Steady-state shear stress(Ք12) and first normal stress difference(N1) of liquid crystalline polymers at low shear rates were examined by using a mesoscopic constitutive equation set including the idea of initial domain size. For the applicability to the weak shear flow at low shear rates, a Hinch-Leal closure approximation was adopted in the calculation of the constitutive equation set. The steady-state rheological behaviors predicted by adopting the Hinch-Leal approximation were compared with those by the Doi simple decoupling approximation. It could by predicted from the plot of N1 versus Ք12 that smaller domains distributed isotropically at a quiescent state might maintain the isotropic domain distribution even at the imposition of moderate shear rate, and then could be changed to the ordered (or partially elongated) domain phase by a further increase of shear rate. Such change of the polydomain structure with the increase in shear rate could be proved more precisely by the transient rheological behaviors of N1 and Ք12 after the start-up of shear flow.
Marrucci G, Greco F, "The Polydomain Problem in Nematics. How to Account for Spatial Gradients in Molecular Orientation," Proc. 11th Intern. Congr. Rheol., 545, 1992