Phase behaviors of binary and ternary mixtures of liquid crystals, three series of trans-4-n-alkylcyclohexane carboxylic acid cyanophenol ester (alkyl=propyl (C3), butyl(C4), pentyl(C5) and trans-1-n-butyl-4-(4'-cyanophenyl) cyclohexane (PCH4) synthesized, were investigated with DSC to determine the transition temperatures of mixtures and with Polarizing microscope for observing the textures of liquid crystalline phase.
The transition temperatures between solid and liquid crystal, and between liquid crystal and isotropic liquid showed the broadest range of temperatures of nematic liquid crystals near the eutectic mixtures. In the phase transition from nematic to solid, the binary mixtures of C3-C4 and C4-C5 formed solid solutions, maybe due to the similarities in molecular structure and chain length but those of PCH4-C3, PCH4-C5 and C3-C5 did not.
Considering the excess free energy for solid-mesophase transition, the phase diagrams were calculated satisfactorily with the incorporation of the chemical theory to the activity coefficients of mesophase.
All of the binary or ternary mixtures showed the nematic texture above the eutectic temperature and the binary mixture of C3-C5 showed the smectic phase between 18-22℃
In the ternary mixture of PCH4-C3-C5, its transition temperature significantly decreased and its eutectic temperature appeared at 8℃, In the calculation using the apparent melting enthalpy of each component, the eutectic temperature and composition were 7.6℃ and 30.88% PCH4, 29.97% C3 respectively, which is in good agreement with the experimental result.
