TUMBLING OF RODLIKE POLYMERS IN THE LIQUID-CRYSTALLINE PHASE UNDER SHEAR-FLOW

The two-dimensional model introduced by Marrucci and Maffettone to describe the nematic phase of rodlike polymers in a shear flow has been explored in the limit of small shear rate. A tumbling motion for the director n of the nematic phase has been found. Explicit expressions for the shear and normal stresses have been derived for both the elastic and viscous contributions. Suitable averages over the multidomain structure give rise to a stationary macroscopic response. Consistently with experiments the normal stresses are found to be positive in the linear limit. The present results, together with those of ref 1, indicate that the model is able to describe the experimentally observed behavior of normal stresses, i.e., the positive to negative to positive transitions with increasing shear rate. The transition from a stationary to a tumbling situation with increasing nematic potential is also analyzed and discussed. © 1990, American Chemical Society. All rights reserved.