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 sizes, waiting times, and rates for surface nucleation were estimated by a mean first passage time analysis. A surface nucleation rate of ∼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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机译:通过分子动力学模拟研究了正戊金刚烷(C50)熔体的晶体生长。在熔化温度以下淬火会导致晶体生长前沿从结晶聚乙烯表面传播到C50熔体中。通过追踪晶体与熔体界面的位置,观察到晶体生长速率在0.02至0.05 m / s之间,淬火深度低于熔点10–70K。这些增长率与Waheed等人先前的研究相提并论。 [Polymer 2005,46,8689-8702]。接下来,通过在平行于增长的生长前沿的层内形成二维的晶体位点簇来识别表面成核。临界核的大小,等待时间和表面成核的速率通过平均首次通过时间分析来估算。观察到表面成核率为〜0.05nm -1 ns -1,并且几乎与温度无关。后临界“扩散”表面核以形成完全结晶的层,并随着更深的过冷而减慢。
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