ORIENTATION-AVERAGED PAIR CORRELATIONS IN A MOLECULAR THEORY OF NEMATIC LIQUID-CRYSTALS .2.

被引:15
作者
FEIJOO, L
RAJAN, VT
WOO, CW
机构
[1] NORTHWESTERN UNIV,MAT RES CTR,EVANSTON,IL 60201
[2] NORTHWESTERN UNIV,DEPT PHYS & ASTRON,EVANSTON,IL 60201
来源
PHYSICAL REVIEW A | 1979年 / 19卷 / 03期
关键词
D O I
10.1103/PhysRevA.19.1263
中图分类号
O43 [光学];
学科分类号
070207 ; 0803 ;
摘要
In a previous paper (I) we carried out a model calculation for nematic liquid crystals which treats spatial correlations between molecules as for a classical isotropic liquid and orientational correlations in the meanfield approximation. Generalized Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) equations were derived for the density function and an orientationally averaged pair-correlation function. They were solved for a simple pairwise potential chosen to fit certain experimental data on p-azoxyanisole (PAA). A free-energy expression was obtained by identifying its Euler-Lagrange equation to the first BBGKY equation. In this paper we reformulated the molecular theory of nematic liquid crystals rigorously on the basis of a general probability distribution function PN(1,...,N). It was shown that both the mean-field theory (MFT) and the above-stated orientation-averaged pair-correlation theory (OAPC) arise from applying low-order approximations to PN. In the case of MFT, PN was approximated as a product of single-particle functions. In the case of OAPC, spatial correlations were introduced, but decoupling of spatial and orientational dependences were assumed. It is now clear how higher-order-approximation schemes can be systematically constructed. Furthermore, for each scheme chosen, the present formulation offers a uniquely consistent formula for the free energy. This places our previous work on a firm theoretical foundation. The theory in OAPC approximation was applied to model systems described by a more general pairwise potential than that employed in I. Potential parameters were chosen to mimic PAA and methoxybenzylidene butylaniline. For each substance we calculated the isotropic-nematic coexistence curve, temperature dependence of the order parameter, latent heat, and volume change at transition. The results were compared to experimental data. © 1979 The American Physical Society.
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页码:1263 / 1271
页数:9
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