Anomalous Heat Capacity Associated with the Incommensurate SmA Phase in DB7OCN + 80CB
A high-sensitivity ac calorimeter has been used to determine the anomalous heat capacity associated with the SmAd-SmAic-SnA2 phase transitions in a smectic liquid crystal mixture of DB7OCN and 80CB. SmAd is a partial bilayer smectic A phase (L < d < 2L) and SmA2 is a bilayer smectic (d = 2L), where L is the molecular length. SmAic is an incommensurate smectic phase exhibiting the simultaneous presence of two collinear mass density modulations with periods whose ratio is not a rational fraction. In addition, heat capacity and x-ray data on pure DB7OCN indicate that the direct SmAd-SmA2 transformation in that material occurs continuously without undergoing a thermodynamic transition.
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