Kinetics of polymorphic transitions of cyclohexanol studied by terahertz spectroscopy

The phase behaviors and kinetics of the polymorphic transitions of cyclohexanol, C₆H₁₁OH, were investigated by terahertz (THz) spectroscopy, over the temperature range from 150 to 330 K. A new phase was found, labelled phase I´, which is more stable than previously observed phase I but less stable than phase III´. The kinetics of the irreversible transitions from phase I to I´, I to III´, and III´ to III were analyzed using Avrami´s theory. The transition geometries of the first two transitions were found to be one-dimensional, while the latter was two-dimensional. The transitions from phase I to III and III to II transitions were revealed to occur through a two-step process. The mechanism of these irreversible transitions is discussed in relation to the formation and dissociation of hydrogen bonds between the hydroxyl groups as well as the steric restriction effects of the cyclohexyl ring.