Biaxial Liquid Crystals

Convergent light observations have been made on three liquid crystalline substances with nematic and smectic phases. The nematic phase was observed to be uniaxial as expected, but smectic $C$ was found to be biaxial. The optic axial angle $2V$ for smectic $C$ was found to be on the order of 20° for all three compounds. Also, the tilt angle for smectic $C$ is nearly 45° for all three liquid-crystal systems. Anisotropy of the degrees of order is suggested as a partial explanation for the biaxial character of smectic $C$.