Phase diagram and evolution of mesophase structure in mixtures of a low molar mass smectic liquid crystal and a nematic side-on side-chain liquid crystalline polymer

Miscibility phase diagrams in mixtures of side-on side-chain liquid crystalline polymers (s-SCLCP) and low molar mass smectic liquid crystals (K36) have been investigated by means of polarized optical microscopy. K36 is a smectic liquid crystal that exhibits a smectic-isotropic transition at 58 degrees C and a smectic-to-crystal transition (crystallization) at 27 degrees C. The nematic/smectic phase diagram of the s-SCLCP/K36 has been analyzed by combining the Flory-Huggins (FH) free energy for isotropic demixing and the Maier-Saupe-McMillan (MSM) free energy for smectic ordering of the mesogens. This combined FH/MSM theory compares reasonably well with the observed nematic/smectic phase diagrams composed of isotropic + nematic, smectic + nematic, smectic + isotropic, pure nematic, and pure smectic regions. Several temperature quench experiments have been conducted to confirm various predicted coexistence regions. However, at present, the combined theory does not include any crystallization processes occurring at a lower temperature.