MULTICRITICAL PHENOMENA IN FLOW OF VISCOELASTIC LIQUIDS - 3 - LIQUID-CRYSTALLINE POLYMERS - THE AKAY-LESLIE ANISOTROPIC LIQUID - VISCOMETRIC FUNCTIONS

The advances in determination of the rheological material functions of liquid-crystalline polymers (LCP) in a wide range of concentrations o r temperatures are briefly examined. Special attention is focused on a discussion of the concentration region of the existence of liquid-cry stalline order and textures initiated by shear flow. the phenomenologi cal rheological equation for an anisotropic liquid proposed by Akay an d Leslie (A-L model) was selected for describing the flow resistance o f LCP, and the problem of simple shear flow of a liquid was solved. It was shown that the A-L model can describe all of the basic characteri stics of the viscometric functions of LCP, including the phenomenon of negative values of the first normal stress difference for some range of concentrations and shear rates. The available data on the initial v iscosity of lyotropic LCP were classified based on the types of cohesi on (dimensionality) of the system, characterized by the exponent of th e concentration dependence of the viscosity. It was found that each ty pe of cohesion has its own kind of viscometric functions and that the A-L rheological model can reflect their basic characteristics. It was shown that by varying the initial ordering parameter of the A-L model, linear (or almost linear) functions N-1(q) and sigma(12)(q) can be de scribed in the region of low shear rates. It was hypothesized that reg ion 1 of the flow curve (Onogi and Asada) inevitably exists in the con tinuous liquid crystalline phase, which could be outside of the region of measurements accessible to rheometry.