中国物理B ›› 2005, Vol. 14 ›› Issue (2): 393-397.doi: 10.1088/1009-1963/14/2/030

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Molecular field theory for nematic liquid crystal film with finite layers

张志东, 李静, 魏怀鹏   

  1. School of Sciences, Hebei University of Technology, Tianjin 300130, China
  • 收稿日期:2004-05-28 修回日期:2004-09-29 出版日期:2005-03-02 发布日期:2005-03-02
  • 基金资助:
    Project supported by the Natural Science Foundation of Hebei Province, China (Grant No 103002), and the Key Subject Construction Project of Hebei Provincial University.

Molecular field theory for nematic liquid crystal film with finite layers

Zhang Zhi-Dong (张志东), Li Jing (李静), Wei Huai-Peng (魏怀鹏)   

  1. School of Sciences, Hebei University of Technology, Tianjin 300130, China
  • Received:2004-05-28 Revised:2004-09-29 Online:2005-03-02 Published:2005-03-02
  • Supported by:
    Project supported by the Natural Science Foundation of Hebei Province, China (Grant No 103002), and the Key Subject Construction Project of Hebei Provincial University.

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摘要： The nematic liquid crystal film composed of n molecular layers is studied based upon a spatially anisotropic pair potential, which reproduces approximately the elastic free energy density. On condition that the system has perfect nematic order, as in the Lebwohl—Lasher model, the director in the film is isotropic. The effect of the temperature is investigated by means of molecular field theory. Some new results are obtained. Firstly, symmetry breaking takes place when taking account of the temperature, and the state with the director along the normal of the film has the lowest free energy. Secondly, the N—I phase transition temperature increases as an effect of finite sizes instead of decreasing as in the Lebwohl—Lasher model. Thirdly, the nematic order is induced in the layers near the surface in the isotropic phase.

关键词: spatially anisotropic pair potential, perfect nematic order, effect of temperature, molecular field theory

Abstract: The nematic liquid crystal film composed of n molecular layers is studied based upon a spatially anisotropic pair potential, which reproduces approximately the elastic free energy density. On condition that the system has perfect nematic order, as in the Lebwohl—Lasher model, the director in the film is isotropic. The effect of the temperature is investigated by means of molecular field theory. Some new results are obtained. Firstly, symmetry breaking takes place when taking account of the temperature, and the state with the director along the normal of the film has the lowest free energy. Secondly, the N—I phase transition temperature increases as an effect of finite sizes instead of decreasing as in the Lebwohl—Lasher model. Thirdly, the nematic order is induced in the layers near the surface in the isotropic phase.

Key words: spatially anisotropic pair potential, perfect nematic order, effect of temperature, molecular field theory

中图分类号:  (Molecular and microscopic models and theories of liquid crystal structure)

  • 61.30.Cz
64.70.M- (Transitions in liquid crystals)