Pressure-Induced Tricritical Behavior of the SmA-Cho Transition in COC

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Abstract
The tricritical nature of the smectic-A-cholesteric (SmA-Cho) transition in cholesteryl oleyl carbonate (COC) was investigated by several methods. Differential thermal analysis (DTA) and volume measurement showed the existence of a tricritical point at 3.1±0.1×103 kg/cm2 and 74°C, where the first-order transition converted to the second-order one. The dynamic properties were studied by ultrasonic measurement, and the differences in the transition processes were observed with a polarized microscope. Spherulites were observed in the smectic-A phase above the tricritical point. The structure of the spherulites and the morphology effects are discussed.