Solid-liquid transitions in homogenous ovalene, hexabenzocoronene and circumcoronene clusters: A molecular dynamics study
Solid-liquid transitions in homogenous ovalene, hexabenzocoronene and circumcoronene clusters: A molecular dynamics study
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DOI：
10.1016/j.combustflame.2014.07.025
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发表时间：
2015-02-01
影响因子：
4.4
通讯作者：
Kraft, Markus
中科院分区：
文献类型：
--
作者：
Chen, Dongping;Akroyd, Jethro;Kraft, Markus
用分子动力学模拟方法研究了卵苯（C32H14）、六苯并蔻（C42H18）和环蔻（C54H18）团簇的熔化行为。分子间能量和林德曼指数的演变被用来确定集团熔点。通过对团簇模拟数据的线性外推，估算了各物质的体相熔点，对卵苯的体相熔点与实验测定的相变温度符合较好。我们发现，笔式稠合多环芳烃的体熔点与其尺寸呈线性关系。外推的六苯并蔻和环蔻的本体熔点符合这种线性关系非常好。根据组成团簇的多环芳烃的大小，构建了一个相图，将团簇的相分为三个区域：液体区域、大小相关区域和固体区域。大小相关区域突出显示了簇的相位也取决于簇大小的范围。由于相似的尺寸和密度，具有50个分子的簇被认为是新生烟灰颗粒的类似物，而PAH分子的本体系统被视为成熟烟灰颗粒的近似物。相图的详细研究表明，在1500 K时，初生和成熟碳烟颗粒在固态下的临界尺寸分别为C76H22和C54H18。(C)2014燃烧研究所爱思唯尔公司出版All rights reserved.
The melting behaviour of ovalene (C32H14), hexabenzocoronene (C42H18) and circumcoronene (C54H18) clusters is analysed using molecular dynamics simulations. The evolution of the intermolecular energy and the Lindemann Index is used to determine the cluster melting points. The bulk melting point of each material is estimated by linear extrapolation of the cluster simulation data, The value obtained for ovalene is in good agreement with the phase-transition temperature determined by experiment. We find that the bulk melting point of pen-condensed PAHs is linearly related to their size. The extrapolated hexabenzocoronene and circumcoronene bulk melting points agree with this linear relationship very well. A phase diagram is constructed which classifies the phase of a cluster into three regions: a liquid region, a size-dependent region and a solid region according to the size of the PAHs which build up the cluster. The size-dependent region highlights the range where the phase of a cluster also depends on the cluster size. Due to the similar size and density, a cluster with 50 molecules is considered an analogue for nascent soot particles whilst the bulk system of PAH molecules is seen as an approximation to mature soot particles. A detailed investigation of the phase diagram reveals that the critical size for nascent and mature soot particles in the solid state is C76H22 and C54H18 at 1500 K respectively. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.