Polymorphism and thermodynamic properties of 4-cyano-3-fluorophenyl 4-pentylbenzoate (5CFPB) liquid crystal

The polymorphism and thermodynamic properties of 4-cyano-3-fluorophenyl 4-pentylbenzoate were elucidated by combining adiabatic calorimetry, differential scanning calorimetry (DSC), simultaneous X-ray diffractometry and DSC (XRD-DSC), and polarized optical microscopy (POM). Seven phases were identified: the nematic phase (T-c = 297.15 K), glass of the nematic phase (T-g & AP; 208 K), crystal I (T-fus = 302.80 K), crystal II, crystal III (T-fus = 303.93 K), crystal IV, and isotropic liquid. A transition between crystal IV and the nematic phase (T-trs = 287.35 K) as well as solid-solid-phase transitions in crystal I (T-trs = 248.8 K) and III (T-trs1 = 121.6 K; T-trs2 = 178.7 K) was detected, and the thermodynamic quantities of the transitions were determined. The relationships between the thermodynamic stabilities of all phases were verified: Crystal I is the most stable below 301 K, whereas crystal III is the most stable between 301 and 304 K. The crystallization kinetics depend on the size and thermal history of the sample: Crystals II and IV were observed only during the measurements of adiabatic calorimetry (gram-amount of the sample being subjected to a lowest temperature of 78 K), whereas crystal I was not prominently observed during the DSC, XRD-DSC, and POM measurements after the sample had been melted (milligram-amount of the sample being subjected to a lowest temperature of 170 K).

Automated summary

The polymorphism and thermodynamic properties of 4-cyano-3-fluorophenyl 4-pentylbenzoate were studied using adiabatic calorimetry, differential scanning calorimetry (DSC), simultaneous X-ray diffractometry and DSC (XRD-DSC), and polarized optical microscopy (POM). Seven phases were identified, including a nematic phase, glass of the nematic phase, and four crystal phases. The thermodynamic stabilities of the phases were determined, and solid-solid phase transitions and crystallization kinetics were observed.