Magnetic Anisotropy and Latent Heat of Some Smectic Liquid Crystals

The magnetic anisotropy of 4'-Methoxybenzylidene-4-aminocinnamic Acid Ethyl Ester, 4'-Methoxybenzylidene-4-aminocinnamic Acid n-Butyl Ester and 4'-n-Butoxybenzylidene-4-aminoacetophenone was measured in the smectic, nematic and isotropic phases. The magnetic anisotropy of their liquid crystals depends on the strength of magnetic field in the smectic phase. It suggests that the domains form in the smectic phase. The order parameter in the smectic and nematic phases was determined by the measurement of magnetic susceptibility. The transition entropy of their liquid crystals at the phase transitions was obtained from the thermal analysis. Their nematic-smectic transitions correspond to the behaviour of the first order transition predicted from the McMillan theory.