Molecular Dynamics Simulation of Surface Nucleation during Growth of an Alkane Crystal
A Bourque and CR Locker and GC Rutledge, MACROMOLECULES, 49, 3619-3629 (2016).
Crystal, growth from the melt of n-pentacontane (C50) was studied by molecular dynamics simulation. Quenching below the melting temperature gives rise to propagation of the crystal growth front into the C50 melt from a crystalline polyethylene surface. By tracking the location of the crystal-melt interface, crystal growth rates between 0.02 and 0.05 m/s were observed, for quench depths of 10-70 K below the melting point. These growth rates compare favorably with those from a previous study by Waheed et al. Polymer 2005, 46, 8689-8702. Next, surface nucleation was identified with the formation of two-dimensional clusters of crystalline sites within layers parallel to the propagating growth front. Critical nucleus sites, waiting times, and rates for surface nucleation were estimated by a mean first passage time analysis. A surface nucleation rate of similar to 0.05 nm(-2) ns(-1) was observed, and it was nearly temperature-independent. Postcritical "spreading" of the surface nuclei to form a completely crystallized layer slowed with deeper supercooling.
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