Liquid Crystal and Its Quasi-Equilibrium Phase Separation

Thermally induced phase separation of liquid crystal and pre-polymer mixtures were studied using liquid crystal K15 and K21, two of the four components of commercially available liquid crystal E7 and a thiol-ene pre-polymer, UV1. The main purpose of this study was to construct quasi-equilibrium phase diagrams of K15/UV1 and K21/UV1. Phase separation of liquid crystal/pre-polymer system was observed using polarized optical microscopy. Liquid crystal/Pre-polymer mixtures (K15/UV1 and K21/UV1 mixtures) were prepared with increasing percentage of liquid crystal in pre-polymer. Each sample was then subjected to quasi-equilibrium thermal cycles. Phase separation was detected by the onset of the formation of liquid crystal droplets in the homogeneous mixture. A quasi-equilibrium phase diagram of K15/UV1 was constructed by plotting quasi-equilibrium phase separation temperature with respect to K15 percentage in UV1 pre-polymer. For K21/UV1 mixtures, quasi-equilibrium thermal cycles resulted in crystallization. We decided to run slow-rate thermal cycles instead of quasi-equilibrium thermal cycles. Phase diagram of K21/UV1 was constructed using the slow-rate thermal cycle data.