Effect of molecular flexibility of Lennard-Jones chains on vapor-liquid interfacial properties.
Effect of molecular flexibility of Lennard-Jones chains on vapor-liquid interfacial properties.
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伦纳德-琼斯链的分子柔性对气液界面性质的影响。
DOI：
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发表时间：
2014
影响因子：
4.4
通讯作者：
L. G. Macdowell
中科院分区：
文献类型：
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作者：
F. J. Blas;A. I. Moreno;J. Algaba;F. J. Martínez;L. G. Macdowell
我们通过直接模拟汽液界面，确定了由切向键合的Lennard-Jones单体单元形成的全柔性短链的界面性质。将得到的结果与文献中先前确定的由相同链长形成的刚性线性链所对应的结果进行比较[F]。J.布拉斯，a.i.m.v。布拉沃，J. M. Míguez， M. M. Piñeiro，和L. G.麦克道尔，J. Chem。物理学报，2003,27(5):559 - 567。利用janeek [J]的一种改进版的非均匀远程修正来解释势的全远程尾。理论物理。化学。[J] .中国科学：地球科学[J]。化学。物理学报，131,074705(2008)]对球形以及刚性和柔性分子系统都有效。考虑了三种不同的模型体系，包括每个分子3、5和6个单体。在正则系综中进行了模拟，并采用测试区法对气液界面张力进行了评估。除了表面张力外，我们还获得了密度分布、共存密度、临界温度和密度以及界面厚度随温度的函数，特别注意了链长和刚性对这些性能的影响。根据我们的研究结果，增加链长（在固定温度下）的主要作用是锐化气液界面和增加双相共存区域的宽度。结果表明，随着分子链的变长，界面厚度减小，表面张力增大。由相同数量的单体单元组成的完全柔性链和刚性线性链的预测比较表明，增加柔性，即从刚性线性链过渡到完全柔性链的主要影响是：(a)减小液体和蒸汽密度之间的差异；(b)降低临界温度，提高临界密度；(c)平滑沿界面区域的密度分布；(d)增加界面厚度；(e)减小汽液表面张力。
We have determined the interfacial properties of short fully flexible chains formed from tangentially bonded Lennard-Jones monomeric units from direct simulation of the vapor-liquid interface. The results obtained are compared with those corresponding to rigid-linear chains formed from the same chain length, previously determined in the literature [F. J. Blas, A. I. M.-V. Bravo, J. M. Míguez, M. M. Piñeiro, and L. G. MacDowell, J. Chem. Phys. 137, 084706 (2012)]. The full long-range tails of the potential are accounted for by means of an improved version of the inhomogeneous long-range corrections of Janeček [J. Phys. Chem. B 129, 6264 (2006)] proposed recently by MacDowell and Blas [J. Chem. Phys. 131, 074705 (2008)] valid for spherical as well as for rigid and flexible molecular systems. Three different model systems comprising of 3, 5, and 6 monomers per molecule are considered. The simulations are performed in the canonical ensemble, and the vapor-liquid interfacial tension is evaluated using the test-area method. In addition to the surface tension, we also obtained density profiles, coexistence densities, critical temperature and density, and interfacial thickness as functions of temperature, paying particular attention to the effect of the chain length and rigidity on these properties. According to our results, the main effect of increasing the chain length (at fixed temperature) is to sharpen the vapor-liquid interface and to increase the width of the biphasic coexistence region. As a result, the interfacial thickness decreases and the surface tension increases as the molecular chains get longer. Comparison between predictions for fully flexible and rigid-linear chains, formed by the same number of monomeric units, indicates that the main effects of increasing the flexibility, i.e., passing from a rigid-linear to a fully flexible chain, are: (a) to decrease the difference between the liquid and vapor densities; (b) to decrease the critical temperature and to increase the critical density; (c) to smooth the density profiles along the interfacial region; (d) to increase the interfacial thickness; and (e) to decrease the vapor-liquid surface tension.