Acta Phys. -Chim. Sin. ›› 1989, Vol. 5 ›› Issue (01): 62-66.doi: 10.3866/PKU.WHXB19890113

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Thermodynamic Study of the Phase Transitions of the Mesogen HpBAB and the Homologous Trend of the Melting Entropies

Wang Bang-Ning;Tan Fu   

  1. Institute of Chemistry, Academia Sinica, Beijing
  • Received:1987-09-17 Revised:1988-02-22 Published:1989-02-15
  • Contact: Wang Bang-Ning

Abstract: The phase transitions of N-(p-n-heptyloxybenzylidene)-p'-aminobenzonitrile (H_pBAB) were studied at various rates within the range 260—380K by DSC. It was revealed by the DSC experiments that the thermotropic nematogen H_pBAB obtained by the repeated recrystallization from absolute ethanol was the glassy crystal at room temperature in addition to the known stable and metastable crystal modifications K(Ⅰ) and K(Ⅱ). This is the first example of glassy crystal among the mesogens in so far as author's knowledge. The temperature and the heat capacity step of the glass transition of H_PBAB are 327.05±0.41 K and 310±27 J K~(-1) mol~(-1), respectively. Its melting temperature and enthalpy and entropy of fusion are 341.16±0.14 K, 32.78±0.22 kJ mol~(-1), 96.07±0.66 J K~(-1) mol~(-1) fro the crystal-I; 332.65±0.25 K, 22.66±0.99 kJ mol~(-1) for the metastable crystal-II, ....