation distinctly happened in iPP melts. Moreover, the higher the iPP M n , the denser the nuclei. Both a decrease in matrix M n and an increase in isothermal crystallization temperature led to an increase in the induction time. The maximum temperature at which the transcrystalline layer can be optically observed increased with the increase of M n . The growth rate of transcrystallinity decreased with the increasing M n and crystallization temperature. Moreover, selective melting of the transcrystalline layers confirmed that it was merely composed of α form crystal for all composites.

Nucleation during solidification in multi-component alloys is a complex process that comprises competition between different crystalline phases as well as chemical composition and ordering. Here, we combine transition interface sampling with an extensive committor analysis to investigate the atomistic mechanisms during the initial stages of nucleation in Ni 3 Al. The formation and growth of crystalline clusters from the melt are strongly influenced by the interplay between three descriptors: the size, crystallinity, and chemical short-range order of the emerging nuclei. We demonstrate that it is essential to include all three features in a multi-dimensional reaction coordinate to correctly describe the nucleation mechanism, where, in particular, the chemical short-range order plays a crucial role in the stability of small clusters. The necessity of identifying multi-dimensional reaction coordinates is expected to be of key importance for the atomistic characterization of nucleation processes in complex, multi-component systems.

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