Frequency dependence of the electrorheological effect in the nematic phase of pentyl cyanobiphenyl

Abstract

The effect of an electric field on the viscosity, the electrorheological (ER) effect, is studied as a function of the frequency of the electric field for the nematic phase of 4-n-pentyl-4'- cyanobiphenyl (5CB). In the frequency region between 10Hz and 1kHz, a gradual change of the ER effect is observed, with its behaviour depending on the shear rate and the amplitude of the electric field. On the basis of a calculation of the orientational motion of the director and its effect on the viscosity, the observed frequency dependence is suggested to occur as a result of an orientational relaxation of the director.