A theory for flowing nematic polymers with orientational distortion

Using a nonlocal nematic potential, we generalize the Doi theory for nemati c polymers to include distortional elasticity. We derive an evolution equat ion for the configuration tensor and a constitutive equation for a nonlocal stress tensor which is consistent with the long-range order in nematic pol ymers. One of the interesting effects of distortional elasticity is the app earance of a mean-field torque on the molecules as they are forced away by flow from their preferred orientation. This torque gives rise to an antisym metric part of the stress tensor. With a few molecular parameters, the comp lete system of equations is capable, we believe, of describing the evolutio n of the texture and the dynamics of disclinations in flowing nematic polym ers. Thus, for the first time, a suitable platform for exploring complex fl ows of nematic polymers is established. In the limit of weak flows and smal l distortions, the theory properly reduces to the Leslie-Ericksen theory. T he Leslie viscosities are derived in terms of molecular parameters. (C) 200 0 The Society of Rheology. [S0148-6055(00)00705-7].