Effect of chain stiffness on the competition between crystallization and glass-formation in model unentangled polymers
HT Nguyen and TB Smith and RS Hoy and NC Karayiannis, JOURNAL OF CHEMICAL PHYSICS, 143, 144901 (2015).
We map out the solid-state morphologies formed by model soft-pearl- necklace polymers as a function of chain stiffness, spanning the range from fully flexible to rodlike chains. The ratio of Kuhn length to bead diameter (l(K)/r(0)) increases monotonically with increasing bending stiffness k(b) and yields a one-parameter model that relates chain shape to bulk morphology. In the flexible limit, monomers occupy the sites of close-packed crystallites while chains retain random-walk-like order. In the rodlike limit, nematic chain ordering typical of lamellar precursors coexists with close-packing. At intermediate values of bending stiffness, the competition between random-walk-like and nematic chain ordering produces glass-formation; the range of k(b) over which this occurs increases with the thermal cooling rate vertical bar(T) over dot vertical bar implemented in our molecular dynamics simulations. Finally, values of k(b) between the glass-forming and rodlike ranges produce complex ordered phases such as close-packed spirals. Our results should provide a useful initial step in a coarse-grained modeling approach to systematically determining the effect of chain stiffness on the crystallization-vs-glass-formation competition in both synthetic and colloidal polymers. (C) 2015 AIP Publishing LLC.
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