Abstract
The heat capacities of the title compound (C3H11,O—C6H4,- CH=N—C6H4,—C4H9, abbreviation 5O ċ 4) with a purity of 99.92 mole percent have been measured with an adiabatic-type calorimeter between 11 and 393 K. The transition temperature and the enthalpy and entropy of phase transition for stable crystal → SG, SG → N and N → isotropic liquid were T c = 299.69 K/ΔH = 22.68 kJ mol−1/ΔS = 75.70 JK−1 mol−1, 325.72/7.11/21.79 and 342.48/1.78/5.22, respectively. The crystal which melts at 285.5 K is a metastable modification. The SA phase hitherto reported in between SG and N does not exist. The glassy So state was realized by rapid cooling of the specimen from the So phase. The molar enthalpy of the glassy SG state at 0 K was by (10.1±0.1) kJ mol−1 higher than that of the stable crystalline state and the residual entropy of the glassy state was (9.40±0.83) JK−1 mol−1. The relaxational heat-capacity anomaly was observed from as low as 100 K and double glass transition phenomenon occurred around 200 K; a quite unusual phenomenon which has never been observed for the glassy states of nematic and cholesteric liquid crystals. The present results give a fair evidence that the unusual glass transition phenomenon previously found for the SG state of 6Oċ4 (a homologous compound) is not exceptional at all but common to the smectic glasses; at least common to the glassy SG states. Two possible origins responsible for the double glass transitions have been discussed.