Infrared spectroscopic study on polytypic transformation of growing single crystal of n-hexatriacontane (n-C36H74)

Abstract There are two polytypic structures, single-layered structure Mon and double-layered structure Orth II for the M 011 modification of n -hexatriacontane ( n -C 36 H 74 ). The solution crystal growth of the two polytypes under controlled supersaturation was investigated by the oblique IR transmission method. As to the supersaturation dependence of growth behavior, there was a significant difference between the two polytypes. While the overgrowth of Orth II took place on the (0 0 1) face of the Mon crystal at moderate supersaturations, the overgrowth of Mon on the Orth II crystals was not confirmed at any supersaturations below 0.30. The growth rate of Mon showed about a second-order dependence on supersaturation, whereas that of Orth II showed a first-order dependence. The growth mechanism of the M 011 modification and the cause for the one-way overgrowth were deduced on the basis of the thermodynamical stabilities and the supersaturation dependence of the growth rates.