Decrease in apparent viscosity in electric fields found in chiral smectic liquid crystals

We report apparent viscosity in an electric field (ER property) of chiral smectic liquid crystals. Seven smectic liquid-crystalline materials, which have various structures and a different magnitude of spontaneous polarization, were prepared. Their ER properties were measured using a cylindrical rotational viscometer. A decrease in the apparent viscosity of the shear flow in a DC field was observed in the SmC* phase of a mixture composed of 5-nonyl-2-(4-nonyloxyphenyl)pyrimidine and (S)-4-(2-methyloctanoyl)-4'-biphenyl 3-chloro-4-octyloxybenzoate. At the same time, the material was found to be transparent. The ER properties in SmC* phases observed by viscosity measurements are discussed in comparison with the textures depending on the change of the molecular ordering observed by thermal optical microscopy.