Molecular theory of nematic liquid crystals viewed as effect of collective excitation in ferromagnetic systems |
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| Authors: | Liu Jian-Jun Shen Man Liu Xiao-Jing and Yang Guo-Chen |
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| Affiliation: | College of Physics, Hebei Normal University, Shijiazhuang 050016, China; Institute of Physics, Hebei University of Technology, Tianjin 300130, China |
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| 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. |
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| Keywords: | nematic liquid crystals collective excitation order parameters |
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