Modelling of shear flow in liquid crystalline materials

Abstract

The flow behaviour of liquid crystalline polymers (LCPs) is quite complex and these materials exhibit varied and complicated textural patterns when subject to a flow field. The complexity arises from two general factors, the first that they are long chained and thus have long relaxation times, and second that they are liquid crystalline, and thus there is co-operative motion of the molecules. In both thermotropic and lyotropic LCPs subject to low shear flows, it is known that defects and disclinations influence the microstructure and rheology, but it is not clear by what mechanisms these distortions shrink or multiply during flow. In this work, a model is developed to examine the behaviour of defects in shear flows. The simulations based on the model show a spectrum of microstrucural development as a function of applied shear rate: reorientation of domains of different alignment associated with disclinations at low shear strains; the multiplication of wall type defects and the orientation of these normal to the shear gradient axis at intermediate shear rates, and the tendency towards disclination annihilation; the generation of a flow-aligned monodomain at higher shear rates.