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研究了由2种十字形液晶分子构成的混合物系统。假设分子间的简单相互作用,运用平均场理论,得到混合物液晶在分子结构参数rA(A类液晶分子短、长棒比)和约化温度t平面内的相图。结果表明,相图存在一Landau点,系统经此点由各向同性相可直接进入双轴向列相。此点所对应的优化分子结构与A,B类分子结构、混合比有关。按等比例混合的棒状、圆盘状液晶分子系统即具有此优化分子结构。随着B类液晶分子短、长棒的比值rB增加,Landau点处的rA减少。对比混合物系统和相分离系统的自由能曲线,发现增加异种液晶分子间的相互作用强度,升高温度,缩小异种分子间的形状差异可使系统不发生相分离。

A binary mixture of two different cross-like molecules is considered.Supposing a simple in-teraction model between molecules,and using mean field approximation,phase diagrams in the plane of molecular structure parameter rA (the length ratio of short and long rods of A type molecule)and reduced temperature t are obtained.The results show there exists a Landau point,through which the binary mixture can enter directly from isotropic phase to biaxial nematic phase.The optimal molecular structure at this point depends on the structures,the number ratio of A and B type molecules.Mixing rod-like and plate-like molecules with equal numbers will lead to this optimal structure.When rB ,the length ratio of short and long rods of B type molecules increases,the rA value at Landau point decrea-ses.Comparing the free energy curves corresponding to mixed system and phase separated system completely,it is found that by increasing the interaction strength between different types of mole-cules,increasing temperature,decreasing the structural difference between different molecules,the chance of phase separation will be reduced.