From Small Beginnings

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Science  06 Sep 2002:
Vol. 297, Issue 5587, pp. 1611
DOI: 10.1126/science.297.5587.1611b

Chainlike polymers are often processed under high-flow fields in order to extend and align the chains, which accelerates the growth rate of crystals. Under quiescent conditions, chain-folded crystals form, and these can grow as secondary crystals on an extended chain backbone, resembling kabobs stuck on a skewer. This shish-kebab morphology was postulated 45 years ago and has recently been observed with atomic force microscopy. Hu et al. have used simulations to study the nucleating influence of a single extended chain on the secondary crystallization. Even though the shish is made up of extended chains, the kabob thickness is only a fraction of the full chain length; the kabob grows outward through back-and-forth folding of the chain. At lower temperatures, the secondary nucleation rate increases, and two growing nuclei can merge and taper into a single kabob. The authors find that crystallization can be advanced by a shish that is only one chain wide. This suggests that alignment of the polymer chains may accelerate not only the growth rates of the polymer crystals in both extended and folded forms, but also the nucleation rates. — MSL

Macromolecules 10.1021/ma0255581 (2002).

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