Abstract
Differential scanning calorimetry measurements performed in the temperature range of 253–393 K for CF2O linkage liquid crystals reveal existence and stability of the phase transitions. Then, we report molar heat capacities for three difluoromethyleneoxy liquid crystalline compounds measured by the heat-pulse relaxation method within the temperature range from 1.9 to 300 K. The heat capacities of these three compounds increase with the temperature increasing and no thermal anomalies have been found in the whole temperature region. The experimental data have been fitted to a function of temperature with a series of theoretical and empirical models for the proper temperature ranges. Standard thermodynamic properties of these three fluorinated liquid crystals are evaluated from the experimental heat capacity temperature dependencies. The standard molar heat capacities of 3-CB(F,F)XB(F,F)-F, 2-BB(F,F)XB(F,F)-F and 2-BB(F)B(F,F)XB(F,F)-F at 298.15 K and 0.1 MPa have been determined to be $$ C_{{{\text{p}},{\text{m}}}}^{\text{o}} $$ = (560.84 ± 5.61) and (464.41 ± 4.64) and (560.58 ± 5.61) J K−1 mol−1, respectively.
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