Structural change of polydomain in the liquid crystalline polymers by weak shear flow

Abstract

Steady-state shear stress (τ12) 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 be predicted from the plot of N1 versus τ12 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 τ12 after the start-up of shear flow.