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

Abstract

Steady-state shear stress (<(tau)over bar>(12)) and first normal stress difference (N-1) 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 now 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 N-1 versus <(tau)over bar>(12) 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 N-1 and <(tau)over bar>(12) after the start-up of shear flow.