Acceleration mechanism of growth rates under shear flow due to the oriented melt-the novel morphology of spiral crystal (spiralite)

Kaori Watanabe, Kiyoka Okada, Akihiko Toda, Shinichi Yamazaki, Takashi Taniguchi, Kiyohito Koyama, Koji Yamada, Masamichi Hikosaka

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

Isothermal crystallization of three-dimensional (3D) spherulites from the bulky melt under low shear rate flow was studied based on new in situ observation along a direction perpendicular to the flow velocity gradient plane (XZ plane) by means of optical microscope, where X- and Z-axes are perpendicular and parallel to the flow direction, respectively. Spherulites are rotating. A novel "spiral pattern" was found on the surface of the rotating "half-spherulite" near the surface of the melt for the first time. The half-spherulite is named "spiralite" which enabled us to have a visible image of the rotation of spherulite. Hence, we could detect the growth rate around the Z-axis V(Z) and that around the X-axis V(X) by using the spiral pattern. We could experimentally obtain V(Z) > V(X) in this study. From kinetic viewpoint, this fact indicates that free energy for formation of a critical nucleus around the Z-axis is smaller than that around the X-axis. From this, it is concluded that the "oriented melt" is formed around the Z-axis. We proved it theoretically by showing that micro shear rate γ̇(Z) on the interface around the Z-axis significantly increases and chains will be elongated even when macro γ̇ is low (γ̇ < 10 s-1). With increase of γ̇(Z), the chain elongation will overcome the entropic relaxation, that results in formation of the "oriented melt". Crystallization mechanism under low shear flow is proposed that the growth rate of spherulite or shish is accelerated around interface, due to formation of the "oriented melt". Finally, we proposed a possible relationship between melt structure and crystallization under anisotropic and Isotropic external fields.

Original languageEnglish
Pages (from-to)1515-1524
Number of pages10
JournalMacromolecules
Volume39
Issue number4
DOIs
Publication statusPublished - Feb 21 2006
Externally publishedYes

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

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