[Two-dimensional infrared correlation spectroscopy on dodecyloxy benzoic acid phase transition].

Thermal spectra of liquid crystal, dodecyloxy benzoic acid were collected over a temperature range of 26-150 degrees C by FTIR microspectroscopy. By taking investigations of temperature-induced changes in dodecyloxy benzoic acid by means of 2D infrared correlation spectroscopy, it was possible to clearly describe the molecular dynamic mechanism of dodecyloxy benzoic acid aggregates in the phase transitions. The analysis shows that p-dodecyloxy benzoic acid crystallized as multi-molecule aggregates through hydrogen bonds between the carboxylic groups, while the long polymethylene residues intermixed each other in solid state. Premelting phenomena in polymethylene residues were observed with temperature up to melting point. It seems that lots of oxy-benzoic acid part recrystallized to cycle dimer as supermolecular liquid crystal during alkyl chain melting in crystal-smectic phase transition. After temperature over 132 degrees C, oxy-benzoic acid part were melted to open dimer and separate molecule in liquid state.