EFFECT OF FILLERS ON THE STEADY-STATE RHEOLOGICAL BEHAVIOR OF LIQUID-CRYSTALLINE POLYMERS

The effect of fillers on the flow curves of polymeric liquid crystals is investigated. Suspensions of polystyrene particles in Liquid crysta lline solutions of hydroxypropylcellulose (HPC) in water are used. By reducing the HPC concentration an isotropic solution can be prepared. It serves as a reference to isolate the effect of the isotropic/anisot ropic structure of the suspending medium on the rheological behaviour. Suspensions in the isotropic solution behave as expected for filled v iscoelastic matrices in general. In the anisotropic medium the shear r ate rather than the shear stress seems to govern the changes in the re lative viscosity. This behaviour is clearly different from isotropic v iscoelastic media. The most dramatic effect however is that even small amounts of particles eliminate or drastically shift the region of neg ative normal stress differences. As far as the structure is concerned, microscopic observations show that particles align in anisotropic as well as in isotropic media. At rest or at relatively low shear stresse s the Liquid crystalline structure is, in the present case, hardly aff ected by the presence of the particles. If anything, it becomes more h omogeneous.