NEMATIC PHASE OF RODLIKE POLYMERS .2. POLYDOMAIN PREDICTIONS IN THE TUMBLING REGIME

The two-dimensional model previously considered is here used to obtain predictions in the complex situation of the tumbling regime which prevails at low shear rates. Although each domain is permanently in a time-dependent, periodic regime, the macroscopic response can be stationary in time because of the well-known polydomain structure. First, the average steady rheological response for this situation is calculated by taking a polydomain structure which neglects interdomain interactions. Although the steady state predictions thus obtained favorably compare with the experimental results throughout the range of shear rates, the transient start-up responses do not, because of the crucial role played by the interactions in such a case. These interactions, due to Frank elasticity, are then introduced in the model in the simplest possible way, i.e., by use of a mean field potential. Under this assumption, also the predictions of transient behavior in the tumbling regime show the correct qualitative features. © 1990, The Society of Rheology. All rights reserved.