Two Shear-Flow Regimes in Nematicp−n−Hexyloxybenzilidene−p′−aminobenzonitrile

The viscous torque induced in a plane shear flow on the director $\overrightarrow{\mathrm{n}}$ of $p-n-\mathrm{Hexyloxybenzilidene}-p^{\prime }-\mathrm{aminobenzonitrile}$ (nematic below $T_c\sim 102$°C) when $\overrightarrow{\mathrm{n}}$ is parallel to the velocity changes sign at a temperature $T_c-8\mathrm{}$°C, in agreement with Gähwiller's experiments on a Poiseuille flow. We compare the instability modes obtained near $T_c$ with the similar problem for $p^{\prime }-\mathrm{methoxybenzylidene}-p-n-\mathrm{butylaniline}$ and give the first discussion of the instability modes in the low-temperature domain.