Structure, thermodynamics, and transition kinetics of nonadecylcyclohexane

The kinetics of crystallization in nonadecylcyclohexane, an asymmetric alkane, was studied using x-ray scattering, differential scanning calorimetry (DSC), and optical microscopy. A transient mesophase was found with a crystallization/melting temperature 13 °C below the melting point of the stable crystal phase. In a bulk sample, nucleation from the melt proceeds though the transient mesophase, which subsequently converts to the stable phase with rather slow kinetics. When quenched to low temperatures, the mesophase does not anneal and can be described as a two-dimensional (2D) Ising-like glass with regard to the up-down orientation of the asymmetric molecules. A second metastable mesomorph was also detected at low temperatures. Using an emulsified sample, homogeneous nucleation was also shown to proceed through the transient phase. The crystal structure of the transient phase is determined.