十字形液晶分子混合物系统的相变

Abstract

A binary mixture of two different cross-like molecules is considered.Supposing a simple interaction 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 rAvalue at Landau point decreases.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 molecules,increasing temperature,decreasing the structural difference between different molecules,the chance of phase separation will be reduced.