Materials Science

The Order of Ordering

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Science  01 Feb 2008:
Vol. 319, Issue 5863, pp. 549
DOI: 10.1126/science.319.5863.549b

When polymers partially crystallize from the melt state, they often pack by formation of lamellae, or stacks of folded, ordered chain segments separated by regions of noncrystalline material. Prior studies suggested that crystallization might be occurring through a spinodal-assisted ordering, associated with the formation of a smectic-like liquid crystalline phase that preceded the formation of the first nuclei. Panine et al. used high-brilliance x-ray scattering to look at the earliest stages of crystallization in isotatic polypropylene. They found ordering in the wide-angle x-ray scattering (WAXS) data before the small-angle x-ray scattering (SAXS) data, thus supporting the formation of ordered nuclei at the local scale before more global, liquid crystalline-like ordering. This finding contrasted with earlier SAXS before WAXS data used to support the spinodal hypothesis, which may have been due to detector limitations. More intriguing is that the earliest SAXS peaks support a smectic-like ordering of the nuclei (rather than just the polymer chains); thus, at these intermediate times, the nuclei may arrange into an ordered structure before growing into the large well-organized lamellae as proposed in a number of recent simulation studies. — MSL

Polymer 10.1016/j.polymer.2007.12.026 (2008).

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