Studies of homogeneous-nucleation-based crystal growth: significant role of phenyl ring in the structure formation

Low-temperature crystal growth was investigated in the fragile liquids of iso-propylbenzene, dimethylphthalate, diphenylphthalate, and 2-methyltetrahydrofuran by using an optical microscope. Homogeneous-nucleation-based (HNB) crystal growth was observed to proceed in the supercooled liquids of the former three substances around and below their glass-transition temperatures, as in the cases of o-terphenyl, toluene, and other fragile liquids, but not detected in 2-methyltetrahydrofuran. Thus far, the growth has been observed only for the substances possessing phenyl group(s) in the molecule. The maximum rates of the growth were found to decrease with increasing the size of substituents to the phenyl ring(s). It was concluded from this fact that the C-H?π(electron) intermolecular interaction between phenyl rings enhances to generate an ordered region required for the crystal nucleation and thereby the HNB crystal growth. Among all the observations of the HNB growth, a rough relation was found that the maximum growth rate increases with an increasing maximum-rate temperature normalized by the respective glass transition temperatures.