Structure, thermodynamics, and transition kinetics of nonadecylcyclohexane

The kinetics of crystallization in nonadecylcyclohexane, an asymmetric alka ne, was studied using x-ray scattering, differential scanning calorimetry ( DSC), and optical microscopy. A transient mesophase was found with a crysta llization/melting temperature 13 degreesC below the melting point of the st able crystal phase. In a bulk sample, nucleation from the melt proceeds tho ugh the transient mesophase, which subsequently converts to the stable phas e with rather slow kinetics. When quenched to low temperatures, the mesopha se does not anneal and can be described as a two-dimensional (2D) Ising-lik e 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 thr ough the transient phase. The crystal structure of the transient phase is d etermined. (C) 2000 American Institute of Physics. [S0021-9606(00)70542-3].