Issue
EPL
Volume 84, Number 1, October 2008
Article Number 16002
Number of page(s) 6
Section Condensed Matter: Structural, Mechanical and Thermal Properties
DOI http://dx.doi.org/10.1209/0295-5075/84/16002
Published online 19 September 2008
EPL, 84 (2008) 16002
DOI: 10.1209/0295-5075/84/16002

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

J. C. Medina and Carlos I. Mendoza

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

cmendoza@iim.unam.mx

received 2 May 2008; accepted in final form 18 August 2008; published October 2008
published online 19 September 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.

PACS
61.30.Gd - Orientational order of liquid crystals; electric and magnetic field effects on order.
47.57.Lj - Flows of liquid crystals.
47.57.Qk - Rheological aspects.

© EPLA 2008