EFFECT OF MOLAR-MASS OF AN EPOXY OLIGOMER ON THE PHASE-SEPARATION IN EPOXY BASED POLYMER-DISPERSED LIQUID-CRYSTALS

Polymer dispersed liquid crystals based on epoxy-amine crosslinked mat rices and a nematic liquid crystal, E7, have been studied over the cou rse of polymerisation, i.e. as a function of the polymerisation conver sion. The influence of epoxy oligomer molar mass on the initial temper ature-concentration and the temperature-conversion phase diagrams has been investigated. An increase of the epoxy oligomer molar mass greatl y reduces the initial liquid crystal solubility and brings the cloud p oints to earlier polymerisation conversions, which have been quantifie d. Thus the phase separation is markedly enhanced. The temperature-con version phase diagrams have been characterised at two isothermal polym erisation temperatures for one liquid crystal composition (50 wt.%). T hese diagrams (isotropic-nematic and nematic-isotropic transition temp eratures) are shown to obey master curves when the epoxy molar mass is varied. Finally, the size of the liquid crystal droplets is shown to decrease when the epoxy molar mass increases. This effect is mainly du e to the viscosity increase resulting from the oligomer mass increase. Viscosity measurements were made at intervals during polymerisation.