Heat Capacity of N-p-n-Hexyloxybenzylidene-p'-n-butylaniline Between 11 and 393 K: Unusual Glassy Smectic Liquid Crystal

Abstract

Heat capacity measurements have been made on a 18 g sample of C₆H₁₃O—C₆H₄—CH=N—C₆H₄—C₄H₉ with an adiabatic-type calorimeter between 11 and 393 K. Purity of the specimen was estimated to be 99.93 mole % by a fractional fusion method. The transition temperature and the enthalpy and entropy of transition for crystal → S_G, S_G → S_B S_B, → S_AS_B → S_A, S_A → N and N → isotropic liquid were determined to be T_C = 306.60 K/δH = 23.29 kJ mol⁻¹/δS = 75.98 J K⁻¹ mol⁻¹, 331.56/0.84/2.53, 332.86/3.37/10.14, 343.24/3.20/9.37 and 350.92/1.89/5.37, respectively. A glassy S_G state was realized by rapid cooling. The heat capacity of the glassy state gave rise to two stepped anomalies due to the enthalpy relaxation around 200 K: a quite unusual phenomenon which has never been observed for other glassy liquid crystals, glassy liquids and glassy crystals. The molar enthalpy of the glassy S_G state at 0 K was by (9.27 ± 0.16) Id mol⁻¹ higher than that of the crystalline state and the residual entropy of the glassy state was determined to be (7.51 ± 0.63) J K⁻¹ mol⁻¹.