Thermal analysis and FTIR study of 4- n -hexadecyloxybenzoic acid (16OB)

We have carried out phase polymorphism studies of 4- n -hexadecyloxybenzoic acid (16OB) in temperature range: from 10 to 150 °C with the use of Differrential Scanning Calorimeter, Thermal Microscopic Polarization and Transmitted Light Intensity. 16OB is a liquid crystal which has smectic C phase (SmC) and rich polymorphism in solid phase. Particularly interesting is one of the transitions in solid state possessing characteristic clear exothermic effect (during heating cycle) which is associated with the transition between the metastable and stable phases. Fourier transform infrared spectroscopy as a function of temperature was used to analyze changes in the nature of hydrogen bonds. The exact analysis of effects shows an existence of the metastable phases. The stable and metastable phases differ from each other in the structure made of hydrogen bonds.