Heat Capacity and Thermodynamic Properties ofp′-Substitutedp-n-Hexyloxybenzylideneanilines II.p-n-Hexyloxybenzylidenamino-p′-Chlorobenzene (HBAC)

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Abstract
The heat capacity of the smectic liquid crystal, HBAC, has been measured from 15 K to 385 K by using an adiabatic calorimeter. Contrary to the previous experimental results on p-n-hexyloxybenzylideneamino-p′-benzonitrile (HBAB), no solid-solid phase transition was observed in HBAC. However, a new intermediate phase was discovered between the crystal and the smectic B phase. Four phase transitions were found at 327.7 K (crystal-intermediate phase S3), 330.90 K (S3-smectic B), 362.98 K (smectic B-smectic A), and 370.38 K (smectic A-isotropic liquid), respectively. The enthalpies and entropies of these transitions were determined to be 10.88 kJmol−1/33.2 JK−1mol−1, 12.35/37.0, 3.39/9.3 and 5.79/15.6, respectively. The standard thermodynamic functions have also been estimated up to 385 K. The total sum of four transition entropies amounts to 95.1 JK−1mol−1 and agrees well with that of three transitions from the crystal II to the isotropic liquid of HBAB.