Electrorheological effect and non-Newtonian behavior of a homogeneous nematic cell under shear flow: Hysteresis, bistability, and directional response

Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México - Apdo. Postal 70-360, 04510 México, D.F., Mexico

Corresponding author: cmendoza@iim.unam.mx

Received: 2 May 2008
Accepted: 18 August 2008

Abstract

We study the flow of a homogeneous nematic cell under the simultaneous action of an applied electric field and an applied shear flow. Using a hydrodynamic model that describes the response of a flow-aligning nematic liquid crystal (5CB) we obtain the director's configuration and the velocity profile at the steady states. From these results we construct a phase diagram in the electric field vs. shear flow space that displays regions for which the system may have different steady-state configurations of the director's field. The selection of a given steady-state configuration depends on the history of the sample. Due to the competition between shear flow and electric field, the system's viscosity shows a complex non-Newtonian response with regions of shear thickening and thinning. Interestingly, as a consequence of the hysteresis of the system, this response may be asymmetric with respect to the direction of the shear flow. The results also show a moderate electrorheological effect which is also dependent on the history of the sample.