Rheological response of mesophase transition of a main-chain liquid crystalline poly (aryl ether ketone)

Abstract

The lg G’-lg G’’ plot known as Han plot in dynamic rheological measurement was used in the characterization of the anisotropic-isotropic, i.e nematic-isotropic transition of a thermotropic liquid crystalline poly(aryl ether ketone) synthesized by copolymerization of 4,4’-biphendiol, 4,4’-difluobenzophenone and t-butylhydroquinone. Dynamic frequency sweeps were carried on Advanced Rheolmetric Expansion System to give lg G’-lg G’’ plots at different temperatures covering the whole temperature range from nematic phase to isotropic phase. It was found that the slopes of the Han plots gradually approach 2.46 with increasing temperature before reaching the isotropic point. In the isotropic phase the slopes become completely independent of temperature. Based on this observation, the nematic-isotropic transition is considered to be the temperature after which the slopes of the plots become constant, which is in our case 2.46.