RHEOLOGY OF LIQUID-CRYSTALLINE POLYMERS

The flow of the nematic phase of liquid crystalline polymers exhibits a much more complex phenomenology than that shown by either an ordinary polymer or a low molecular weight nematic. For example, the normal stress effect in a shear flow, which in ordinary polymers has always a positive sign, shows two sign reversals with increasing the rate of shear in nematic polymers. At high shear rates, the observed behaviour appears to be correctly predicted by a mean field theory of rodlike molecules. At low shear rates, where the same theory predicts that the nematic phase is of the tumbling type, it appears necessary to introduce into the Leslie-Ericksen theory the concept of a distortion saturation.