Phase diagrams of phenyl benzoate side group liquid crystal polymers and similar low molecular mass liquid crystals

Abstract

The miscibility of a phenyl benzoate side group liquid crystal polymer (LCP) with a similar low molecular mass liquid crystal (LC) has been studied as a function of temperature and molecular mass by calorimetry and optical microscopy. The nematic to isotropic transition temperatures of the pure polymer and the LC are 112 and 48.8°C, respectively. There is a broad miscibility gap for polymer weight fractions below 50% and temperatures below 72°C. A relatively small increase in miscibility is observed when the polymer molecular mass decreases. In the systems investigated here, the experimental temperature/weight fraction phase diagram is well reproduced by a mean field model combining the Flory-Huggins model for isotropic mixing and the Maier-Saupe theory for nematic ordering. Consequences of the miscibility gap with regard to the behaviour of LCP brushes swollen in a similar low molecular mass nematic liquid crystal are discussed.