A Determination of the Cholesteric Liquid Crystalline Temperature Range by Birefringence Measurements in an Abbe Refractometer

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Abstract
Determination of a cholesteric liquid crystal's mesomorphic temperature range is of paramount importance in studying its physical properties. There are several methods for determining this temperature range, such as: nuclear magnetic resonance, differential thermal analysis, viscosity, optical rotation, dielectric constant and birefringence measurements. We have worked out a new simple method for determining cholesteric liquid crystal temperature range by measuring its birefringence in an Abbe refractometer. For isotropic liquids, a single border line, dividing the field of vision, may be observed in the lunette of the refractometer. The image in the lunette is divided by two border lines with different intensity in the case of cholesteric liquid crystals. Each border line is related to the refractive index of light of the ordinary and extraordinary ray, respectively. The liquid crystal temperature range may be determined by measuring the temperature of appearance and disappearance of the second border line. Cholesteryl oleyl carbonate has been investigated by this method.