摘要
在260～380K范围内,用DSC法研究液晶HpBAB的相变。实验查明HpBAB在室温还以玻璃性晶体状态存在。它的玻璃转变、熔化和清亮过程的热力学参数准确地被测到。提出对-正烷氧基亚苄基-对-氨基苯腈同系列中熔化熵和烷基碳原子数的线性关系;改进Aranow统计模型并估算直线斜率为Rln(3/g)(1<g<3)。
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 HpBAB are 327.05±0.41 K and 310±27J K^(-1) mol^(-1), respectively. Its melting temperature and enthalpy and entropy of fusion are 341.16±0.14K, 32.78±0.22 kJ mol^(-1), 96.07±0.66J K^(-1) mol^(-1) for the crystal-I; 332.65±0.25K, 22.66±0.09kJ mol^(-1) for the mctastable crystal-Ⅱ, respectively. Its clearing point and enthalpy and entropy of clearing are 370.63±0.15K, 714±9J mol^(-1), 1.93±0.03J K^(-1) mol^(-1), respectively. On the basis of the present author's results and the reliable literature data, the linear relations of the melting entropies with the numbers of carbon atoms in the flexible terminal alkyl groups are presented in the homologues of N-(p-n-alkyloxybenzylidene)-p'-aminonitriles. Improved the Aranow's statistical approach, the slopes of the linear relations have been estimated and are equal to Rln(3/g)(1<g<3).
出处
《物理化学学报》
SCIE
CAS
CSCD
北大核心
1989年第1期62-66,共5页
Acta Physico-Chimica Sinica
