Applied Physics

Watching Crystals Grow

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Science  20 Aug 2004:
Vol. 305, Issue 5687, pp. 1079
DOI: 10.1126/science.305.5687.1079d

Solvents are commonly used to process polymers because they make it possible to cast thin films or to spin strong fibers that cannot be fabricated directly from the melt. Solvents can also change the stability of certain morphologies or crystal forms, as is the case for syndiotactic polystyrene (s-PS); solvent treatment leads to less stable helical crystal forms that cannot be reached via heat treatment alone.

Gupper et al. have applied Fourier transform infrared (FT-IR) imaging to track the motion of toluene through s-PS and simultaneously to observe local changes in crystallinity. Toluene was introduced orthogonally to the IR beam, and specific IR bands were monitored over time. The diffusion of toluene was found to obey Fick's Law. However, the crystallization process at the surface occurred much faster than previous studies had indicated, which suggests that the notion that there is a delay period during which critical sequence lengths organize may not be true. They also found that there is a minimum solvent concentration needed for crystallization to occur, but that longer exposure times do not increase the overall crystal fraction. — MSL

Macromolecules 10.1021/ma049313v (2004).

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