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 belo
w 114
![](/images/entities/deg.gif)
C (region III), the CrI phase formed first despite itsmetastable nature (monotropic) due to the faster crystallization kinetics of the ColR
![](/images/entities/rarr.gif)
CrI phase in this region. TheCrI
![](/images/entities/rarr.gif)
CrII phase transformation then follo
wed. Ho
wever,
when the
Tc ![](/images/entities/ge.gif)
115
![](/images/entities/deg.gif)
C in region I,
which
was close to themelting temperature (
Tm) of the CrI phase (
Tm = 121
![](/images/entities/deg.gif)
C), only the CrII phase formed directly from the ColR phase.In the narro
w Tc region II
where 114
![](/images/entities/deg.gif)
C
Tc < 115
![](/images/entities/deg.gif)
C, primary nucleation and overall crystallization rates of CrIand CrII phases
were reversed. Linear crystal gro
wth rate measurements in PLM revealed that a minimum in theCrII phase gro
wth rate
was found in region II. This indicated that as long as the gro
wth rates of both phases
weresimilar and on the same gro
wth front, the CrII phase formation could be hampered by the gro
wth of the metastableCrI phase.