Adiabatic scanning calorimetry of the nematic-smectic A1and the smectic A1–smectic A transitions in frustrated smectic mixtures at low temperatures

Phase diagram results and high resolution adiabatic scanning calorimetric data are presented for several binary mixtures of 4-cyanocyclohexyl-4'-n-butyl-cyclohexane and 1 amino-9-fluorenone showing smectic A1 and smectic à phases at low temperatures. Contrary to present theoretical expectations and experimental evidence for other systems, we find strongly first order nematic to smectic A1 transitions with a latent heat of about 2 kJ/mol for all the mixtures investigated. The enthalpy change related to the smectic A1 to smectic à transitions is two orders of magnitude smaller and corresponds most likely to a fluctuation induced first order transition.