The thermotropic liquid crystalline behavior of mesophase pitches with different chemical structures

Abstract Chemical structure-dependent liquid crystalline behaviors of two commercial mesophase pitches, M-AR and T-MP, which are synthesized with different raw materials of naphthalene and coal tar, respectively, were comparatively examined. The NMR analysis together with preparation procedure enabled us to suggest that M-AR consisted of linear semi-rigid molecules and T-MP, irregularly shaped rigid molecules. Between 320 and 370 °C M-AR showed marbled texture whereas T-MP, a change from schlieren/marbled to schlieren texture. WXRD results indicated that M-AR exhibited a gradual change of d 002 and L c with temperature but T-MP, a drastic change. A point shear stress made M-AR produce oriented flow domains but T-MP retained schlieren texture even in the oriented structure. In the temperature range producing biphase, M-AR showed a shoulder on the plot of viscosity versus temperature but T-MP, a peak. As temperature was increased M-AR gave an increase of loss tangent but a decrease of yield stress while T-MP gave a saturation point at 330 °C, at which temperature loss tangent was maximum and yield stress was minimum. Both mesophase pitches gave viscosity curves matched with the Asada–Onogi model. In the temperature range producing dispersed polydomain system, however, T-MP showed almost shear rate-independent plateau while shear-dependence was observed in M-AR.