The static and dynamic behavior of the Frederiks transition for twist of a uniform planar nematic sample in an external magnetic field has been studied by monitoring the associated conoscopic figure. In particular, the decay of this figure after the field has been switched off is considered in detail in order to obtain results for the twist viscosity ggr;1. Results for the twist elastic constantK2and for the viscosity ggr;1are reported for the homologous series ofp,pprime;hyphen;dialkylazoxybenzenes.K2is found to be smaller than bothK1andK3, whileK2varies little along the series. The temperature dependence of ggr;1can be described by a combination of an activated process and a term depending on the orientational order parameter.
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