Crystal polymorphism of 8OCB liquid crystal consisting of strongly polar rod-like molecules

Abstract

The studies on crystal polymorphism of 8OCB liquid crystal showing a metastable PP phase and a heterogeneous CP phase as the stable ground state.

Analysis of differential scanning calorimetry (DSC): determining the transition temperatures, and enthalpy and heat capacity changes in multicomponent systems by analytical model fitting

“…The obtained temperature of each transition, T 0 m , for these peaks is, respectively, at 55.62 ± 0.00 °C, 66.96 ± 0.00 °C, and 80.16 ± 0.00 °C which could be attributed to the transitions ΔH/J g −1 216.5 [25] 215.73 ± 0.01 213.99 ± 0.01 T 0 m /°C 69.3 [26] 70.57 ± 0.00 70.48 ± 0.00 α/K −1 NA 0.82 ± 0.00 0.81 ± 0.00 β/K −2 6.08 ± 0.07 7.05 ± 0.08 ΔC p,m /W g −1 K −1 − 0.02 ± 0.00 − 0.02 ± 0.00 from crystalline to Smectic-A phase (K-SmA) at 53.54 °C, Smectic-A to Nematic (SmA-N) at 65.25 °C, and Nematic to isotropic (N-I) at 78.53 °C, respectively (Table 6). The enthalpy change of these transitions was obtained from the DSC N (T), which was in good agreement with the values reported in the literature [27][28][29]. The difference in the obtained enthalpy change and the reported values is due to different calibration approaches, setting peak value instead of the onset value.…”

Observation of banded spherulite in a pure compound by rhythmic growth

“…S5 in the Supplementary Material ). Thus the amorphous component after softening gradually transforms to the crystallites and smectic phase on heating which accounts for the observed increase in dielectric constant with increasing temperature before complete melting of the sample to the smectic phase at 327.6 K [32].…”

“…3a) of banded spherulite is identical to that of the commercial powder or CP crystal phase of 8OCB. We have recently shown that the CP crystal phase is composed of fibrillar nano crystallites of the compound embedded in its own amorphous solid state [32]. All the peaks observed in the XRD profile are associated with the monoclinic crystal structure of the nano crystallites.…”

“…S4 in the Supplementary Material). The fitted intense peak positioned at 2235 cm −1 arises from the nano crystallites of the banded spherulite and less intense shoulder peak positioned at 2226 cm −1 originates from the amorphous component [32]. The ratio of the intensities of these peaks obtained in the crystallite-rich and crystallite-poor zones along the radial direction of the banded spherulite is shown in Fig.…”

“…The temperature variation of dielectric constant of the sample was measured using a homemade setup. The detail of this setup has been discussed elsewhere [32]. A commercially available liquid crystal cell (INSTEC Inc.) of sample thickness 5 µm and electrode area 5×5 mm 2 was used for dielectric measurement.…”