Role of Polymorphous Metastability in Crystal Formation Kinetics of 2,3,6,7,10,11-Hexa(4'-Octyloxybenzoyloxy)-Triphenylene Discotic Molecules
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- 作者：Benjamin Y. Tang ; Alexander J. Jing ; Christopher Y. Li ; Zhihao Shen ; Huabin Wang ; Frank W. Harris ; and Stephen Z. D. Cheng
- 刊名：Crystal Growth & Design
- 出版年：2003
- 出版时间：May 2003
- 年：2003
- 卷：3
- 期：3
- 页码：375 - 382
- 全文大小：510K
- 年卷期：v.3,no.3(May 2003)
- ISSN：1528-7505
文摘
Phase transition behaviors of a discotic liquid crystal 2,3,6,7,10,11-hexa(4'-octyloxybenzoyloxy)-triphenylene (HOBT-C8) were investigated. Four phases having different orders and symmetries existed in thissystem: a discotic nematic phase, a rectangular columnar (ColR) phase, an orthorhombic crystalline (CrI) phasedeveloped upon cooling, and a monoclinic crystalline (CrII) phase formed during heating (Tang, B. Y., et al. Mater.Chem. 2001, 13, 78). The CrI phase represented a metastable phase compared to the CrII phase. On the basis of theresults of differential scanning calorimetry, wide-angle X-ray diffraction, and polarized light microscopy (PLM)experiments, three crystallization-temperature (Tc) regions were identified to help study the crystallization kineticsof the CrI and CrII phases. In the large Tc region below 114 
C (region III), the CrI phase formed first despite itsmetastable nature (monotropic) due to the faster crystallization kinetics of the ColR 
CrI phase in this region. TheCrI CrII phase transformation then followed. However, when the Tc 
115 C in region I, which was close to themelting temperature (Tm) of the CrI phase (Tm = 121 C), only the CrII phase formed directly from the ColR phase.In the narrow Tc region II where 114 C 
Tc < 115 C, primary nucleation and overall crystallization rates of CrIand CrII phases were reversed. Linear crystal growth rate measurements in PLM revealed that a minimum in theCrII phase growth rate was found in region II. This indicated that as long as the growth rates of both phases weresimilar and on the same growth front, the CrII phase formation could be hampered by the growth of the metastableCrI phase.
C (region III), the CrI phase formed first despite itsmetastable nature (monotropic) due to the faster crystallization kinetics of the ColR CrI phase in this region. TheCrI CrII phase transformation then followed. However, when the Tc 115 C in region I, which was close to themelting temperature (Tm) of the CrI phase (Tm = 121 C), only the CrII phase formed directly from the ColR phase.In the narrow Tc region II where 114 C Tc < 115 C, primary nucleation and overall crystallization rates of CrIand CrII phases were reversed. Linear crystal growth rate measurements in PLM revealed that a minimum in theCrII phase growth rate was found in region II. This indicated that as long as the growth rates of both phases weresimilar and on the same growth front, the CrII phase formation could be hampered by the growth of the metastableCrI phase.