FLOW-MEASUREMENTS OF THE VISCOSITY COEFFICIENTS OF 2 NEMATIC LIQUID-CRYSTALLINE AZOXYBENZENES

To determine the Miesowicz viscosity coefficients a shear-flow set-up has been built, which allows the measurement of η1, η2, η3 and η12. These coefficients are determined by pressing the liquid crystal through a rectangular capillary which forms part of a thermostated set-up placed between the poles of a magnet in order to control the director n. In addition, the flow-alignment angle θ 0 is determined from the change in optical path difference between the ordinary and extraordinary components of polarized light, comparing the situation with n aligned along the flow-direction and with flow-alignment, respectively. Results are given for the complete set of viscosity coefficients of p-methoxy-p'-butylazoxybenzene and p, p'-dibutylazoxybenzene. The results show good agreement with visco-elastic ratios found with light-scattering techniques. Within the experimental accuracy the Onsager-Parodi relation is well fulfilled