PHASE DIAGRAMS AND PHASE SEPARATION DYNAMICS IN MIXTURES OF SIDE-CHAIN LIQUID CRYSTALLINE POLYMERS AND LOW MOLAR MASS LIQUID CRYSTALS

摘要

Miscibility phase diagrams and phase separation dynamics in mixtures of side-chain liquid crystalline polymers (SCLCP) and monomeric liquid crystals have been investigated experimentally in order to test with theoretical predictions. The theoretical calculation on equilibrium phase diagrams of binary nematic mixtures involves a combination of the Flory-Huggins (FH) free energy for isotropic mixing in conjunction with the Maier-Saupe (MS) free energy for nematic ordering of the mesogenic units. Two orientational order parameters and two nematic-isotropic (NI) transitions of the constituent mesogens are taken into consideration in the calculation. This combined FH-MS theory predicts a variety of phase diagrams depending on the relative strength of the cross-interaction between two dissimilar mesogens as compared to that in the same species. A series of epoxy resins [ethylene glycol glycidyl ether (EGDE)] grafted with mesogenic amines 4-(omega-aminoalkoxy)-4'-cyanobiphenyl were synthesized. The temperature-composition phase diagrams of these SCLCP mixtures and the eutectic low molar mass liquid crystal (E7) have been established by a cloud point method. The calculated phase diagrams are found to accord well with the experimental phase diagrams. The dynamics of phase separation has been investigated by means of time-resolved light scattering and optical microscopy. The time evolution of the structure factor following various temperature quenches into the nematic-liquid and/or nematic-nematic coexistence regions has been analyzed in terms of a power law scheme. [References: 27]