中国物理B ›› 2007, Vol. 16 ›› Issue (8): 2296-2303.doi: 10.1088/1009-1963/16/8/023

• GENERAL • 上一篇    下一篇

Density functional theory for molecular orientation of hard rod fluids in hard slits

曹达鹏, 程礼盛, 汪文川   

  1. Division of Molecular and Materials Simulation, Key Laboratory of Nanomaterials, Ministry of Education Beijing University of Chemical Technology, Beijing 100029, China
  • 收稿日期:2007-01-10 修回日期:2007-03-01 出版日期:2007-08-20 发布日期:2007-08-20
  • 基金资助:
    Project supported by the National Natural Science Foundation of China (Grant No 20646001), the Beijing Novel Program (Grant No 2006B17), the Program for New Century Excellent Talents in University (NCET), the ``Chemical Grid Program" and the Excellent Tal

Density functional theory for molecular orientation of hard rod fluids in hard slits

Cao Da-Peng(曹达鹏)†,Cheng Li-Sheng(程礼盛), and Wang Wen-Chuan (汪文川)   

  1. Division of Molecular and Materials Simulation, Key Laboratory of Nanomaterials, Ministry of Education Beijing University of Chemical Technology, Beijing 100029, China
  • Received:2007-01-10 Revised:2007-03-01 Online:2007-08-20 Published:2007-08-20
  • Supported by:
    Project supported by the National Natural Science Foundation of China (Grant No 20646001), the Beijing Novel Program (Grant No 2006B17), the Program for New Century Excellent Talents in University (NCET), the ``Chemical Grid Program" and the Excellent Tal

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摘要： A density functional theory (DFT) is used to investigate molecular orientation of hard rod fluids in a hard slit. The DFT approach combines a modified fundamental measure theory (MFMT) for excluded-volume effect with the first order thermodynamics perturbation theory for chain connectivity. In the DFT approach, the intra-molecular bonding orientation function is introduced. We consider the effects of molecular length (i.e. aspect ratio of rod) and packing fraction on the orientations of hard rod fluids and flexible chains. For the flexible chains, the chain length has no significant effect while the packing fraction shows slight effect on the molecular orientation distribution. In contrast, for the hard rod fluids, the chain length determines the molecular orientation distribution, while the packing fraction has no significant effect on the molecular orientation distribution. By making a comparison between molecular orientations of the flexible chain and the hard rod fluid, we find that the molecular stiffness distinctly affects the molecular orientation. In addition, partitioning coefficient indicates that the longer rodlike molecule is more difficult to enter the confined phase, especially at low bulk packing fractions.

Abstract: A density functional theory (DFT) is used to investigate molecular orientation of hard rod fluids in a hard slit. The DFT approach combines a modified fundamental measure theory (MFMT) for excluded-volume effect with the first order thermodynamics perturbation theory for chain connectivity. In the DFT approach, the intra-molecular bonding orientation function is introduced. We consider the effects of molecular length (i.e. aspect ratio of rod) and packing fraction on the orientations of hard rod fluids and flexible chains. For the flexible chains, the chain length has no significant effect while the packing fraction shows slight effect on the molecular orientation distribution. In contrast, for the hard rod fluids, the chain length determines the molecular orientation distribution, while the packing fraction has no significant effect on the molecular orientation distribution. By making a comparison between molecular orientations of the flexible chain and the hard rod fluid, we find that the molecular stiffness distinctly affects the molecular orientation. In addition, partitioning coefficient indicates that the longer rodlike molecule is more difficult to enter the confined phase, especially at low bulk packing fractions.

Key words: density functional theory, rodlike chain, molecular orientation, flexible chain

中图分类号:  (Theory and models of liquid structure)

  • 61.20.Gy
61.25.Em (Molecular liquids) 65.20.-w (Thermal properties of liquids)