Phase Behavior and Thermodynamic Functions of Liquid Crystalline Material 6O2OCB

Heat capacity measurements were made for 4-(2-hexyloxy-ethyloxy)-4'-cyanobiphenyl (6O2OCB) by adiabatic calorimetry between 5 K and 320 K. A rich polymorphism was confirmed; two crystalline phases (phase I: Tfus = 296.79 K and phase II: Tfus = 293.08 K), a smectic liquid crystal and an isotropic liquid. The glassy states of the isotropic liquid (Tg ~ 210 K) and the smectic phase (Tg ~ 223 K) were also identified. A small anomaly was found at 154.58 K for the phase II, which is due to a transition to another crystalline phase (phase III). The thermodynamic functions (enthalpy, entropy, and Gibbs energy) were calculated. The phase II did not transform into the phase I, although the Gibbs functions cross each other at 266.75 K.

(by H. Suzuki & A. Inaba)

	Fig. 1. Molecular structure of 6O2OCB.
	Fig. 2. Molar heat capacity of 6O2OCB. The ordinate is for the phase I. The results for the other three phases are successively shifted upward by 100 J K-1 mol-1.
	Fig. 3. Gibbs energy plotted as G/T2 against T for 6O2OCB. The Gibbs functions of the phase I and II cross each other at TX = 266.75 K.
	Fig. 4. Molar heat capacity plotted as Cp/T3 against T for 6O2OCB. The phase I shows larger heat capacity than the phase III, indicating that the phase I has looser molecular packing.