Measurement of Phase Transition Temperatures in Liquid Crystals Using the Temperature-Dependent Dielectric Constant

Abstract

This work describes a technique for the accurate determination of phase transition temperatures in liquid crystals. It is based on the temperature-dependent dielectric constant (TDDC) which shows discontinuities at phase transitions. A plot of the dielectric constant differentiated with respect to temperature (dε_r/dT) versus teraperature, exhibits peaks as the materials are heated or cooled through phase transitions. It has been shown that this technique easily detects transitions such as that from smectic A to smectic C, which other techniques have difficulty detecting.

The work is illustrated with two materials, and results from seven materials covering a wide variety of phase transitions are compared with values given by other techniques.

Key Words:

• phase transitions
• dielectric constants