Simulation of texture evolution for nematic liquid crystalline polymers under shear flow

Abstract

The development of microstructure in nematic liquid crystalline polymers under shear flow is investigated through computational simulation. By using a tensorial expression for the elastic torque, the nemato-dynamic equation is numerically resolved. The simulation shows that elastic anisotropy has a strong influence on the evolution of the director and that the ‘log-rolling’ orientation of the directors emerges for tumbling nematics if the twist constant is smaller than the splay and the bend constants, even though one starts from a structure in which the directors are aligned within the velocity and velocity gradient plane. The interaction of wedge disclination pairs subject to a shear flow field is also simulated. The generation, multiplication and interaction of inversion wall defects during shearing have been revealed. In general the wall moves to the boundaries and is absorbed by the boundaries. When two walls of opposite orientation meet, a loop may form, then shrink, and finally collapse. Correspondingly, if they have the same orientation, commutation will occur.