MAGNETIC-SUSCEPTIBILITY AND ORDER PARAMETER OF NEMATIC LIQUID-CRYSTALS AS DETERMINED BY A HIGH-TEMPERATURE SQUID MAGNETOMETER

The design and operation of a high-temperature measuring cell for SQUID magnetometers is described. It is demonstrated this device is well suited for precision measurements of magnetic susceptibility up to approximately 600 K. Thus, the SQUID method can be employed for the study of phase transitions of most thermotropic liquid crystals and LC polymers. To access the influence of molecular biaxiality on the determination of the order parameter, measurements were performed on a homologous series of four nematic oxybenzoate trimers varying in shape. Since the conformation of those model compounds is well known, the molecular susceptibility can be calculated by the incremental scheme devised by Flygare [Chem. Rev. 74, 653 (1974)]. Data obtained therefrom compare favorably with the values of the molecular susceptibility as extrapolated according to the Haller [Prog. Solid State Chem. 10, 103 (1975)] method.