High-resolution calorimetric study of a liquid crystalline organo-siloxane tetrapode with a biaxial nematic phase

High-resolution adiabatic scanning calorimetry and di®erential scanning calorimetry have been employed to study the thermal behaviour of an organo-siloxane tetrapode reported to exhibit a biaxial nematic phase. No signature of the uniaxial to biaxial nematic phase transition could be retraced in sequential heating and cooling runs under di®erent scanning rates, within the experi- mental resolution. The results obtained in this work reveal that an extremely small heat should be involved in the uniaxial to biaxial nematic phase transition. The isotropic to uniaxial nematic transition at 318 § 0.01 K is very stable and it is weakly ¯rst order with a rather small latent heat of 0.20 § 0.02 J/g.