Crystallization and glass formation processes in methylcyclohexane: Vibrational dynamics as a possible molecular indicator of the liquid-glass transition

We present the result of Raman studies on vibrational dynamics and static properties of the CH2 rocking mode of methylcyclohexane as a function of temperature and cooling rate. We have found that vibrational dynamics as well as the static properties are very sensitive indicators to specify phases and phase transitions at the molecular level. It was found that methylcyclohexane in the undercooled liquid phase may form distinct thermodynamic states that strongly depend on the quenching rate. We have identified the characteristic temperature T* that is quenching rate dependent which is the no-return-point between crystallization and amorphization. Below this temperature the undercooled methylcyclohexane exists in either the liquid state that is out of equilibrium and represents nonergodic behavior that leads to glass forming or in the metastable equilibrium ergodic state that leads to crystallization. (C) 2001 American Institute of Physics.