中国物理B ›› 2006, Vol. 15 ›› Issue (1): 163-171.doi: 10.1088/1009-1963/15/1/026

• CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES • 上一篇    下一篇

Molecular theory of nematic liquid crystals viewed as effect of collective excitation in ferromagnetic systems

刘建军1, 沈曼1, 刘晓静1, 杨国琛2   

  1. (1)College of Physics, Hebei Normal University, Shijiazhuang 050016, China; (2)Institute of Physics, Hebei University of Technology, Tianjin 300130, China
  • 收稿日期:2005-04-08 修回日期:2005-05-26 出版日期:2006-01-20 发布日期:2006-01-20
  • 基金资助:
    Project supported by the Hebei Natural Science Foundation, China (Grant No A2004000140) and the Natural Science Foundation of Hebei Educational Committee, China (Grant No 2003107).

Molecular theory of nematic liquid crystals viewed as effect of collective excitation in ferromagnetic systems

Liu Jian-Jun (刘建军)a, Shen Man (沈曼)a, Liu Xiao-Jing (刘晓静)a, Yang Guo-Chen (杨国琛)b   

  1. a College of Physics, Hebei Normal University, Shijiazhuang 050016, China; b Institute of Physics, Hebei University of Technology, Tianjin 300130, China
  • Received:2005-04-08 Revised:2005-05-26 Online:2006-01-20 Published:2006-01-20
  • Supported by:
    Project supported by the Hebei Natural Science Foundation, China (Grant No A2004000140) and the Natural Science Foundation of Hebei Educational Committee, China (Grant No 2003107).

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摘要： We develop a microscopic theory of the nematic phase with consideration of the effect of the collective excitation on properties of nematic liquid crystals. The model is based on the Heisenberg's exchange model of the ferromagnetic materials. Since the orientation of the molecular long axis and the angular momentum of the molecule rotating around its long axis have the same direction, operators can be introduced to research the nematic liquid crystals. Using the lattice model and the Holstein--Primakoff transformation, the Hamiltonian of the system can be obtained, which has the same form as that of the ferromagnetic substance. The relation between the order parameter and reduced temperature can be gotten. It is in good agreement with the experimental results in the low temperature region, the accordance is better than that of the molecular field theory and the computer simulation. In high temperature region close to the transition point, by considering the effect of the higher-order terms in the Hamiltonian, theoretical prediction is in better agreement with the experiment. That indicates the many-body effect is important to nematic liquid crystals.

Abstract: We develop a microscopic theory of the nematic phase with consideration of the effect of the collective excitation on properties of nematic liquid crystals. The model is based on the Heisenberg's exchange model of the ferromagnetic materials. Since the orientation of the molecular long axis and the angular momentum of the molecule rotating around its long axis have the same direction, operators can be introduced to research the nematic liquid crystals. Using the lattice model and the Holstein--Primakoff transformation, the Hamiltonian of the system can be obtained, which has the same form as that of the ferromagnetic substance. The relation between the order parameter and reduced temperature can be gotten. It is in good agreement with the experimental results in the low temperature region, the accordance is better than that of the molecular field theory and the computer simulation. In high temperature region close to the transition point, by considering the effect of the higher-order terms in the Hamiltonian, theoretical prediction is in better agreement with the experiment. That indicates the many-body effect is important to nematic liquid crystals.

Key words: nematic liquid crystals, collective excitation, order parameters

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)