RHEOLOGY OF A MIXTURE OF LIQUID-CRYSTAL POLYMERS IN SOLUTION

The rheological behavior of a mixture of two liquid-crystal polymers, hydroxypropyl cellulose and ethyl cellulose, in acetone solution is st udied. The total polymer concentration in the solvent is held constant (40%) as the ratio of the two polymers is varied. The mixtures are an isotropic, isotropic, or biphasic (isotropic/anisotropic), depending o n the concentration. Curves of viscosity vs shear rate for all the mix tures studied show three regions of viscosity, as described by Onogi a nd Asada for liquid-crystal polymers. The viscosity as a function of t he weight ratio of the two polymers at constant shear rate exhibits de viations from additivity of viscosities of the two components at all c oncentrations. In mixtures of two polymers in the melt, deviations are also observed; the negative ones are attributed to phase separation a nd the positive ones to homogenous mixing (comparison with the phase d iagram). All the mixtures studied (anisotropic, isotropic, or biphasic ), show ranges of shear rates where the first normal-stress difference is negative, as is generally observed for anisotropic liquid-crystal polymers. It is concluded that the isotropic solutions become anisotro pic under shear, as they are not far from the critical concentration. (C) 1994 John Wiley & Sons, Inc.