Snapshots of Crystallization

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Science  09 Feb 2001:
Vol. 291, Issue 5506, pp. 949
DOI: 10.1126/science.291.5506.949C

When polymers crystallize, they can adopt a spherulitic morphology, where the lamellae (ribbons of folded chains) grow outward radially, or a shish kabob morphology, which results if the polymer chains are highly oriented. What is unclear from models of polymer crystallization is how growth progresses and how lamellae interact when they come into contact with each other.

Now, two atomic force microscopy (AFM) studies have imaged these processes. Li et al. show that secondary lamellae, which give rise to the curvature in a spherulite, form through branching caused by secondary nuclei that originate from leftover chain segments trapped in the parent lamellae (cilia). Upon impingement of two lamellae, crystalline growth does not necessarily halt. Hobbs and Miles tackled a different problem, the influence of processing conditions on polymer morphology. By shearing a polyethylene melt and then cooling it to just below its melt temperature, they observed the formation of the shish kabob morphology and, in particular, the interdigitation of the kabob branches that is believed to play a role in the toughness of oriented structures. — MSL

Macromolecules34, 316 (2001); Macromolecules34, 353 (2001).

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